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#1
Posted to rec.audio.tubes
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Explanation still required for triode superiority
In an effort to be agreeable, I tried hard to give you negative
feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute |
#2
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Andrew Jute McCoy wrote its usual fallacious arguments: Called "begging the question". Triodes are neither "superior" nor "inferior" when it comes to amplifiers. However, they do have many difficulties. Not the least of which a Flea Power. Expensive to create. Difficult to make operational (as your model so clearly illustrated). So, if one suspends belief sufficiently to actually beg said question, then further discussion is optional. Just like any given Science-Fiction movie/novel/premise. Oh, RIGHT!! McCoy failed in this venue as well. Silly me. Never mind. Peter Wieck Wyncote, PA |
#3
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:
In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute I know the answer! It's distance!! In a triode, there is a great distance between elements, forcing the electrons to be linear! In a transistor, things are so close and crowded that any electron going through has to grab a few buddies to take along... and the more going through, even more extras tag along - clearly exponential! And in ICs, which sound even worse then discrete transistors, things are even closer, so sound lots worse because they are even more exponential!! Simple. |
#4
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote:
But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. If, by "you", you mean the newsgroup in general, who "must" offer a reason, then prepare yourself for quite a... what's the word? Anyway, Caveat Emptor (Latin for "take a flashlight into the supposedly empty cave") and Habeas Corpus (Latin for "habanero sauce is good on the corpse"). Lotsa misinformation abounds. But if by "you" you mean "me", who's been the bitchiest about the topic, then, no, I don't have any pat answers. I can offer a couple topics for possible discussion, but the topic doesn't lend itself to pat answers. And, I would generally agree about your conclusion, at least in appropriate circumstances. Not all circumstances are appropriate, YMMV, yadayada. But, yeah. Much thanks, as always, Chris Hornbeck |
#5
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Soundhaspriority wrote:
Of course. "Distance makes the heart grow fonder." A minor correction. The saying actaully is: " Distance makes heart grow yonder." 22/7 |
#6
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Andre Jute wrote:
In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, like Otala claimed in his talk/paper (assuming a paper ever followed the talk!). When Patrick was defending feedback, he mentioned that poorly designed amps sound like crap when they have lots of feedback, but that if you fix them up a bit, meaning get rid of much of their excessive nonlinearities -- read, *amplitude* nonlinearities -- then adding feedback sounds okay. Now, if we eliminate the idea that feedback produces random noise -- and we *know* that it reduces amplitude non-linearities -- then the only distortion mechanism left, I believe, is phase-shifting. However, I want to describe the usual "constant 20 degrees phase lag at 40 KHz" as "phase-shifting," and a dynamic, microsecond to microsecond shifting back and forth of one frequency relative to another as "phase-smearing," or "time-smearing." What Otala was saying is that applying feedback to circuits with lots of open-loop distortions, which are (I believe) almost always amplitude distortions, converts these distortions into a back and forth smearing of the high frequencies relative to the low frequencies (and it may smear both in terms of the delay through the amp). Nor can we assume that this time-smearing is a simple function of the low frequency amplitude, because it is probably proportional to the magnitude of the distortions, as well as the LF amplitude: VERY non-musical. When enough feedback is applied to badly designed amps, the amplitude distortions become quite small, so why did Patrick find that they sounded much worse than the same amp sounds when touched up enough to reduce the larger open-loop amplitude distortions? As you say, *something* is wrong, and if it isn't high amplitude distortions (it can't be), and if feedback doesn't produce spurious noises, then the only thing left is exactly what Otala said, time-smearing. In essence, feedback *connects* two things that are normally separate in an amp, namely amplitude distortions, and phase-smearing. It achieves a balance between these two, a balance which is determined by the speed of the amp, the amount of feedback, and the amount of amplitude distortion. Contrary to what you say, Otala was *not* referring to TIM, and transistors did not become so much faster after 1980 than the ones used in his '73 article to make the problem he described go away. Yes, the amps had to be designed well enough to avoid TIM, but that was not a real problem even in '73 *if* you knew what you were doing. The problem he described in '80 was quite different, and even high MHz tubes are subject to it. The interesting things, assuming that feedback problems are indeed time-smearing (regardless of whether this comes from the conversion of amplitude distortions), are one, a single tone will reveal nothing of this, giving very low THD numbers, and two, multiple tones should show something, although looking at it in the amplitude realm will only show higher than expected IMD. There should be a fairly easy way to test to see if this really produces time-smearing. In general, we put a 4 volt 60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of feedback, preferably using non-linear sections of the amplifying devices (say, use two 12AX7 type triodes where the plate curves vary from widely spaced to closely spaced, and use about 60 to 80 dB of feedback to get the overall gain down to 1). Use a high pass filter to see only the 20 KHz signal, and use the 20 KHz signal from the generator to trigger the 'scope. If time-smearing exists, then the 20 KHz signal will appear "fuzzy" on the scope, since it is being shifted back and forth. Repeat without the 60 Hz signal to make sure the time-smearing isn't coming from somewhere else, and then also divide the output from each tube down so that you get the same amplitude output *without* using feedback, and see if the time-smearing goes away. Finally, if possible test over a region where the curves are fairly linear, to see if that also reduces the time-smearing. If so, you have proof that feedback transformed the amplitude distortion into time-smearing. I will try to do this, but I have little time, less energy, and not the best test bench in the world, so it may be a while! If you or someone else both can and wants to try this, I suspect we will get an answer much faster than if I do it. Note that we can use pentodes or transistors, too, but using solid state has the disadvantage of possibly introducing other complications due to the poor quality silicon parasitic capacitances. Also, I am suggesting the use of very different magnitudes as well as frequencies for the two signals, in case equal magnitudes somehow avoids this problem, or at least masks it from this test. And again, contrary to what Patrick said, the idea that *if* this were true, then by now someone would have already tries it, and the results would have become widely know, is just naive. The human race simply isn't that intelligent, at least not yet. An interesting conclusion, assuming this feedback time-smear mechanism exists, is that the output of a feedback amp does *not* match the input when multiple signals exist! However, our normal tests cannot see this, since they tend to focus on one frequency at a time. I believe that Patrick, as well as Otala, said that using local feedback to achieve good open loop linearity, combined with some global feedback, tends to sound pretty good. This makes sense for two reasons, first because although the local feedback will produce phase-smearing, it does so at *very* high speed, which I believe directly reduces the amount of smearing (common sense says that as the speed of devices approaches infinity, feedback becomes "perfect"). Second, the result does contain some mis-match between input and output, even given the high speed of local feedback, but now the global feedback will not only reduce the remaining "normal" amplitude distortions, it should also reduce the time-smearing produced by the local feedback, since this time-smearing will still produce an error signal for the global feedback. Of course, this reduction in time-smearing will itself produce more time-smearing, but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of time-smearing is reduced by "dividing up" the total feedback into local plus global. Finally, you saw the review of Otala that Phil Allison gave, and I think you were as impressed by it as I was (although it looked bad to PA). When a man who was as talented, knowledgeable, and honest as Otala produces a PROOF that negative feedback *always* transforms the amplitude distortions of the open loop into phase smears of the closed loop, we should not dismiss it as simply a problem of "old devices," a problem that a slight increase in speed can make go away, especially when the discussion that led to his analysis (the Audio Critic BS session) included a lot of talk about vacuum tubes, and how their speed advantage made it easier to use them with feedback. We really should do at least one or two tests before dismissing his conclusions. Again, I will try to do so, but if you want to know anytime soon, you should probably rely on someone else. Phil |
