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#81
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Transformer attenuators
In article ,
"Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Ian Iveson" wrote: One thing I wonder about. It is common to use a capacitor in series at the input of a valve power amp, and this may be used to limit the LF response. If you use a transformer then arguably you don't need the series cap for its dc-blocking role. So it may seem that you can rely on the transformer also for the role of limiting LF. Would that be wise? I am concerned about the possibility of ensuing distortion. I don't see why distortion would become any more of a problem below the lowest frequency the transformer the transformer is rated for, assuming the LF signal level is no higher than the signal level the transformer is designed for in its specified range. Distortion is more of a problem at low frequencies because of core saturation effects: http://www.rane.com/note159.html "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies. "Saturation has nothing to do with power delivery: the onset of saturation depends only on the voltage waveform applied to the primary." That quote should be corrected to state that saturation depends on frequency as well as voltage. Why? the previous quote already said that once! Why, because the meaning of the statement "the onset of saturation depends only on the voltage waveform applied to the primary" is ambiguous although theoretically correct. The reason distortion (saturation) would not be a problem when a transformer is being used to limit the LF response as the OP was asking about, It is the frequency and amplitude of the applied voltage that counts. Isn't that essentially what I just got through saying in the part of my post that you snipped out? Please note that there was a typo in that part of my post when I said "low pass" filter when I meant "high pass" filter, this typo should have been obvious to the reader since we are talking about limiting the LF response, which means a high pass filter. When a transformer is being used as a high pass filter, its primary is receiving the applied voltage. Can you explain how a transformer could act as a high pass filter when the "primary is receiving the applied voltage", assuming you are not depending on saturation effects to produce a pseudo low pass filter effect? To act as a high pass filter the "voltage" can't be "applied" directly to the transformer's primary, there must be a source impedance involved in the equation between the source voltage and the transformer primary. This source impedance could consist of the resistive component of the impedance of the transformer's primary winding, assuming it is large enough to create the desired high pass effect in conjunction with the inductive component of the primary winding's impedance. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#82
Posted to rec.audio.tubes
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Transformer attenuators
John Byrns wrote
Ian Iveson wrote: One thing I wonder about. It is common to use a capacitor in series at the input of a valve power amp, and this may be used to limit the LF response. If you use a transformer then arguably you don't need the series cap for its dc-blocking role. So it may seem that you can rely on the transformer also for the role of limiting LF. Would that be wise? I am concerned about the possibility of ensuing distortion. I don't see why distortion would become any more of a problem below the lowest frequency the transformer the transformer is rated for, assuming the LF signal level is no higher than the signal level the transformer is designed for in its specified range. Distortion is more of a problem at low frequencies because of core saturation effects: http://www.rane.com/note159.html "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies. "Saturation has nothing to do with power delivery: the onset of saturation depends only on the voltage waveform applied to the primary." That quote should be corrected to state that saturation depends on frequency as well as voltage. *Magnetising current* is directly responsible for flux density. Voltage and frequency relations are derived. The reason distortion (saturation) would not be a problem when a transformer is being used to limit the LF response as the OP was asking about, is because what we are talking about then is a low pass filter where the source resistance driving the transformer primary operates in conjunction with the transformer's primary inductance to roll of the LF response below a specific point. This roll off of the primary voltage at lower frequencies prevents the core from going into saturation (distortion) at lower frequencies as would happen if the primary voltage were held constant as the frequency decreases. Not with my maths. Please post yours. Think of it like this. You have current due to load, and in parallel you have magnetising current. An increase in magnetising current at lower frequencies is responsible for the roll-off, given a finite source resistance. An increase in magnetising current means that the core traverses a greater part of the BH curve, hence distortion will increase. In the extreme, saturation will occur if Vs/Rs is great enough at f=0, ie for DC, when *all* the current is magnetising. If Vs/Rs is greater than that, then saturation will occur at some frequency higher than 0. Yes, effective primary voltage falls with frequency, but not by enough to hold the magnetising current constant. If your mathematical argument disagrees with this please post it. So far you have merely asserted, not demonstrated. Ian |
#83
Posted to rec.audio.tubes
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Transformer attenuators
"John Byrns" wrote in message
