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#1
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How Important Is the Sound Of the Phase Inverter?
I know that the sections should be well matched, but how much does the PI
affect the overall sound of an amp, gain notwithstanding? Thanks. |
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#2
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Armand wrote: I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Any stage in an amplifier is like a link in a chain. If you have a weak link, the chain will break no matter how strong the rest of the links are. So if your phase inverter introduces a lot of distortion, you'll have a lot of distortion! There are a great many ways of accomplishing phase inversion; they all have certain characteristics which *can* affect the overall result -- just like any other amplifier stage. Cheers, Fred -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ |
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#3
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#4
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"Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. |
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#5
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Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm should sound very nice, because the Concertina PI isn't being driven hard, and nor is the tube ahead of it. The CPI tube itself has a gain of only 2, counting cathode and anode output voltages combined, compared to the grid input. so when a 12AX7 is used for this stage, there is local FB which reduces the open loop gain about 30 times, and the thd at 2 x 5 volts output is less than 0.05%. BUT, the input tube on its own has to make just over 5 volts will have much more thd, which will total perhaps 0.3%, and all 2H. To this we could add the the thd of the output stage, which might be 3%, and mainly all 3H. So at the output, expect to measure about 3.3%, and this is without FB, for a class AB UL amp. When FB is added, ALL this thd gets reduced perhaps by 5 times, to 0.6%. The mix of distortion products stays about constant for the first few watts, with or without FB, and its just the quantity that is reduced by FB. Some extra higher harmonics are created by the FB, but usually, these "second order" artifacts are not audible in well made tube amps. And the sound? That's for you to find out for yourself. I think one should be mentally flexible about drive amp circuits; I like to stick to medium U triodes, perhaps with a 12AX/AT/AY7 at the input. Patrick Turner. |
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#7
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Hi RATs!
Yes. Buy as many tubes as you can find. Use the one you like the best. Nobody but you knows what you will like, and you won't, neither, unless you try. Do not assume price is the way to perfection  Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
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#8
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Ronald wrote: What do you guys think of this splitter : http://www.angelfire.com/electronic2...6L6schema.html I think it works great in this / my amp ..... Ronald. Your PI is what's known as the paraphase splitter. In your case the drive for the bottom gain driver tube comes from the the low output Z of the top follower tube. Since the 6SL7 is a very linear triode when it sees a high Z load value as you have there, this phase inverter should work fine, up to a high F. The Ro from the mu-follower as you have done it might be as low as 5kohms, so driving the outputs is no problem, especially since they are in tetrode mode, and have low miller input C. Probably, the balance of such a paraphase amp could vary. so some form of trimmer R could be used temporarily when setting up, and then find the right value for balance, then replace with a fixed value R, and the balance shouldn't change for years. Even 5% unbalance in signal drive won't be heard. BTW, in your case, NFB can be applied to the cathode of the input valve from the amp output if needed. Trimming the R values may still be needed, but I see you have the variety of paraphase which is self balancing, with the 3 x 180k arranged just so. I'd prefer to have even lower bias R than 180k for the output tubes, probably OK for 6L6, but they'd need to be lower value for 6550. Just watch out for LF instability with FB, because there is CR coupling between the gain tubes and followers on top, and then the CR to output grids, then you have bypassed Rk at the outputs, and one of the input tubes, and then there is the inductance of the OPT across the load, and the gain of the output tubes is high, especially with no load, so beware LF oscillations. Patrick Turner. "Patrick Turner" schreef in bericht ... Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm should sound very nice, because the Concertina PI isn't being driven hard, and nor is the tube ahead of it. The CPI tube itself has a gain of only 2, counting cathode and anode output voltages combined, compared to the grid input. so when a 12AX7 is used for this stage, there is local FB which reduces the open loop gain about 30 times, and the thd at 2 x 5 volts output is less than 0.05%. BUT, the input tube on its own has to make just over 5 volts will have much more thd, which will total perhaps 0.3%, and all 2H. To this we could add the the thd of the output stage, which might be 3%, and mainly all 3H. So at the output, expect to measure about 3.3%, and this is without FB, for a class AB UL amp. When FB is added, ALL this thd gets reduced perhaps by 5 times, to 0.6%. The mix of distortion products stays about constant for the first few watts, with or without FB, and its just the quantity that is reduced by FB. Some extra higher harmonics are created by the FB, but usually, these "second order" artifacts are not audible in well made tube amps. And the sound? That's for you to find out for yourself. I think one should be mentally flexible about drive amp circuits; I like to stick to medium U triodes, perhaps with a 12AX/AT/AY7 at the input. Patrick Turner. |
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#9
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jim wrote: "Patrick Turner" wrote in message ... Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm Well ?????? The man asked whether you could 'HEAR' the difference between different phase inverters. No, done properly, you can't . .... Phase inversion is a pain in the arse. Bust it in two halves and stitch it back together with two valves and a split arse transformer is just asking for trouble... which sort of invertor sounds better ???? You tell me !!! The LTP ?? Well, yeah ...... it does the job, but to get it to balance you either need a CCS, or a fiddle with the anode loads, and what about a difference in the Gm of the two halves of the double triode ?? Well old mate, you could have a 12AU7 on one side of the LTP, and a 6DJ8 on the other, and as long as there is a CCS and equal RLs to each side, voila, equal output voltages. All that would change would be the slight amount of uncancelled 2H. Not today or tomorrow but next month as things age. Or if I decide to put another make of 12AX7 in the hole ?? Concertina ?? Easy, cheap and sensible but no gain. ??? My main point, however, is that you are blatantly advertizing Turnip Audio again !!! My circuits have been used, in essence, by Mullard, Leak, VTL, to name a few. All I did was drag their circuits kicking and screaming into the modern tube age by means of using a transistor as a pure slave to the whims of the cathodes and their currents. At least the free box of turnips that go with every amp I sell is a step in the right direction for customer goodwill. I have reported this to Andre, Arny and Stewart They will be contacting you shortly regards jim Last time I had to complain about Andre whacking me around with a damp lettuce leaf until I turned green, and it wasn't even St Paddy's day. Patrick Turner. |
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#10
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jim wrote: "Armand" wrote in message ... Thanks. That answers my question for the most part. But I was also thinking about the tube used. Should one spend the money for say an RCA BP 6SL7, the inverter in this case, or settle for something less expensive? No, no, no........ If you want to spend some money, spend it on the OP transformer. The larger the better. A concertina inverter works with 100% NFB so whether the valve was made in Libya or Birmingham, the result will be the same. 6SL7 ?? Looks pretty but is inferior to the ****ty little 9 pin 12A?? series things in terms of gain and interelectrode capacitances. In LTP configuration a 6SL7 or a 12AX7 are fine, but neither are good as a concertina due to their high anode resistance....... in concertina mode, you go for a 6SN7 or a 12AU/AT7 But horses for courses Jim. In my ealier post one of the amps I linked to was a 10 watt thinge with 6GW8. The triode half of one tube is the CPI, and triode in other tube is the input tube. The circuit with 17dB of NFB is sensitive to about a volt of input. Thousands of such circuits were used, and both bean counters and listeners were winners. The drive voltages are about 7 vrms max to each outptu pentode. The output impedance of the CPI is LOW, providing the load the anode and cathode see is the same, and it is, in all circuits, until at HF, some phase shift occurs, and the anode output voltage rolls off more than the cathode voltage. Measured separately, anode and cathode output R is very different, but so what, the CPI stays well balanced to well over 50kHz, even with 12AX7/6SL7. The Williamson used 6SN7, the best triode of all time, and the CPI acts as a buffer between input tube and the balanced driver stage, which results in a terrific bandwidth for the whole four triode driver stage. Not that you will 'HEAR' whatever you put in as an inverter. What make ???................. My $3 Chinese 6SN7s sound great, NOS Brimars sound pretty much the same.... you choose..... regards jim I don't hear much difference. A PI is just another stage you must have for a PP amp, unless the amp has a balanced input, then no PI is required. Patrick Turner. |
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#11
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jim wrote: snip, Well old mate, you could have a 12AU7 on one side of the LTP, and a 6DJ8 on the other, and as long as there is a CCS and equal RLs to each side, voila, equal output voltages. All that would change would be the slight amount of uncancelled 2H. I don't think I'm quite ready to grasp that I can have a 6SL7 in one hole and an ECC83 in the other and have perfect balance from 1 to 20 kHz , but the answer to the man's question is --- no, you will not hear the inverter..... I have never heard an inverter, .. inverting .. I must admit, I have never heard anyone claim that thay could hear their music partially or wholly inverted, or that they thought their music was upside down sound. But then reversing the speaker leads for phase turns everything upside down, but there is no need to stand on one's head, or face away from the speakers.. A conventional R tailed LTP is a cathode follower driving the second half of the triode hence the 10% difference in the two outputs. Theory says that if the tail load is infinite, the anode outputs must be equal.... irrespective of the active device. I cannot argue with this... It all just seems to use so many bits ..... neg supplies, CCS pentode or MJE ?? etc, etc.. Well, I reckon the LTP, used by so many ppl has less parts than a williamson. But the 10-10 litle amp has even fewer. Now its possible to build a sublime 50 watt amp using 6 or 8 x EL84, and have only two input triodes, and a paralleled 12AX7 for the input, and a paralleled 12AT7 for the CPI would be a fine way to build the driver. I,m going to LTP/CCS an ECC83 and a 6L6GC with G2 connected to the anode, as an LTP splitter, and see what happens........... Not today or tomorrow but next month as things age. Or if I decide to put another make of 12AX7 in the hole ?? Concertina ?? Easy, cheap and sensible but no gain. ??? My main point, however, is that you are blatantly advertizing Turnip Audio again !!! My circuits have been used, in essence, by Mullard, Leak, VTL, to name a few. All I did was drag their circuits kicking and screaming into the modern tube age So, nothing is new. It's all been done. We have tighter spec passives and silicon things which we can hang on our valves........ It matters not that newness be daily invented, but that out time be spent on making other people happy from our labours, and great it is that much tubecraft has survived the passing of the ages. Patrick Turner. by means of using a transistor as a pure slave to the whims of the cathodes and their currents. At least the free box of turnips that go with every amp I sell is a step in the right direction for customer goodwill. I have reported this to Andre, Arny and Stewart They will be contacting you shortly regards jim Last time I had to complain about Andre whacking me around with a damp lettuce leaf until I turned green, and it wasn't even St Paddy's day. Patrick Turner. |
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#12
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Hi Patrick (and all others) ,