#7
Posted to rec.audio.tubes
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Explanation still required for triode superiority
22/7 wrote: Soundhaspriority wrote: Of course. "Distance makes the heart grow fonder." A minor correction. The saying actaully is: " Distance makes heart grow yonder." 22/7 I think you're right, No. 22. But if you used a spelling checker your meaning would be so much clearer: "Distance makes the heart thunder." That we can all agree to. Long rooms, permitting greater separation of ears and speakers, definitely do have better bass, and deep bass increases the respiration rate; it is an ur-instinct reaction to threat. Hope this explains everything including the price of fish beyond Alpha Centauri (1). For this insight I have recommended that you be promoted to No. 21. Andre Jute (1) Once after lunch with a lady from our publishers, Douglas Adams and I walked up four floors of a narrow stairwell behind her. She wore a transparent plastic raincoat over a skintight flesh coloured body stocking. We discussed the price of fish beyond Alpha Centauri. I swear that's what we discussed. |
#8
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Chris Hornbeck wrote: On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote: But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. If, by "you", you mean the newsgroup in general, who "must" offer a reason, then prepare yourself for quite a... what's the word? Anyway, Caveat Emptor (Latin for "take a flashlight into the supposedly empty cave") and Habeas Corpus (Latin for "habanero sauce is good on the corpse"). Lotsa misinformation abounds. I'd say "****'em" but their minds are clearly syphiclically degenerated (the NFB of the immoral) so touching them physically may expose one to contamination. As for "must", sure thing. The most amazing thing about the amateur flamers on RAT is not their incompetence in both electronics and polemics but there blind hypocrisy, best seen in their pretension of being "scientific". But if by "you" you mean "me", who's been the bitchiest about the topic, then, no, I don't have any pat answers. I can offer a couple topics for possible discussion, but the topic doesn't lend itself to pat answers. Bring on your topics, Chris. We could do with some fresh air in RAT. And, I would generally agree about your conclusion, at least in appropriate circumstances. Not all circumstances are appropriate, YMMV, yadayada. But, yeah. Which conclusion? That "triodes sound better" or that "there must be an electrical explanation"? Much thanks, as always, Chris Hornbeck Andre Jute "Take the money and run" -- Len Deighton |
#9
Posted to rec.audio.tubes
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Explanation still required for triode superiority
22/7 wrote:
Soundhaspriority wrote: Of course. "Distance makes the heart grow fonder." A minor correction. The saying actaully is: " Distance makes heart grow yonder." 22/7 Or "absinthe makes the heart grow fonder", as Crowley put it |
#10
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Andre Jute wrote: Which conclusion? That "triodes sound better" That's your opinion. or that "there must be an electrical explanation"? Of course there must be. Added low order distortion of course. It's basically an 'effect' like SRS or BBE 'sound enhancement'. With toobs you can't turn if off though Graham |
#11
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Andre Jute wrote: Chris Hornbeck wrote: On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote: But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. If, by "you", you mean the newsgroup in general, who "must" offer a reason, then prepare yourself for quite a... what's the word? Anyway, Caveat Emptor (Latin for "take a flashlight into the supposedly empty cave") and Habeas Corpus (Latin for "habanero sauce is good on the corpse"). Lotsa misinformation abounds. I'd say "****'em" but their minds are clearly syphiclically degenerated (the NFB of the immoral) so touching them physically may expose one to contamination. As for "must", sure thing. The most amazing thing about the amateur flamers on RAT is not their incompetence in both electronics and polemics but there blind hypocrisy, best seen in their pretension of being "scientific". And down with IBM's ViaVoice too for that "there" for "their". In the same sentence as "pretension" too! -- AJ But if by "you" you mean "me", who's been the bitchiest about the topic, then, no, I don't have any pat answers. I can offer a couple topics for possible discussion, but the topic doesn't lend itself to pat answers. Bring on your topics, Chris. We could do with some fresh air in RAT. And, I would generally agree about your conclusion, at least in appropriate circumstances. Not all circumstances are appropriate, YMMV, yadayada. But, yeah. Which conclusion? That "triodes sound better" or that "there must be an electrical explanation"? Much thanks, as always, Chris Hornbeck Andre Jute "Take the money and run" -- Len Deighton |
#12
Posted to rec.audio.tubes
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Explanation still required for triode superiority
I've read your arguments, Phil. Their subtext is methods to make NFB
more usable, less damaging to reproduced sound. That is a legitimate outlook for Otala, who has to fit into an existing industrial environment where NFB is an ineradicable part of that dominant electronics cost-accounting system in which the explicit purpose of NFB is to make cheap parts tolerable. But that has buggerall to do with me as a DIYer. I can afford to take the far simpler, more fundamental course of making my amps so superior in design and components right from the start -- that I can do without NFB and without the damage that NFB does. So I design amps without NFB, period. I shortcut the problem of NFB and eliminate it before it arises. My amps are ultra-silent without NFB; they do not need NFB for any purpose whatsoever. Since one of my ZNFB amps is capable of 80W when in its PSE mode, more than enough to drive electrostatic panels to power-rivetter volume, I take the view that any designer who requires NFB to make his hi-fi amps work has either permitted cost-accountants to bully him, is an impressionable fashion victim, or is too thick to put his mind in gear, tick one or more boxes. The rest is interesting speculation but not of such consuming interest to me that I will spend a morning setting up bench experiments to prove the details of something I already know: that NFB smears the sound. A complete summary of my view on NFB can be found here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm and here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm I haven't changed my mind one jot or tittle over the recent discussion. I have heard absolutely nothing that proves a contrary case. That is not to say you may not be right, that the psycho-acoustic effect which gives Class A1 ZNFB (or very low NFB) amps their distinct superiority is a subliminal reaction to the HF phase- smearing in NFB amps that you say Otala posits. I just haven't seen any proof yet, and know that, when I do see such proof, I will consider it of intellectual interest -- and continue to build the sort of ZNFB amps I have always built, in which NFB is excluded for its amplitude smearing at frequencies starting below 100c/s, so that HF phase smearing, if it exists in NFB tube amps, is no danger to my sound. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Phil wrote: Andre Jute wrote: In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, like Otala claimed in his talk/paper (assuming a paper ever followed the talk!). When Patrick was defending feedback, he mentioned that poorly designed amps sound like crap when they have lots of feedback, but that if you fix them up a bit, meaning get rid of much of their excessive nonlinearities -- read, *amplitude* nonlinearities -- then adding feedback sounds okay. Now, if we eliminate the idea that feedback produces random noise -- and we *know* that it reduces amplitude non-linearities -- then the only distortion mechanism left, I believe, is phase-shifting. However, I want to describe the usual "constant 20 degrees phase lag at 40 KHz" as "phase-shifting," and a dynamic, microsecond to microsecond shifting back and forth of one frequency relative to another as "phase-smearing," or "time-smearing." What Otala was saying is that applying feedback to circuits with lots of open-loop distortions, which are (I believe) almost always amplitude distortions, converts these distortions into a back and forth smearing of the high frequencies relative to the low frequencies (and it may smear both in terms of the delay through the amp). Nor can we assume that this time-smearing is a simple function of the low frequency amplitude, because it is probably proportional to the magnitude of the distortions, as well as the LF amplitude: VERY non-musical. When enough feedback is applied to badly designed amps, the amplitude distortions become quite small, so why did Patrick find that they sounded much worse than the same amp sounds when touched up enough to reduce the larger open-loop amplitude distortions? As you say, *something* is wrong, and if it isn't high amplitude distortions (it can't be), and if feedback doesn't produce spurious noises, then the only thing left is exactly what Otala said, time-smearing. In essence, feedback *connects* two things that are normally separate in an amp, namely amplitude distortions, and phase-smearing. It achieves a balance between these two, a balance which is determined by the speed of the amp, the amount of feedback, and the amount of amplitude distortion. Contrary to what you say, Otala was *not* referring to TIM, and transistors did not become so much faster after 1980 than the ones used in his '73 article to make the problem he described go away. Yes, the amps had to be designed well enough to avoid TIM, but that was not a real problem even in '73 *if* you knew what you were doing. The problem he described in '80 was quite different, and even high MHz tubes are subject to it. The interesting things, assuming that feedback problems are indeed time-smearing (regardless of whether this comes from the conversion of amplitude distortions), are one, a single tone will reveal nothing of this, giving very low THD numbers, and two, multiple tones should show something, although looking at it in the amplitude realm will only show higher than expected IMD. There should be a fairly easy way to test to see if this really produces time-smearing. In general, we put a 4 volt 60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of feedback, preferably using non-linear sections of the amplifying devices (say, use two 12AX7 type triodes where the plate curves vary from widely spaced to closely spaced, and use about 60 to 80 dB of feedback to get the overall gain down to 1). Use a high pass filter to see only the 20 KHz signal, and use the 20 KHz signal from the generator to trigger the 'scope. If time-smearing exists, then the 20 KHz signal will appear "fuzzy" on the scope, since it is being shifted back and forth. Repeat without the 60 Hz signal to make sure the time-smearing isn't coming from somewhere else, and then also divide the output from each tube down so that you get the same amplitude output *without* using feedback, and see if the time-smearing goes away. Finally, if possible test over a region where the curves are fairly linear, to see if that also reduces the time-smearing. If so, you have proof that feedback transformed the amplitude distortion into time-smearing. I will try to do this, but I have little time, less energy, and not the best test bench in the world, so it may be a while! If you or someone else both can and wants to try this, I suspect we will get an answer much faster than if I do it. Note that we can use pentodes or transistors, too, but using solid state has the disadvantage of possibly introducing other complications due to the poor quality silicon parasitic capacitances. Also, I am suggesting the use of very different magnitudes as well as frequencies for the two signals, in case equal magnitudes somehow avoids this problem, or at least masks it from this test. And again, contrary to what Patrick said, the idea that *if* this were true, then by now someone would have already tries it, and the results would have become widely know, is just naive. The human race simply isn't that intelligent, at least not yet. An interesting conclusion, assuming this feedback time-smear mechanism exists, is that the output of a feedback amp does *not* match the input when multiple signals exist! However, our normal tests cannot see this, since they tend to focus on one frequency at a time. I believe that Patrick, as well as Otala, said that using local feedback to achieve good open loop linearity, combined with some global feedback, tends to sound pretty good. This makes sense for two reasons, first because although the local feedback will produce phase-smearing, it does so at *very* high speed, which I believe directly reduces the amount of smearing (common sense says that as the speed of devices approaches infinity, feedback becomes "perfect"). Second, the result does contain some mis-match between input and output, even given the high speed of local feedback, but now the global feedback will not only reduce the remaining "normal" amplitude distortions, it should also reduce the time-smearing produced by the local feedback, since this time-smearing will still produce an error signal for the global feedback. Of course, this reduction in time-smearing will itself produce more time-smearing, but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of time-smearing is reduced by "dividing up" the total feedback into local plus global. Finally, you saw the review of Otala that Phil Allison gave, and I think you were as impressed by it as I was (although it looked bad to PA). When a man who was as talented, knowledgeable, and honest as Otala produces a PROOF that negative feedback *always* transforms the amplitude distortions of the open loop into phase smears of the closed loop, we should not dismiss it as simply a problem of "old devices," a problem that a slight increase in speed can make go away, especially when the discussion that led to his analysis (the Audio Critic BS session) included a lot of talk about vacuum tubes, and how their speed advantage made it easier to use them with feedback. We really should do at least one or two tests before dismissing his conclusions. Again, I will try to do so, but if you want to know anytime soon, you should probably rely on someone else. Phil |
#13
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Phil wrote: Andre Jute wrote: In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, like Otala claimed in his talk/paper (assuming a paper ever followed the talk!). When Patrick was defending feedback, he mentioned that poorly designed amps sound like crap when they have lots of feedback, but that if you fix them up a bit, meaning get rid of much of their excessive nonlinearities -- read, *amplitude* nonlinearities -- then adding feedback sounds okay. Now, if we eliminate the idea that feedback produces random noise -- and we *know* that it reduces amplitude non-linearities -- then the only distortion mechanism left, I believe, is phase-shifting. However, I want to describe the usual "constant 20 degrees phase lag at 40 KHz" as "phase-shifting," and a dynamic, microsecond to microsecond shifting back and forth of one frequency relative to another as "phase-smearing," or "time-smearing." What Otala was saying is that applying feedback to circuits with lots of open-loop distortions, which are (I believe) almost always amplitude distortions, converts these distortions into a back and forth smearing of the high frequencies relative to the low frequencies (and it may smear both in terms of the delay through the amp). Nor can we assume that this time-smearing is a simple function of the low frequency amplitude, because it is probably proportional to the magnitude of the distortions, as well as the LF amplitude: VERY non-musical. When enough feedback is applied to badly designed amps, the amplitude distortions become quite small, so why did Patrick find that they sounded much worse than the same amp sounds when touched up enough to reduce the larger open-loop amplitude distortions? As you say, *something* is wrong, and if it isn't high amplitude distortions (it can't be), and if feedback doesn't produce spurious noises, then the only thing left is exactly what Otala