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#1
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
While surfing around the web for
any decently measured THD or IMD measurements carried out on pentode tubes, I came up wuth very little of interest that at least I didn't know a lot about already. There is more mention of triode THD and some about IMD. Some of what i found was up to the standard of the 1950s RDH4 examinations of THD and IMD, and basically nobody has provided the well set out analysis of a typical 6AU6 including the schematic, and with levels of THD products from 2H to 10H as they rise in level for the progressive rise of fundemental F. So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. Basically, he seems to be saying the sound we hear is distorted by the ear which is a very non linear microphone, but the brain filters the harmonics out, but where an amp produces harmonics, ( or speakers, microphone, or other device )then unless the relationship of the harmonics relate to what a brain does with harmonics, it affects the sound far more than we think using accepted methods, and an SET amp can thus sound a heck of a lot better than a high NFB amp using bjts. He has a lot of mathematics to proove his point, or tend to proove it at least. He cites samples of new tube amplifiers costing many thousands made by CJ and others where the use of loop NFB has been reduced drastically. So what do people think about My Cheever's thoughts? Patrick Turner. |
#2
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
Patrick Turner wrote:
But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf snip So what do people think about My Cheever's thoughts? ********, and illiterate ******** at that. Apparently he got an MSc. for it! -- Eiron. |
#3
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
In article ,
Patrick Turner wrote: http://web.mit.edu/cheever/www/cheever_thesis.pdf There's 87 pages in that thesis that must be read before one can form an opinion. I wonder what Arnie thinks about all this. I wonder is the "TAD" is the same "new" distortion testing methodology that was discussed in this group a couple of years ago? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#4
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
Hi RATs!
Local in ear and head and body distortions becomes a 'known value' to some of us. When modified by a cold or something, the world sounds funny. Even beloved recordings on a favorite system become strange. None of this matters to the meter readers. They think everything is simpler than it sometimes appears and that everything important is 'out there'. Some is. Some is 'in here' and some is 'not fully known'. We fling cowpies at each other on newsnets and internets. It is jolly good fun. What we think we know about what others' hear is the true nonsense. We don't care We form opinions as we type them ... Happy Ears! Al |
#5
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
John Byrns said:
http://web.mit.edu/cheever/www/cheever_thesis.pdf There's 87 pages in that thesis that must be read before one can form an opinion. I wonder what Arnie thinks about all this. I wonder is the "TAD" is the same "new" distortion testing methodology that was discussed in this group a couple of years ago? There has been some discussion about this thesis in the past. The usual outcome: those who like tubes agreed with most of it, those who loathe tubes disagreed with most of it. -- - Maggies are an addiction for life. - |
#6
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
Patrick Turner wrote:
While surfing around the web for any decently measured THD or IMD measurements carried out on pentode tubes, I came up wuth very little of interest that at least I didn't know a lot about already. There is more mention of triode THD and some about IMD. Some of what i found was up to the standard of the 1950s RDH4 examinations of THD and IMD, and basically nobody has provided the well set out analysis of a typical 6AU6 including the schematic, and with levels of THD products from 2H to 10H as they rise in level for the progressive rise of fundemental F. So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm Ian |
#7
Posted to rec.audio.tubes
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Distortion in amplifiers.
"Ian Bell" But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) ........ Phil |
#8
Posted to rec.audio.tubes
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Distortion in amplifiers.
The Score So Far, one says "********, and illitertate boolocks at that", two asks, " ..I wonder what Arnie says?" three says "we get weird sound when we get a cold and we type opinions as we type them.." four says that the thesis favoured tube amps at the expense of SS amps, five said ....."might explain why the empirically arrived at minimum level necessary for 'undetectable distortion' changed dramatically when transistors replaced tubes, though." And five also said a lot of other things which proved he had more understanding of what Cheever said about ears, ear distortions and brains. six said "For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm I had a look at that but don't have time right now to read Gedlee's 1.6MB dissertation, and seven said, "** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) Without immediately knowing what relevance Mr Townshend has, I am at a loss to comment. TAD, ot Total Audio Discononance is not to be confused with TID, Transient Induced Distortion. It seems to me Cheever tries to show that the ears will produce harmonic voltages from the hairs in the cochlea in your ear when a pure tone is used as a signal. The brain he says, filters out the harmonics, and we hear the tone as pure. To me this defies common sense, because it implies the brain would do a lot of filtering with music or noise which is riddled with many harmonics. Humans are notoriously erroneous creatures. God isn't perfect, let alone understandable, if we take a look at his creations over the millions of years or trial and error. But if Cheever is correct, and the brain does away with much of what the ear microphones feed to it then its easy to see how MP3 formatted sound gets away with it... Anyone who has listened to the effects of clipping of clean sine wave in an amp would know what the threshold level is for THD of the tone; a 400Hz tone seems to suddently become "harder" sounding when the clipping becomes easily visible on the CRO. Pop music guitar players would say visibly undistorted sound is dull and lifeless; they set their levels so THD is 15% minimum most days... But Cheever's treatise includes the effect of using NFB in an amp making 10% 2H, and this is not ******** at all; using say 8 dB of NFB around a gain stage with 10% THD with no NFB does not improove the sonics even though the 2H is reduced a bit. The phenomena of using a very mild amount of NFB, say 5dB to 14dB around an amp with 10% open loop Dn and its creation of other harmonics of a higher F has been well documented in the past. The past examiners of this phenomena have concluded that where open loop THD was 10%, and there was sufficient open loop gain present, ie, the amp wasn't clipping, and still had considerable headroom in its output and drive amp stages, then you simply need to apply a lot more FB and then all original open loop AND ARTIFACTS CREATED BY THE NFB are reduced at a constant rate once NFB exceeded about 20dB, and this is shown in Cheever's graphs, if anyone here is able to read a graph by looking at it long enough. Since many SS amps with NFB make THD 0.005% quite routinely at 1 dB below clipping, and perhaps 0.001% at say 2 watts, and that open loop THD at 1dB below clip was 3% typically, then just how does the ear and brain tell us something is drastically wrong and make some listeners go running to the shop for an SET amp? Surely there have to be limits of audibility of distortion. If it simply ain't there on the basis of it being totally inaudible if played to listeners on its own without the wanted undistorted sound, then how do we perceive the distortion? 