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A question for the cognoscenti autoformersI am not familiar with the "Zechendorff" circuit, but I am quite familiar with autotransformers.
The basic selling point of the autotransformer is that not all of the energy that passes through the transformer need pass through the magnetic circuit. Theoretically, this could result in a smaller magnetic circuit, less weight, etc. However, these advantages are only realized if the transformation ratio is small. An autotransformer wound to achieve a 10:1 impedance transformation will only save about 1/3 of the needed magnetic circuit as compared to a two-winding transformer. Then, of course you also give up the isolation achieved with a two-winding transformer. An autotransformer would be good to match, for example, a 6 ohm amplifier to an 8 or 4 ohm speaker, and, as a point of fact, McIntosh used to do this with their "better" line of SS power amps. I don't think you would get a great advantage at the transformation ratios typically used in tube circuits, however. "Jon Yaeger" wrote in message ... Assuming that a tube amplifier can be built with a balanced output (e.g. the Zechendorff circuit), what are the pros and cons of using an autoformer to match output impedance vs. a standard transformer? It would seem offhand that an autoformer could have sonic advantages (e.g lower losses, no coupling degradation, etc.). Would it cost less to manufacture? And finally, would a toroid be a suitable implementation (I am aware of toroid problems, especially with saturation, when used for standard output coupling). TIA, Jon |
#2
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A question for the cognoscenti autoformers
Assuming that a tube amplifier can be built with a balanced output (e.g. the
Zechendorff circuit), what are the pros and cons of using an autoformer to match output impedance vs. a standard transformer? It would seem offhand that an autoformer could have sonic advantages (e.g lower losses, no coupling degradation, etc.). Would it cost less to manufacture? And finally, would a toroid be a suitable implementation (I am aware of toroid problems, especially with saturation, when used for standard output coupling). TIA, Jon |
#3
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"Jon Yaeger" wrote in message
... It would seem offhand that an autoformer could have sonic advantages (e.g lower losses, no coupling degradation, etc.). Until you touch your speaker wires and suddenly realize that they are floating around 400VDC. ;o) An autotransformer is more turns-efficient than a transformer, true, but the need for isolation and high turns ratio makes this useless. (Of course the latter doesn't make any difference, it's just more of a 'why bother' case.) Tim -- In the immortal words of Ned Flanders: "No foot longs!" Website @ http://webpages.charter.net/dawill/tmoranwms |
#4
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In addition to sensible advice so far, and linked to the turns ratio
thing...a transformer allows for thick, high-current output winding, and thin (therefore compact, low-leakage etc.) primary. An autotransformer could do the same but only by compromising the advantages you state. For high-quality hi-fi amplifiers, the harder saturation characteristics of a torroid should not be a problem because you won't get near saturation anyway. The best torroids are better than the best EI, period. cheers, Ian "Jon Yaeger" wrote in message ... Assuming that a tube amplifier can be built with a balanced output (e.g. the Zechendorff circuit), what are the pros and cons of using an autoformer to match output impedance vs. a standard transformer? It would seem offhand that an autoformer could have sonic advantages (e.g lower losses, no coupling degradation, etc.). Would it cost less to manufacture? And finally, would a toroid be a suitable implementation (I am aware of toroid problems, especially with saturation, when used for standard output coupling). TIA, Jon |
#5
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"Ian Iveson" wrote in message ... In addition to sensible advice so far, and linked to the turns ratio thing...a transformer allows for thick, high-current output winding, and thin (therefore compact, low-leakage etc.) primary. An autotransformer could do the same but only by compromising the advantages you state. ** Autos have less copper losses and much better bandwidth than a isolation type. Wanna compare figures on a 4:1 impedance step down toroidal with a 160 VA size core ? ............ Phil |
#6