Thanks for your answer . I knew already it is a paraphase splitter , but a schematic tells more than 1000 words ..... I also did some tweaking on the circuit already . I had a nasty 60kHz oscillation . I skipped the bypass-C on the power tubes cathode and the R-network for the splitter is somewhat different now . It works great now ..... I only posted the link because the paraphase looked to be forgotten ...... And I like the principle of the paraphase very much . Also there's no need for matcing tubes . It even works with a 6SN7 on top and a 6SL7 for the bottom tube . The only thing is you won't get the same Z-out for both halfs ..... The mu-follower variant will be able to drive the output tubes into AB2 I think . For the same reason it will drive (almost) any power tube ..... Ronald . "Patrick Turner" schreef in bericht ... Ronald wrote: What do you guys think of this splitter : http://www.angelfire.com/electronic2...6L6schema.html I think it works great in this / my amp ..... Ronald. Your PI is what's known as the paraphase splitter. In your case the drive for the bottom gain driver tube comes from the the low output Z of the top follower tube. Since the 6SL7 is a very linear triode when it sees a high Z load value as you have there, this phase inverter should work fine, up to a high F. The Ro from the mu-follower as you have done it might be as low as 5kohms, so driving the outputs is no problem, especially since they are in tetrode mode, and have low miller input C. Probably, the balance of such a paraphase amp could vary. so some form of trimmer R could be used temporarily when setting up, and then find the right value for balance, then replace with a fixed value R, and the balance shouldn't change for years. Even 5% unbalance in signal drive won't be heard. BTW, in your case, NFB can be applied to the cathode of the input valve from the amp output if needed. Trimming the R values may still be needed, but I see you have the variety of paraphase which is self balancing, with the 3 x 180k arranged just so. I'd prefer to have even lower bias R than 180k for the output tubes, probably OK for 6L6, but they'd need to be lower value for 6550. Just watch out for LF instability with FB, because there is CR coupling between the gain tubes and followers on top, and then the CR to output grids, then you have bypassed Rk at the outputs, and one of the input tubes, and then there is the inductance of the OPT across the load, and the gain of the output tubes is high, especially with no load, so beware LF oscillations. Patrick Turner. "Patrick Turner" schreef in bericht ... Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm should sound very nice, because the Concertina PI isn't being driven hard, and nor is the tube ahead of it. The CPI tube itself has a gain of only 2, counting cathode and anode output voltages combined, compared to the grid input. so when a 12AX7 is used for this stage, there is local FB which reduces the open loop gain about 30 times, and the thd at 2 x 5 volts output is less than 0.05%. BUT, the input tube on its own has to make just over 5 volts will have much more thd, which will total perhaps 0.3%, and all 2H. To this we could add the the thd of the output stage, which might be 3%, and mainly all 3H. So at the output, expect to measure about 3.3%, and this is without FB, for a class AB UL amp. When FB is added, ALL this thd gets reduced perhaps by 5 times, to 0.6%. The mix of distortion products stays about constant for the first few watts, with or without FB, and its just the quantity that is reduced by FB. Some extra higher harmonics are created by the FB, but usually, these "second order" artifacts are not audible in well made tube amps. And the sound? That's for you to find out for yourself. I think one should be mentally flexible about drive amp circuits; I like to stick to medium U triodes, perhaps with a 12AX/AT/AY7 at the input. Patrick Turner. |
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#13
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"Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Hi, Armand, Short answer. It doesn't.!!!!!! I have often rebuilt the same PP design with different inverters. The distortion contributed by the inverter stage is nothing compared to that produced by the following stages, and you certainly won't hear it, provided the two antiphase outputs are closely balanced. So why are there different inverter configurations and which one is best ?? Only two inverters seem to be regularly used now. The cathodyne and the LTP. Which you choose is not dictated by which sounds best, it is decided by the AC output required, the impedance of the output load you are driving, and the available B+ voltage. kind regards jim |
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#14
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Also, most importantly in my case, it depends on the linearity of
the driven impedance, and hence on how the output stage is biased. Not just on how big it is. One of Van der Veen's designs, for example, uses a cathodyne ECC81 for 6*EL34. But the slightest bit of grid current causes the cathodyne anode output to collapse resulting in a flurry of odd harmonics at the output of the amp. I think there is an issue of slew rate limiting too, and/or imbalance at HF. Current-derived cathode feedback is good for turning a problem into a crisis. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. What we need to do is to create an inverted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. For example, how much HT you have available depends partly on how much hum you can tolerate at the driver stage, which also depends on how good the hum rejection is of the driver. cheers, Ian "jim" wrote in message ... "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Hi, Armand, Short answer. It doesn't.!!!!!! I have often rebuilt the same PP design with different inverters. The distortion contributed by the inverter stage is nothing compared to that produced by the following stages, and you certainly won't hear it, provided the two antiphase outputs are closely balanced. So why are there different inverter configurations and which one is best ?? Only two inverters seem to be regularly used now. The cathodyne and the LTP. Which you choose is not dictated by which sounds best, it is decided by the AC output required, the impedance of the output load you are driving, and the available B+ voltage. kind regards jim |
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#15
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But it's big in Europe, I understand, or at least in Germany. Dunno
what the French use. Actually we don't hear much from them at all. Maybe they don't have amplifiers in France. That'll be because of the cafes I suppose. Must be worse in the antipodes, where music just means banging sticks and blowing raspberries. Especially if you're in class A and especially if you're trying to avoid odd harmonics. The quad 2 uses a floating paraphase for everything and there aren't too many bits. It is quite complex in operation though and is intended for fairly unusual output demands. If other splitters have a sound it is a bad sound. The paraphase can sound OK I am told. cheers, Ian "jim" wrote Paraphase ?? If you like it, that's fine by me. Don,t change it. What it sounds like is more important than how it measures to me. If I was bothered about 0.0001% THD and 1% phase shift at 2 Mhz, I would have joined up to uk.rec.audio Seems to use a lot of bits though. regards jim |
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#16
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"Patrick Turner" wrote in message ... Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm Well ?????? The man asked whether you could 'HEAR' the difference between different phase inverters. No, done properly, you can't . .... Phase inversion is a pain in the arse. Bust it in two halves and stitch it back together with two valves and a split arse transformer is just asking for trouble... which sort of invertor sounds better ???? You tell me !!! The LTP ?? Well, yeah ...... it does the job, but to get it to balance you either need a CCS, or a fiddle with the anode loads, and what about a difference in the Gm of the two halves of the double triode ?? Not today or tomorrow but next month as things age. Or if I decide to put another make of 12AX7 in the hole ?? Concertina ?? Easy, cheap and sensible but no gain. ??? My main point, however, is that you are blatantly advertizing Turnip Audio again !!! I have reported this to Andre, Arny and Stewart They will be contacting you shortly regards jim |
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#17
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"Armand" wrote in message ... Thanks. That answers my question for the most part. But I was also thinking about the tube used. Should one spend the money for say an RCA BP 6SL7, the inverter in this case, or settle for something less expensive? No, no, no........ If you want to spend some money, spend it on the OP transformer. The larger the better. A concertina inverter works with 100% NFB so whether the valve was made in Libya or Birmingham, the result will be the same. 6SL7 ?? Looks pretty but is inferior to the ****ty little 9 pin 12A?? series things in terms of gain and interelectrode capacitances. In LTP configuration a 6SL7 or a 12AX7 are fine, but neither are good as a concertina due to their high anode resistance....... in concertina mode, you go for a 6SN7 or a 12AU/AT7 Not that you will 'HEAR' whatever you put in as an inverter. What make ???................. My $3 Chinese 6SN7s sound great, NOS Brimars sound pretty much the same.... you choose..... regards jim |
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#18
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concertina,LTP,mumbo jumbo........
use xformer for PI that's what real tubies does hehe -- Choky Prodanovic Aleksandar YU "jim" wrote in message ... No, no, no........ If you want to spend some money, spend it on the OP transformer. The larger the better. A concertina inverter works with 100% NFB so whether the valve was made in Libya or Birmingham, the result will be the same. 6SL7 ?? Looks pretty but is inferior to the ****ty little 9 pin 12A?? series things in terms of gain and interelectrode capacitances. In LTP configuration a 6SL7 or a 12AX7 are fine, but neither are good as a concertina due to their high anode resistance....... in concertina mode, you go for a 6SN7 or a 12AU/AT7 But horses for courses Jim. In my ealier post one of the amps I linked to was a 10 watt thinge with 6GW8. 6GW8 ?? .. Is this one of those little TP things ?? The triode half of one tube is the CPI, and triode in other tube is the input tube. The circuit with 17dB of NFB is sensitive to about a volt of input. Thousands of such circuits were used, and both bean counters and listeners were winners. The drive voltages are about 7 vrms max to each outptu pentode. Now, you're taking the ****, here...... I had a Dansette record player with an ECL82 in it in 1972.. I thought we were trying to move on.... IV input ?? Oh, wow !!! For what out ?? 10W ?? In terms of efficiency, my electric fire does a better job ....... The output impedance of the CPI is LOW, No it isn't. It's variable. The OP impedances of the two outputs go in opposite directions as the frequency changes. They are however low/equal enough to be only of interest to my dog !!!!!! providing the load the anode and cathode see is the same, and it is, in all circuits, until at HF, some phase shift occurs, and the anode output voltage rolls off more than the cathode voltage. Measured separately, anode and cathode output R is very different, but so what, the CPI stays well balanced to well over 50kHz, even with 12AX7/6SL7. The Williamson used 6SN7, the best triode of all time, At least we agree on something...... and the CPI acts as a buffer between input tube and the balanced driver stage, which results in a terrific bandwidth for the whole four triode driver stage. So why are we not all building Williamson lookalikes ?? Not that you will 'HEAR' whatever you put in as an inverter. What make ???................. My $3 Chinese 6SN7s sound great, NOS Brimars sound pretty much the same.... you choose..... regards jim I don't hear much difference. A PI is just another stage you must have for a PP amp, unless the amp has a balanced input, then no PI is required. Well. yes.. You want to even try thinking about the earth/earth loop problems with seperate turntable, CD player, tape, radio, etc...... Patrick Turner. |
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#19
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... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm Well ?????? The man asked whether you could 'HEAR' the difference between different phase inverters. No, done properly, you can't . .... Phase inversion is a pain in the arse. Bust it in two halves and stitch it back together with two valves and a split arse transformer is just asking for trouble... which sort of invertor sounds better ???? You tell me !!! The LTP ?? Well, yeah ...... it does the job, but to get it to balance you either need a CCS, or a fiddle with the anode loads, and what about a difference in the Gm of the two halves of the double triode ?? Well old mate, you could have a 12AU7 on one side of the LTP, and a 6DJ8 on the other, and as long as there is a CCS and equal RLs to each side, voila, equal output voltages. All that would change would be the slight amount of uncancelled 2H. I don't think I'm quite ready to grasp that I can have a 6SL7 in one hole and an ECC83 in the other and have perfect balance from 1 to 20 kHz , but the answer to the man's question is --- no, you will not hear the inverter..... I have never heard an inverter, .. inverting .. A conventional R tailed LTP is a cathode follower driving the second half of the triode hence the 10% difference in the two outputs. Theory says that if the tail load is infinite, the anode outputs must be equal.... irrespective of the active device. I cannot argue with this... It all just seems to use so many bits ..... neg supplies, CCS pentode or MJE ?? etc, etc.. I,m going to LTP/CCS an ECC83 and a 6L6GC with G2 connected to the anode, as an LTP splitter, and see what happens........... Not today or tomorrow but next month as things age. Or if I decide to put another make of 12AX7 in the hole ?? Concertina ?? Easy, cheap and sensible but no gain. ??? My main point, however, is that you are blatantly advertizing Turnip Audio again !!! My circuits have been used, in essence, by Mullard, Leak, VTL, to name a few. All I did was drag their circuits kicking and screaming into the modern tube age So, nothing is new. It's all been done. We have tighter spec passives and silicon things which we can hang on our valves........ by means of using a transistor as a pure slave to the whims of the cathodes and their currents. At least the free box of turnips that go with every amp I sell is a step in the right direction for customer goodwill. I have reported this to Andre, Arny and Stewart They will be contacting you shortly regards jim Last time I had to complain about Andre whacking me around with a damp lettuce leaf until I turned green, and it wasn't even St Paddy's day. Patrick Turner. |
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#20