In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Ian Iveson" wrote: One thing I wonder about. It is common to use a capacitor in series at the input of a valve power amp, and this may be used to limit the LF response. If you use a transformer then arguably you don't need the series cap for its dc-blocking role. So it may seem that you can rely on the transformer also for the role of limiting LF. Would that be wise? I am concerned about the possibility of ensuing distortion. I don't see why distortion would become any more of a problem below the lowest frequency the transformer the transformer is rated for, assuming the LF signal level is no higher than the signal level the transformer is designed for in its specified range. Distortion is more of a problem at low frequencies because of core saturation effects: http://www.rane.com/note159.html "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies. "Saturation has nothing to do with power delivery: the onset of saturation depends only on the voltage waveform applied to the primary." That quote should be corrected to state that saturation depends on frequency as well as voltage. Why? the previous quote already said that once! Why, because the meaning of the statement "the onset of saturation depends only on the voltage waveform applied to the primary" is ambiguous although theoretically correct. Why did you remove the part of the paragraph that explained the frequency dependency? To repeat: "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies The reason distortion (saturation) would not be a problem when a transformer is being used to limit the LF response as the OP was asking about, It is the frequency and amplitude of the applied voltage that counts. Isn't that essentially what I just got through saying in the part of my post that you snipped out? No, that's what you snipped out of my post. |
#84
Posted to rec.audio.tubes
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Transformer attenuators
This might be a bit interesting:
http://www.ivesonaudio.pwp.blueyonde...nByrnsTest.GIF For what's in the coil and core models: http://www.ivesonaudio.pwp.blueyonde...byrnstest2.GIF http://www.ivesonaudio.pwp.blueyonde...byrnstest3.GIF Ian |
#85
Posted to rec.audio.tubes
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Transformer attenuators
"flipper" wrote in message ... On Thu, 07 Jun 2007 04:03:01 GMT, Eeyore wrote: west wrote: "Eeyore" wrote Iain Churches wrote: 2. Are they actually better than a passive stepped attenuator controller? Better ? Explain what better is first ! As I've discoverd, in the tube audio world, "better" has no correlation with measured technical accuracy / performance is is merely a subjective matter. I fail to see thefore how "better" can be anything other than a personal opinion. Why are you always trying to pick fly **** out of pepper? Maybe you should frequent alt.lawyers. Let's stop this bs. I know what he means. I'd like to see you post something in his language. Food for thought. "Better" has no definable meaning. That's the question he's asking: for an explanation or definition of why it's supposedly 'better', or by what 'definition one would claim it's 'better', and why one would use it. E.g. one often hears here that SET's are better than other amplifiers types yet they are demonstrably hugely technically inferior in almost every respect. If this is to determine what 'better' means then better = worse. How about asking a question that has a possible meaningful answer instead ? He did. You just want to play word games rather than deal with the intent of the question. Or alternatively use the word 'nice' so there's no confusion with technical accuracy. The statement "SET's are nicer than other types of amplifier" would be a more honest expression of opinion than using the word 'better'. Graham I believe most of us know what the spirit of the term "better" means in this case, no matter what the T crossers and the I dotter experts say. If a potentiometer is placed in the signal path, there is a compromise to the audio quality. Anything that improves on that compromise is BETTER. Give it a break. Let's all learn from each other, without the anal retentiveness nitpicking. west |
#86
Posted to rec.audio.tubes
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Transformer attenuators
PS Perhaps I should explain that the two graphs show how flux varies
on a linear vertical scale, and how gain varies on a log vertical scale, on the same horizontal frequency scale. The model assumes a linear relationship between H and B, unfortunately. Although the flux plot looks like a BH curve, it isn't. The apparent saturation is due to the fact that the source resistance eventually becomes a virtual current source because it is so high compared to the coil impedance at very low frequencies. The vertical scale for the flux graph is a bit mysterious. First, to get the flux density, you would need to divide by the core area (A, in the model). Then you need to appreciate that "gain" means relative to the small-signal voltage input (a numerical comparison regardless of units). I can't remember what system of units I used. It should be obvious if magnetic things happen to be fresh in your mind. I constructed the models ages ago but gave up trying to contrive how to incorporate a realistic BH curve. Ian "Ian Iveson" wrote in message k... This might be a bit interesting: http://www.ivesonaudio.pwp.blueyonde...nByrnsTest.GIF For what's in the coil and core models: http://www.ivesonaudio.pwp.blueyonde...byrnstest2.GIF http://www.ivesonaudio.pwp.blueyonde...byrnstest3.GIF Ian |
#87
Posted to rec.audio.tubes
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Transformer attenuators
In article ,