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Jon Yaeger wrote: Assuming that a tube amplifier can be built with a balanced output (e.g. the Zechendorff circuit), what are the pros and cons of using an autoformer to match output impedance vs. a standard transformer? It would seem offhand that an autoformer could have sonic advantages (e.g lower losses, no coupling degradation, etc.). Would it cost less to manufacture? And finally, would a toroid be a suitable implementation (I am aware of toroid problems, especially with saturation, when used for standard output coupling). TIA, Jon An auto transformer is useful to match awkward speaker impedances to impedance sensitive amps. To get a good match of a 2 ohm speaker, to say an amp which runs best with 8 ohms, a 2:1 step down ratio is required. The impedance ratio is 4:1, so you get 8 ohms to 2 ohms. To achive this transformation, with a typical low power tube amp, which puts out only say 20 watts into 8 ohms, one could use a toroidal power tranny, of around 300VA, with 2 x 40 volt windings in series, and leave the mains primary unterminated. Such a tranny will have a B of perhaps 1.2 Tesla at 40v at 50 Hz, for one 40v winding, but at 20 watts into 8 ohms the voltage is only 12.6 vrms, so with this voltage applied to two "40" volt windings, the B at 50 Hz is only 0.189 Tesla, and at 12.5 Hz its still only 0.756 Hz, and so still well away from saturation. The BW is usually 100 kHz so the toroidal isn't a bad device to couple speakers with, to get an impedance match at low losses, and wide BW. Various taps down the one winding can be placed to get a wide range of impedance matches, so driving a woofer, midrange, or a tweeter at any selected voltage level can be done can be done without using series resistances, to achieve well equalised levels, and the output impedance at the taps is always lower than the amplifier impedance, unless one tries to step up the output voltage, which imho, is pointless. SO, those who do have 4 or lower Z speakers could easily make a match to tube amps best suited to 16 ohms, such as Quad II, even when set on the amp for 8 ohms. There are plenty of tube amps which have the poor method of impedance matches done by simply having a single secondary OPT winding for 16 ohms, with tap at 0.7 times the total turns for 8 ohms, and a CT for 4 ohms, which means that half the sec is not carrying speaker current when 4 ohms is used, and HF response is poorer. The auto tranny at the speaker allows the amp to enjoy the 16 ohms it prefers, and less OPT winding losses. The winding losses in the toroidal auto tranny are minor. The turns per volt required for a mains 300 VA tranny could be about 2 turns per volt, so 80 turns are required fore 40v at mains F. 160 total winding turns would be fine for a 20 watt amp. Its easy to place 160 turns of wire by hand around a toroidal core, using a shuttle made from a piece of old plastic tube, or broom handle with notches. Use about 1.3 mm dia wire, and wind the right length for say 1/2 the winding on the shuttle, then wind it off the shuttle onto the toroid and set the wires straight, tightly, and true, and neatly. Tape insulation is easy to apply in lengths. I have re-wound complete toroidal power transformers like this, and of course it took ages to do the thin wire high voltage turns, since there are so many turns. The low voltage heater windings were dead easy to do, once I made a sort of clamp to hold the partially wound tranny as I placed on the turns. Using auto trannies to have the primary in series with a speaker secondary doesn't convey a huge advantage. But in a PP amp, one could deliberately split the primary into cathode and plate windings, a'la Quad acoustical, and have each half cathode winding in series with a grounded and centre tapped speaker secondary, perhaps with other symetically placed taps to allow impedance matchings. The feedback effect is enhance this way. The Quad OPTs don't allow for such elegant use of the speaker sec, since it isn't a centre tapped winding. The text books, including RDH4, will explain the winding losses with two winding isolation trannies, and with auto trannies, which are more efficient, especially with a 2:1 step down transformer. Where there is a will, there is a way. Patrick Turner. |
#7
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Phil Allison" wrote
** Autos have less copper losses and much better bandwidth than a isolation type. Sometimes. Is that what ** means? Wanna compare figures on a 4:1 impedance step down toroidal with a 160 VA size core ? Read the other posts that I agreed with. 4:1 is easy. 400:1 is nearer what most people would use here. Neither would 160VA be appropriate in most cases. Care to cite a reasonable comparison? Care to back up your statement about "much" wider bandwidth, in the context of an OPT for a domestic valve amp? Can you think of any other important parameters other than copper losses and bandwidth? Ever wondered why no-one uses, or supplies, auto-transformers for valve amp OPTs? cheers, Ian |
#8