said, time-smearing. In essence, feedback *connects* two things that are normally separate in an amp, namely amplitude distortions, and phase-smearing. It achieves a balance between these two, a balance which is determined by the speed of the amp, the amount of feedback, and the amount of amplitude distortion. Contrary to what you say, Otala was *not* referring to TIM, and transistors did not become so much faster after 1980 than the ones used in his '73 article to make the problem he described go away. Yes, the amps had to be designed well enough to avoid TIM, but that was not a real problem even in '73 *if* you knew what you were doing. The problem he described in '80 was quite different, and even high MHz tubes are subject to it. The interesting things, assuming that feedback problems are indeed time-smearing (regardless of whether this comes from the conversion of amplitude distortions), are one, a single tone will reveal nothing of this, giving very low THD numbers, and two, multiple tones should show something, although looking at it in the amplitude realm will only show higher than expected IMD. There should be a fairly easy way to test to see if this really produces time-smearing. In general, we put a 4 volt 60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of feedback, preferably using non-linear sections of the amplifying devices (say, use two 12AX7 type triodes where the plate curves vary from widely spaced to closely spaced, and use about 60 to 80 dB of feedback to get the overall gain down to 1). Use a high pass filter to see only the 20 KHz signal, and use the 20 KHz signal from the generator to trigger the 'scope. If time-smearing exists, then the 20 KHz signal will appear "fuzzy" on the scope, since it is being shifted back and forth. Repeat without the 60 Hz signal to make sure the time-smearing isn't coming from somewhere else, and then also divide the output from each tube down so that you get the same amplitude output *without* using feedback, and see if the time-smearing goes away. Finally, if possible test over a region where the curves are fairly linear, to see if that also reduces the time-smearing. If so, you have proof that feedback transformed the amplitude distortion into time-smearing. I will try to do this, but I have little time, less energy, and not the best test bench in the world, so it may be a while! If you or someone else both can and wants to try this, I suspect we will get an answer much faster than if I do it. Note that we can use pentodes or transistors, too, but using solid state has the disadvantage of possibly introducing other complications due to the poor quality silicon parasitic capacitances. Also, I am suggesting the use of very different magnitudes as well as frequencies for the two signals, in case equal magnitudes somehow avoids this problem, or at least masks it from this test. And again, contrary to what Patrick said, the idea that *if* this were true, then by now someone would have already tries it, and the results would have become widely know, is just naive. The human race simply isn't that intelligent, at least not yet. An interesting conclusion, assuming this feedback time-smear mechanism exists, is that the output of a feedback amp does *not* match the input when multiple signals exist! However, our normal tests cannot see this, since they tend to focus on one frequency at a time. I believe that Patrick, as well as Otala, said that using local feedback to achieve good open loop linearity, combined with some global feedback, tends to sound pretty good. This makes sense for two reasons, first because although the local feedback will produce phase-smearing, it does so at *very* high speed, which I believe directly reduces the amount of smearing (common sense says that as the speed of devices approaches infinity, feedback becomes "perfect"). Second, the result does contain some mis-match between input and output, even given the high speed of local feedback, but now the global feedback will not only reduce the remaining "normal" amplitude distortions, it should also reduce the time-smearing produced by the local feedback, since this time-smearing will still produce an error signal for the global feedback. Of course, this reduction in time-smearing will itself produce more time-smearing, but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of time-smearing is reduced by "dividing up" the total feedback into local plus global. Finally, you saw the review of Otala that Phil Allison gave, and I think you were as impressed by it as I was (although it looked bad to PA). When a man who was as talented, knowledgeable, and honest as Otala produces a PROOF that negative feedback *always* transforms the amplitude distortions of the open loop into phase smears of the closed loop, we should not dismiss it as simply a problem of "old devices," a problem that a slight increase in speed can make go away, especially when the discussion that led to his analysis (the Audio Critic BS session) included a lot of talk about vacuum tubes, and how their speed advantage made it easier to use them with feedback. We really should do at least one or two tests before dismissing his conclusions. Again, I will try to do so, but if you want to know anytime soon, you should probably rely on someone else. Phil I have seen no evidence of the time smearing you are talking about. The essence of time smearing you speak of when testing say 5kHz with 60Hz present as a larger signal is that the 60Hz affects the devices as a changing reactance load on the devices so that the phase of the 5kHz waves are phase advanced and phase lagged alternatively 60 times persecond. Phase modulation and FM modulation was gained deliberately in reactance tube modulators which exploited the change in gm with Ia in a tube thus shifting the F of an oscillator or the phase of an RF carrier. There is much about thei is old books. But dynamic phase shift of a fraction of a 5kHz wave I have not seen due to dynamic action by a lower F. The NFB reduces ALL artifacts and such phase shifting is reduced in the open loop character of an amp where it allegedly should exist. I repeatedly gave the conditions needed where the application of NFB didn't make any improvement to the sound, and made little difference to the measured THD artifacts especially when weighted for audibibilty, and increased the number of artifacts significantly. Far greater minds than I have spelled it all out in Wireless World years ago. I suggest you read all your local university library archives containing the magazine with its brilliant audio articles between when it first appeared in 1917 to now. ( I assume your local uni isn't full of football magazines in the archives ). I have only read and copied out the audio stuff up to about 1996. In all of this literature on the effects NFB there wasn't much about FB causing dynamic phase shift that I can recall. Perhaps if you read what I read you'll find something I missed. Seriously, methinks you NEED to do some real study. Perhaps you'd like to re-iterate what I said to all about open loop bw, phase shift, and the amount of applied NFB and the amount of open loop THD. The fuzziness you say is observed when viewing the HF wave in a cascaded 12AX7 amp where the gain has been reduced to 1 is hard to believe. A cascaded pair of 12AX7 would have an open loop gain = at least 3,000, and applying FB to reduce gain to 1.0 = 70dB of applied NFB. Any dynamic phase shifting in any signal before FB is applied should be easily visible / measurable / quantifiable before NFB is connected, but after a reduction of 70dB it would most definately be invisible on a CRO. Do offer my sincerest respects to Mr Otala and ask him to tell you all about what you appear to maybe not understand as well as he may. I suspect you instead remain delighted by the jargon and terminology around the subject rather than staying with the cold hard facts about applied NFB and its effects and the conditions under which it is applied, all of which cannot easily be dealt with without being utterly precise at all times, which seems right considering the books and magazine articles which have been written about NFB so far. Patrick Turner. |
#14
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Explanation still required for triode superiority
Arny Krueger wrote: "Phil" wrote in message ... Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, There is no reliable theoretical or measurable support for this idea. There's no support based on reliable listening tests. In contrast, there are zillions of examples of equipment with tons of negative feedback that has marvelous phase accuracy, both measured and heard. Proven theory says this is exactly as it should be. How thoroughly does something need to be disproved to be abandoned? Furthermore it can easily be shown to be yet another myth by the application of mathematics ! Graham |