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Ronald wrote: Hi Patrick (and all others) , Thanks for your answer . I knew already it is a paraphase splitter , but a schematic tells more than 1000 words ..... I also did some tweaking on the circuit already . I had a nasty 60kHz oscillation . I skipped the bypass-C on the power tubes cathode and the R-network for the splitter is somewhat different now . It works great now ..... I only posted the link because the paraphase looked to be forgotten ...... And I like the principle of the paraphase very much . Also there's no need for matcing tubes . It even works with a 6SN7 on top and a 6SL7 for the bottom tube . The only thing is you won't get the same Z-out for both halfs ..... The mu-follower variant will be able to drive the output tubes into AB2 I think . For the same reason it will drive (almost) any power tube ..... I mentioned paraphase for the benefit of others in the group who may not be familiar with such things. The mu follower won't be a very good driver for class AB2, because the grid current will charge up the coupling caps, and you have cathode bias, which will shift as the Ck charge up, during sustained levels where grid flows. For AB2, you need fixed bias, and full cathode follower drive, with the cathodes direct coupled to the output tube grids, and cathode R taken to about -150v, and with the biasing done by applying the adjustable fixed bias to the cathode follower grid, which is then cap coupled to the anode circuit of a gain tube. There are other methods, using transformers and chokes, but a really low drive impedance is needed for grid current operation, since the input impedance to the grid when trying to force the grid to go to +10v is very low. Patrick Turner. Ronald . "Patrick Turner" schreef in bericht ... Ronald wrote: What do you guys think of this splitter : http://www.angelfire.com/electronic2...6L6schema.html I think it works great in this / my amp ..... Ronald. Your PI is what's known as the paraphase splitter. In your case the drive for the bottom gain driver tube comes from the the low output Z of the top follower tube. Since the 6SL7 is a very linear triode when it sees a high Z load value as you have there, this phase inverter should work fine, up to a high F. The Ro from the mu-follower as you have done it might be as low as 5kohms, so driving the outputs is no problem, especially since they are in tetrode mode, and have low miller input C. Probably, the balance of such a paraphase amp could vary. so some form of trimmer R could be used temporarily when setting up, and then find the right value for balance, then replace with a fixed value R, and the balance shouldn't change for years. Even 5% unbalance in signal drive won't be heard. BTW, in your case, NFB can be applied to the cathode of the input valve from the amp output if needed. Trimming the R values may still be needed, but I see you have the variety of paraphase which is self balancing, with the 3 x 180k arranged just so. I'd prefer to have even lower bias R than 180k for the output tubes, probably OK for 6L6, but they'd need to be lower value for 6550. Just watch out for LF instability with FB, because there is CR coupling between the gain tubes and followers on top, and then the CR to output grids, then you have bypassed Rk at the outputs, and one of the input tubes, and then there is the inductance of the OPT across the load, and the gain of the output tubes is high, especially with no load, so beware LF oscillations. Patrick Turner. "Patrick Turner" schreef in bericht ... Henry 007 wrote: "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. I like to use a dual triode for each channel, with an AC balance adjustment on the anode resistors, which allows you to adjust the balance of drive to the output tubes before NFB is applied. Basically a knob which allows you to balance the output of the drivers. The PI with the lowest THD and widest BW and highest voltage swing, and which is easy to drive, and with adequate gain, and with excellent balanced drive is the long tail pair, for all the large octal power tubes. A typical circuit is shown at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm But for circuits using EL84, 6V6, the circuit at http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm should sound very nice, because the Concertina PI isn't being driven hard, and nor is the tube ahead of it. The CPI tube itself has a gain of only 2, counting cathode and anode output voltages combined, compared to the grid input. so when a 12AX7 is used for this stage, there is local FB which reduces the open loop gain about 30 times, and the thd at 2 x 5 volts output is less than 0.05%. BUT, the input tube on its own has to make just over 5 volts will have much more thd, which will total perhaps 0.3%, and all 2H. To this we could add the the thd of the output stage, which might be 3%, and mainly all 3H. So at the output, expect to measure about 3.3%, and this is without FB, for a class AB UL amp. When FB is added, ALL this thd gets reduced perhaps by 5 times, to 0.6%. The mix of distortion products stays about constant for the first few watts, with or without FB, and its just the quantity that is reduced by FB. Some extra higher harmonics are created by the FB, but usually, these "second order" artifacts are not audible in well made tube amps. And the sound? That's for you to find out for yourself. I think one should be mentally flexible about drive amp circuits; I like to stick to medium U triodes, perhaps with a 12AX/AT/AY7 at the input. Patrick Turner. |
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#21
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jim wrote: No, no, no........ If you want to spend some money, spend it on the OP transformer. The larger the better. A concertina inverter works with 100% NFB so whether the valve was made in Libya or Birmingham, the result will be the same. 6SL7 ?? Looks pretty but is inferior to the ****ty little 9 pin 12A?? series things in terms of gain and interelectrode capacitances. In LTP configuration a 6SL7 or a 12AX7 are fine, but neither are good as a concertina due to their high anode resistance....... in concertina mode, you go for a 6SN7 or a 12AU/AT7 But horses for courses Jim. In my ealier post one of the amps I linked to was a 10 watt thinge with 6GW8. 6GW8 ?? .. Is this one of those little TP things ?? Yes, but two can make the same as 2 x EL84, 6V6. The triode half of one tube is the CPI, and triode in other tube is the input tube. The circuit with 17dB of NFB is sensitive to about a volt of input. Thousands of such circuits were used, and both bean counters and listeners were winners. The drive voltages are about 7 vrms max to each outptu pentode. Now, you're taking the ****, here...... I had a Dansette record player with an ECL82 in it in 1972.. I thought we were trying to move on.... IV input ?? Oh, wow !!! For what out ?? 10W ?? In terms of efficiency, my electric fire does a better job ....... But all the old world amps had a single 12AX7 for a line stage, which included a passive tone control and volume control. So, with 0.2v standard value line input level was amped up 50 times to 10vrms, and the losses in the tone control and volume was 20dB, so 1 volt came out, and ppl thought it was luverly. The output impedance of the CPI is LOW, No it isn't. It's variable. The OP impedances of the two outputs go in opposite directions as the frequency changes. They are however low/equal enough to be only of interest to my dog !!!!!! .....and to anyone using NFB! providing the load the anode and cathode see is the same, and it is, in all circuits, until at HF, some phase shift occurs, and the anode output voltage rolls off more than the cathode voltage. Measured separately, anode and cathode output R is very different, but so what, the CPI stays well balanced to well over 50kHz, even with 12AX7/6SL7. The Williamson used 6SN7, the best triode of all time, At least we agree on something...... and the CPI acts as a buffer between input tube and the balanced driver stage, which results in a terrific bandwidth for the whole four triode driver stage. So why are we not all building Williamson lookalikes ?? Why does the car industry produce more than one model? Didn't you know, there are redheads, brunnettes, and blondes. Just think if all women were clones, noboody would know whose wife was who's. Not that you will 'HEAR' whatever you put in as an inverter. What make ???................. My $3 Chinese 6SN7s sound great, NOS Brimars sound pretty much the same.... you choose..... regards jim I don't hear much difference. A PI is just another stage you must have for a PP amp, unless the amp has a balanced input, then no PI is required. Well. yes.. You want to even try thinking about the earth/earth loop problems with seperate turntable, CD player, tape, radio, etc...... I don't have hum problems, so I get by with half the tubes used for all balanced. Patrick Turner. |
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#22
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We agree on nearly everything Jim.
But there are matters of degree. As perhaps you know by now my own amps are just 4*6CH6 with UL a distributed load. As I run them now, I get 12W class A which is plenty into my not-very-sensitive speakers and small room. Apart from these fairly distortion-free watts, I like a few for what I believe the experts call headroom. we're dealing with music here, right? Not just testing with sine waves. I feel it is important to consider what defines the edges of the headroom. If I bias the my output valves to the recommended 40mA or more each, then grid current comes before cutoff. Driven with a typical cathodyne I am then lucky to get 9W before it totally falls apart. A LTP copes much better but I don't like them. A paraphase copes better still and that is what I might change to. Yes I could make a bigger cathodyne...I don't need you to tell me that. But it would have to be much bigger. At the moment I get the 12 clean watts further towards AB1. However, this means that the 1W I hear most of the time is not as good as it could be. Not as linear, quite, and with a higher output impedance. Now headroom is limited by soft clipping at first before...the cathodyne crashes. I don't want heaps of grid current, I just want a splitter that can cope with a little every now and then. I could add cathode followers or a short-tailed pair like Williamson but that defeats the object of simplicity. Yes, yes, yes you can say I just need bigger output valves. There is more to these things than size though, Jim. I like as far as I can to use finesse rather than brute force. We appear to have very different attitudes in this respect. cheers, Ian "jim" wrote in message ... "Ian Iveson" wrote in message ... Also, most importantly in my case, it depends on the linearity of the driven impedance, and hence on how the output stage is biased. Not just on how big it is. One of Van der Veen's designs, for example, uses a cathodyne ECC81 for 6*EL34. But the slightest bit of grid current causes the cathodyne anode output to collapse resulting in a flurry of odd harmonics at the output of the amp. Hi Ian, Is this suprising ?? It is working entirely outside it's design envelope. My wife's Peugeot diesel is easily outpaced by a Ferrari. Should I complain. ?? No inverter we are using is designed to supply current. If you need a current supply to the OP valve grids you need CFs or a transformer hanging on them. This is AB2 or B. Neither are related to high end audio. They are about a big noise, efficiency and bangs per buck Nothing wrong with Menno Van der Veens concertina driving 6 x EL34s. Not seen the circuit but assume it's cathode biased to retain a fairly high grid impedance for the concertina to work into. Parallelling 6 x EL34s provides the output power without asking the concertina to provide a big voltage swing and keeps the circuit simple and stable. I think there is an issue of slew rate limiting too, and/oce at HF. Current-derived cathode feedback is good for turning a problem into a crisis. There is an imbalance between the cathode and anode outputs but this is usually outside the limits of audibility. This is not a problem if we can't hear it, but since the concertina has no gain it is usually necessary to insert another gain stage to get the drive voltages we need for large valves. A Williamson. We now have four stages and since each stage shifts phase, complete inversion can occur at the extremes of frequency. It is unstable. We have an oscillator. Add in global NFB and unless the bandwidth is restricted it may well all get away from you. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. All the inverters we use should be restricted to AB1 None of them are current generators. A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. Only the concertina could be classed as elegant...with a direct coupled voltage amp up front. The LTP and paraphase are a compromise of a gain and inverter stage combined. Patrick has probably taken the LTP as far as it can go and tells me I can have a 6SN7 as one half and an ECC83 as the other and, with a CCJ tail, will still achieve perfect balance of the two outputs. I cannot dispute this, he knows what he is doing. The paraphase ?? Seems even more difficult to balance and keep balanced and I have rarely used it. By combining inversion and gain in one stage both the paraphase and the LTP do have the advantage of of reducing the number of stages and suggest a more stable design. What we need to do is to create an inverted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. Exactly. It is possible to build fine 10-15W amplifiers with simple circuitry and few components. These are maximum ratings however and with inefficient speakers you could be running close to overload at normal listening volumes. To design a 15W amp and ask it to sound good at 20W is a non starter. I like 50W as a design target. Times two for stereo. The whole question of pushing it to the design limits and watching it get out of shape does not then occur. Most of what I am ever going to hear is Class A. No crossover distortion and a driver design which can put 90v Pk-pk on the OP valve grids without really trying. The drawback is that including the PSU, it is big, heavy, and expensive kind regards jim For example, how much HT you have available depends partly on how much hum you can tolerate at the driver stage, which also depends on how good the hum rejection is of the driver. cheers, Ian "jim" wrote in message ... "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Hi, Armand, Short answer. It doesn't.!!!!!! I have often rebuilt the same PP design with different inverters. The distortion contributed by the inverter stage is nothing compared to that produced by the following stages, and you certainly won't hear it, provided the two antiphase outputs are closely balanced. So why are there different inverter configurations and which one is best ?? Only two inverters seem to be regularly used now. The cathodyne and the LTP. Which you choose is not dictated by which sounds best, it is decided by the AC output required, the impedance of the output load you are driving, and the available B+ voltage. kind regards jim |
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At last. Someone else realises a couple of KT88 are always going to do better
than a pair of EL34, or '84. - Patrick Turner. Hi RATs! Do is not out there as a tidy, independent reality. It and we share time and space. Well, temporarily Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
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#24
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TubeGarden wrote: At last. Someone else realises a couple of KT88 are always going to do better than a pair of EL34, or '84. - Patrick Turner. Hi RATs! Do is not out there as a tidy, independent reality. It and we share time and space. Well, temporarily Happy Ears! Al Alan J. Marcy Phoenix, AZ John paul Satre said "to do is to be", something my ex-wife never realised, somebody also said, "to be is to do" and maybe he was Dr Doolittle. But Frank Sinatra had it right, he just sang "tobe to beto to beto toobe..." and to remember what to sing, he had to read the words from a prompt carefully set up. PWC/mystic/Earhead Feel fee to be as mystical as you wish, its the weekend! Patrick Turner. |