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"Ian Iveson" wrote in message ... Phil Allison" ** Better leave this para in since this is the one I referred to. In addition to sensible advice so far, and linked to the turns ratio thing...a transformer allows for thick, high-current output winding, and thin (therefore compact, low-leakage etc.) primary. An autotransformer could do the same but only by compromising the advantages you state. ** Autos have less copper losses and much better bandwidth than an isolation type. Sometimes. Is that what ** means? ** Nope. ** Wanna compare figures on a 4:1 impedance step down toroidal with a 160 VA size core ? Read the other posts that I agreed with. 4:1 is easy. 400:1 is nearer what most people would use here. ** Even then it would not need to be inferior to a isolation type. Neither would 160VA be appropriate in most cases. ** The same comment applies to a wide range of VAs . Care to cite a reasonable comparison? ** Your face and a monkey's behind ? Care to back up your statement about "much" wider bandwidth, in the context of an OPT for a domestic valve amp? ** My remark sits quite well in the original context. Can you think of any other important parameters other than copper losses and bandwidth? ** None that relate to my comment. Ever wondered why no-one uses, or supplies, auto-transformers for valve amp OPTs? ** Never wondered at all. The reason is so bleeding obvious. ............. Phil |
#9
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Ian Iveson wrote: Phil Allison" wrote ** Autos have less copper losses and much better bandwidth than a isolation type. Sometimes. Is that what ** means? Wanna compare figures on a 4:1 impedance step down toroidal with a 160 VA size core ? Read the other posts that I agreed with. 4:1 is easy. 400:1 is nearer what most people would use here. Neither would 160VA be appropriate in most cases. Care to cite a reasonable comparison? Care to back up your statement about "much" wider bandwidth, in the context of an OPT for a domestic valve amp? Can you think of any other important parameters other than copper losses and bandwidth? Ever wondered why no-one uses, or supplies, auto-transformers for valve amp OPTs? In my last post on the subject, where I described the use of a symetrically balanced OPT with a centre tapped secondary, with plate, ( or cathode currents ) flowing through the speaker winding is not done because there really isn't great benefits to transformer efficiencies, and the cost isn't seen as worth it. But the other benefit of the fully isolated traditional OPT is that you have a far safer amp, since lethal plate voltages are unable to leap out and kill a child, adult, or a dog. 160 to 500 VA toroidals will have naturally low leakage inductances, since the sections of windings can be wound over each other in close proximity, and equivalent to a wide traverse width in a plain bobbin wind up. Such a plain bobbin wound tranny could be used for a low voltage audio tranny, and the layers could be simply interleaved to tightly couple the windings to extend BW to 300 kHz if desired. I have wound UL OPTs for 300 watt applications using 1.1k to 5 ohms ratio, with 6S and 5P sections, to get 20Hz to 300 kHz at full power. If my trannies were used as balanced auto OPT, the BW might extend slightly further. In the case of a 300 watt amp the speaker secondaries could have a CT, and be grounded, and the 38 vrms created to make 300 watts into 5 ohms is an ideal amount of voltage which can be +/-19v either side of the CT, and then fed to the cathodes of multiple OPV to provide enough cathode FB for an acoustical connection to then be effective to achieve the power of the tetrode, but the low distortion and Ro of the triode. So there thus need to be only a primary, and a secondary, and the tube current circuit and speaker current circuit "share" the same path, but in actual fact the signal current in the shared portion, ie, the speaker winding is equal to to the speaker current MINUS the cathode signal current. Winding losses will then be slightly lower than the two separate windings with full isolation. But the above idea is only of benefit with tubes like KT88/6550/EL34etc, when you have perhaps a dozen involved; when just two OPV are used, the speaker voltage isn't high enough to provide much useful CFB to the OPV cathodes. But 4:1 impedance ratio for a speaker matching application is a neat way to achieve matching, and maintain the damping factor, or improove it. This idea makes sense if you have