"Ian Iveson" wrote: John Byrns wrote Ian Iveson wrote: One thing I wonder about. It is common to use a capacitor in series at the input of a valve power amp, and this may be used to limit the LF response. If you use a transformer then arguably you don't need the series cap for its dc-blocking role. So it may seem that you can rely on the transformer also for the role of limiting LF. Would that be wise? I am concerned about the possibility of ensuing distortion. I don't see why distortion would become any more of a problem below the lowest frequency the transformer the transformer is rated for, assuming the LF signal level is no higher than the signal level the transformer is designed for in its specified range. Distortion is more of a problem at low frequencies because of core saturation effects: http://www.rane.com/note159.html "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies. "Saturation has nothing to do with power delivery: the onset of saturation depends only on the voltage waveform applied to the primary." That quote should be corrected to state that saturation depends on frequency as well as voltage. *Magnetising current* is directly responsible for flux density. Voltage and frequency relations are derived. The reason distortion (saturation) would not be a problem when a transformer is being used to limit the LF response as the OP was asking about, is because what we are talking about then is a low pass filter where the source resistance driving the transformer primary operates in conjunction with the transformer's primary inductance to roll of the LF response below a specific point. This roll off of the primary voltage at lower frequencies prevents the core from going into saturation (distortion) at lower frequencies as would happen if the primary voltage were held constant as the frequency decreases. Not with my maths. Please post yours. Think of it like this. You have current due to load, and in parallel you have magnetising current. An increase in magnetising current at lower frequencies is responsible for the roll-off, given a finite source resistance. An increase in magnetising current means that the core traverses a greater part of the BH curve, hence distortion will increase. In the extreme, saturation will occur if Vs/Rs is great enough at f=0, ie for DC, when *all* the current is magnetising. If Vs/Rs is greater than that, then saturation will occur at some frequency higher than 0. Yes, effective primary voltage falls with frequency, but not by enough to hold the magnetising current constant. If your mathematical argument disagrees with this please post it. So far you have merely asserted, not demonstrated. My argument depends on two assumptions, please dispute one or the other, or both if you wish, if you agree with both assumptions then my original claim stands. Assumption #1: I am not a transformer engineer, but those who know more than I do about transformers have told me that for a given degree of core saturation (distortion), if the frequency is cut in half, then the voltage applied to the winding must also be cut in half to avoid saturation. This means that the applied voltage must be made proportional to the frequency (or lower) if saturation (distortion) is to be avoided. Assumption #2: If the transformer is being used to limit the LF response of the system, then assuming no load on the secondary, the source resistance feeding the primary of the transformer must be made equal to the primary inductance at the desired cutoff frequency of the resulting high pass filter. Below cutoff the voltage out of such a filter, at the primary of the transformer in this case, falls at rate that makes the voltage proportional to the frequency. This is exactly the sort of voltage response we need on the primary to prevent saturation of the transformer, hence saturation shouldn't be a problem. So which one of these assumptions is wrong, or if both assumptions are correct, where did my logic fail? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#88
Posted to rec.audio.tubes
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Transformer attenuators
In article ,
"Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Arny Krueger" wrote: "John Byrns" wrote in message In article , "Ian Iveson" wrote: One thing I wonder about. It is common to use a capacitor in series at the input of a valve power amp, and this may be used to limit the LF response. If you use a transformer then arguably you don't need the series cap for its dc-blocking role. So it may seem that you can rely on the transformer also for the role of limiting LF. Would that be wise? I am concerned about the possibility of ensuing distortion. I don't see why distortion would become any more of a problem below the lowest frequency the transformer the transformer is rated for, assuming the LF signal level is no higher than the signal level the transformer is designed for in its specified range. Distortion is more of a problem at low frequencies because of core saturation effects: http://www.rane.com/note159.html "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies. "Saturation has nothing to do with power delivery: the onset of saturation depends only on the voltage waveform applied to the primary." That quote should be corrected to state that saturation depends on frequency as well as voltage. Why? the previous quote already said that once! Why, because the meaning of the statement "the onset of saturation depends only on the voltage waveform applied to the primary" is ambiguous although theoretically correct. Why did you remove the part of the paragraph that explained the frequency dependency? Arny, you are a bald faced liar, go back and read my post again, I did not remove a single word of your post that I was replying to. To repeat: "Core saturation happens when the magnetic field in the core reaches its maximum possible density, which is what happens when the applied voltage polarity remains the same for too long." Obviously, the applied voltage polarity remains the same for a longer time at lower frequencies than higher frequencies The reason distortion (saturation) would not be a problem when a transformer is being used to limit the LF response as the OP was asking about, It is the frequency and amplitude of the applied voltage that counts. Isn't that essentially what I just got through saying in the part of my post that you snipped out? No, that's what you snipped out of my post. Go back and read my post again, and then go away, I am not going to try and talk to a liar. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#89