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jim wrote: Hi, Ian, . We agree on nearly everything Jim. That's unusual. People rarely agree with anything I say !! But there are matters of degree. Of course. A design target of 1200W for home listening is unnecessary ... On the other hand, the 3W from my old Dansette is inadequate. As perhaps you know by now my own amps are just 4*6CH6 with UL a distributed load. As I run them now, I get 12W class A which is plenty into my not-very-sensitive speakers and small room. Apart from these fairly distortion-free watts, I like a few for what I believe the experts call headroom. we're dealing with music here, right? Not just testing with sine waves. Exactly, testing is carried out with ajustable amplitude waveforms. Increasing the amplitude finds the point where unacceptable distortion can be measured and this is the maximum useful output power of the amplifier A music source is not of fixed amplitude, and as we have discussed before, there appears to be no standard governing by how much transient peaks can exceed the mean level. Since you have to set a lower volume level to allow for these peaks, how much rated power do we need ?? It depends on speakers, don't it? if you had 95 Db/watt speakers, 12 watts id fine. to get the same dynamic headroom, low thd etc, with modern speakers of 89 dB, we should have 48 watts. I still find a 12 watt amp with my 89 dB speakers isn't too bad. I feel it is important to consider what defines the edges of the headroom. You cannot do this with any measure of accuracy and put figures to it. We have discussed this before and you know what I am going to say. I only repeat it because , apart from you, there may be somebody else out there who thinks I know what I am talking about !!! Our ears hear best at mid frequencies. Depending on the music content the volume control has to be adjusted accordingly to maintain the same percieved loudness. 50W output at 5Hz is no problem for my ears but the KT88s are still working very hard. My wife says I am deaf because I play music at high levels. I prefer it that way. Her ears may be more sensitive. Indeed, and women are queer about men and hi-fi; they are likely to think we need a hearing aid, rather than more watts, and besides, they subconsciously hate anything occuring in the home which competes with attention and expenditure in their direction. Women exist to drain men of goods and services, and they are like bottomless chasms to be filled up with all you have, and more, more, more! Hi-fi represents cheeky male assertions, and like sex, isn't comprehended by female brains as audiological erotica, something sensuous, to be savoured. Women use sex for power, and its the power over men that turns them on, not the dirty act itself. But music, and musing by men with glasses of cabernet is indulgence, and independant indulgence, and the interest in tubes and speacial gear is like a mistress. My ex-wife truly hated my hi-fi interest, and resented my not planning for a holiday under palm trees at horrendous expense. She NEVER brought a cup of coffee to me in the garage as I worked to build things I thought WE might need to live. Other wives I knew of my peer group all those years ago dreaded their dopey husband's efforts restoring old cars, and working on the yard, or the house. A lot of the women sulked about, as we seemed to enjoy all this stuff with our mates. One older shiela said of my loungeroom, recently, and disparingly "its very like a batchelor's room" I just smiled, and thought " and WTF would you do to make life for US more better?" We also hear logarithmically, hence log pots for volume control. Twice as loud as 10W is 100W. Add in the variables of speaker efficiency, and room size and how much power do you actually need.?? Even the furnishings come in here. Take all the furniture and carpets out and anything else which absorbes rather than reflects sound energy. Rooms are very important, and a room without carpets, drapes, lots of cushions, is indeed an audio horror, besides, no place to sit down.... But you know all this, but the question ---- is 10W enough ? --- has no answer. W=VI and is therefore a very poor way to measure sound levels or judge where to start a design, and this is unfortunately where the design has to start -- at the end If I bias the my output valves to the recommended 40mA or more each, then grid current comes before cutoff. Driven with a typical cathodyne I am then lucky to get 9W before it totally falls apart. I thought you had a clean 12W ?? If he has class A, then grid current indeed occurs before cut off, because the Gm of the tubes is more when the tubes are being turned on, than off, and the 3H distortion in class A is from the difference in complementary Gm and and when grid current does occur, flattening of the sine wave peaks begins on both top and bottom of the sine wave, and when 3H reaches 3%, with a sudden increase with a small % in output voltage, clipping is deemed to have begun. and that's where maximum AB power is said to be, and for 4 x EL84, depending on load, and bias, this could be up to around 75 watts with B+ = 700v. Maximum class A power it could be 17 watts, if maximum idle power was 48 watts, and efficiency was 35%. A LTP copes much better but I don't like them. A paraphase copes better still and that is what I might change to. Yes I could make a bigger cathodyne...I don't need you to tell me that. But it would have to be much bigger. I don't understand this bit. If you are driving the OP valves into grid current or cutoff, why would altering the inverter improve things. ?? The cathodyne or CPI clips symetrically when the onset of grid current occurs, but AFTER innitial clipping things get very asymetical. The anode circuit has less power output into the charging up of grid coupling caps to the OPVs, and the clipping is asymetrical, ie, the clipped wave has 2H in the squared waves. LTPs clip more evenly on each side of 0V, and seem to recover better. But in hi-fi situations, we never go near clipping;, its only of interest to rock and roll artistes. They adore square waves. Remember I am a hobby boy, not Patrick, but if you are driving the grids positive, AB2, and looking for an inverter which can supply this drive, the parahase and LTP have high OP impedances and are not very good at supplying current. Undistorted output watts is decided by the available HT voltage, OPT load impedance, grid drive voltage and max anode dissipation of the OP valves isn't it ?? Load lines ...Everything in front of the OP valves is just there to provide the voltage swing to make it happen. Changing the inverter/driver won't get 50W out of an EL84....... You do not want to get into AB2, Ian, .. all sorts of nasty things happen there ....... Some tubes, like the 807/6L6 thrive in well concieved AB2 designs. AFAIK, EL84, and EL34, just don't. One can build a triode amp with 807, and get a lousy 14 watts AB1 fairly easy, regardless of what phase inverter is used, if it is used as the driver, either paraphase, LTP or CPI will do, providing enough undistorted drive voltage is available. Then indeed, grid current limits the power output. With beam tetrode or pentode operation, the drive voltage never gets near causing grid current, as the load swing voltage is limited by the plate characteristics and the B+ rails. So we get 25 watts from the same 807 in class A. But say we use whatever drive amp we want with a a cathode follower to each OPV grid, directly coupled, then the triode class A1 power out could still be 14 watts, but we could get an extra 12 watts with the same load. pushing into class AB2, since the CF input grid will not itself draw grid current when driving the output grids. There will be some compression, or increased 3H, but NFB can minimise this, and the triode power is quite high. 30 watts of AB2 triode power isn't unrealisable. If the B+ for 807 is raised to 750V and the screens kept at 300v, and the load a-a raised to 10ka-a, then we can extract a heap more power in class AB2 beam tetrode mode, maybe 80+ watts. THD tends to be quite high. At the moment I get the 12 clean watts further towards AB1. However, this means that the 1W I hear most of the time is not as good as it could be. Not as linear, quite, and with a higher output impedance. Now headroom is limited by soft clipping at first before...the cathodyne crashes. I don't want heaps of grid current, I just want a splitter that can cope with a little every now and then. I could add cathode followers or a short-tailed pair like Williamson but that defeats the object of simplicity. Gee, why worry? I have a sledgehammer approach to valve audio which actually makes design very simple. I have to say that 12W is just not enough. Consider a slightly Williamson circuit which can make a pair of 60vRMS signals available on the OP valve grids... At that level, I have to go outside.. If I want to come back inside, the drivers are loafing along at 15-20vRMS, the room's full of noise, and I have to look very closely at the 'scope for anything out of shape. If I want quiet backgound sound, on my 89db speakers, I use SE pentode amps in my ancient Trio AM/FM reciever. Then if I have ppl around to hear something special, I might use my 100w monoblocs, with their 40 watts class A ability, but more often I'll use the 22 w SEUL amps, and these seem to sound loud, clean, detailed, and more like 30 watt amps, and with the magical warm midrange. Would I sit in the front row with an orchestra of 100 players? No way, I'd get way back. But at age 25 I might have done so happily. Yes, yes, yes you can say I just need bigger output valves. There is more to these things than size though, Jim. I like as far as I can to use finesse rather than brute force. We appear to have very different attitudes in this respect. Tubes ain't like sex, I mean, if the willy is small, use it twice a night, but it don't make sense with tubes, if you need more than a small tube, you must use a bigger one, or more of the small ones in parallel, all acting together. Baird make amps with 6 x EL84, and they have a fine sound. EL84 is a fine tube, my favourite smally. Musical Reference run 2 x EL84 to get 36 watts with 14k a-a, and 700 v for Ea. Definately class AB1. Its possible to use a CPI driver stage with a single gain stage ahead of it. Then of course we haven't even touched on the Dynaco ST70 method, which uses the CPI to provide a bootstrapped load for the input pentode, so the pentode gain is unusually high, so that when 20 dB od NFB is applied, the amp is a lot more sensitive than a williamson, Quad II, or the 10-10 w amp at my website, used so often in so many countless receiver or amp designs. We do, but electricity is cheap and valves are very inefficient. You are an academic and will search out efficiency and numbers which add up. I don't think valve audio is about that at all... Thank goodness it isn't. Using a PC or an electric heater is wasteful. But it is all hugely innefficient, modern life, as humanity exhausts the earth's reserves of non renewable energy sources to uphold a way of life. we will have to genetically alter ouselves to eat garbage at rubbish tips, and then create alternative energy forms in the thousands of years ahead. Don't be too concerned about the use of a few tubes within our life times, and don't scorn those whose interest it is to restore steam locomotives, or old cars. Don't let the modern technocrats make you feel guilty running triode amps, when those same *******s drive expensive cars to airconditioned offices and comfy chairs to get into a position to rave at us. Silicon is, but valves are about a big warm open sound and a smile on your face. Hear,hear! I think you need a 2 x 100w KT88 stereo pair for a few minutes, and work back from there.. Does he? regards as always jim I hope youse have a great weekend. Patrick Turner. cheers, Ian "jim" wrote in message ... "Ian Iveson" wrote in message ... Also, most importantly in my case, it depends on the linearity of the driven impedance, and hence on how the output stage is biased. Not just on how big it is. One of Van der Veen's designs, for example, uses a cathodyne ECC81 for 6*EL34. But the slightest bit of grid current causes the cathodyne anode output to collapse resulting in a flurry of odd harmonics at the output of the amp. Hi Ian, Is this suprising ?? It is working entirely outside it's design envelope. My wife's Peugeot diesel is easily outpaced by a Ferrari. Should I complain. ?? No inverter we are using is designed to supply current. If you need a current supply to the OP valve grids you need CFs or a transformer hanging on them. This is AB2 or B. Neither are related to high end audio. They are about a big noise, efficiency and bangs per buck Nothing wrong with Menno Van der Veens concertina driving 6 x EL34s. Not seen the circuit but assume it's cathode biased to retain a fairly high grid impedance for the concertina to work into. Parallelling 6 x EL34s provides the output power without asking the concertina to provide a big voltage swing and keeps the circuit simple and stable. I think there is an issue of slew rate limiting too, and/oce at HF. Current-derived cathode feedback is good for turning a problem into a crisis. There is an imbalance between the cathode and anode outputs but this is usually outside the limits of audibility. This is not a problem if we can't hear it, but since the concertina has no gain it is usually necessary to insert another gain stage to get the drive voltages we need for large valves. A Williamson. We now have four stages and since each stage shifts phase, complete inversion can occur at the extremes of frequency. It is unstable. We have an oscillator. Add in global NFB and unless the bandwidth is restricted it may well all get away from you. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. All the inverters we use should be restricted to AB1 None of them are current generators. A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. Only the concertina could be classed as elegant...with a direct coupled voltage amp up front. The LTP and paraphase are a compromise of a gain and inverter stage combined. Patrick has probably taken the LTP as far as it can go and tells me I can have a 6SN7 as one half and an ECC83 as the other and, with a CCJ tail, will still achieve perfect balance of the two outputs. I cannot dispute this, he knows what he is doing. The paraphase ?? Seems even more difficult to balance and keep balanced and I have rarely used it. By combining inversion and gain in one stage both the paraphase and the LTP do have the advantage of of reducing the number of stages and suggest a more stable design. What we need to do is to create an inverted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. Exactly. It is possible to build fine 10-15W amplifiers with simple circuitry and few components. These are maximum ratings however and with inefficient speakers you could be running close to overload at normal listening volumes. To design a 15W amp and ask it to sound good at 20W is a non starter. I like 50W as a design target. Times two for stereo. The whole question of pushing it to the design limits and watching it get out of shape does not then occur. Most of what I am ever going to hear is Class A. No crossover distortion and a driver design which can put 90v Pk-pk on the OP valve grids without really trying. The drawback is that including the PSU, it is big, heavy, and expensive kind regards jim For example, how much HT you have available depends partly on how much hum you can tolerate at the driver stage, which also depends on how good the hum rejection is of the driver. cheers, Ian "jim" wrote in message ... "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Hi, Armand, Short answer. It doesn't.!!!!!! I have often rebuilt the same PP design with different inverters. The distortion contributed by the inverter stage is nothing compared to that produced by the following stages, and you certainly won't hear it, provided the two antiphase outputs are closely balanced. So why are there different inverter configurations and which one is best ?? Only two inverters seem to be regularly used now. The cathodyne and the LTP. Which you choose is not dictated by which sounds best, it is decided by the AC output required, the impedance of the output load you are driving, and the available B+ voltage. kind regards jim |