say 4 x "8 ohm" woofers in parallel, and where 200 watts is required for a decent ceiling. Many amps, including SS might baulk at 2 ohm or lower loads trying to make 200 watts, but the matching transformer allows the amp to think it has 8 ohms connected, and it may be able to drive that easily, but at the speakers, the voltage is halved, and current doubled, so you get 200 watts into the speakers, so its a win-win situtation. I have yet to see this application of auto trannies for speaker use used commercially, because of beancounter concerns. The other benefit with an auto tranny when using an SS amp is that if the amp blows up, and a supply rail becomes directly connected to the auto tranny, the rail fuse WILL then blow, because the DC from the SS amp has an easy shunt path, instead of burning out the voice coils of the woofers. So the VA of the auto tranny core and wind up details for speaker use should be carefully worked out to ensure the Bmax is less than 0.3 Tesla at 50 Hz, to ensure Fsat is low. This applies regardless of the U of the iron. During normal use, such a low B, especially with GOSS toroidals cores, or other GOSS laminations, will give excellent low distortion and low losses. Patrick Turner. cheers, Ian |
#10
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"Phil Allison" wrote Sometimes. Is that what ** means? ** Nope. Is that sometimes no? cheers, Ian |
#11
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"Patrick Turner" wrote
...see below Absolutely. Autotransformers are good for low ratios where isolation is not important. The cathode feedback, or more properly named distributed load in the example you give, is another kettle of fish, of course. Dunno what it's got to do with autotransformers though, except that you say speaker windings in series...that then makes an autotransformer between cathodes and speaker. So then the speaker winding is *part* of the cathode winding..."in series" doesn't quite capture the meaning IMO. Interesting all the same. So, with reference to my original point about wire thickness, how would you deal with this in practise? Let's take an example. I use a cathode windings of 10%, Zaa 5k and speaker 6ohms. Roughly speaking, that gives me 3% speaker winding, a ratio of 3 to 1 compared to the cathode. So I could tap about a third of the cathode windings to drive the speaker. However, I require the speaker winding to carry several amps, whereas the cathodes only require around 100mA. If I accomodate both with the same wire necessary for the speaker, then there is more leakage in the cathode circuit than would otherwise need to be the case. If I use two windings of different wire gauge in series, part of the cathode winding is thicker than need be, giving some penalty in terms of leakage in the anode/cathode circuit. My tendency has been in the opposite direction: to minimise a-to-k leakage, at the expense of added capacitance, which I want anyway. So my cathode windings are bifilar with the anodes'. I don't have a bandwidth problem (about 16 to 45k without overall nfb), so the autotransformer would not be worthwhile in my case, and defeat the objective of the bifilar winding. There is another issue he precisely where is best for the nfb to come from. There are arguments for and against using the speaker winding in the feedback loop. I prefer the simplicity of not doing so, and suffer the slightly higher (but I believe less malevolent) distortion as a result. cheers, Ian An auto transformer is useful to match awkward speaker impedances to impedance sensitive amps. To get a good match of a 2 ohm speaker, to say an amp which runs best with 8 ohms, a 2:1 step down ratio is required. The impedance ratio is 4:1, so you get 8 ohms to 2 ohms. To achive this transformation, with a typical low power tube amp, which puts out only say 20 watts into 8 ohms, one could use a toroidal power tranny, of around 300VA, with 2 x 40 volt windings in series, and leave the mains primary unterminated. Such a tranny will have a B of perhaps 1.2 Tesla at 40v at 50 Hz, for one 40v winding, but at 20 watts into 8 ohms the voltage is only 12.6 vrms, so with this voltage applied to two "40" volt windings, the B at 50 Hz is only 0.189 Tesla, and at 12.5 Hz its still only 0.756 Hz, and so still well away from saturation. The BW is usually 100 kHz so the toroidal isn't a bad device to couple speakers with, to get an impedance match at low losses, and wide BW. Various taps down the one winding can be placed to get a wide range of impedance matches, so driving a woofer, midrange, or a tweeter at any selected voltage level can be done can be done without using series resistances, to achieve well equalised levels, and the output impedance at the taps