Posted to rec.audio.tubes
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Transformer attenuators
John Byrns wrote: Assumption #1: I am not a transformer engineer, but those who know more than I do about transformers have told me that for a given degree of core saturation (distortion), if the frequency is cut in half, then the voltage applied to the winding must also be cut in half to avoid saturation. This means that the applied voltage must be made proportional to the frequency (or lower) if saturation (distortion) is to be avoided. Correct. When I was getting into transforemr design for SMPSs a couple of years back I cane across the term 'volt seconds' which helps explain a lot. The more volt-seconds, the higher the flux. Graham |
#90
Posted to rec.audio.tubes
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Transformer attenuators
John Byrns wrote:
Assumption #1: I am not a transformer engineer, but those who know more than I do about transformers have told me that for a given degree of core saturation (distortion), if the frequency is cut in half, then the voltage applied to the winding must also be cut in half to avoid saturation. This means that the applied voltage must be made proportional to the frequency (or lower) if saturation (distortion) is to be avoided. Assumption #2: If the transformer is being used to limit the LF response of the system, then assuming no load on the secondary, the source resistance feeding the primary of the transformer must be made equal to the primary inductance at the desired cutoff frequency of the resulting high pass filter. Below cutoff the voltage out of such a filter, at the primary of the transformer in this case, falls at rate that makes the voltage proportional to the frequency. This is exactly the sort of voltage response we need on the primary to prevent saturation of the transformer, hence saturation shouldn't be a problem. So which one of these assumptions is wrong, or if both assumptions are correct, where did my logic fail? Your assumption #2 is certainly false. It is not a sharp corner followed by a straight line: -6dB per octave is an asymptote. Your assumption of no secondary load is not appropriate for a transformer. However, my simulation uses such a light load that no load would not make much difference. I have given one explanation for why the flux flattens at very low f in my simulation. Translated to your thinking, it gets flatter as your approximation gets closer to the truth. By that time the damage, as it were, has been done. See my maths, and my illustrations, which I trust tally. Magnetising current is proportional to: Vs / {Rs + K.f.Lp.(1 + Rs / B.RL)} whe K = 2 x pi . N is the turns ratio B = the square of the turns ratio f is the frequency Vs is the source voltage Rs is the source resistance RL is the load resistance Lp is the primary inductance Ian |
#91
Posted to rec.audio.tubes
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Transformer attenuators
"Ian Iveson" I don't think it's a question of distortion either,and besides, the Sowter has a THD of 0.03% at +20dBu at 50Hz. But what is it for a 2V input at, say 20Hz, or whatever is the lowest frequency it may encounter? ** +20dBu = 7.75 volts rms so this is the input voltage for 0.03% THD. Assuming THD is all due to the onset of core saturation ( very likely the case ) the same THD level will be found at proportionally lower frequencies and input levels. Eg: At 25 Hz with 3.875 volts rms. At 5 Hz with 775 mV rms. Typically THD rises dramatically with reducing frequency and fixed input level, once the onset frequency has been reached. I had a small 1:1 audio input balancing tranny on hand, rated at 10 kohms to 10 kohms. http://www.altronics.com.au/index.as...=item&id=M0706 The following test result were found: -3 dB bandwidth: 1 Hz to 44kHz ( no mistake, tested with 50 mV rms input and a 250 ohm source ) Saturation: 3% THD at 32 Hz with 2.5 volts rms input. 3% THD at 3.2 Hz with 250 mV rms input. But circa 50% THD at 25 Hz and 2.5 volts rms input !!! Conclusion: Such transformers have very wide small signal bandwidths and do not inherently roll off sub sonic frequencies - unless driven into gross saturation and hence gross distortion. A suitable size capacitor can be fitted in series with the primary winding to prevent this - if large sub sonic input signals exist. ....... Phil |
#92
Posted to rec.audio.tubes
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Transformer attenuators
Eeyore wrote:
When I was getting into transforemr design for SMPSs a couple of years back I cane across the term 'volt seconds' which helps explain a lot. The more volt-seconds, the higher the flux. Useful because they work with switched DC...aka square waves...and low source resistance. Less obvious for proper waves, where voltage is variable, and/or when source resistance is significant. Ian |
#93
Posted to rec.audio.tubes
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Transformer attenuators
In article ,