0.001% of say 4Vrms into 8 ohms, 2 watts, makes noise lower than an ant walking across the floor in front of the speakers. I have heard music via SS amps which tend to make a noise similar to people tearing up paper in time with the music levels, but many SS amps just don't, and are as clean as a whistle, so to speak, even clinically clean, too darn clean in fact for some listeners, and clean in an objectionable way compared to when they listen to a tube amp, which may measure 50 times worse, but nevertheless still measure quite well with less than 0.04% THD for an SE amp, and 0.02% for something PP. I have found it quite easy to make a clean sounding SS amp, and several that sound ok when compared to class A tube amps of similar power ceilings and low THD at low levels used during continuous actual listening. I could say that the use of very good passive filtering of rail supplies in all the amps concerned leads to a clean sound, as well as a high% of class A working before the amp moves to class AB helps the NFB do its job. In many SS amps the noise in the open loop signal is far greater than the THD/IMD, so much so that examining the output waveform on a CRO is marred with hum levels, even at high output levels. Reducing the injected PS noise with careful filtering allows the open loop to actually be plotted and graphed. Before NFB is applied many an SS amp then resembles a giant phono amp which amplifies say 1mV of input to 25Vrms output at 100Hz with bandwidth rolling off at 6dB/octave after some low F pole which can be as low as perhaps 100Hz. The open loop response usually includes the local output stage emitter follower NFB which equates to typically 40dB of local loop series voltage NFB, ( the definition of the variety of NFB is important ). So the response and THD one sees is mainly that created by the class A bjt input and driver stages. And if anyone gets that to less than 3% at 25Vrms, they are doing well. If they also have open loop bandwidth from say 20hz to 5kHz, they are doing a lot better. Having an open loop pole at 100Hz means that at if the global NFB is say 60dB at 100Hz, then at 1kHz, its 40 dB, and at 10kHz its 20 dB, and by 100kHz, there is no effective NFB applied because gain has dropped to unity. Just as well, because we get stability more easily. Its very easy to reduce the 3% of THD to 0.003% with 60dB of GNFB. My view is that the this 60dB is more effective if there is a low amount of noise in the signal to begin with; the applied NFB has an easier task to perform, ie, cleaning out the spuriae, which if not cleaned out would leave things sounding worse, surely, even if by some miracle, we could totally reduce PS noise, and extend the open loop BW out to 20kHz? Extending the open loop BW out to 20kHz isn't all that easy with bjts because we'd have to use either global NFB around the voltage amp gain stage/s or have cascaded stages of gain each with its own local FB and when you have say 3 gain stages cascaded each not using much NFB, I cannot see how the spuriae will not be better than if one simple effective GNFB loop is applied around ALL 3 cascaded stages. Amplifiers without emitter follower output stages, ie, common emitter outputs will have much more open loop THD, and I cannot see how FB could be dispensed with at all, one other reason being that collector resistance like pentode anode resistance or drain resistance in mosfets gives an amp with output resistance far to high to be usable, and well above speaker impedances. Meanwhile, triodes are passable without any global NFB and can operate in common cathode and still remain listenable, and their internal NFB makes them able to have output resistance well below speaker impedances. A customer of mine maintains he prefers the sound of a quad of 300B in PP for each channel without any GNFB. The NFB is adjustable and he can make the comparisons easily at the trun of a switch knob. But we are stuck with distortion regardless of what we do, and the only way to avoid it is to attend live music, and where the instruments are NOT amplified. Nevertheless I'd swear I was at a concert when I listen to music from the local ABC Classic FM radio station here, despite the whole process of recording onto a CD, replay, sending the signal to a satelite and back, then encoding it all to be able to re-constructed into stereo vi a multiplexed 100MHz carrier, in my humble all tubed FM tuner, which has switching diodes to create the stereo, and the less I tell you all about the process, the better. My lounge room is never really the best seat in the theatre though, mainly because I'm at home, and not out, all dressed up for the occasion, with friends, and with the aura of the theatre and human togetherness affecting my subjective senses. But plenty of times my lounge room has brought me closer than the best theatre seat ever could to a performer. I have plenty of LPs recorded as far back as 1958 which put me in the same studio room with the artists. And this luxury is possible despite all that has been said about noise and distortions. Patrick Turner. |
#9
Posted to rec.audio.tubes
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Distortion in amplifiers.
Phil Allison wrote:
"Ian Bell" But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) To be fair to the gedlee work, it is properly scientific, makes no distinction between tubes and SS and did include a good sized sample of double blind tests. Ian |
#10
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
"Patrick Turner" wrote in message
... So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at Here he talks about the increase in harmonic trash within a signal caused by NFB.You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. So what do people think about My Cheever's thoughts? Patrick Turner. Here's what I think: Pentodes = evil Global negative feedback = the spawn of Satan Digitial = the work of the Devil Cheers. Doug ;-) |
#11
Posted to rec.audio.tubes
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Distortion in amplifiers.
"Ian Bell" Phil Allison wrote: But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) To be fair to the gedlee work, it is properly scientific, makes no distinction between tubes and SS and did include a good sized sample of double blind tests. ** The problems with it are to do with underlying assumptions and relevance. It ain't relevant to anything in modern audio electronics. ( Save for a few wackos with SET amps maybe. ) BTW I assume you got the Pete Townshend reference ;-) ...... Phil |
#12
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
Doug Flynn wrote: "Patrick Turner" wrote in message ... So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at Here he talks about the increase in harmonic trash within a signal caused by NFB.You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. So what do people think about My Cheever's thoughts? Patrick Turner. Here's what I think: Pentodes = evil Global negative feedback = the spawn of Satan Digitial = the work of the Devil Cheers. Doug ;-) R U Obsessed with the devil today or what, eh? I hope Mr Rudd does not legitimise witch hunts when he's voted in. I wouldn't like to see you become a 'group leader of alternative thinking limiting agents' Say a warm HELLO to all the NFB in your triodes tonight. If you hate NFB so much, then why doncha try a pentode? Patrick Turner. |
#13
Posted to rec.audio.tubes
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Distortion in amplifiers.