is always lower than the amplifier impedance, unless one tries to step up the output voltage, which imho, is pointless. SO, those who do have 4 or lower Z speakers could easily make a match to tube amps best suited to 16 ohms, such as Quad II, even when set on the amp for 8 ohms. There are plenty of tube amps which have the poor method of impedance matches done by simply having a single secondary OPT winding for 16 ohms, with tap at 0.7 times the total turns for 8 ohms, and a CT for 4 ohms, which means that half the sec is not carrying speaker current when 4 ohms is used, and HF response is poorer. The auto tranny at the speaker allows the amp to enjoy the 16 ohms it prefers, and less OPT winding losses. The winding losses in the toroidal auto tranny are minor. The turns per volt required for a mains 300 VA tranny could be about 2 turns per volt, so 80 turns are required fore 40v at mains F. 160 total winding turns would be fine for a 20 watt amp. Its easy to place 160 turns of wire by hand around a toroidal core, using a shuttle made from a piece of old plastic tube, or broom handle with notches. Use about 1.3 mm dia wire, and wind the right length for say 1/2 the winding on the shuttle, then wind it off the shuttle onto the toroid and set the wires straight, tightly, and true, and neatly. Tape insulation is easy to apply in lengths. I have re-wound complete toroidal power transformers like this, and of course it took ages to do the thin wire high voltage turns, since there are so many turns. The low voltage heater windings were dead easy to do, once I made a sort of clamp to hold the partially wound tranny as I placed on the turns. Using auto trannies to have the primary in series with a speaker secondary doesn't convey a huge advantage. But in a PP amp, one could deliberately split the primary into cathode and plate windings, a'la Quad acoustical, and have each half cathode winding in series with a grounded and centre tapped speaker secondary, perhaps with other symetically placed taps to allow impedance matchings. The feedback effect is enhance this way. The Quad OPTs don't allow for such elegant use of the speaker sec, since it isn't a centre tapped winding. The text books, including RDH4, will explain the winding losses with two winding isolation trannies, and with auto trannies, which are more efficient, especially with a 2:1 step down transformer. Where there is a will, there is a way. Patrick Turner. |
#12
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On Mon, 29 Sep 2003 16:41:03 +0100, the highly esteemed Ian Iveson
enlightened us with these pearls of wisdom: "Phil Allison" wrote Sometimes. Is that what ** means? ** Nope. Is that sometimes no? cheers, Ian C'mon Ian, killfile that retard already, would ya?! -- Greg --The software said it requires Win2000 or better, so I installed Linux. |
#13
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"Greg Pierce" wrote in message news On Mon, 29 Sep 2003 16:41:03 +0100, the highly esteemed Ian Iveson enlightened us with these pearls of wisdom: "Phil Allison" wrote Sometimes. Is that what ** means? ** Nope. Is that sometimes no? cheers, Ian C'mon Ian, killfile that retard already, would ya?! ** Two more self obsessed ****wits identified beyond all doubt. ............ Phil |
#14
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Ian Iveson wrote: "Patrick Turner" wrote ...see below Absolutely. Autotransformers are good for low ratios where isolation is not important. The cathode feedback, or more properly named distributed load in the example you give, is another kettle of fish, of course. Dunno what it's got to do with autotransformers though, except that you say speaker windings in series...that then makes an autotransformer between cathodes and speaker. So then the speaker winding is *part* of the cathode winding..."in series" doesn't quite capture the meaning IMO. Indeed, but it doesn't matter in principle where the amplifier device is placed, it can be at the top of an auto tranny, or at the bottom, or in between seriesed windings. Interesting all the same. So, with reference to my original point about wire thickness, how would you deal with this in practise? Let's take an example. I use a cathode windings of 10%, Zaa 5k and speaker 6ohms. Roughly speaking, that gives me 3% speaker winding, a ratio of 3 to 1 compared to the cathode. So I could tap about a third of the cathode windings to drive the speaker. Indeed. I did a similar thing once with the SE 6BQ5 amps in an old sterogram, I found there was room to place more secondary turns on the transformers, which were quite small, and the speaker winding had been wound on first, then the plate coil, and I was able to add another section of one layer