"Ian Iveson" wrote: John Byrns wrote: Assumption #1: I am not a transformer engineer, but those who know more than I do about transformers have told me that for a given degree of core saturation (distortion), if the frequency is cut in half, then the voltage applied to the winding must also be cut in half to avoid saturation. This means that the applied voltage must be made proportional to the frequency (or lower) if saturation (distortion) is to be avoided. Assumption #2: If the transformer is being used to limit the LF response of the system, then assuming no load on the secondary, the source resistance feeding the primary of the transformer must be made equal to the primary inductance at the desired cutoff frequency of the resulting high pass filter. Below cutoff the voltage out of such a filter, at the primary of the transformer in this case, falls at rate that makes the voltage proportional to the frequency. This is exactly the sort of voltage response we need on the primary to prevent saturation of the transformer, hence saturation shouldn't be a problem. So which one of these assumptions is wrong, or if both assumptions are correct, where did my logic fail? Your assumption #2 is certainly false. It is not a sharp corner followed by a straight line: -6dB per octave is an asymptote. My assumption #2 has nothing to do with transformers directly, so it is the one assumption of the two that I know to be actually true. I am aware that it is not a sharp corner, but so what I believe that it all works out anyway, and if it doesn't we could just spec the transformer with a tiny bit of extra margin. Let's think about an example, I'm doing this in my head so a mistake is possible. Say we want the -3 dB point of our high pass to be at 25 Hz. We pick the source resistance and the primary inductance of the transformer to achieve that turn over point. Then we determine the maximum level we wish to handle and spec. the transformer so that it can handle that level at 25 Hz assuming the source impedance is zero. When we check we find that we have an extra margin of 3 dB to the saturation point at 25 kHz, and the level asymptotically approaches the line representing the saturation point from assumption #1 as the frequency is decreased. Your assumption of no secondary load is not appropriate for a transformer. However, my simulation uses such a light load that no load would not make much difference. I was simply trying not to complicate the model in order to help promote understanding, but the secondary load is irrelevant, we can simply reflect it back to the primary side of the transformer and incorporate it into the source impedance. Besides changing the effective source impedance seen by the primary, this also slightly complicates picking the required operating level of the transformer because we must take the resulting voltage divider effect into account when specifying the required operating level of the transformer. I have given one explanation for why the flux flattens at very low f in my simulation. Translated to your thinking, it gets flatter as your approximation gets closer to the truth. By that time the damage, as it were, has been done. What damage is already done? If you found any damage then you didn't pick the maximum operating level of the transformer correctly, see my comment on this above. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#94
Posted to rec.audio.tubes
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Transformer attenuators
"Phil Allison" ** Typo: http://www.altronics.com.au/index.as...=item&id=M0706 The following test result were found: -3 dB bandwidth: 1 Hz to 84 kHz Not " 44 kHz" as previously posted. ...... Phil |
#95
Posted to rec.audio.tubes
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Transformer attenuators
Ian Iveson wrote: Eeyore wrote: When I was getting into transforemr design for SMPSs a couple of years back I cane across the term 'volt seconds' which helps explain a lot. The more volt-seconds, the higher the flux. Useful because they work with switched DC...aka square waves...and low source resistance. Less obvious for proper waves, where voltage is variable, and/or when source resistance is significant. Since where was a square wave not 'proper' ? You just can't help saying daft things can you ? Graham |
#96
Posted to rec.audio.tubes
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Transformer attenuators
"Arny Krueger" wrote in message . .. "Iain Churches" wrote in message i.fi http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg Butt-ugly amplfier if there ever was one. Arny. I would be *very* worried indeed if *you* liked it:-) But most other people do, and that's what *really* matters. Cordially, Iain |
#97
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote in message I thought volume controls are usually inside the amplifier because it's simply convenient to put them there. In these days of high level sources, no preamp is actually required, so one can mount a pair stepped attenuators in the power amp chassis, and feed the CD player direct. http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg For many decades I didn't own a preamp. Everything of mine had line level outs anyway (including my turntable). The current one only qualifies as a preamp since it has a phono input but in reality it's just a source switcher the way I use it. Yes. You could also fit the input selector (source switcher) to the power amp also, to make it a line level integrated amplifier. I use a separate phono stage mounted close to the turntable with balanced line output. Iain |
#98
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. There's *no way* a variable R costs as much as tapped transformers in the real world. The TKD stereo attenuator costs about Euro 270 plus tax and shipping. The transformers are about UKP 90 each. Not a lot of difference For a simple source selector and volume control I'd use a pot followed by a high-performance op-amp buffer of course. Tubist might consider replacing the op-amp with a cathode follower, which is about as blameless as tube audio gets. Yep. That's the concept on which my own preamp is based. I was toying with the idea of a DC battery powered CF stage actually. Rechargeable via a wall wart. Sounds like a fun project:-) How is it progressing?? I chose a separate regulated psu. Iain |