Phil Allison wrote: "Ian Bell" Phil Allison wrote: But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) To be fair to the gedlee work, it is properly scientific, makes no distinction between tubes and SS and did include a good sized sample of double blind tests. ** The problems with it are to do with underlying assumptions and relevance. It ain't relevant to anything in modern audio electronics. It would seem it is beyond Phil's abilities to constructively point out the errors of Mr Gedlee and Cheever their entourage agents. Merely claiming these guys are irelevant to electronics isn't enough to substantiate shrill howls of ******** etc. Patrick Turner. ( Save for a few wackos with SET amps maybe. ) BTW I assume you got the Pete Townshend reference ;-) ..... Phil |
#14
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
And in addition to what i said below, there was a brilliant series of articles in the 1978-1979 copies of monthly Wireless World on the way in which low levels of NFB can make the sound worse. It was penned by one Peter Baxandall, his part 6 article appears in Feb'79, and has very similar graphs of the NFB effects on THD spectra as Mr Cheever has drawn, except that Baxandall's efforts look more plausible. The math involved are at a level fit only for a masochist with lots of time, but Baxandall does manage to get the point across regarding applying NFB and its effect on spectra in THD. To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. Patrick Turner. The Score So Far, one says "********, and illitertate boolocks at that", two asks, " ..I wonder what Arnie says?" three says "we get weird sound when we get a cold and we type opinions as we type them.." four says that the thesis favoured tube amps at the expense of SS amps, five said ...."might explain why the empirically arrived at minimum level necessary for 'undetectable distortion' changed dramatically when transistors replaced tubes, though." And five also said a lot of other things which proved he had more understanding of what Cheever said about ears, ear distortions and brains. six said "For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm I had a look at that but don't have time right now to read Gedlee's 1.6MB dissertation, and seven said, "** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) Without immediately knowing what relevance Mr Townshend has, I am at a loss to comment. TAD, ot Total Audio Discononance is not to be confused with TID, Transient Induced Distortion. It seems to me Cheever tries to show that the ears will produce harmonic voltages from the hairs in the cochlea in your ear when a pure tone is used as a signal. The brain he says, filters out the harmonics, and we hear the tone as pure. To me this defies common sense, because it implies the brain would do a lot of filtering with music or noise which is riddled with many harmonics. Humans are notoriously erroneous creatures. God isn't perfect, let alone understandable, if we take a look at his creations over the millions of years or trial and error. But if Cheever is correct, and the brain does away with much of what the ear microphones feed to it then its easy to see how MP3 formatted sound gets away with it... Anyone who has listened to the effects of clipping of clean sine wave in an amp would know what the threshold level is for THD of the tone; a 400Hz tone seems to suddently become "harder" sounding when the clipping becomes easily visible on the CRO. Pop music guitar players would say visibly undistorted sound is dull and lifeless; they set their levels so THD is 15% minimum most days... But Cheever's treatise includes the effect of using NFB in an amp making 10% 2H, and this is not ******** at all; using say 8 dB of NFB around a gain stage with 10% THD with no NFB does not improove the sonics even though the 2H is reduced a bit. The phenomena of using a very mild amount of NFB, say 5dB to 14dB around an amp with 10% open loop Dn and its creation of other harmonics of a higher F has been well documented in the past. The past examiners of this phenomena have concluded that where open loop THD was 10%, and there was sufficient open loop gain present, ie, the amp wasn't clipping, and still had considerable headroom in its output and drive amp stages, then you simply need to apply a lot more FB and then all original open loop AND ARTIFACTS CREATED BY THE NFB are reduced at a constant rate once NFB exceeded about 20dB, and this is shown in Cheever's graphs, if anyone here is able to read a graph by looking at it long enough. Since many SS amps with NFB make THD 0.005% quite routinely at 1 dB below clipping, and perhaps 0.001% at say 2 watts, and that open loop THD at 1dB below clip was 3% typically, then just how does the ear and brain tell us something is drastically wrong and make some listeners go running to the shop for an SET amp? Surely there have to be limits of audibility of distortion. If it simply ain't there on the basis of it being totally inaudible if played to listeners on its own without the wanted undistorted sound, then how do we perceive the distortion? 0.001% of say 4Vrms into 8 ohms, 2 watts, makes noise lower than an ant walking across the floor in front of the speakers. I have heard music via SS amps which tend to make a noise similar to people tearing up paper in time with the music levels, but many SS amps just don't, and are as clean as a whistle, so to speak, even clinically clean, too darn clean in fact for some listeners, and clean in an objectionable way compared to when they listen to a tube amp, which may measure 50 times worse, but nevertheless still measure quite well with less than 0.04% THD for an SE amp, and 0.02% for something PP. I have found it quite easy to make a clean sounding SS amp, and several that sound ok when compared to class A tube amps of similar power ceilings and low THD at low levels used during continuous actual listening. I could say that the use of very good passive filtering of rail supplies in all the amps concerned leads to a clean sound, as well as a high% of class A working before the amp moves to class AB helps the NFB do its job. In many SS amps the noise in the open loop signal is far greater than the THD/IMD, so much so that examining the output waveform on a CRO is marred with hum levels, even at high output levels. Reducing the injected PS noise with careful filtering allows the open loop to actually be plotted and graphed. Before NFB is applied many an SS amp then resembles a giant phono amp which amplifies say 1mV of input to 25Vrms output at 100Hz with bandwidth rolling off at 6dB/octave after some low F pole which can be as low as perhaps 100Hz. The open loop response usually includes the local output stage emitter follower NFB which equates to typically 40dB of local loop series voltage NFB, ( the definition of the variety of NFB is important ). So the response and THD one sees is mainly that created by the class A bjt input and driver stages. And if anyone gets that to less than 3% at 25Vrms, they are doing well. If they also have open loop bandwidth from say 20hz to 5kHz, they are doing a lot better. Having an open loop pole at 100Hz means that at if the global NFB is say 60dB at 100Hz, then at 1kHz, its 40 dB, and at 10kHz its 20 dB, and by 100kHz, there is no effective NFB applied because gain has dropped to unity. Just as well, because we get stability more easily. Its very easy to reduce the 3% of THD to 0.003% with 60dB of GNFB. My view is that the this 60dB is more effective if there is a low amount of noise in the signal to begin with; the applied NFB has an easier task to perform, ie, cleaning out the spuriae, which if not cleaned out would leave things sounding worse, surely, even if by some miracle, we could totally reduce PS noise, and extend the open loop BW out to 20kHz? Extending the open loop BW out to 20kHz isn't all that easy with bjts because we'd have to use either global NFB around the voltage amp gain stage/s or have cascaded stages of gain each with its own local FB and when you have say 3 gain stages cascaded each not using much NFB, I cannot see how the spuriae will not be better than if one simple effective