#15
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Explanation still required for triode superiority
"Phil" wrote in message ... Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, There is no reliable theoretical or measurable support for this idea. There's no support based on reliable listening tests. In contrast, there are zillions of examples of equipment with tons of negative feedback that has marvelous phase accuracy, both measured and heard. Proven theory says this is exactly as it should be. How thoroughly does something need to be disproved to be abandoned? |
#16
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Explanation still required for triode superiority
Eeyore wrote: Andre Jute wrote: Which conclusion? That "triodes sound better" That's your opinion. or that "there must be an electrical explanation"? Of course there must be. Added low order distortion of course. It's basically an 'effect' like SRS or BBE 'sound enhancement'. With toobs you can't turn if off though Graham I am not sure triodes are superior. They are just 3 terminal devices with inbuilt NFB. In the 1950s and 60s in many recording studios, gear was used that was mostly designed by cloth eared engineers with 100% regard only for numbers and such gear had SHIRTLOADS of pentodes and beam tetrodes and transformers and NFB. We hear the results today on well recorded and preserved vinyl recordings. Not a digit or PN junction used anywhere. Great stuff when it turned out right. Was it dependant on triodes? maybe, but also maybe not. Why would any engineer use 3 triodes where two pentodes would do? The final link for us lesser latterday mortals is from recording to speaker, and triodes are a good choice. Not necessarily superior IMHO, and i say that after trying such tubes as the 13Ei SEUL with mild NFB that I believe will give ANY triode amp some real competion, providing the power ceiling is the same. As a later SE amp development I tried a quad of humble cheap EH 6CA7, actually Sovtek prettied up, to get 35 watts SE with CFB, and again the measurements were NOT typically inferior to PP designs and the sound was detailed, sparkling and natural sounding and all that anyone may wish for. I have built SET amps with 2A3 or 300B, and found they gave the best 8 and 4 watts i have ever heard with 7 db of NFB to reduce Rout compared to tubes like a single EL84 in pentode or a single EL34 in pentode, respectively, but with 20dB of NFB needed to get the same Rout. The CFB connection transcends the UL connection which transcends pentode. Triode is somewhere in their between CFB and UL IMHO. Experimenters may experiment to verify/discount my opinions. See my web pages for more on such matters. http://www.turneraudio.com.au Patrick Turner. |
#17
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Explanation still required for triode superiority
Stuart Krivis wrote: On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote: But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. First we would have to accept these things as true. :-) In the face of overwhelming evidence that as far as accuracy is concerned, triodes are really quite flawed. The simple explanation being that for some, accuracy of reproduction is not what they seek, they simply seek what they consider to be 'a nice sound'. Which is all fine and well but accuracy ain't part of it. Graham |
#18
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Explanation still required for triode superiority
Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Peter Wieck wrote: Andrew Jute McCoy wrote its usual fallacious arguments: Called "begging the question". Triodes are neither "superior" nor "inferior" when it comes to amplifiers. However, they do have many difficulties. Not the least of which a Flea Power. Expensive to create. Difficult to make operational (as your model so clearly illustrated). Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) The toobies don't care though ! Graham |
#19
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Explanation still required for triode superiority
Stuart Krivis wrote: On Mon, 25 Sep 2006 14:06:16 +0100, Eeyore wrote: Arny Krueger wrote: "Phil" wrote: Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, There is no reliable theoretical or measurable support for this idea. There's no support based on reliable listening tests. In contrast, there are zillions of examples of equipment with tons of negative feedback that has marvelous phase accuracy, both measured and heard. Proven theory says this is exactly as it should be. How thoroughly does something need to be disproved to be abandoned? Furthermore it can easily be shown to be yet another myth by the application of mathematics ! Don't mention math! You'll get them all confuzzled. :-) They would seem to be confuzzled already with their talk of 'HF smearing' ! Graham |
#20
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Explanation still required for triode superiority
Eeyore said:
The simple explanation being that for some, accuracy of reproduction is not what they seek, they simply seek what they consider to be 'a nice sound'. Which is all fine and well but accuracy ain't part of it. You won't hear me say anything else, regarding my own hobby designs. -- "Due knot trussed yore spell chequer two fined awl miss steaks." |
#21
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Explanation still required for triode superiority
Sander deWaal wrote: Eeyore said: The simple explanation being that for some, accuracy of reproduction is not what they seek, they simply seek what they consider to be 'a nice sound'. Which is all fine and well but accuracy ain't part of it. You won't hear me say anything else, regarding my own hobby designs. That because you're honest Sander ! :~) Unlike some here. Graham |
#22
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Explanation still required for triode superiority
Bret Ludwig wrote: Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else you would have had nothing but Morse code. And since when was AM 'hi-fi' ? Graham |
#23
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Explanation still required for triode superiority
Bret Ludwig wrote: Eeyore wrote: Bret Ludwig wrote: Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else you would have had nothing but Morse code. And since when was AM 'hi-fi' ? That would be before VHF FM became dominant. On days with little electrical storm activity in the hemisphere and in the right locations very fine broadcast fidelity was possible. Even today, at a place I visited in north central Missouri I heard KXTR from Kansas City through a passive Millen tuner (essentially a crystal radio) in astonishing fidelity at an elderly hi-fi buff's house. Shame everything they play is by the appalling Sir Neville Marriner at the Academy of St-Martin-in-the-Fields. Vintage Toscanini and other classic conductors' recordings would be so much better, but instead they play that LOAD continually. They say LF transmissions in England and Germany were even more impressive. The problem with AM AUIU was always one of bandwidth for one part and of course that any interference was directly demodulated. Those old valve sets did sound rather good though ( I had one myself - an EKCO ! ) but that for the most part was mainly due to the excellent design of the RF circuitry. Graham |
#24
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Explanation still required for triode superiority
Chris Hornbeck wrote: 1. Unweighted THD is useless as an indicator of quality. So why do you think I regularly mention the order of the distortion ? Graham |
#25
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Explanation still required for triode superiority
On 25 Sep 2006 03:09:39 -0700, "Andre Jute" wrote:
Bring on your topics, Chris. We could do with some fresh air in RAT. Some folks who I'd hoped to be refreshing have turned out to be terminally boring. Sorry for having encouraged 'em. We live and don't learn... or something. Again, sorry, all. No time this week to give any adequate or deserving response to yours or Henry's provocative posts, but, if I may, a few possibilities: 1. Unweighted THD is useless as an indicator of quality. 2. Unweighted IMD " " " 3. We make totally unwarranted assumptions of monotonicity. This is a fatal flaw in our thinking, and we all do it, all the time. 4. We make often unwarranted assumptions about input signal bandwidth. 5. We *always* *without exception* forget to properly weight the importance of simply being upstream in the signal path. Always. 6. Loud voices will say that everything (that doesn't include the dreaded vacuum valve, scourge of nations) sounds the same. This has recently been expanded to include transistor amplifiers from the early 1970's, by certain especially vocal ideologes, in another thread, this very week. Against such a religious fervor, nothing can stand. Been reading about weaponry this week; no real purpose; haven't needed a weapon since discharged from the Army in 1972; just looking, ya know? It seems that the US military converted from the Colt .45 caliber pistol in standard issue since 1911(!) to a Berreta of some NATO gauge in the mid 1980's. But it seems it doesn't work, despite all the high powered analysis. Ya shoot sombody with it, but they keep comin'. What's so sadly wrong with the story is that the US military went through the whole exact same hand-wringing back 100+ years ago in the Phillippines, leading to the adoption of, wait for it, the .45 caliber. Modeling and analysis are essential; but the map is not the world. Which conclusion? That "triodes sound better" or that "there must be an electrical explanation"? Strong agreement with the former; strong disagreement ('cause that ain't science!) with the latter. "Take the money and run" -- Len Deighton And also... who? Bob Segar? Somebody like that, anyway. Much thanks, as always, Chris Hornbeck |
#26
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Explanation still required for triode superiority
On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore
wrote: 1. Unweighted THD is useless as an indicator of quality. So why do you think I regularly mention the order of the distortion ? Wanna *not* be a major disappointment? Post something positive and educational on the topic. Right here; right now. Lord knows you're capable, and all the latterday endless cheap shots are beneath you. Step up to the plate and take a swing! This *could* be a very interesting newsgroup again someday. Gonna take everybody; no slackers. As always, Chris Hornbeck |
#27
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Explanation still required for triode superiority
Eeyore wrote: Stuart Krivis wrote: On 24 Sep 2006 16:18:06 -0700, "Andre Jute" wrote: But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. First we would have to accept these things as true. :-) In the face of overwhelming evidence that as far as accuracy is concerned, triodes are really quite flawed. The simple explanation being that for some, accuracy of reproduction is not what they seek, they simply seek what they consider to be 'a nice sound'. Which is all fine and well but accuracy ain't part of it. Graham Graham, you may not realise it, but you speak with a flawed reasoning ability on this issue, IMHO. Its easily possible to build a class A triode PP amp with say a pair of KT90 strapped as triodes fo 30 watts at about 0.7% thd with no global NFB. If 26dB of global NFB is connected (as it used to be done so often in 1955), THD at 30 watts drops to 0.035% and at normal average listening levels of a watt the THD is quite negligible at around 0.01% and accuracy is what would be heard in your ears and accuracy is what you want and it depends on the measuable artfacts being audible or not. Since artifacts of 0.01% are inaudible, mainly a tiny amount of 3H and without any crossover distortions etc, the music is accurate, no? Perhaps you need to buy a pair of Halcros made in Sth Aust and they give only 0.0001% at 200 watts at 20 kHz. All the accuracy anyone might crave for. Meanwhile, many ppl don't mind THD being 0.1% or more, and are flat out trying to determine if that is audible or not. Patrick Turner. |
#28
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Explanation still required for triode superiority
Eeyore wrote: Bret Ludwig wrote: Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else you would have had nothing but Morse code. And since when was AM 'hi-fi' ? Graham The best transmissions here have 9kHz of audio modulation. In 1999 I built a tubed AM radio with a flat AF bw of 10Hz to 10kHz, which meant the IFT had to be carefully contructed for a wide pass band of about 17kHz, and some treble boosting compensates for the sideband cutting. So although 10khz is missing from the 20kHz of AF bw needed for true hi-fi, my AM radio is unsurpassable compared to all other AM radios I have ever worked on. All brand name AM tuners and radios have less AF bw than my set because they were designed to give about 7kHz max of IF bw so AF is restricted to 3.5kHz if one is very lucky and with many SS AM sets the AF is about 2kHz, and the distortion is much higher. The audio amp in the radio is an EL34 in triode with 12AX7 driver and with 12 dB of NFB. There is a full range two way speaker in a floor standing reflex box under the radio set. The radio provides truly wonderful, musical, undistorted and non tiring listening. Patrick Turner. |
#29
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Explanation still required for triode superiority
Eeyore wrote: Bret Ludwig wrote: Eeyore wrote: Bret Ludwig wrote: Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else you would have had nothing but Morse code. And since when was AM 'hi-fi' ? That would be before VHF FM became dominant. On days with little electrical storm activity in the hemisphere and in the right locations very fine broadcast fidelity was possible. Even today, at a place I visited in north central Missouri I heard KXTR from Kansas City through a passive Millen tuner (essentially a crystal radio) in astonishing fidelity at an elderly hi-fi buff's house. Shame everything they play is by the appalling Sir Neville Marriner at the Academy of St-Martin-in-the-Fields. Vintage Toscanini and other classic conductors' recordings would be so much better, but instead they play that LOAD continually. They say LF transmissions in England and Germany were even more impressive. The problem with AM AUIU was always one of bandwidth for one part and of course that any interference was directly demodulated. Those old valve sets did sound rather good though ( I had one myself - an EKCO ! ) but that for the most part was mainly due to the excellent design of the RF circuitry. Graham Most AM tube radios were built down to a price rather than up to a quality. Most are just examples of poor performing junk. Worse are 95% of SS radios. But AM could have been wonderful but having many stations spaced at 9kHz apart thus limiting the AF bw due to side band interference was more important than ****ing fidelity. One would require 40kHz of RF bw for 20kHz of AF bw, so there would be much fewer AM stations on the band if this had been used for the standard. With FM, the problems were reduced, but even then they settled for second rate specs of only 15kHz of bw for audio, pilot at 19kHz and a subcarrier F for stereo at 38kHz when it should have been at 100kHz, thus allowing the pilot tone to be at say 25kHz. Now we are supposed to be getting better when digital broadcasting gets started but I never see exactly what the specs are for that... Patrick Turner. |
#30
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Explanation still required for triode superiority
Chris Hornbeck wrote: On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore wrote: 1. Unweighted THD is useless as an indicator of quality. So why do you think I regularly mention the order of the distortion ? Wanna *not* be a major disappointment? Post something positive and educational on the topic. Right here; right now. Lord knows you're capable, and all the latterday endless cheap shots are beneath you. Step up to the plate and take a swing! This *could* be a very interesting newsgroup again someday. Gonna take everybody; no slackers. It's a subject that truly intruiges me. Where I suspect I'd differ with you is that I'd expect a DSP simulation to sound just the same as the beloved triode. It is something that I'm looking into btw. As for the effect of the order of the distortion, does anyone recall who wrote that thesis about it and the weighting thereof ? Graham |
#31
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Explanation still required for triode superiority
Phil wrote: As frustrated as I sometimes get with this guy's arguments, this is why I love the guy ... Patrick's post are regularly most interesting indeed. Graham |
#32
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Explanation still required for triode superiority
As frustrated as I sometimes get with this guy's arguments, this is why