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Hi, Ian,
.. We agree on nearly everything Jim. That's unusual. People rarely agree with anything I say !! But there are matters of degree. Of course. A design target of 1200W for home listening is unnecessary ... On the other hand, the 3W from my old Dansette is inadequate. As perhaps you know by now my own amps are just 4*6CH6 with UL a distributed load. As I run them now, I get 12W class A which is plenty into my not-very-sensitive speakers and small room. Apart from these fairly distortion-free watts, I like a few for what I believe the experts call headroom. we're dealing with music here, right? Not just testing with sine waves. Exactly, testing is carried out with ajustable amplitude waveforms. Increasing the amplitude finds the point where unacceptable distortion can be measured and this is the maximum useful output power of the amplifier A music source is not of fixed amplitude, and as we have discussed before, there appears to be no standard governing by how much transient peaks can exceed the mean level. Since you have to set a lower volume level to allow for these peaks, how much rated power do we need ?? I feel it is important to consider what defines the edges of the headroom. You cannot do this with any measure of accuracy and put figures to it. We have discussed this before and you know what I am going to say. I only repeat it because , apart from you, there may be somebody else out there who thinks I know what I am talking about !!! Our ears hear best at mid frequencies. Depending on the music content the volume control has to be adjusted accordingly to maintain the same percieved loudness. 50W output at 5Hz is no problem for my ears but the KT88s are still working very hard. My wife says I am deaf because I play music at high levels. I prefer it that way. Her ears may be more sensitive. We also hear logarithmically, hence log pots for volume control. Twice as loud as 10W is 100W. Add in the variables of speaker efficiency, and room size and how much power do you actually need.?? Even the furnishings come in here. Take all the furniture and carpets out and anything else which absorbes rather than reflects sound energy. You know all this, but the question ---- is 10W enough ? --- has no answer. W=VI and is therefore a very poor way to measure sound levels or judge where to start a design, and this is unfortunately where the design has to start -- at the end If I bias the my output valves to the recommended 40mA or more each, then grid current comes before cutoff. Driven with a typical cathodyne I am then lucky to get 9W before it totally falls apart. I thought you had a clean 12W ?? A LTP copes much better but I don't like them. A paraphase copes better still and that is what I might change to. Yes I could make a bigger cathodyne...I don't need you to tell me that. But it would have to be much bigger. I don't understand this bit. If you are driving the OP valves into grid current or cutoff, why would altering the inverter improve things. ?? Remember I am a hobby boy, not Patrick, but if you are driving the grids positive, AB2, and looking for an inverter which can supply this drive, the parahase and LTP have high OP impedances and are not very good at supplying current. Undistorted output watts is decided by the available HT voltage, OPT load impedance, grid drive voltage and max anode dissipation of the OP valves isn't it ?? Load lines ...Everything in front of the OP valves is just there to provide the voltage swing to make it happen. Changing the inverter/driver won't get 50W out of an EL84....... You do not want to get into AB2, Ian, .. all sorts of nasty things happen there ....... At the moment I get the 12 clean watts further towards AB1. However, this means that the 1W I hear most of the time is not as good as it could be. Not as linear, quite, and with a higher output impedance. Now headroom is limited by soft clipping at first before...the cathodyne crashes. I don't want heaps of grid current, I just want a splitter that can cope with a little every now and then. I could add cathode followers or a short-tailed pair like Williamson but that defeats the object of simplicity. I have a sledgehammer approach to valve audio which actually makes design very simple. I have to say that 12W is just not enough. Consider a slightly Williamson circuit which can make a pair of 60vRMS signals available on the OP valve grids... At that level, I have to go outside.. If I want to come back inside, the drivers are loafing along at 15-20vRMS, the room's full of noise, and I have to look very closely at the 'scope for anything out of shape. Yes, yes, yes you can say I just need bigger output valves. There is more to these things than size though, Jim. I like as far as I can to use finesse rather than brute force. We appear to have very different attitudes in this respect. We do, but electricity is cheap and valves are very inefficient. You are an academic and will search out efficiency and numbers which add up. I don't think valve audio is about that at all... Silicon is, but valves are about a big warm open sound and a smile on your face. I think you need a 2 x 100w KT88 stereo pair for a few minutes, and work back from there.. regards as always jim cheers, Ian "jim" wrote in message ... "Ian Iveson" wrote in message ... Also, most importantly in my case, it depends on the linearity of the driven impedance, and hence on how the output stage is biased. Not just on how big it is. One of Van der Veen's designs, for example, uses a cathodyne ECC81 for 6*EL34. But the slightest bit of grid current causes the cathodyne anode output to collapse resulting in a flurry of odd harmonics at the output of the amp. Hi Ian, Is this suprising ?? It is working entirely outside it's design envelope. My wife's Peugeot diesel is easily outpaced by a Ferrari. Should I complain. ?? No inverter we are using is designed to supply current. If you need a current supply to the OP valve grids you need CFs or a transformer hanging on them. This is AB2 or B. Neither are related to high end audio. They are about a big noise, efficiency and bangs per buck Nothing wrong with Menno Van der Veens concertina driving 6 x EL34s. Not seen the circuit but assume it's cathode biased to retain a fairly high grid impedance for the concertina to work into. Parallelling 6 x EL34s provides the output power without asking the concertina to provide a big voltage swing and keeps the circuit simple and stable. I think there is an issue of slew rate limiting too, and/oce at HF. Current-derived cathode feedback is good for turning a problem into a crisis. There is an imbalance between the cathode and anode outputs but this is usually outside the limits of audibility. This is not a problem if we can't hear it, but since the concertina has no gain it is usually necessary to insert another gain stage to get the drive voltages we need for large valves. A Williamson. We now have four stages and since each stage shifts phase, complete inversion can occur at the extremes of frequency. It is unstable. We have an oscillator. Add in global NFB and unless the bandwidth is restricted it may well all get away from you. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. All the inverters we use should be restricted to AB1 None of them are current generators. A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. Only the concertina could be classed as elegant...with a direct coupled voltage amp up front. The LTP and paraphase are a compromise of a gain and inverter stage combined. Patrick has probably taken the LTP as far as it can go and tells me I can have a 6SN7 as one half and an ECC83 as the other and, with a CCJ tail, will still achieve perfect balance of the two outputs. I cannot dispute this, he knows what he is doing. The paraphase ?? Seems even more difficult to balance and keep balanced and I have rarely used it. By combining inversion and gain in one stage both the paraphase and the LTP do have the advantage of of reducing the number of stages and suggest a more stable design. What we need to do is to create an inverted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. Exactly. It is possible to build fine 10-15W amplifiers with simple circuitry and few components. These are maximum ratings however and with inefficient speakers you could be running close to overload at normal listening volumes. To design a 15W amp and ask it to sound good at 20W is a non starter. I like 50W as a design target. Times two for stereo. The whole question of pushing it to the design limits and watching it get out of shape does not then occur. Most of what I am ever going to hear is Class A. No crossover distortion and a driver design which can put 90v Pk-pk on the OP valve grids without really trying. The drawback is that including the PSU, it is big, heavy, and expensive kind regards jim For example, how much HT you have available depends partly on how much hum you can tolerate at the driver stage, which also depends on how good the hum rejection is of the driver. cheers, Ian "jim" wrote in message ... "Armand" wrote in message ... I know that the sections should be well matched, but how much does the PI affect the overall sound of an amp, gain notwithstanding? Thanks. Hi, Armand, Short answer. It doesn't.!!!!!! I have often rebuilt the same PP design with different inverters. The distortion contributed by the inverter stage is nothing compared to that produced by the following stages, and you certainly won't hear it, provided the two antiphase outputs are closely balanced. So why are there different inverter configurations and which one is best ?? Only two inverters seem to be regularly used now. The cathodyne and the LTP. Which you choose is not dictated by which sounds best, it is decided by the AC output required, the impedance of the output load you are driving, and the available B+ voltage. kind regards jim |
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There is little need for high current bias flow in an LTPdriver/CPI driver were it not for the input C of the stage being driven. The higher the idle current, the higher the bandwidth of the driver stage, since the capacitance can be charged and discharged with enough current to maintain the voltage swing at HF. Hiya, Patrick... In the case of the CPI, a small C across the Rk of the stage will boost the HF response from the anode, which tends to roll off first. Yes, O.K. .... If you need a current supply to the OP valve grids you need CFs or a transformer hanging on them. This is AB2 or B. Neither are related to high end audio. They are about a big noise, efficiency and bangs per buck Nothing wrong with Menno Van der Veens concertina driving 6 x EL34s. Not seen the circuit but assume it's cathode biased to retain a fairly high grid impedance for the concertina to work into. But the cathode bias itself causes input grid impedance to be no higher than fixed bias, since grid current occurs only when the peak swing input voltage goes higher than the value of grid bias. I'm looking at the load the driver has to work into.. Cathode bias does not alter the grid impedance per se, as you say, but the grid leak can be made higher because of the self regulating effect of the cathode resistor. The grid leak is the load. We have 6 EL34s here with grid leaks in parallel. I'm just trying to avoid a coupling cap the size of a 45 gallon oil drum and a time constant round about last Thursday !!!! Parallelling 6 x EL34s provides the output power without asking the concertina to provide a big voltage swing and keeps the circuit simple and stable. 12 x EL84 would do about the same thing, and be even easier to drive!. You trying to put one over on me ?? I ain't going to apologise for being a hobby boy. Go up one paragraph ... 12 EL34s ??? Driver design, please ?? You planning on a Dodge or a Chrysler to move this lot ?? I think there is an issue of slew rate limiting too, and/oce at HF. Current-derived cathode feedback is good for turning a problem into a crisis. There is an imbalance between the cathode and anode outputs but this is usually outside the limits of audibility. This is not a problem if we can't hear it, but since the concertina has no gain it is usually necessary to insert another gain stage to get the drive voltages we need for large valves. A Williamson. We now have four stages and since each stage shifts phase, complete inversion can occur at the extremes of frequency. It is unstable. We have an oscillator. Add in global NFB and unless the bandwidth is restricted it may well all get away from you. But to STOP the oscillation, which is normally due to a lousy OPT, and NOT the williamson driver circuit, it is necessary to place a zobel network across the main RL of V1, and williamson recommended a 470pF and 4.7k in parallel with the 47 k load of the 1/2 6SN7 which was V1. Twelve months ago you took my head off about dumping things and introducing extra time constants when I suggested restricting the bandwidth by dumping things you can't hear across V1R and removing them from the feedback chain ....... Whether the OPT is lousy or wonderful, a C across V1R will kill it stone dead....... Why would I want to listen to anything over 30kHz ?? The Williamson 3 stage driver circuit has more bandwidth than an LTP using the same tubes, since the CPI acts as a buffer against the effects of the miller C of the balanced diver stage causing a pole too early at V1, whose Ro is high because the cathode R isn't bypassed. So, bypass it. I usually do....or partially, if I need a feedback point. The stepped HF response raises the pole F caused by the driver stage, but reduces its gain by 12 dB at this HF, ie, about 200 kHz, and therefore the amount of applied NFB at 200 kHz is lowered, and stability is increased. Patrick, we're in the medium waveband here ....... Your designs may have no effect on Radio Canberra, but personally, I don't give a **** whether Radio Canberra gets my LPs full on or not. It will probably be better than the **** they normally play...... Adjust the CR around V1 and 200kHz isn't in there. What does 200kHz sound like ?? I may have it and not know it !! Tune in , now, I'm going to put a Roy Orbison track on !....... Suitable zobel networks are shown also at my website schematics. You dump the **** you can't hear so it can't come back and bite you .. The bandwidth of all my amps are tailored to at least 65 kHz, and any sized cap can be connected at the output without oscillations occuring. It is unconditional stability. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. Indeed, but if CF bufferes after the cathodyne (CPI) are used, direct coupled to the OPV grids, no worries, you can go AB2, if the voltage swing is wide enough. But Ian is going for elegant simplicity. He doesn't want a an extra ECC 81 stuck in there.. He doesn't want to be into AB2. He doesn't really want to be in AB1 An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. All the inverters we use should be restricted to AB1 None of them are current generators. I think you have that wrong. I may have. I will rephrase it. None are low impedance current generators. As I see it, a low impedance driver for AB2 cannot include a 100K anode load resistor and a coupling cap as in parahase/LTP, hanging on the OP valve grid. I may even have this wrong. You will probably put me right... None are voltage sources, like a cathode follower. Most drivers/inverters have highish Ro, and are limited current sources. Pentodes are current sources, since the voltage is determined by the load, andout put current is more nearly constant, and voltage is anywhere. Eh ?? A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. I think its very elegant. What makes it inelegant? Is is the hobnail boots and hairy legs worn with the pink frock? No, it's all the bits and pieces dangling off the side of it which makes it look a complete ****. !!!! How can you trust anything which looks like that !!! Christ !! It's American !!! Where's me concertina ?? Only the concertina could be classed as elegant...with a direct coupled voltage amp up front. The LTP and paraphase are a compromise of a gain and inverter stage combined. Compromise? Have you been drinking too much cheap english ale? No, it's a compromise. How can we get a valve to do two jobs. Gain and inversion. The word compromise implies imperfection .. less than perfect.. How well it measures up is for you to decide. I keep an open mind..... I do not have a favourite inverter. Patrick has probably taken the LTP as far as it can go and tells me I can have a 6SN7 as one half and an ECC83 as the other and, with a CCJ tail, will still achieve perfect balance of the two outputs. I cannot dispute this, he knows what he is doing. Well its true. Once the CCS and equal RLs is established, it is impossible for the increase in current in one RL to be different in value to the reduction of current in the other RL. So balance is assured by RL accuracy, easy in today's world of plentiful 1% R values. One wouldn't dream of using different tubes for each 1/2 of the LTP. But you could if you wanted to. Maybe a triode pentode, like the 6U8. Then it'd be high gain. Theoretically, I cannot deny you are right, and, no, of course you wouldn't use dissimilar triodes for the two halves. Furthermore you have practical circuits up and running which prove the point. As I said, you have taken the LTP about as far as it will go. The paraphase ?? Seems even more difficult to balance and keep balanced and I have rarely used it. By combining inversion and gain in one stage both the paraphase and the LTP do have the advantage of of reducing the number of stages and suggest a more stable design. Not necessarily more stable; see above. No comment .. it has always looked like a mongrel to me .. It could be wonderful.. or not.. I do not know.. erted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. Exactly. It is possible to build fine 10-15W amplifiers with simple circuitry and few components. These are maximum ratings however and with inefficient speakers you could be running close to overload at normal listening volumes. To design a 15W amp and ask it to sound good at 20W is a non starter. I like 50W as a design target. Times two for stereo. The whole question of pushing it to the design limits and watching it get out of shape does not then occur. At last. Someone else realises a couple of KT88 are always going to do better than a pair of EL34, or '84. At last ?? I don't build girls amps !! of what I am ever going to hear is Class A. No crossover distortion and a driver design which can put 90v Pk-pk on the OP valve grids without really trying. The drawback is that including the PSU, it is big, heavy, and expensive kind regards jim PS don't have to be huge if class A is all you want, and +380v for class A triode/pentode/UL/acoustical is easy. No, no no.... Never below 450V and octals... 40 years tells me it's a waste of time... Nowadays we're into rinky dink girly things however. Amps ought to bite your arse .. Regards as always jim Patrick Turner. |
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jim wrote: There is little need for high current bias flow in an LTPdriver/CPI driver were it not for the input C of the stage being driven. The higher the idle current, the higher the bandwidth of the driver stage, since the capacitance can be charged and discharged with enough current to maintain the voltage swing at HF. Hiya, Patrick... In the case of the CPI, a small C across the Rk of the stage will boost the HF response from the anode, which tends to roll off first. Yes, O.K. .... If you need a current supply to the OP valve grids you need CFs or a transformer hanging on them. This is AB2 or B. Neither are related to high end audio. They are about a big noise, efficiency and bangs per buck Nothing wrong with Menno Van der Veens concertina driving 6 x EL34s. Not seen the circuit but assume it's cathode biased to retain a fairly high grid impedance for the concertina to work into. But the cathode bias itself causes input grid impedance to be no higher than fixed bias, since grid current occurs only when the peak swing input voltage goes higher than the value of grid bias. I'm looking at the load the driver has to work into.. Cathode bias does not alter the grid impedance per se, as you say, but the grid leak can be made higher because of the self regulating effect of the cathode resistor. The grid leak is the load. Indeed, the grid R can be higher value when using cathode bias. We have 6 EL34s here with grid leaks in parallel. I'm just trying to avoid a coupling cap the size of a 45 gallon oil drum and a time constant round about last Thursday !!!! In my 300 watt amps, the 12 x 6550 each have 0.47 and 120k, so the load seen by the driver stage is 20k per side, driven by the equivalent of 6 x 0.47 uF in parallel, or about 3 uF, which is easy to arrange in such large amps. To reduce the loading effects on the driver, I use a choke with CT to supply the DC to the LTP, which uses 2 x EL84 in triode, which is as effective as 4 x 6SN7 in parallel. But since you like octals, try a 6V6, or even an EL34. The 40k a-a load seen by the LTP driver means the thd is negligible. the low Ro means the miller C of the OPVs have little effect until well over 100 kHz. The circuit is at http://www.turneraudio.com.au/websch...ma550w335h.gif Parallelling 6 x EL34s provides the output power without asking the concertina to provide a big voltage swing and keeps the circuit simple and stable. 12 x EL84 would do about the same thing, and be even easier to drive!. You trying to put one over on me ?? I ain't going to apologise for being a hobby boy. Go up one paragraph ... 12 EL34s ??? Driver design, please ?? You planning on a Dodge or a Chrysler to move this lot ?? See above, its easy to drive multiple output tubes. I think there is an issue of slew rate limiting too, and/oce at HF. Current-derived cathode feedback is good for turning a problem into a crisis. There is an imbalance between the cathode and anode outputs but this is usually outside the limits of audibility. This is not a problem if we can't hear it, but since the concertina has no gain it is usually necessary to insert another gain stage to get the drive voltages we need for large valves. A Williamson. We now have four stages and since each stage shifts phase, complete inversion can occur at the extremes of frequency. It is unstable. We have an oscillator. Add in global NFB and unless the bandwidth is restricted it may well all get away from you. But to STOP the oscillation, which is normally due to a lousy OPT, and NOT the williamson driver circuit, it is necessary to place a zobel network across the main RL of V1, and williamson recommended a 470pF and 4.7k in parallel with the 47 k load of the 1/2 6SN7 which was V1. Twelve months ago you took my head off about dumping things and introducing extra time constants when I suggested restricting the bandwidth by dumping things you can't hear across V1R and removing them from the feedback chain ...... Whether the OPT is lousy or wonderful, a C across V1R will kill it stone dead....... Why would I want to listen to anything over 30kHz ?? Tim De Paravicini once said of Peter Walker's idea of current dumping, " the worst thing you can do with a current, is dump it..." I don't recall performing a headectomy on you, over "dumping" anything. I do believe in critical damping, in FB amps, to make coexistance with our amps easier without smoky listening rooms a more definite possibility. I have been trying to get the public to understand what I mean, and which is described in RDH4, but in a completely obscure manner. Basically, every amp is a bandpass filter, with a fairly narrow bandwidth without FB. When FB is added, BW increases dramatically, and unless the BW AND OPEN LOOP GAIN at extremes of the BW is reduced in some way without adding extra phase shift, then oscillation is likely with some types of loads, and depending on the quality of the OPT. This message is lost on so many ppl, since they refuse to allow their brains to realise that 6 things are simultaneously contributing to an outcome in a very simple audio device, an amplifier. They want it all to be so simple, but alas, it just cannot be like that. You don't want to listen to anything over 30 kHz, and probably, like me, struggle with anything over 14 kHz, but we do want the amp to stay stable and not misbehave regardless of load, at frequencies above 30 kHz, and below 100 Hz! The Williamson 3 stage driver circuit has more bandwidth than an LTP using the same tubes, since the CPI acts as a buffer against the effects of the miller C of the balanced diver stage causing a pole too early at V1, whose Ro is high because the cathode R isn't bypassed. So, bypass it. I usually do....or partially, if I need a feedback point. I do that to, as my circuits indicate, and the Ro of V1 is lowered about 2.5 times, but I still need to use a zobel network to attain critical damping, and I use a radio tuning cap and a series pot mounted on it to establish the best values of C&R, with about 0.22uF on the output, no R load, and with a 5 kHz square wave, where I nearly minimise ringing.. The stepped HF response raises the pole F caused by the driver stage, but reduces its gain by 12 dB at this HF, ie, about 200 kHz, and therefore the amount of applied NFB at 200 kHz is lowered, and stability is increased. Patrick, we're in the medium waveband here ....... Your designs may have no effect on Radio Canberra, but personally, I don't give a **** whether Radio Canberra gets my LPs full on or not. It will probably be better than the **** they normally play...... Adjust the CR around V1 and 200kHz isn't in there. What does 200kHz sound like ?? I may have it and not know it !! Tune in , now, I'm going to put a Roy Orbison track on !....... Suitable zobel networks are shown also at my website schematics. You dump the **** you can't hear so it can't come back and bite you .. I build amplifiers, not oscillators, and if an amp is merrily oscillating at 200 kHz, there is a power loss, and possibly the amplitude could be high enough to cause tweeter damage, or cause interference, or saturate the drive amp, labouring under its presence. I am a firm believer that only the audio frequencies we want be present in the output of an audio amp of any kind, regardless of the loading conditions. The bandwidth of all my amps are tailored to at least 65 kHz, and any sized cap can be connected at the output without oscillations occuring. It is unconditional stability. So the cathodyne should be restricted to AB1 output stages, and it should idle with plenty of current. Indeed, but if CF bufferes after the cathodyne (CPI) are used, direct coupled to the OPV grids, no worries, you can go AB2, if the voltage swing is wide enough. But Ian is going for elegant simplicity. He doesn't want a an extra ECC 81 stuck in there.. He doesn't want to be into AB2. He doesn't really want to be in AB1 He like class A1, and so do I. Class A1 in most of the gear I build covers 99.9% of what I listen to. An ECC83 is unlikely to be a good candidate. An '82 or an '81 is better, as might be an '88. You have to get enough voltage swing and enough current capability for the task. All the inverters we use should be restricted to AB1 None of them are current generators. I think you have that wrong. I may have. I will rephrase it. None are low impedance current generators. Engineering terminology regards a "low impedance current generator" as a voltage source, ie, the Ro of the voltage source is low compared to the load being driven. Triode drivers provide this. Pentode drivers ususlly don't, unless RL is low, and the low RL in comparison with the following Cap coupled high value Rg, might mean the pentode circuit as a whole is a voltage source. When ever blokes say "current generators" it means the Ro of the that current is very high in comparison with the load, which is true of pentode, or cascoded triode outputs, or outputs from triodes with large value Rk, as is the case with ther CPI at its anode circuit, if measured singly. As I see it, a low impedance driver for AB2 cannot include a 100K anode load resistor and a coupling cap as in parahase/LTP, hanging on the OP valve grid. I may even have this wrong. You will probably put me right... One could build an equivalent circuit of an output grid circuit. Imagine we have a typically designed cathode bais circuit, with the voltage at the cathode sittng at say +30v for an EL34. Imagine having a diode with its anode connected to the tube grid, and its cathode connected to the +30 at the cathode, but via say a 1 k resistor. Imagine for a moment, that grid current was impossible, regardless of a high +ve grid voltage swing. But with the above arrangement of diode and R, there is no current input to the grid from the driver, but when the grid voltage swings +ve enough, ie, about 31 peak volts, the diode starts to conduct, and the the impedance seen by the driver is not just the 100k grid bias R, but it suddenly becomes 1k, the R in series with our imaginery diode. The gain of the driver suddently stalls, because gain = U x RL / ( Ra + RL ), which is true for all tubes. Also, the voltage difference across the coupling cap, which is its charge which is maintained at a constant value during non grid current operation, suddenly starts to change to a higher value of volts. So when the driver voltage swings negative, the diode has switched off, but the coupling cap carries the extra charge which slowly tries to discharge through Rg. Sustained over driving of the output tube into AB2 conditions causes considerable extra direct voltage to be built up in the coupling cap, resulting in the tube being operated at an effectively lower bias point. In effect, our imaginery diode plus certain low value resistor DOES exist, because as soon as a grid goes +ve, it attracts and absorbs negatively charged electrons, which are not fussy where they go, as long as its to a positive something. When music signals become large enough to cause occasional rail clipping, then ususally, there is grid current being