GNFB loop is applied around ALL 3 cascaded stages. Amplifiers without emitter follower output stages, ie, common emitter outputs will have much more open loop THD, and I cannot see how FB could be dispensed with at all, one other reason being that collector resistance like pentode anode resistance or drain resistance in mosfets gives an amp with output resistance far to high to be usable, and well above speaker impedances. Meanwhile, triodes are passable without any global NFB and can operate in common cathode and still remain listenable, and their internal NFB makes them able to have output resistance well below speaker impedances. A customer of mine maintains he prefers the sound of a quad of 300B in PP for each channel without any GNFB. The NFB is adjustable and he can make the comparisons easily at the trun of a switch knob. But we are stuck with distortion regardless of what we do, and the only way to avoid it is to attend live music, and where the instruments are NOT amplified. Nevertheless I'd swear I was at a concert when I listen to music from the local ABC Classic FM radio station here, despite the whole process of recording onto a CD, replay, sending the signal to a satelite and back, then encoding it all to be able to re-constructed into stereo vi a multiplexed 100MHz carrier, in my humble all tubed FM tuner, which has switching diodes to create the stereo, and the less I tell you all about the process, the better. My lounge room is never really the best seat in the theatre though, mainly because I'm at home, and not out, all dressed up for the occasion, with friends, and with the aura of the theatre and human togetherness affecting my subjective senses. But plenty of times my lounge room has brought me closer than the best theatre seat ever could to a performer. I have plenty of LPs recorded as far back as 1958 which put me in the same studio room with the artists. And this luxury is possible despite all that has been said about noise and distortions. Patrick Turner. |
#15
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
"Patrick Turner" wrote in message ... Say a warm HELLO to all the NFB in your triodes tonight. If you hate NFB so much, then why doncha try a pentode? Patrick Turner. Now you're just being pedantic (or should that be pentode-antic?) Doug ;-) |
#16
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
"Patrick Turner" wrote in message
While surfing around the web for any decently measured THD or IMD measurements carried out on pentode tubes, I came up wuth very little of interest that at least I didn't know a lot about already. There is more mention of triode THD and some about IMD. Some of what i found was up to the standard of the 1950s RDH4 examinations of THD and IMD, and basically nobody has provided the well set out analysis of a typical 6AU6 including the schematic, and with levels of THD products from 2H to 10H as they rise in level for the progressive rise of fundemental F. So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. Basically, he seems to be saying the sound we hear is distorted by the ear which is a very non linear microphone, but the brain filters the harmonics out, but where an amp produces harmonics, ( or speakers, microphone, or other device )then unless the relationship of the harmonics relate to what a brain does with harmonics, it affects the sound far more than we think using accepted methods, and an SET amp can thus sound a heck of a lot better than a high NFB amp using bjts. That's nuts. He has a lot of mathematics to proove his point, or tend to proove it at least. Anybody can scribble equations on paper. He cites samples of new tube amplifiers costing many thousands made by CJ and others where the use of loop NFB has been reduced drastically. Niche products don't define technology. So what do people think about My Cheever's thoughts? I pointed a friend of mine who has written several books about audio and a number of AES conference papers and JAES articles at the site, and he basically said that Cheever was nuts. Oh, there's a kernal of truth to some of what he says, but a lot of it is way off the deep end. |
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Distortion in amplifiers.
"John Byrns" wrote in message
In article , Patrick Turner wrote: http://web.mit.edu/cheever/www/cheever_thesis.pdf There's 87 pages in that thesis that must be read before one can form an opinion. I wonder what Arnie thinks about all this. I wonder is the "TAD" is the same "new" distortion testing methodology that was discussed in this group a couple of years ago? The only "new" credible nonlinear distortion methodology I know of was the work of Geddes and Lee. http://www.aes.org/e-lib/browse.cfm?elib=12465 http://www.record-producer.com/learn.cfm?a=3651 http://forums.soundandvisionmag.com/...ssage.id=72717 http://www.gedlee.com/downloads/THD_.pdf etc. |
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Distortion in amplifiers.
"Sander deWaal" wrote in message
John Byrns said: http://web.mit.edu/cheever/www/cheever_thesis.pdf There's 87 pages in that thesis that must be read before one can form an opinion. I wonder what Arnie thinks about all this. I wonder is the "TAD" is the same "new" distortion testing methodology that was discussed in this group a couple of years ago? There has been some discussion about this thesis in the past. The usual outcome: those who like tubes agreed with most of it, those who loathe tubes disagreed with most of it. Typical of Sander's overly-confrontational approach to technology he can't properly understand. |
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Distortion in amplifiers.
On Mon, 19 Mar 2007 10:40:10 GMT, "Doug Flynn"
wrote: "Patrick Turner" wrote in message ... Say a warm HELLO to all the NFB in your triodes tonight. If you hate NFB so much, then why doncha try a pentode? Patrick Turner. Now you're just being pedantic (or should that be pentode-antic?) Doug ;-) Careful. People have blown tubes thinking up worse jokes than that. |
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Distortion in amplifiers.
"Phil Allison" wrote in message
"Ian Bell" Phil Allison wrote: But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. For more recent work (2005) along very similar lines but with slightly different conclusions see http://www.gedlee.com/distortion_perception.htm ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) To be fair to the gedlee work, it is properly scientific, makes no distinction between tubes and SS and did include a good sized sample of double blind tests. ** The problems with it are to do with underlying assumptions and relevance. It ain't relevant to anything in modern audio electronics. True, as it is pretty trivial to build electronics that are sonically transparent. Geddes and Lee's work does have application to loudspeakers, which are Gedde's major area of interest. |
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Distortion in amplifiers.
"Patrick Turner" wrote in message
To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. False claim. You just build the SS amp with enough local feedback to overcome the bad design decision to avoid loop feedback. I've done it, and so can anybody with reasonable circuit knowlege. A now-defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. |
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Distortion in amplifiers.
Patrick Turner wrote:
To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. Now you're just being silly. There's no reason why a solid state amp shouldn't have linear gain stages and low open-loop distortion. -- Eiron. |
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Distortion in amplifiers.
"Arny Krueger" wrote in message ... A now-defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. I believe Peter Stein of ME Australia would take exception to that statement. Not to mention Trevor Wilson when he sees it ;-) see http://www.me-au.com/ Maybe "hiatus" would have been a more appropriate description than defunct ;-) He is in fact still manufacturing and repairing. Regards TT |
#24
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Distortion in amplifiers.