I love the guy ... Admiring Phil Patrick Turner wrote: Eeyore wrote: Bret Ludwig wrote: Stuart Krivis wrote: On 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" wrote: Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. AM transmitters are a bit orthogonal to the topic at hand. :-) Don't MAKE me get Allison on you! Every one had a BIG AUDIO AMP. Else you would have had nothing but Morse code. And since when was AM 'hi-fi' ? Graham The best transmissions here have 9kHz of audio modulation. In 1999 I built a tubed AM radio with a flat AF bw of 10Hz to 10kHz, which meant the IFT had to be carefully contructed for a wide pass band of about 17kHz, and some treble boosting compensates for the sideband cutting. So although 10khz is missing from the 20kHz of AF bw needed for true hi-fi, my AM radio is unsurpassable compared to all other AM radios I have ever worked on. All brand name AM tuners and radios have less AF bw than my set because they were designed to give about 7kHz max of IF bw so AF is restricted to 3.5kHz if one is very lucky and with many SS AM sets the AF is about 2kHz, and the distortion is much higher. The audio amp in the radio is an EL34 in triode with 12AX7 driver and with 12 dB of NFB. There is a full range two way speaker in a floor standing reflex box under the radio set. The radio provides truly wonderful, musical, undistorted and non tiring listening. Patrick Turner. |
#33
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Explanation still required for triode superiority
Andre Jute wrote:
I've read your arguments, Phil. Their subtext is methods to make NFB more usable, less damaging to reproduced sound. That is a legitimate outlook for Otala, who has to fit into an existing industrial environment where NFB is an ineradicable part of that dominant electronics cost-accounting system in which the explicit purpose of NFB is to make cheap parts tolerable. But that has buggerall to do with me as a DIYer. I can afford to take the far simpler, more fundamental course of making my amps so superior in design and components right from the start -- that I can do without NFB and without the damage that NFB does. So I design amps without NFB, period. I shortcut the problem of NFB and eliminate it before it arises. My amps are ultra-silent without NFB; they do not need NFB for any purpose whatsoever. Since one of my ZNFB amps is capable of 80W when in its PSE mode, more than enough to drive electrostatic panels to power-rivetter volume, I take the view that any designer who requires NFB to make his hi-fi amps work has either permitted cost-accountants to bully him, is an impressionable fashion victim, or is too thick to put his mind in gear, tick one or more boxes. The rest is interesting speculation but not of such consuming interest to me that I will spend a morning setting up bench experiments to prove the details of something I already know: that NFB smears the sound. A complete summary of my view on NFB can be found here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm and here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm I haven't changed my mind one jot or tittle over the recent discussion. I have heard absolutely nothing that proves a contrary case. That is not to say you may not be right, that the psycho-acoustic effect which gives Class A1 ZNFB (or very low NFB) amps their distinct superiority is a subliminal reaction to the HF phase- smearing in NFB amps that you say Otala posits. I just haven't seen any proof yet, and know that, when I do see such proof, I will consider it of intellectual interest -- and continue to build the sort of ZNFB amps I have always built, in which NFB is excluded for its amplitude smearing at frequencies starting below 100c/s, so that HF phase smearing, if it exists in NFB tube amps, is no danger to my sound. Be fair now, you didn't ask, "Why should I build high feedback pentode amps," you asked, "Why do do [no feedback] triode amps sound better?" I merely attempted to give you an answer. You believe that triodes have an internal feedback mechanism, and you wondered why they (still) sound better. The basic core of my response/answer is that (1) negative feedback transforms relatively benign amplitude distortion into much less musical phase distortion, and (2) either triodes do *not* have this distortion mechanism, or it occurs at such staggeringly high frequencies that triodes can "get away with it," since the amount of phase distortion produced decreases as the high frequency limit increases. And I proposed a test, which may not work anyway, and which apparently only I have any interest in performing! However, I believe you when you say you already know that feedback smears the sound somehow, and don't need a test to "justify" your decisions, which is a stand I do respect. For a while there, all of us had to face serious criticisms for saying that in our own experience, cables do sound different, and it really is a mark of character to stand up and say something that is true, but "officially" stupid. If only the "official" beliefs didn't so often turn out to be the ones that are actually stupid, we could all be mindless sheep, and be better off for it! ;-) However, there are sometimes good reasons for more fully understanding something. If we assume for a moment that my analysis -- which is basically my attempt to guess at the rest of what Otala was saying, since I have yet to see the full text -- is correct, then several interesting things follow. First, since a threshold below which we cannot hear phase distortion realistically *must* exist -- and again, for Patrick's benefit, this is phase-smearing, and *not* the simple phase shifting which feedback does correct -- we should be able to add some feedback and get "all gain, no pain." Patrick said that he added 6 dB to lower output Z, and it sounded fantastic, as opposed to a 20 dB version of the same amp. Well, maybe this is completely true, but if we *know* that it is true, then, for example, amps that use high-mu transmitter tubes with positive grid drive and a bit of feedback to get the Zout down begin to make sense, especially when the feedback is used in a two-stage configuration that does not include the output transformer, meaning that it can have a *very* high upper frequency limit (you don't need to "dumb down" a stage like you often need to do with a three-stage to prevent oscillation), which limits the damage feedback can do to sub-threshold levels. Many people report that they LOVE the sound of these things, but an unjustified, in this case, bias against *any* use of feedback could prevent us from even trying one. Or, let's look at the home builder who wants to make a solid state amp -- what the hell -- or at least one with a SS output stage. There are basically two forms of feedback, the normal one, and the "active-error" version described by J. R. MacDonald and others. The active-error version only "corrects" the output when an actual error exists, whereas the standard version has to correct the open-loop gain even when the load is a steady resistance and the devices are behaving with perfect linearity. If tests show more phase-smearing with the standard version than with the active-error version, well, I know which version I would want to use, or have in a new television. As a bit of a side note, with better sounding SS output stages, maybe we can more easily hear the advantage, assuming one exists, of using a tube to produce the error signal (a tube doesn't have poor quality parasitic capacitances to potentially mess up the low level information). All of this may sound like something only of interest to home builders, but at least some manufacturers actually would be happy to produce noticeably better sounding products, if they could do so for about the same money! If EE's in general become aware of the full characteristics of feedback -- and if home builders start to do this, many EE's and high end manufacturers will indeed follow, eventually -- then we might actually see better products in cars and TV's. No, I'm not saying do this so that we will get better products, but a good understanding of what is needed to make better audio products does tend to help everyone, sooner or later. Low output Z triodes are in fact the theoretically best audio devices at this time, sound-wise, but they require an expensive, heavy, big, high quality output transformer, and that will always limit their use. Or, maybe someone just wants to write an article for AudioXpress about the true nature of feedback, and how to best use it, if its use cannot be avoided! Phil Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Phil wrote: Andre Jute wrote: In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, like Otala claimed in his talk/paper (assuming a paper ever followed the talk!). When Patrick was defending feedback, he mentioned that poorly designed amps sound like crap when they have lots of feedback, but that if you fix them up a bit, meaning get rid of much of their excessive nonlinearities -- read, *amplitude* nonlinearities -- then adding feedback sounds okay. Now, if we eliminate the idea that feedback produces random noise -- and we *know* that it reduces amplitude non-linearities -- then the only distortion mechanism left, I believe, is