#99
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Transformer attenuators
Iain Churches wrote: "Arny Krueger" wrote in message . .. "Iain Churches" wrote in message i.fi http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg Butt-ugly amplfier if there ever was one. Arny. I would be *very* worried indeed if *you* liked it:-) But most other people do, and that's what *really* matters. Cordially, Iain Are there tubes in the "heatsink" on top of the chassis? How does such an amount of surrounding metal help keep the tubes cool? Most audiophiles would immediately search for the screws holding down such a cover, remove them all, and throw away the offending metalwork, so they'd get a more "open sound". And perhaps less smoke. Patrick Turner. |
#100
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. There's *no way* a variable R costs as much as tapped transformers in the real world. The TKD stereo attenuator costs about Euro 270 plus tax and shipping. The transformers are about UKP 90 each. Not a lot of difference Sounds to me like ripoff pricing. There's plenty of accurate attenuators out there that I've come across. The better ones use thick film resistors screened onto what's effectively a multi-pole switch manufactured using potentiometer technology. For a simple source selector and volume control I'd use a pot followed by a high-performance op-amp buffer of course. Tubist might consider replacing the op-amp with a cathode follower, which is about as blameless as tube audio gets. Yep. That's the concept on which my own preamp is based. I was toying with the idea of a DC battery powered CF stage actually. Rechargeable via a wall wart. Sounds like a fun project:-) How is it progressing?? I chose a separate regulated psu. Just a concept that crossed my mind as I was reading these posts. It would be trivially simple to make one. I thought the battery powered bit would appeal to the audiophools. The batteries could feed the heater directly but it would need a tiny inverter for the B+. Graham |
#101
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Transformer attenuators
"Patrick Turner" wrote in message ... http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg Are there tubes in the "heatsink" on top of the chassis? How does such an amount of surrounding metal help keep the tubes cool? It is a cooling stack. Aluminium plates spaced 10mm apart, (narrower than the smallest finger) which do quite a good job of dissipating the heat. The tubes are cooled by convection, through the bottom of the chassis and up the sides of the tubes. Most audiophiles would immediately search for the screws holding down such a cover, remove them all, and throw away the offending metalwork, so they'd get a more "open sound". In this part of the world, the safety regs, and also domestic insurance, require a cage or metal protection for the tubes in Class I amplifiers, which can only be removed by the use of a tool (so press fit cages are taboo) Whether or not the owner removes the cage, is entirely his/her own affair, and the responsibility , if the cage is removed and someone burns themselves, is transferred from builder to owner. And perhaps less smoke. A number of these amps have been built. The oldest is now seven years old. They are owned by responsible people who know how to check the bias. None have developed faults to date. Iain |
#102
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Transformer attenuators
Iain Churches wrote: "Patrick Turner" wrote in message ... http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg Are there tubes in the "heatsink" on top of the chassis? How does such an amount of surrounding metal help keep the tubes cool? It is a cooling stack. Aluminium plates spaced 10mm apart, (narrower than the smallest finger) which do quite a good job of dissipating the heat. The tubes are cooled by convection, through the bottom of the chassis and up the sides of the tubes. Most audiophiles would immediately search for the screws holding down such a cover, remove them all, and throw away the offending metalwork, so they'd get a more "open sound". In this part of the world, the safety regs, and also domestic insurance, require a cage or metal protection for the tubes in Class I amplifiers, which can only be removed by the use of a tool (so press fit cages are taboo) Whether or not the owner removes the cage, is entirely his/her own affair, and the responsibility , if the cage is removed and someone burns themselves, is transferred from builder to owner. And perhaps less smoke. A number of these amps have been built. The oldest is now seven years old. They are owned by responsible people who know how to check the bias. None have developed faults to date. Iain Sugden class A solid state amps had horrible heatsinks with fins 10mm apart, about 50mm long, and running along the length of the side of the box, and flat, like yours, and thus greatly reducing any possible natural air flow. They ran scorching hot, and MUCH hotter than if the same fin area was mounted so the fins were vertical, thus generating a much faster effective air flow, such as in Quad 405. So the way you have your heatsink provides compliance with safety regs, but very poor air flow, and lousy heat removal compared to what could have been achieved with more intelligent design of the metal work, ie, with radial but verical fins, and an open mesh cover over the lot, or no damn fins anywhere, and just a decent cage, like Quad 40, but with lots of 6mm holes around where the tube sockets BOLT SOLIDLY TO THE CHASSIS, and with well perforated bottom plate. This allows air flow in through the bottom, and up around the tubes, and out the mesh with very low restrictions. In Oz where room temps are 30C on summer days often, good natural cooling for amps is a MUST. In early tubed electronics in aircraft, they had tubes clamped in metal heat sinks, and exposed to cooling air flow. As planes went higher and faster, they had to refrigerate the air flow because speed increases air temp. Failures of tubes become far more common if T is allowed to be high. In domestic hi-fi, naked tubes but with surround holes for good airflow and cage for safety is all thats needed, and if buyers can see the tubes at night easily through the mesh covers they won't remove them. Patrick Turner. |