Doug Flynn wrote: "Patrick Turner" wrote in message ... Say a warm HELLO to all the NFB in your triodes tonight. If you hate NFB so much, then why doncha try a pentode? Patrick Turner. Now you're just being pedantic (or should that be pentode-antic?) Doug ;-) Was not the five pointed star some kind of devilish symbol? Five is definately an odd order number, like 3, and 7 and 9 etc. Such a statement is meaningless, like saying even number devices like diodes and tetrodes and sexodes have even order distortions. Anyway, the load for a pentode and many SS devices will determine the harmonic spectra, and who is to say that one particular load might not suit your ears? If you hate pentodes, then you should have a reason. Same goes for beam tetrodes I guess. It is possible you are reason-less, in which case we wish you bon voyage in your musical persuits, but please rememember that so many of the vinyl treasures you like so much are chocablok full of pentode and NFB artifacts because many of the very best old vinyl analog recordings we hear were the result of routine use of the highest safe amount of NFB possible around circuits having as much safe open loop gain as possible using as few tubes as possible, which meant using shirtloads and bundles of EF86, perhaps a few 6SH7, 6AU6 etc. Had the studios tried to use nice simple triode circuitry without any global NFB, its possible a few may have managed the low N&D by the time a record was issued to the public, but also perhaps unlikely. Certainly they were prone to buying what was cheap, had all the bells and whistles, and what needed the least sevicing. And can you tell us if you are listening to a filthy recording produced using all transistor based gear? I think I prefer the sound of the radio stations that have NFB built into their carrier modulators, so that at the station a receiver module produces audio from the radiated RF signal, then compares that with the audio used to modulate the RF signal, and applies an error signal to reduce N&D to sub audible levels. I am wondering if I would like the whole transmission done without any loop FB, or if I would like a cutting head propelled without NFB. Maybe I will never be able to answer such questions fully, so my mind can't allow the irrationality of hate for a pentoad. And in fact I have too many good sounding EL34 based amps even with EF86 input tubes which sound well to doubt that pentoads can sound well. Then I have listened carefully with Quad-II amps which I have revised using all triode drivers and pentode drivers and heard not a huge amount to complain about, especially after the circuit revisions I have performed on such amps. I even like j-fets, but these critters have a square law transfer like a pentoad, but unlike a bjt, whose transfer is exponential, and one generating more harmonic garbage, for which more NFB must be used to reduce, allowable because the transconductance of the bjt is very high, so gain is high.... I place the priorities for good sound on the room, then speakers, then programme source, then source medium, then amplifiers and tube choice. Choice of BJTs does not seem to make any difference, if I am to believe the discussions about bjt choices. It is to be assumed the home electronics involved at least conform to 0.1% N&D max and full 20Hz to 20kHz BW and damping factor of 5 at average levels which isn't hard if that's only 1/2 a watt per channel. I have heard exceptions where on one occasison a group of 15 audio enthusiasts huddled in a room in a shop witnessed the dramatic improvement in sound when a 23 watt SET amp was used instead of a Gyphon 100 watt class A monster. There would be plenty of occasions where the SET would be NBG, if the level was high, and ear crushing pop was selected into insensitive speakers. Horses for courses. Patrick Turner. |
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Distortion in amplifiers.
"Eiron" wrote in message
Patrick Turner wrote: To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. Now you're just being silly. Agreed. I remember when Pat could say sane things about SS. There's no reason why a solid state amp shouldn't have linear gain stages and low open-loop distortion. Agreed that there is nothing that necessarily stops a SS amp from having low distortion before loop feedback is applied. However, the steps you take to reduce open loop distortion, reduce the effectiveness of loop feedback. Loop feedback has a lot of benefits and no practical disadvantages when done right. It may take a degree in engineering with a concentration in electronics or control systems to know how to do it right. That stops many basement diddlers. |
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Distortion in amplifiers.
Arny Krueger wrote: "Patrick Turner" wrote in message While surfing around the web for any decently measured THD or IMD measurements carried out on pentode tubes, I came up wuth very little of interest that at least I didn't know a lot about already. There is more mention of triode THD and some about IMD. Some of what i found was up to the standard of the 1950s RDH4 examinations of THD and IMD, and basically nobody has provided the well set out analysis of a typical 6AU6 including the schematic, and with levels of THD products from 2H to 10H as they rise in level for the progressive rise of fundemental F. So we really only know that THD and IMD exist in devices, and that it all rises with output levels and load values. But while looking around Google under 'pentode distortion measurements' I came across a thesis drafted up by one Mr Daniel H Cheever, posted at http://web.mit.edu/cheever/www/cheever_thesis.pdf Here he talks about the increase in harmonic trash within a signal caused by NFB. You all thought NFB reduced the trash, but he has other ideas supported by his calculations and observations fairly well presented. But his conclusions must be considered in the context of his ideas presented about the Total Aural Disconsonance figure of merit, or TAD. Basically, he seems to be saying the sound we hear is distorted by the ear which is a very non linear microphone, but the brain filters the harmonics out, but where an amp produces harmonics, ( or speakers, microphone, or other device )then unless the relationship of the harmonics relate to what a brain does with harmonics, it affects the sound far more than we think using accepted methods, and an SET amp can thus sound a heck of a lot better than a high NFB amp using bjts. That's nuts. He has a lot of mathematics to proove his point, or tend to proove it at least. Anybody can scribble equations on paper. He cites samples of new tube amplifiers costing many thousands made by CJ and others where the use of loop NFB has been reduced drastically. Niche products don't define technology. So what do people think about My Cheever's thoughts? I pointed a friend of mine who has written several books about audio and a number of AES conference papers and JAES articles at the site, and he basically said that Cheever was nuts. Oh, there's a kernal of truth to some of what he says, but a lot of it is way off the deep end. Whether Cheever is nuts or not doesn't change what we have to work with for most of us; I for one will not adopt a carefree anything goes attitude to THD and IMD just because one guy says i am not measuring things properly. Anyway though, nothing YOU have said prooves Cheever IS NUTS. I remain open minded, and I don't believe what I hear is all down to what we know we can measure so far. Why is it so that many ppl need subtitles for opera sung in english, but other ppl understand it all, and have no trouble humming along as well? Hearing and people's brains vary somewhat enormously. I cannot see why the brain may not indeed screen out much of the signal its gets from the microphone functions in our ears. A brain is a seriously wonderful development in evolution, and I don't underestimate its unique sub-conscious abilities to tailor sound signals to however it wants to in real time to enable information for best survival to register as fast as possible. But alas I am no audiologist, and no expert, and I doubt I could easily construct test gear for TAD tests, and then demonstrate to a sceptical audience that TAD evaluation methods were truly valid. I recall that when someone said the Earth went around the Sun, a certain religious organisation took a very dim view and cut the guys ears off. The organisation was begun by Jesus Christ, a liberated thinker of his time, and you'd think his followers would also allow some free thoughts. How about you guys permitting free thought without calling someone nuts? Patrick Turner. |
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Distortion in amplifiers.