drawn, and the idle bias condition shifts, and thd becomes several times higher. when the levels are increased futher, the amp sounds like its choking, which is due to paralysis caused by the charge in the coupling caps, and musiscians with electric geetahs lerve this sound If a sine wave is used, and grid current is drawn, you have the OPVs simply acting as switches for a square wave, and biased fairly off, and the power in the load can be huge compared to the rated undistorted power. With hi-fi, we never go there. None are voltage sources, like a cathode follower. Most drivers/inverters have highish Ro, and are limited current sources. Pentodes are current sources, since the voltage is determined by the load, andout put current is more nearly constant, and voltage is anywhere. Eh ?? See above. A LTP makes a good differential amplifier and you can call it a splitter or an inverter if you want, but it's a very inelegant approach, IMO. I think its very elegant. What makes it inelegant? Is is the hobnail boots and hairy legs worn with the pink frock? No, it's all the bits and pieces dangling off the side of it which makes it look a complete ****. !!!! How can you trust anything which looks like that !!! Christ !! It's American !!! Where's me concertina ?? But even an american sheila with nice tits a dangle dingling about is OK, even with hobnail boots, and nearly wearing her pink frock! Only the concertina could be classed as elegant...with a direct coupled voltage amp up front. The LTP and paraphase are a compromise of a gain and inverter stage combined. Compromise? Have you been drinking too much cheap english ale? No, it's a compromise. How can we get a valve to do two jobs. Gain and inversion. The word compromise implies imperfection .. less than perfect.. How well it measures up is for you to decide. I keep an open mind..... I do not have a favourite inverter. I don't either, but what I use depends on the output stage. Patrick has probably taken the LTP as far as it can go and tells me I can have a 6SN7 as one half and an ECC83 as the other and, with a CCJ tail, will still achieve perfect balance of the two outputs. I cannot dispute this, he knows what he is doing. Well its true. Once the CCS and equal RLs is established, it is impossible for the increase in current in one RL to be different in value to the reduction of current in the other RL. So balance is assured by RL accuracy, easy in today's world of plentiful 1% R values. One wouldn't dream of using different tubes for each 1/2 of the LTP. But you could if you wanted to. Maybe a triode pentode, like the 6U8. Then it'd be high gain. Theoretically, I cannot deny you are right, and, no, of course you wouldn't use dissimilar triodes for the two halves. Furthermore you have practical circuits up and running which prove the point. As I said, you have taken the LTP about as far as it will go. Nope, I am working on one with current mirrors, using PNP transitors. I'd like to use PNP toobes, but toobes are all NPN formatted. The paraphase ?? Seems even more difficult to balance and keep balanced and I have rarely used it. By combining inversion and gain in one stage both the paraphase and the LTP do have the advantage of of reducing the number of stages and suggest a more stable design. Not necessarily more stable; see above. No comment .. it has always looked like a mongrel to me .. It could be wonderful.. or not.. I do not know.. erted copy of the original signal. This is more than inverting, or splitting (whatever that means). The copying part naturally raises the issue of distortion. The paraphase might seem awkward for those looking for symmetry. But you why should copying and inverting be a symmetrical process? The paraphase uses a valve to produce an inverted copy. Perfect. Tricky to get the details right so it stays in balance of course, but so is the LTP. All in all, the cathodyne used as a driver ensures balance and low distortion only within a comparatively narrow corridor of operation, outside of which it goes badly awry. A paraphase is always slightly awry but maintains this over a much wider proportion of available HT and load conditions. A LTP falls somewhere between the two. Really you have to consider the amp as a whole. Exactly. It is possible to build fine 10-15W amplifiers with simple circuitry and few components. These are maximum ratings however and with inefficient speakers you could be running close to overload at normal listening volumes. To design a 15W amp and ask it to sound good at 20W is a non starter. I like 50W as a design target. Times two for stereo. The whole question of pushing it to the design limits and watching it get out of shape does not then occur. At last. Someone else realises a couple of KT88 are always going to do better than a pair of EL34, or '84. At last ?? I don't build girls amps !! of what I am ever going to hear is Class A. No crossover distortion and a driver design which can put 90v Pk-pk on the OP valve grids without really trying. The drawback is that including the PSU, it is big, heavy, and expensive kind regards jim PS don't have to be huge if class A is all you want, and +380v for class A triode/pentode/UL/acoustical is easy. No, no no.... Never below 450V and octals... 40 years tells me it's a waste of time... Nowadays we're into rinky dink girly things however. Amps ought to bite your arse .. I am choosy about how I like my arse being bit, and she has to be good looking before I'll let her. But for class A, 450v is sometimes too much, and 375v is plenty for low THD and class A, with octals in tetrode, pentode, UL, acoustical. But for triode connected tubes, 450v is OK. Patrick Turner. Regards as always jim |
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#29
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jim wrote: Hiya, Patrick, We've all been on your website. Thanks for contributing. I love you, desperately !!!! ... You have no faith in women...... I may be prepared to become homosexual if it furthers my knowledge of a KT88.... Come back to me... I could be yours !! Oh Dahling, I thought you'd never care for me, but youse is so ugly, and I is so fussay...... Part 2 of this header is irrelevant. I cannot----- HEAR----- a phase inverter. If you can, it needs a rethink.!!! I never said I couldn't hear it, or that I could, or could have heard it, if the amp wasn't switched on.... We may be able to measure things way past the point at which it is supposed to operate, but normally, we cannot hear an inverter. Well, every tube, or amplifying device inverts the phase. the signal goes in negative, and comes out positive, so what's the fuss? Does an inverted signal sound like a man talking while he stands on his head? Maybe. Your comments on driving multiple pairs are relevant, and accurate, but I think most of us, here, are listening to music at home, and 2 x50W is about as far as we need to go. 2 x 50W is fairly easy. .... 6L6GC/5881/KT88/6550 .... 450v HT/B+... Somebody out there is going to use 48 CRTs or GZ34s, in parallel because the load lines look good, but I just like to think that valves designed for audio are the best bet. Indeed I agree. Easy to drive too... LTP or concertina/Williamson.... I have been into LTP/concertina and ocassionally paraphase. I still like the symmetry, coupling simplicity, and low imp drive of a CT transformer, but it will probably not happen in my lifetime. It looks simple on paper, but one needs iron, wire, and patience, a lathe, wax, bobbins, and no swearing when you break the fine wire when turning it up. Most ppl use resistors, which are cheaper, easier, but the thd is 3 times that of the long way around the iron. There is an answer to the ultimate driver/power amp. Most of us have realized that it is silicon. Fortunately, none of is going to admit it...... I will be with you, all the way, ..we are all behind you ..to plumb the depths and hit the highs of an ECC83, no matter what Texas Instruments throws at us...... regards jim. Oh Jimmy, I was nearly going to fall in love, but then you said that; about SS, an I'm allergic to some sillycon, and now I've gone all bashful and shy. Patrick Turner. |
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#30
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"jim" wrote:
: My main point, however, is that you are blatantly advertizing Turnip Audio : again !!! : I have reported this to Andre, Arny and Stewart : They will be contacting you shortly : regards : jim I think dat Turnip Audio has already been hexed into jive, man:=)) Dig dat design philsophy! Slap mah fro! :=}) http://tinyurl.com/itxl But the previous discussion has been enlightening ... Cheers, Pat! |
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#31
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Ross Matheson wrote: "jim" wrote: : My main point, however, is that you are blatantly advertizing Turnip Audio : again !!! : I have reported this to Andre, Arny and Stewart : They will be contacting you shortly : regards : jim I think dat Turnip Audio has already been hexed into jive, man:=)) Dig dat design philsophy! Slap mah fro! :=}) http://tinyurl.com/itxl But the previous discussion has been enlightening ... Cheers, Pat! LOL! Where do you find this stuff ??? I especially liked "Vacuum Tube Amplifiers and Loudrapa' Systems" Hehehe.. Even the links to other pages are "dialectisized." Clever bit of coding, this Dialectizer! Cheers, Fred -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects, Vacuum Tubes & other stuff: | | http://www.dogstar.dantimax.dk | +--------------------------------------------+ |
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#32
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"jim" feverishly worked up new ad copy:-
in , on Stardate Mon, 4 Aug 2003 14:30:05 -0700, : : "Patrick Turner" wrote in message : ... : : : jim wrote: : : Hiya, Patrick, : We've all been on your website. Thanks for contributing. I love you, : desperately !!!! ... You have no faith in women...... I may be : prepared to become homosexual if it furthers my knowledge of a KT88.... : Come back to me... I could be yours !! : : Oh Dahling, I thought you'd never care for me, : but youse is so ugly, and I is so fussay...... : : **** off, you old ****.!!!!!! : (sorry, Uselessnet-- I won't swear again) : I got a picture of you standing behind a 6550 barby looking as if the Queen : and Prince Philip were going to turn up at any minute........... Don't give : me that 'choosy' line... I look like you.. You take anything on : offer...............!!! It's got a pulse.... you go for it !!!! : : : Part 2 of this header is irrelevant. I cannot----- : HEAR----- a phase inverter. If you can, it needs a rethink.!!! {([SNIP])} We clearly need a marketing re-think here!!! Let's do some X-RESEARCH!  Those funky dialects are just tame compared to entering a favourite URL at [[[[[ R 18 WARNING!!! ]]]]] http://www.pornolize.com/ {([ HIT Refresh! ]}) [Hit refresh and it changes again ... might be even for the better!] : I will be with you, all the way, ..we are all behind you ..to plumb the : depths and hit the highs of an ECC83, no matter what Texas Instruments : throws at us...... : regards : jim. : : Oh Jimmy, I was nearly going to fall in love, but then you said that; : about SS, an I'm allergic to some sillycon, and now I've gone all bashful : and shy. : : Bugger off, Patty !! May I call you Patty, darling ?? Mmmmmmmmmm .. : : Patrick Turner. Forget Venus! Mars is heading straight for Canberra, right this minute!!! http://tinyurl.com/iyvl RdM::==}) |
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Hiya, Patrick,
We've all been on your website. Thanks for contributing. I love you, desperately !!!! ... You have no faith in women...... I may be prepared to become homosexual if it furthers my knowledge of a KT88.... Come back to me... I could be yours !! Part 2 of this header is irrelevant. I cannot----- HEAR----- a phase inverter. If you can, it needs a rethink.!!! We may be able to measure things way past the point at which it is supposed to operate, but normally, we cannot hear an inverter. Your comments on driving multiple pairs are relevant, and accurate, but I think most of us, here, are listening to music at home, and 2 x50W is about as far as we need to go. 2 x 50W is fairly easy. .... 6L6GC/5881/KT88/6550 .... 450v HT/B+... Somebody out there is going to use 48 CRTs or GZ34s, in parallel because the load lines look good, but I just like to think that valves designed for audio are the best bet. Easy to drive too... LTP or concertina/Williamson.... I have been into LTP/concertina and ocassionally paraphase. I still like the symmetry, coupling simplicity, and low imp drive of a CT transformer, but it will probably not happen in my lifetime. There is an answer to the ultimate driver/power amp. Most of us have realized that it is silicon. Fortunately, none of is going to admit it...... I will be with you, all the way, ..we are all behind you ..to plumb the depths and hit the highs of an ECC83, no matter what Texas Instruments throws at us...... regards jim. |
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#34
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"Patrick Turner" wrote in message ... jim wrote: Hiya, Patrick, We've all been on your website. Thanks for contributing. I love you, desperately !!!! ... You have no faith in women...... I may be prepared to become homosexual if it furthers my knowledge of a KT88.... Come back to me... I could be yours !! Oh Dahling, I thought you'd never care for me, but youse is so ugly, and I is so fussay...... **** off, you old ****.!!!!!! (sorry, Uselessnet-- I won't swear again) I got a picture of you standing behind a 6550 barby looking as if the Queen and Prince Philip were going to turn up at any minute........... Don't give me that 'choosy' line... I look like you.. You take anything on offer...............!!! It's got a pulse.... you go for it !!!! Part 2 of this header is irrelevant. I cannot----- HEAR----- a phase inverter. If you can, it needs a rethink.!!! I never said I couldn't hear it, or that I could, or could have heard it, if the amp wasn't switched on.... I sometimes hear it when the amp is off. I often hear it after a few cans of something or other .......If the amp is on, or not, it could be better, or not, or on, or not, I don't really know....... We may be able to measure things way past the point at which it is supposed to operate, but normally, we cannot hear an inverter. Now, let's be serious... Well, every tube, or amplifying device inverts the phase. the signal goes in negative, and comes out positive, so what's the fuss? Does an inverted signal sound like a man talking while he stands on his head? Maybe. Try as they might, Americans and Belgians cannot speak English. Australians only get near.. Why am I trying to reduce the THD when people can't even talk properly ?? Why are we talking about distortion with people with speech defects ?? Your comments on driving multiple pairs are relevant, and accurate, but I think most of us, here, are listening to music at home, and 2 x50W is about as far as we need to go. 2 x 50W is fairly easy. .... 6L6GC/5881/KT88/6550 .... 450v HT/B+... Somebody out there is going to use 48 CRTs or GZ34s, in parallel because the load lines look good, but I just like to think that valves designed for audio are the best bet. Indeed I agree. What !!!!!!!!!! You agree ?? With the Hobby Boy ????? Easy to drive too... LTP or concertina/Williamson.... I have been into LTP/concertina and ocassionally paraphase. I still like the symmetry, coupling simplicity, and low imp drive of a CT transformer, but it will probably not happen in my lifetime. It looks simple on paper, but one needs iron, wire, and patience, a lathe, wax, bobbins, and no swearing when you break the fine wire when turning it up. Most ppl use resistors, which are cheaper, easier, but the thd is 3 times that of the long way around the iron. I have not gone very far down the split phase driver transfomer route. I actually haven't gone anywhere at all. It is a dream and you may well invent it. I have to go to work every day. There is an answer to the ultimate driver/power amp. Most of us have realized that it is silicon. Fortunately, none of is going to admit it...... I will be with you, all the way, ..we are all behind you ..to plumb the depths and hit the highs of an ECC83, no matter what Texas Instruments throws at us...... regards jim. Oh Jimmy, I was nearly going to fall in love, but then you said that; about SS, an I'm allergic to some sillycon, and now I've gone all bashful and shy. Bugger off, Patty !! May I call you Patty, darling ?? Mmmmmmmmmm .. Patrick Turner. |