#103
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. DACT stepped attenuators are high on the list. Some insist on TKD. If a manufacturer want to sell to in this market, he must meet the expectations of the customer. There's *no way* a variable R costs as much as tapped transformers in the real world. The TKD stereo attenuator costs about Euro 270 plus tax and shipping. The transformers are about UKP 90 each. Not a lot of difference Sounds to me like ripoff pricing. That's the reality I am afraid. Quality comes at a price. There's plenty of accurate attenuators out there that I've come across. The better ones use thick film resistors screened onto what's effectively a multi-pole switch manufactured using potentiometer technology. Yes. DACT use Elma switches, IIRC. There are some other good SA's using switches from Grayhill. I was toying with the idea of a DC battery powered CF stage actually. Rechargeable via a wall wart. Sounds like a fun project:-) How is it progressing?? I chose a separate regulated psu. Just a concept that crossed my mind as I was reading these posts. It would be trivially simple to make one. I thought the battery powered bit would appeal to the audiophools. The batteries could feed the heater directly but it would need a tiny inverter for the B+. There are preamps and phono stages available like this already. |
#104
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. That's their problem not mine. Brand name =/= any guarantee of performance / quality etc. In fact it's the ultimate fool's paradise. Graham |
#105
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote in message I was toying with the idea of a DC battery powered CF stage actually. Rechargeable via a wall wart. Sounds like a fun project:-) How is it progressing?? I chose a separate regulated psu. Just a concept that crossed my mind as I was reading these posts. It would be trivially simple to make one. I thought the battery powered bit would appeal to the audiophools. The batteries could feed the heater directly but it would need a tiny inverter for the B+. There are preamps and phono stages available like this already. I suspected as much. No doubt they cost megabucks. It would be fun to burst their balloon by offering one just as good for say $200. Graham |
#106
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: Some insist on TKD. What exactly do TDK offer that others don't ? Nothing I expect. Graham |
#107
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote in message There's plenty of accurate attenuators out there that I've come across. The better ones use thick film resistors screened onto what's effectively a multi-pole switch manufactured using potentiometer technology. Yes. DACT use Elma switches, IIRC. There are some other good SA's using switches from Grayhill. None of these use potentiometer technology. Graham |
#108
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. That's their problem not mine. Brand name =/= any guarantee of performance / quality etc. In fact it's the ultimate fool's paradise. Graham I agree entirely, but if a maker wants to sell a product, any product, he must give the customer what they (think they) want. Iain |
#109
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote in message I was toying with the idea of a DC battery powered CF stage actually. Rechargeable via a wall wart. Sounds like a fun project:-) How is it progressing?? I chose a separate regulated psu. Just a concept that crossed my mind as I was reading these posts. It would be trivially simple to make one. I thought the battery powered bit would appeal to the audiophools. The batteries could feed the heater directly but it would need a tiny inverter for the B+. There are preamps and phono stages available like this already. I suspected as much. No doubt they cost megabucks. It would be fun to burst their balloon by offering one just as good for say $200. IIRC the ones I have seen were Chinese, and cheap as chips. |
#110
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote in message Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. That's their problem not mine. Brand name =/= any guarantee of performance / quality etc. In fact it's the ultimate fool's paradise. I agree entirely, but if a maker wants to sell a product, any product, he must give the customer what they (think they) want. If it's simply a large price tag, I'm all for that ! More fool the purchaser. Graham |
#111
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: There are preamps and phono stages available like this already. I suspected as much. No doubt they cost megabucks. It would be fun to burst their balloon by offering one just as good for say $200. IIRC the ones I have seen were Chinese, and cheap as chips. So, are they any good ? Any links ? Graham |
#112
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: Some insist on TKD. What exactly do TDK offer that others don't ? Nothing I expect. Graham It has forty steps, in contrast to the more common 24 steps. Some makers have 60 step attenuators but these are available only in OEM quantities. The DACT has an open construction. The TKD reminds one of a smaller version of the fully-enclosed studded rotary faders you used to see in studio equipment. Iain |
#113