"Arny Krueger" Phil Allison wrote: ** Meet the NEW load of ********... Same as the old load of ********. ( Apologies to Pete Townshend ) To be fair to the gedlee work, it is properly scientific, makes no distinction between tubes and SS and did include a good sized sample of double blind tests. ** The problems with it are to do with underlying assumptions and relevance. It ain't relevant to anything in modern audio electronics. True, as it is pretty trivial to build electronics that are sonically transparent. ** Precisely - as anyone with even a modicum of insight into audio electronics has long known. Unless they are complete dopes or terminally asleep. Guess who qualifies for both .... ? Geddes and Lee's work does have application to loudspeakers, which are Gedde's major area of interest. ** Shame the speakers I listen to ( Quad ESL63s ) have virtually no audible THD or IM whatever. Small wonder they so sound " lifeless " and " boring " ....... Maybe a nice SET harmonic enhancer will improve things .... ....... Phil |
#28
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Distortion in amplifiers.
"Patrick Turner" wrote in message
Arny Krueger wrote: "Patrick Turner" wrote in message So what do people think about My Cheever's thoughts? I pointed a friend of mine who has written several books about audio and a number of AES conference papers and JAES articles at the site, and he basically said that Cheever was nuts. Oh, there's a kernal of truth to some of what he says, but a lot of it is way off the deep end. Whether Cheever is nuts or not doesn't change what we have to work with for most of us; I for one will not adopt a carefree anything goes attitude to THD and IMD just because one guy says i am not measuring things properly. I agree with that. Anyway though, nothing YOU have said proves Cheever IS NUTS. I long ago quit trying to dissuade true believers with logic and science. The point is that with electronics, its possible to get all measurable forms of distortion so low that the fact that THD and most forms of IM are suboptimal measures is irrelevant. Even with all their suboptimalities, get them low enough and you're done. And, while some tubed equipment has enough nonlinear distortion that the Geddes-Lee results can apply, it is also possible to get the nonlinear distortion in tubed equipment low enough so that it doesn't matter. The logical justification for the Gedees-Lee papers is not electronics, it is transducers particularly speakers. I remain open minded, and I don't believe what I hear is all down to what we know we can measure so far. Patrick, given that you eschew bias-controlled listening, that has to be true. Prejudice and bias can have very strong effects on listeners. Why is it so that many ppl need subtitles for opera sung in english, but other ppl understand it all, and have no trouble humming along as well? Preferences and training. Hearing and people's brains vary somewhat enormously. The brain is the most powerful organ in the body. I cannot see why the brain may not indeed screen out much of the signal its gets from the microphone functions in our ears. It's not a matter of *may*, its a matter of *does*. If the brain studied only waveforms, MP3s wouldn't work as well as they do. |
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Distortion in amplifiers.
In article ,
Patrick Turner wrote: I think I prefer the sound of the radio stations that have NFB built into their carrier modulators, so that at the station a receiver module produces audio from the radiated RF signal, then compares that with the audio used to modulate the RF signal, and applies an error signal to reduce N&D to sub audible levels. I am wondering if I would like the whole transmission done without any loop FB, Did you actually check out what sorts of "carrier modulators" the various radio stations were actually using, so that you can truthfully say you have correlated the sound of the stations with the "carrier modulators" they used? It's probably too late to do this experiment today, what with digital modulation schemes having taken over the field. Assuming that you actually investigated what sort of "carrier modulators" were being used by the stations you preferred, as well as those you didn't, how did you eliminate the possibility that it wasn't the overall loop negative feedback that produced the sound you liked, but was some other factor common to the transmitters using overall loop negative feedback? I can think of one factor that is common to most analog transmitters that didn't use overall loop negative feedback, i.e. demodulated RF, that I suspect was more likely to have contributed to your dislike of them. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Distortion in amplifiers.
Arny Krueger wrote: "Patrick Turner" wrote in message To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. False claim. You just build the SS amp with enough local feedback to overcome the bad design decision to avoid loop feedback. My claim was not false. The triode has NFB built in, and no external LOCAL or GLOBAL NFB is needed for a listenable outcome. This is simply not possible with a solid state power amplifier where you MUST use extensive local FB such as emitter follower connection and local current FB to linearize the signal. I've done it, and so can anybody with reasonable circuit knowlege. But you must use external loop FB. You have never built a BJT based amplifier without some external loop NFB, such as the emitter follower connection et all. I am saying this is not necessary with triodes. There is a distinction and please do not misrepresent what i said. I have nothing against NFB as such, and use it routinely and afaiac, in the interests of better musical performance. A defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. ME amplifiers used a large amount of NFB around two consecutive stages each containing a few sub stages. Have you analysed the ME schematics? I repeat again, you cannot have a BJT based power amplifier unless you use a lot of external NFB in the way the device is connected. The drain or collector resistance is way too high just like the anode resistance of a beam tetrode of pentode to allow amplifiers without a lot of NFB, usually 20dB at least if the devices are working in class A. Patrick Turner. |
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Distortion in amplifiers.
Eiron wrote: Patrick Turner wrote: To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. Now you're just being silly. There's no reason why a solid state amp shouldn't have linear gain stages and low open-loop distortion. In fact SS amps have appalling open loop performance, high THD/IMD, poor phase shift character, lousy bandwidth, and lots of noise, and perhaps appallingly high output resistance. NFB reduces all the defects by the amount of NFB used, and typically its 60dB, so that where you see that THD = 0.005% at a db below clipping, without NFB the same amp makes THD = 5% at the same power. I am speaking about the facts of the engineering. I have led myself to think NFB allows devices to sing the way they were meant to. But I also allow that other reasoning about amplifier behaviour is worth consideration, but I am not about to throw out known techniques that appear to work fine so far.. Patrick Turner. -- Eiron. |
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Distortion in amplifiers.
TT wrote: "Arny Krueger" wrote in message ... A now-defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. I believe Peter Stein of ME Australia would take exception to that statement. Not to mention Trevor Wilson when he sees it ;-) see http://www.me-au.com/ Maybe "hiatus" would have been a more appropriate description than defunct ;-) He is in fact still manufacturing and repairing. Regards TT Peter Stein is just a man, and no man alive can gurrantee safe passage through a marriage, and when his came to an end, his wife and all the lawyers involved settled so they each got half the family wealth under Australian Family Law, and this included the ME company. That's how I understand what went wrong. Divorce can easily wreck the family business, and its hard for someone to climb back up to where they were. So in case we may think Peter's amp production failed because of design, we should all consider the real reason, and one so many of us can sympathise with. Its remarkable Peter may still be trying to re-establish; most of us at his age would retire to something else after 30 years in the business, and just enjoy the fishing. Its really difficult to make any business last a long time, and Peter's 25 years deserves a darn medal. I dunno how he could have structured his business so it could not have closed over a divorce, but then all such businesses require an interested head persona to keep them running, and its simply not easy in Oz with imports and absurd customer expectations pressing always towards business unviability. Australia has a large history of failed audio industry enterprizes. But then the list of cafes and restaurants that went broke just last year probably outnumber all the audio businesses ever started. You can all nit-pick Peter's achievements, and sure there are better/worse amps than ME, but give the man a fair go please! Patrick Turner. |
#33
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Distortion in amplifiers.