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Patrick,
I just know you are going to tell me that my dog is ****ing up the wrong tree..... My picture is a paralelled 6SN7 -- about 15mA...you can start a truck with it ..... and a 1:2 CT split phase driver .. Anode or cathode loaded. ?? You choose...... But don't come back and poke me in the eye and tell me I have it wrong, . Unless you know you are right............. ..regards jim |
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jim wrote: Patrick, I just know you are going to tell me that my dog is ****ing up the wrong tree..... My picture is a paralelled 6SN7 -- about 15mA...you can start a truck with it ..... and a 1:2 CT split phase driver .. Anode or cathode loaded. ?? You choose...... But don't come back and poke me in the eye and tell me I have it wrong, . Unless you know you are right............. .regards jim Last time I poked someone in the eye, the big bully bashed me up, and mussed up my nice new hairdo, and made me cry. If the tranny has wide bandwidth, and a flat response which gets more unlikely as the step up ratio increases, then the 6SN7 is a nice driver for this, or even better, a 6V6 in triode. The use of a CF to drive the input to the primary means the bandwidth and response is more likely to be better, and thd of the iron will be lower, since that also reduces with the lower drive impedance. But the tranny does have parasitic inductances, and shunt C, and leakage L, and hence resonances, and use of FB is limited, since extra phase shift occurs. A second input 6SN7 needs to be used for gain. But you like them and they look nice on the chassis.... But in triode amps with no FB, IST inverters are fine. Lundahl make a nice IST 1:2 for an inverter. Patrick Turner. |
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#37
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jim wrote: "Patrick Turner" wrote in message Last time I poked someone in the eye, the big bully bashed me up, and mussed up my nice new hairdo, and made me cry. Hiya, So, my lad did find you, then !! It was so late at night, and dark in that alley way, And I don't know what your whippersnapper lad was looking for, but he wasn't going to take liberties with ME! If the tranny has wide bandwidth, and a flat response which gets more unlikely as the step up ratio increases, then the 6SN7 is a nice driver for this, or even better, a 6V6 in triode. The use of a CF to drive the input to the primary means the bandwidth and response is more likely to be better, and thd of the iron will be lower, since that also reduces with the lower drive impedance. But the tranny does have parasitic inductances, and shunt C, and leakage L, and hence resonances, and use of FB is limited, since extra phase shift occurs. A second input 6SN7 needs to be used for gain. But you like them and they look nice on the chassis.... We've had this conversation before. I only keep dragging it up again in the hope that you will think about it rather than keep giving me those negative waves. We are agreed that dedicated audio valves are probably the best things to use for audio. Since the KT88/90/6550 are available and just a pair of them will frighten most people, possibly we have the nucleus of the ultimate valve amp, here. ?? Multiple pairs of EL84s are not a step forward because the impedances go in opposite directions. Paralleling them might result in a simpler OPT, but the driver design becomes more complex. Nah, paralleling EL84 makes the driver desigm MORE simple, since all one needs is a gain tube, maybe just a CPI, which only has to make about 6vrms to each side of the OPV grids, and the input tube only has to make this maximum lowish voltage. Baird use a sixpack of EL84, good for 60 watts, which is too much, and 36 watts would be better, or use 8 tubes for 50 watts. 4 x EL84 is the equivalent of a tube with Gm = 44 mA/v, Ra = 10k, and U of 440, in pentode mode. This means that with acoustical connection, the use of 10 dB of OPT CFB will work very effectively, and give an output stage giving 50 watts, with triode like character, and sound, and still be no worse to drive than KT88 in plain UL. The paralleled tubes have a "higher figure of merit" than a single KT88, for about the same figure of maximum plate dissipation. Costs are similar. OPT for 8 x EL84 would be the same size as for 2 X KT88. So, let's go down the road a bit... The KT88/90/6550 as triodes or pentodes/beam tets are pretty good. Turnipaudio.com will have no problem matching up to any speaker you choose with a full range of, hand crafted, individually signed, limited edition, personally comissioned, OPT,s (now available in gold, silver or brushed walnut finish) All OPTs now come with a signed photo of the main man standing behind his 6550 barbecue, and are fully approved by Andre Jute, Neddy Seagoon and Kylie Minogue.... ( Patrick's big one is the best I have ever come across.. That's what Kylie and Nicole told me, but they say that to all the fellas..... quote.. Rangoon Auto Trader 29.07.2003) The back end is fairly easy, then. Up the front, it is just a matter of getting a bit of voltage to excite the inverter. Then we all go off in opposite directions with lots of Rs and Cs and neg supplies and silicon for a gain of bugger all, ... just to get two opposite phase drives.. The back and front end are easy. Put your head around the middle bit. Actually, throw the LTP over the hedge and get a blank sheet of paper. My kindest regards, big boy...... jim We have such tall hedges here in Oz, its difficult to throw things over... I will take on board your comments re the foregoing matters, and forward them to the specialist in our organisation. Patrick Turner. |
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"Patrick Turner" wrote in message ... jim wrote: Patrick, I just know you are going to tell me that my dog is ****ing up the wrong tree..... My picture is a paralelled 6SN7 -- about 15mA...you can start a truck with it ..... and a 1:2 CT split phase driver .. Anode or cathode loaded. ?? You choose...... But don't come back and poke me in the eye and tell me I have it wrong, . Unless you know you are right............. .regards jim Last time I poked someone in the eye, the big bully bashed me up, and mussed up my nice new hairdo, and made me cry. Hiya, So, my lad did find you, then !! If the tranny has wide bandwidth, and a flat response which gets more unlikely as the step up ratio increases, then the 6SN7 is a nice driver for this, or even better, a 6V6 in triode. The use of a CF to drive the input to the primary means the bandwidth and response is more likely to be better, and thd of the iron will be lower, since that also reduces with the lower drive impedance. But the tranny does have parasitic inductances, and shunt C, and leakage L, and hence resonances, and use of FB is limited, since extra phase shift occurs. A second input 6SN7 needs to be used for gain. But you like them and they look nice on the chassis.... We've had this conversation before. I only keep dragging it up again in the hope that you will think about it rather than keep giving me those negative waves. We are agreed that dedicated audio valves are probably the best things to use for audio. Since the KT88/90/6550 are available and just a pair of them will frighten most people, possibly we have the nucleus of the ultimate valve amp, here. ?? Multiple pairs of EL84s are not a step forward because the impedances go in opposite directions. Paralleling them might result in a simpler OPT, but the driver design becomes more complex. So, let's go down the road a bit... The KT88/90/6550 as triodes or pentodes/beam tets are pretty good. Turnipaudio.com will have no problem matching up to any speaker you choose with a full range of, hand crafted, individually signed, limited edition, personally comissioned, OPT,s (now available in gold, silver or brushed walnut finish) All OPTs now come with a signed photo of the main man standing behind his 6550 barbecue, and are fully approved by Andre Jute, Neddy Seagoon and Kylie Minogue.... ( Patrick's big one is the best I have ever come across.. quote.. Rangoon Auto Trader 29.07.2003) The back end is fairly easy, then. Up the front, it is just a matter of getting a bit of voltage to excite the inverter. Then we all go off in opposite directions with lots of Rs and Cs and neg supplies and silicon for a gain of bugger all, ... just to get two opposite phase drives.. The back and front end are easy. Put your head around the middle bit. Actually, throw the LTP over the hedge and get a blank sheet of paper. My kindest regards, big boy...... jim But in triode amps with no FB, IST inverters are fine. Lundahl make a nice IST 1:2 for an inverter. Patrick Turner. |
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"Patrick Turner" wrote in message ... jim wrote: "Patrick Turner" wrote in message Last time I poked someone in the eye, the big bully bashed me up, and mussed up my nice new hairdo, and made me cry. Hiya, So, my lad did find you, then !! It was so late at night, and dark in that alley way, And I don't know what your whippersnapper lad was looking for, but he wasn't going to take liberties with ME! I told him to be gentle..... This guy is going to give us the ultimate inverter, I said !! If the tranny has wide bandwidth, and a flat response which gets more unlikely as the step up ratio increases, then the 6SN7 is a nice driver for this, or even better, a 6V6 in triode. The use of a CF to drive the input to the primary means the bandwidth and response is more likely to be better, and thd of the iron will be lower, since that also reduces with the lower drive impedance. But the tranny does have parasitic inductances, and shunt C, and leakage L, and hence resonances, and use of FB is limited, since extra phase shift occurs. A second input 6SN7 needs to be used for gain. But you like them and they look nice on the chassis.... We've had this conversation before. I only keep dragging it up again in the hope that you will think about it rather than keep giving me those negative waves. We are agreed that dedicated audio valves are probably the best things to use for audio. Since the KT88/90/6550 are available and just a pair of them will frighten most people, possibly we have the nucleus of the ultimate valve amp, here. ?? Multiple pairs of EL84s are not a step forward because the impedances go in opposite directions. Paralleling them might result in a simpler OPT, but the driver design becomes more complex. Nah, paralleling EL84 makes the driver desigm MORE simple, since all one needs is a gain tube, maybe just a CPI, which only has to make about 6vrms to each side of the OPV grids, and the input tube only has to make this maximum lowish voltage. Thought we agreed that KT88/90/6550 was a good idea ?? What's with this nine pin stuff ?? Baird use a sixpack of EL84, good for 60 watts, which is too much, and 36 watts would be better, or use 8 tubes for 50 watts. Times two for a stereo pair equals 16 x EL84s...... It's no more difficult to drive than 4 x 6550s.. OK ... but why don't we just go for the 6550s and save all those holes, sockets and heater amps ?? Get simple, just use the 6550s !! 4 x EL84 is the equivalent of a tube with Gm = 44 mA/v, Ra = 10k, and U of 440, in pentode mode. This means that with acoustical connection, the use of 10 dB of OPT CFB will work very effectively, and give an output stage giving 50 watts, with triode like character, and sound, and still be no worse to drive than KT88 in plain UL. The paralleled tubes have a "higher figure of merit" ????? What's that mean ?? than a single KT88, for about the same figure of maximum plate dissipation. Costs are similar. OPT for 8 x EL84 would be the same size as for 2 X KT88. We're just going to fall out, here... As far as I am concerned, the fact that I cannot connect my Shure M75 directly to the speakers is a disadvantage and means that I have to put something between them. What goes in the middle should be as simple and uncomplicated as possible. Everything I put between them will degrade, corrupt or distort what my Shure is trying to say. Why would I want to drive 12/16 nine pins when 4 octals will do the same job ?? Every cap and resistor is going to do something. How few can I get away with ??? Ian is trying to go the same way. Elegant simplicity are his words. We just have different output levels. So, let's go down the road a bit... The KT88/90/6550 as triodes or pentodes/beam tets are pretty good. Turnipaudio.com will have no problem matching up to any speaker you choose with a full range of, hand crafted, individually signed, limited edition, personally comissioned, OPT,s (now available in gold, silver or brushed walnut finish) All OPTs now come with a signed photo of the main man standing behind his 6550 barbecue, and are fully approved by Andre Jute, Neddy Seagoon and Kylie Minogue.... ( Patrick's big one is the best I have ever come across.. That's what Kylie and Nicole told me, but they say that to all the fellas..... Nicole ??? You haven't filled us in on Nicole ?? Hey !! quote.. Rangoon Auto Trader 29.07.2003) The back end is fairly easy, then. Up the front, it is just a matter of getting a bit of voltage to excite the inverter. Then we all go off in opposite directions with lots of Rs and Cs and neg supplies and silicon for a gain of bugger all, ... just to get two opposite phase drives.. The back and front end are easy. Put your head around the middle bit. Actually, throw the LTP over the hedge and get a blank sheet of paper. My kindest regards, big boy...... jim We have such tall hedges here in Oz, its difficult to throw things over... I have a hedge trimmer design which uses 120 EL84s in parallel I could let you have ...... I will take on board your comments re the foregoing matters, and forward them to the specialist in our organisation. Patrick Turner. |
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