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote in message Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. That's their problem not mine. Brand name =/= any guarantee of performance / quality etc. In fact it's the ultimate fool's paradise. I agree entirely, but if a maker wants to sell a product, any product, he must give the customer what they (think they) want. If it's simply a large price tag, I'm all for that ! More fool the purchaser. A high end dealer, a good friend of mine, tells me that he thinks that PQ (perceived quality) is 40% of the purchasing decision! Iain |
#114
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: There are preamps and phono stages available like this already. I suspected as much. No doubt they cost megabucks. It would be fun to burst their balloon by offering one just as good for say $200. IIRC the ones I have seen were Chinese, and cheap as chips. So, are they any good ? Can't say. I noticed the lack of a CE mark, and put it down again:-) Any links ?' A local shop sells them. I will try to get some info. Graham |
#115
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote in message Iain Churches wrote: Some insist on TKD. What exactly do TDK offer that others don't ? Nothing I expect. It has forty steps, in contrast to the more common 24 steps. Some makers have 60 step attenuators but these are available only in OEM quantities. The DACT has an open construction. The TKD reminds one of a smaller version of the fully-enclosed studded rotary faders you used to see in studio equipment. Used to being the operative phrase. No studio equipment today would use such a deficient design. In fact, the last time I saw studded attenutors was in 1969 and they were being scrapped at that time. No-one wanted to buy them since a P&G conductive plastic fader was simply so much better. Graham |
#116
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Actually, even if you buy from the most expensive maker in the UK, a pair of transformers cost about the same as the TKD variable attenuator, which for many is a standard choice. Whose standard ? The people who want to have stepped attenuators of course. That doesn't really answer the question. High end tube audiophiles expect certain brand name components to be used. That's their problem not mine. Brand name =/= any guarantee of performance / quality etc. In fact it's the ultimate fool's paradise. I agree entirely, but if a maker wants to sell a product, any product, he must give the customer what they (think they) want. If it's simply a large price tag, I'm all for that ! More fool the purchaser. A high end dealer, a good friend of mine, tells me that he thinks that PQ (perceived quality) is 40% of the purchasing decision! I don't doubt you (or him). The question has to be, where do they get these ideas about perceived value from ? It's a nice con-trick whilst you can continue to play it. Graham |
#117
Posted to rec.audio.tubes
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Transformer attenuators
Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: "Eeyore" wrote Iain Churches wrote: There are preamps and phono stages available like this already. I suspected as much. No doubt they cost megabucks. It would be fun to burst their balloon by offering one just as good for say $200. IIRC the ones I have seen were Chinese, and cheap as chips. So, are they any good ? Can't say. I noticed the lack of a CE mark, and put it down again:-) LOL ! If it's battery operated it arguably doesn't need one. The CE marking regulations are far from being clear on such points. Certainly, if battery powered, it wouldn't need to comply with the 'low voltage directive' (low voltage meaning basically wall socket type volts). It ought to have to comply with the EMC Directive though. Any links ?' A local shop sells them. I will try to get some info. Thank you kindly. Graham |
#118
Posted to rec.audio.tubes
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Transformer attenuators
Eeyore said:
No studio equipment today would use such a deficient design. In fact, the last time I saw studded attenutors was in 1969 and they were being scrapped at that time. No-one wanted to buy them since a P&G conductive plastic fader was simply so much better. Please define "better". ***grin*** -- - Maggies are an addiction for life. - |
#119
Posted to rec.audio.tubes
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Transformer attenuators
"Eeyore" wrote in message ... Iain Churches wrote: "Eeyore" wrote in message Iain Churches wrote: Some insist on TKD. What exactly do TDK offer that others don't ? Nothing I expect. It has forty steps, in contrast to the more common 24 steps. Some makers have 60 step attenuators but these are available only in OEM quantities. The DACT has an open construction. The TKD reminds one of a smaller version of the fully-enclosed studded rotary faders you used to see in studio equipment. Used to being the operative phrase. No studio equipment today would use such a deficient design. In fact, the last time I saw studded attenutors was in 1969 and they were being scrapped at that time. No-one wanted to buy them since a P&G conductive plastic fader was simply so much better. Following stud rotary faders came the Paignton "quadrant" design, - long before P+G. Hifi amps still have rotary attenuators amd TKD is considered one of the best. (they also manufacture conductive plastic faders for studio consoles) Iain |
#120
Posted to rec.audio.tubes
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Transformer attenuators
Sander deWaal wrote: Eeyore said: No studio equipment today would use such a deficient design. In fact, the last time I saw studded attenutors was in 1969 and they were being scrapped at that time. No-one wanted to buy them since a P&G conductive plastic fader was simply so much better. Please define "better". ***grin*** LOL. Well..... effectively infinite resolution for one thing plus noiseless operation. Graham |
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