John Byrns wrote: In article , Patrick Turner wrote: I think I prefer the sound of the radio stations that have NFB built into their carrier modulators, so that at the station a receiver module produces audio from the radiated RF signal, then compares that with the audio used to modulate the RF signal, and applies an error signal to reduce N&D to sub audible levels. I am wondering if I would like the whole transmission done without any loop FB, Did you actually check out what sorts of "carrier modulators" the various radio stations were actually using, so that you can truthfully say you have correlated the sound of the stations with the "carrier modulators" they used? It's probably too late to do this experiment today, what with digital modulation schemes having taken over the field. Assuming that you actually investigated what sort of "carrier modulators" were being used by the stations you preferred, as well as those you didn't, how did you eliminate the possibility that it wasn't the overall loop negative feedback that produced the sound you liked, but was some other factor common to the transmitters using overall loop negative feedback? I can think of one factor that is common to most analog transmitters that didn't use overall loop negative feedback, i.e. demodulated RF, that I suspect was more likely to have contributed to your dislike of them. What i do know is that for present AM and FM transmissions in Oz the waves must remain compatible for existing analog receivers to decode audio from the RF carrier waves, and the recovered audio cannot be more linear than the transmitter modulator permits, and so I have assumed modulators have inbuilt means to use NFB to ensure modulation is as linear as possible. Engineers have told me but I admit I have not seen ths latest transmitters' schematics and analysed them. If you want to build a really low thd RF oscillator with say an AM function to allow between say 0% and 100% modulation levels of a tone, its not hard to make one up which uses NFB to linearize the modulation to an extent where the receiver demodulation THD/IMD will always be higher, unless rather extraordinary measures are taken with RF and IF amplifications and AM detection methods. With the very simple methods used in tubed superhet receivers, THD of 5% isn't uncommon, but its not because of the transmissions which imho are better than ever much of the time. One may argue id MP3 pop music is worse than old analog transmissions direct from a record groove, or tape, but the challenge of linearizing transmissions remains. Anyone who really knows about radio transmissions like to comment? Patrick Turner. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Distortion in amplifiers.
tubegarden wrote: Hi RATs! Local in ear and head and body distortions becomes a 'known value' to some of us. When modified by a cold or something, the world sounds funny. Even beloved recordings on a favorite system become strange. None of this matters to the meter readers. They think everything is simpler than it sometimes appears and that everything important is 'out there'. It *is* simple. But complicated too ! ;~) Graham |
#35
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Distortion in amplifiers.
"Patrick Turner" wrote in message
Arny Krueger wrote: "Patrick Turner" wrote in message To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. False claim. You just build the SS amp with enough local feedback to overcome the bad design decision to avoid loop feedback. My claim was not false. The triode has NFB built in, and no external LOCAL or GLOBAL NFB is needed for a listenable outcome. Patrick, that's one way to always be right - change your statement after it has been responded to. You only barred loop feedback in the statements I responded to. Now, you've changed your story quite extensively. This is simply not possible with a solid state power amplifier where you MUST use extensive local FB such as emitter follower connection Emitter followers are prohibited but cathode followers are OK? LOL! and local current FB to linearize the signal. Pardon me while I decline to get hyper about five cent resistors. I've done it, and so can anybody with reasonable circuit knowlege. But you must use external loop FB. Nope. You have never built a BJT based amplifier without some external loop NFB, such as the emitter follower connection et all. Emitter resistors are loop feedback? On what planet? They are an example of local feedback. I am saying this is not necessary with triodes. There is a distinction and please do not misrepresent what i said. You kept piling on nonesensical distinctions after I responded. I have nothing against NFB as such, and use it routinely and afaiac, in the interests of better musical performance. I never said you did, Patrick. But you don't seem to have a problem with changing your story after its been responded to. A defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. ME amplifiers used a large amount of NFB around two consecutive stages each containing a few sub stages. That's interesting. Would that be what most people call local feedback, or was it really loop feedback? Have you analysed the ME schematics? I only know what Trevor tells me. I repeat again, you cannot have a BJT based power amplifier unless you use a lot of external NFB in the way the device is connected. So how long are you going to stick by this new story, Patrick? The drain or collector resistance is way too high just like the anode resistance of a beam tetrode of pentode to allow amplifiers without a lot of NFB, usually 20dB at least if the devices are working in class A. As you say Patrick, there's no problem with applying feedback. |
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Distortion in amplifiers.
Patrick Turner wrote:
Eiron wrote: Patrick Turner wrote: To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. Now you're just being silly. There's no reason why a solid state amp shouldn't have linear gain stages and low open-loop distortion. In fact SS amps have appalling open loop performance, high THD/IMD, poor phase shift character, lousy bandwidth, and lots of noise, and perhaps appallingly high output resistance. NFB reduces all the defects by the amount of NFB used, and typically its 60dB, so that where you see that THD = 0.005% at a db below clipping, without NFB the same amp makes THD = 5% at the same power. I am speaking about the facts of the engineering. So your example of an SS amp produces 5% THD without feedback, yet you say that to produce less than 10% is extremely difficult. I needn't go and measure anything, I'll just use your example to show that you are being very silly. -- Eiron. |
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Distortion in amplifiers.