without pulling the tranny apart. Then there were two section of cathode coils, and one was used for the speaker. The BW was then much improved, and the sound was far better. However, I require the speaker winding to carry several amps, whereas the cathodes only require around 100mA. If I accomodate both with the same wire necessary for the speaker, then there is more leakage in the cathode circuit than would otherwise need to be the case. If I use two windings of different wire gauge in series, part of the cathode winding is thicker than need be, giving some penalty in terms of leakage in the anode/cathode circuit. The current in the shared section of the auto tranny which would be your speaker winding is the speaker current of say 3 amps, minus the 100 mA of tube current. So in the case of a tapped cathode winding, sure, the speaker winding still needs to be heavy wire, but all the rest can be fine guage. The speaker secondary can be set up as several paralleled sections, just like a normal interleaved transformer, with these speaker windings in close proximity with the section of cathode windings, so the bandwidth is high, and the speaker errors all appear at the cathode of the tube, to cause feedback corrective action. My tendency has been in the opposite direction: to minimise a-to-k leakage, at the expense of added capacitance, which I want anyway. So my cathode windings are bifilar with the anodes'. Perhaps you have a lot of capacitance that way. I DON'T see a need for bifilar windings, ever, in OPTs. I don't have a bandwidth problem (about 16 to 45k without overall nfb), so the autotransformer would not be worthwhile in my case, and defeat the objective of the bifilar winding. You could have seriesed windings which are still well interleaved, or bifilar wound, depending on layout. In my most recent designs for SE acoustical amps, there is a layer of fine wire sandwitched between the pairs of layers of speaker windings, so coupling between speaker and cathode FB turns is extremely tight, ie, LL there is very low. I am not using auto connection with speaker windings in series, because I don't want the 0.3 amps of idle current in the tubes to create a DC offset across the speaker secondaries. But using say 4 two layer speaker secs, with a layer of cathode turns between each is the best way to arrange the speaker and cathode feedback turns. The plate winding would be 5 sections, interleaved as normal. If all the turns are used for the tube current in a PP set up, and the speaker winding has a CT, then equal DC offset appears at each of the two balanced speaker terminals, so there is no DC offset across the speaker. There is another issue he precisely where is best for the nfb to come from. There are arguments for and against using the speaker winding in the feedback loop. I prefer the simplicity of not doing so, and suffer the slightly higher (but I believe less malevolent) distortion as a result. It depends how well you design the OPT as to how "malevolent", ie, unstable your amp will be with CFB + speaker winding included. I like the acoustical connection, its far better than plain UL. You have the advantages of reducing the thd spectral content to that of triodes, and a low Eg2 can be used compared to Ea, further lowering thd. Screen supply is simple, and need not be well regulated for music use. Far less overall FB need be used, so stability can be better than if plain tetrode/pentode is used, with an equal total amount of NFB used. For best results, interleave the OPT quite a lot, and it'll be stable. With say KT88, with lower Eg2, the G1 bias voltage can be much lower. With say 400 v for Ea, 300v can be used for Eg2, and Eg2 reduced from say -50 to -35, and if cathode bias is used, the Rk is lower value, so less heat is wasted at the Rk. Usually, Rk can be halved again, and have say only 18v of cathode bias, and apply a fixed -17v to all output tubes. The cathode Rk will still regulate the cathode current, and hence the bias condition, but you have a much more DC stable cathode voltage, with less variation in the AB operation. Patrick Turner. cheers, Ian An auto transformer is useful to match awkward speaker impedances to impedance sensitive amps. To get a good match of a 2 ohm speaker, to say an amp which runs best with 8 ohms, a 2:1 step down ratio is required. The impedance ratio is 4:1, so you get 8 ohms to 2 ohms. To achive this transformation, with a typical low power tube amp, which puts out only say 20 watts into 8 ohms, one could use a toroidal power tranny, of around 300VA, with 2 x 40 volt windings in series, and leave the mains primary unterminated. Such a tranny will have a B of perhaps 1.2 Tesla at 40v at 50 Hz, for one 40v winding, but