"Patrick Turner" wrote in message
In fact SS amps have appalling open loop performance, high THD/IMD, poor phase shift character, lousy bandwidth, and lots of noise, and perhaps appallingly high output resistance. This is true only if you design SS amps in accordance with Patrick's rules for intentionally designing crappy amps. It's possible to optimize a SS amp for good open loop performance. This isn't done very much because it would be a really stupid thing. In essence, what Patrick is telling us is that the only way he can come up with a favorable comparisons between tubed and SS amps is to force the SS amp to be designed in accordance with 2 sets of stupid rules. The first stupid rule of Patrick's is that the SS amp must be designed without loop feedback. The second stupid rule of Patrick's is that the SS amp must be designed without local feedback of the usual kinds. NFB reduces all the defects by the amount of NFB used, and typically its 60dB, so that where you see that THD = 0.005% at a db below clipping, without NFB the same amp makes THD = 5% at the same power. This would work for either tubes or transistors. You don't see a lot of tubed amps with 60 dB NFB for two reasons: (1) It's hard to get enough excess gain with tubes to sacrifice 60 dB or gain, no matter how good the reason. (2) Tubed amps tend to have too much phase shift to have 60 dB NFB and still be stable. I am speaking about the facts of the engineering. Subject to some absolutly crazy rules. I have led myself to think NFB allows devices to sing the way they were meant to. It works for either tubes or transistors. |
#38
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
"Patrick Turner" wrote in message ... TT wrote: "Arny Krueger" wrote in message ... A now-defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. I believe Peter Stein of ME Australia would take exception to that statement. Not to mention Trevor Wilson when he sees it ;-) see http://www.me-au.com/ Maybe "hiatus" would have been a more appropriate description than defunct ;-) He is in fact still manufacturing and repairing. Regards TT Peter Stein is just a man, and no man alive can gurrantee safe passage through a marriage, and when his came to an end, his wife and all the lawyers involved settled so they each got half the family wealth under Australian Family Law, and this included the ME company. That's how I understand what went wrong. Divorce can easily wreck the family business, and its hard for someone to climb back up to where they were. So in case we may think Peter's amp production failed because of design, we should all consider the real reason, and one so many of us can sympathise with. Its remarkable Peter may still be trying to re-establish; most of us at his age would retire to something else after 30 years in the business, and just enjoy the fishing. Its really difficult to make any business last a long time, and Peter's 25 years deserves a darn medal. I dunno how he could have structured his business so it could not have closed over a divorce, but then all such businesses require an interested head persona to keep them running, and its simply not easy in Oz with imports and absurd customer expectations pressing always towards business unviability. Australia has a large history of failed audio industry enterprizes. But then the list of cafes and restaurants that went broke just last year probably outnumber all the audio businesses ever started. You can all nit-pick Peter's achievements, and sure there are better/worse amps than ME, but give the man a fair go please! Patrick Turner. Well said Patrick and I'm sure Peter will appreciate your kind words. BTW it is always a pleasure to correct Arny ;-) Cheers TT |
#39
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
Arny Krueger wrote: "Patrick Turner" wrote in message Arny Krueger wrote: "Patrick Turner" wrote in message To avoid the worst of what Baxandall and Cheever are saying, it would seem prudent to ensuring open loop distortions before NFB is applied be kept well below the 10% level they use in the examples for their analysis. Fortunately, this is easily possible with triode amps, but extremely difficult with any SS devices. False claim. You just build the SS amp with enough local feedback to overcome the bad design decision to avoid loop feedback. My claim was not false. The triode has NFB built in, and no external LOCAL or GLOBAL NFB is needed for a listenable outcome. Patrick, that's one way to always be right - change your statement after it has been responded to. You only barred loop feedback in the statements I responded to. Now, you've changed your story quite extensively. This is simply not possible with a solid state power amplifier where you MUST use extensive local FB such as emitter follower connection Emitter followers are prohibited but cathode followers are OK? LOL! and local current FB to linearize the signal. Pardon me while I decline to get hyper about five cent resistors. I've done it, and so can anybody with reasonable circuit knowlege. But you must use external loop FB. Nope. You have never built a BJT based amplifier without some external loop NFB, such as the emitter follower connection et all. Emitter resistors are loop feedback? On what planet? Emitter resistors are used in many SS amps as local applications of series current NFB to linearize the otherwise appalling voltage linearity of BJTs. They also raise the effective base input resistance, appallingly low without such NFB. These local NFB apps ARE local LOOP FB. Do not try to evade the issue that it is impossible to build a listenable bjt amp without loop NFB of some kind, or external NFB of any kind. NOW READ ME CAREFULLY, ARNY, A TYPICAL 6SN7 DOES NOT NEED ITS CATHODE RESISTOR TO BE UNBYPASSED TO PROVIDE LINEARISING LOCAL NFB, YOU GOT IT!!? I am saying this is not necessary with triodes. There is a distinction and please do not misrepresent what i said. You kept piling on nonesensical distinctions after I responded. You keep lying arny, and acting like slime, and your reputation follows you. Somehow, you expect us to agree BJT amps can be made without NFB, but they cannot. I have nothing against NFB as such, and use it routinely and afaiac, in the interests of better musical performance. I never said you did, Patrick. But you don't seem to have a problem with changing your story after its been responded to. A defunct Australian manufacturer named I believe ME did it. It's not rocket science, just a waste of time, effort, and good electronic components. ME amplifiers used a large amount of NFB around two consecutive stages each containing a few sub stages. That's interesting. Would that be what most people call local feedback, or was it really loop feedback? TWO LOOPS OF LOOP FB, YOU GOT THAT!! Have you analysed the ME schematics? I only know what Trevor tells me. well, you would be PIG IGNORANT if you relied on information about how amplifiers worked from Trevor Wilson. The fact is you just made absurd allegations about ME amps without knowing the facts about how they worked, or without seeing a schematic. This makes you a pig brained fool arny. And No, I won't enlighten you by sending you a copy of the schematic. Find your bloody own copy. I repeat again, you cannot have a BJT based power amplifier unless you use a lot of external NFB in the way the device is connected. So how long are you going to stick by this new story, Patrick? Its the same old story, and I will stick by it. Get used to ppl thinking you are just plain dull. Patrick Turner. The drain or collector resistance is way too high just like the anode resistance of a beam tetrode of pentode to allow amplifiers without a lot of NFB, usually 20dB at least if the devices are working in class A. As you say Patrick, there's no problem with applying feedback. |
#40
Posted to rec.audio.tubes,aus.hi-fi
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Distortion in amplifiers.
"Arny Krueger" said:
"Sander deWaal" wrote in message John Byrns said: http://web.mit.edu/cheever/www/cheever_thesis.pdf There's 87 pages in that thesis that must be read before one can form an opinion. I wonder what Arnie thinks about all this. I wonder is the "TAD" is the same "new" distortion testing methodology that was discussed in this group a couple of years ago? There has been some discussion about this thesis in the past. The usual outcome: those who like tubes agreed with most of it, those who loathe tubes disagreed with most of it. Typical of Sander's overly-confrontational approach to technology he can't properly understand. ROFL!! That's why I design amps for a living, and you fix computers and work on your "usenet career", hmmm? ;-) -- - Maggies are an addiction for life. - |
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