at 20 watts into 8 ohms the voltage is only 12.6 vrms, so with this voltage applied to two "40" volt windings, the B at 50 Hz is only 0.189 Tesla, and at 12.5 Hz its still only 0.756 Hz, and so still well away from saturation. The BW is usually 100 kHz so the toroidal isn't a bad device to couple speakers with, to get an impedance match at low losses, and wide BW. Various taps down the one winding can be placed to get a wide range of impedance matches, so driving a woofer, midrange, or a tweeter at any selected voltage level can be done can be done without using series resistances, to achieve well equalised levels, and the output impedance at the taps is always lower than the amplifier impedance, unless one tries to step up the output voltage, which imho, is pointless. SO, those who do have 4 or lower Z speakers could easily make a match to tube amps best suited to 16 ohms, such as Quad II, even when set on the amp for 8 ohms. There are plenty of tube amps which have the poor method of impedance matches done by simply having a single secondary OPT winding for 16 ohms, with tap at 0.7 times the total turns for 8 ohms, and a CT for 4 ohms, which means that half the sec is not carrying speaker current when 4 ohms is used, and HF response is poorer. The auto tranny at the speaker allows the amp to enjoy the 16 ohms it prefers, and less OPT winding losses. The winding losses in the toroidal auto tranny are minor. The turns per volt required for a mains 300 VA tranny could be about 2 turns per volt, so 80 turns are required fore 40v at mains F. 160 total winding turns would be fine for a 20 watt amp. Its easy to place 160 turns of wire by hand around a toroidal core, using a shuttle made from a piece of old plastic tube, or broom handle with notches. Use about 1.3 mm dia wire, and wind the right length for say 1/2 the winding on the shuttle, then wind it off the shuttle onto the toroid and set the wires straight, tightly, and true, and neatly. Tape insulation is easy to apply in lengths. I have re-wound complete toroidal power transformers like this, and of course it took ages to do the thin wire high voltage turns, since there are so many turns. The low voltage heater windings were dead easy to do, once I made a sort of clamp to hold the partially wound tranny as I placed on the turns. Using auto trannies to have the primary in series with a speaker secondary doesn't convey a huge advantage. But in a PP amp, one could deliberately split the primary into cathode and plate windings, a'la Quad acoustical, and have each half cathode winding in series with a grounded and centre tapped speaker secondary, perhaps with other symetically placed taps to allow impedance matchings. The feedback effect is enhance this way. The Quad OPTs don't allow for such elegant use of the speaker sec, since it isn't a centre tapped winding. The text books, including RDH4, will explain the winding losses with two winding isolation trannies, and with auto trannies, which are more efficient, especially with a 2:1 step down transformer. Where there is a will, there is a way. Patrick Turner. |
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Sorry. Done
cheers, Ian "Greg Pierce" wrote in message news On Mon, 29 Sep 2003 16:41:03 +0100, the highly esteemed Ian Iveson enlightened us with these pearls of wisdom: "Phil Allison" wrote Sometimes. Is that what ** means? ** Nope. Is that sometimes no? cheers, Ian C'mon Ian, killfile that retard already, would ya?! -- Greg --The software said it requires Win2000 or better, so I installed Linux. |
#16
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"Ian Iveson" wrote in message ... Sorry. Done cheers, Ian ** Wimp and well as ******. ........... Phil |
#17
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On Tue, 30 Sep 2003 10:52:07 +0100, the highly esteemed Ian Iveson
enlightened us with these pearls of wisdom: Sorry. Done cheers, Ian Ahh, the lovely killfile - how sweet the sound :-) -- Greg --The software said it requires Win2000 or better, so I installed Linux. |
#18
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"Greg Pierce" wrote in message news On Tue, 30 Sep 2003 10:52:07 +0100, the highly esteemed Ian Iveson enlightened us with these pearls of wisdom: Sorry. Done cheers, Ian Ahh, the lovely killfile - how sweet the sound :-) ** You two are a couple of bum boys - right ?? ............ Phil |
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prick
"Phil Allison" wrote in message u... |
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prick
"Phil Allison" wrote in message u... |
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prick
"Phil Allison" wrote in message u... |
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