phase-shifting. However, I want to describe the usual "constant 20 degrees phase lag at 40 KHz" as "phase-shifting," and a dynamic, microsecond to microsecond shifting back and forth of one frequency relative to another as "phase-smearing," or "time-smearing." What Otala was saying is that applying feedback to circuits with lots of open-loop distortions, which are (I believe) almost always amplitude distortions, converts these distortions into a back and forth smearing of the high frequencies relative to the low frequencies (and it may smear both in terms of the delay through the amp). Nor can we assume that this time-smearing is a simple function of the low frequency amplitude, because it is probably proportional to the magnitude of the distortions, as well as the LF amplitude: VERY non-musical. When enough feedback is applied to badly designed amps, the amplitude distortions become quite small, so why did Patrick find that they sounded much worse than the same amp sounds when touched up enough to reduce the larger open-loop amplitude distortions? As you say, *something* is wrong, and if it isn't high amplitude distortions (it can't be), and if feedback doesn't produce spurious noises, then the only thing left is exactly what Otala said, time-smearing. In essence, feedback *connects* two things that are normally separate in an amp, namely amplitude distortions, and phase-smearing. It achieves a balance between these two, a balance which is determined by the speed of the amp, the amount of feedback, and the amount of amplitude distortion. Contrary to what you say, Otala was *not* referring to TIM, and transistors did not become so much faster after 1980 than the ones used in his '73 article to make the problem he described go away. Yes, the amps had to be designed well enough to avoid TIM, but that was not a real problem even in '73 *if* you knew what you were doing. The problem he described in '80 was quite different, and even high MHz tubes are subject to it. The interesting things, assuming that feedback problems are indeed time-smearing (regardless of whether this comes from the conversion of amplitude distortions), are one, a single tone will reveal nothing of this, giving very low THD numbers, and two, multiple tones should show something, although looking at it in the amplitude realm will only show higher than expected IMD. There should be a fairly easy way to test to see if this really produces time-smearing. In general, we put a 4 volt 60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of feedback, preferably using non-linear sections of the amplifying devices (say, use two 12AX7 type triodes where the plate curves vary from widely spaced to closely spaced, and use about 60 to 80 dB of feedback to get the overall gain down to 1). Use a high pass filter to see only the 20 KHz signal, and use the 20 KHz signal from the generator to trigger the 'scope. If time-smearing exists, then the 20 KHz signal will appear "fuzzy" on the scope, since it is being shifted back and forth. Repeat without the 60 Hz signal to make sure the time-smearing isn't coming from somewhere else, and then also divide the output from each tube down so that you get the same amplitude output *without* using feedback, and see if the time-smearing goes away. Finally, if possible test over a region where the curves are fairly linear, to see if that also reduces the time-smearing. If so, you have proof that feedback transformed the amplitude distortion into time-smearing. I will try to do this, but I have little time, less energy, and not the best test bench in the world, so it may be a while! If you or someone else both can and wants to try this, I suspect we will get an answer much faster than if I do it. Note that we can use pentodes or transistors, too, but using solid state has the disadvantage of possibly introducing other complications due to the poor quality silicon parasitic capacitances. Also, I am suggesting the use of very different magnitudes as well as frequencies for the two signals, in case equal magnitudes somehow avoids this problem, or at least masks it from this test. And again, contrary to what Patrick said, the idea that *if* this were true, then by now someone would have already tries it, and the results would have become widely know, is just naive. The human race simply isn't that intelligent, at least not yet. An interesting conclusion, assuming this feedback time-smear mechanism exists, is that the output of a feedback amp does *not* match the input when multiple signals exist! However, our normal tests cannot see this, since they tend to focus on one frequency at a time. I believe that Patrick, as well as Otala, said that using local feedback to achieve good open loop linearity, combined with some global feedback, tends to sound pretty good. This makes sense for two reasons, first because although the local feedback will produce phase-smearing, it does so at *very* high speed, which I believe directly reduces the amount of smearing (common sense says that as the speed of devices approaches infinity, feedback becomes "perfect"). Second, the result does contain some mis-match between input and output, even given the high speed of local feedback, but now the global feedback will not only reduce the remaining "normal" amplitude distortions, it should also reduce the time-smearing produced by the local feedback, since this time-smearing will still produce an error signal for the global feedback. Of course, this reduction in time-smearing will itself produce more time-smearing, but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of time-smearing is reduced by "dividing up" the total feedback into local plus global. Finally, you saw the review of Otala that Phil Allison gave, and I think you were as impressed by it as I was (although it looked bad to PA). When a man who was as talented, knowledgeable, and honest as Otala produces a PROOF that negative feedback *always* transforms the amplitude distortions of the open loop into phase smears of the closed loop, we should not dismiss it as simply a problem of "old devices," a problem that a slight increase in speed can make go away, especially when the discussion that led to his analysis (the Audio Critic BS session) included a lot of talk about vacuum tubes, and how their speed advantage made it easier to use them with feedback. We really should do at least one or two tests before dismissing his conclusions. Again, I will try to do so, but if you want to know anytime soon, you should probably rely on someone else. Phil |
#34
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Explanation still required for triode superiority
Stuart Krivis wrote: On Tue, 26 Sep 2006 10:01:18 +0100, Eeyore wrote: Chris Hornbeck wrote: On Tue, 26 Sep 2006 05:07:55 +0100, Eeyore wrote: 1. Unweighted THD is useless as an indicator of quality. So why do you think I regularly mention the order of the distortion ? Wanna *not* be a major disappointment? Post something positive and educational on the topic. Right here; right now. Lord knows you're capable, and all the latterday endless cheap shots are beneath you. Step up to the plate and take a swing! This *could* be a very interesting newsgroup again someday. Gonna take everybody; no slackers. It's a subject that truly intruiges me. Where I suspect I'd differ with you is that I'd expect a DSP simulation to sound just the same as the beloved triode. It is something that I'm looking into btw. As for the effect of the order of the distortion, does anyone recall who wrote that thesis about it and the weighting thereof ? Hamm? He wrote that joke of a paper purporting to compare tubes and transistors. It's something quite recent I have in mind. Graham |
#35
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Eeyore said:
As for the effect of the order of the distortion, does anyone recall who wrote that thesis about it and the weighting thereof ? Hamm? He wrote that joke of a paper purporting to compare tubes and transistors. It's something quite recent I have in mind. Daniel Cheever: http://www.next-power.net/next-tube/...b_menu_item=99 -- "Due knot trussed yore spell chequer two fined awl miss steaks." |
#36
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Chris Hornbeck wrote: On 25 Sep 2006 03:09:39 -0700, "Andre Jute" wrote: Bring on your topics, Chris. We could do with some fresh air in RAT. [various snips] if I may, a few possibilities: 1. Unweighted THD is useless as an indicator of quality. 2. Unweighted IMD " " " No argument about points 1 and 2; I just normally put it more emotively. 3. We make totally unwarranted assumptions of monotonicity. This is a fatal flaw in our thinking, and we all do it, all the time. 4. We make often unwarranted assumptions about input signal bandwidth. 5. We *always* *without exception* forget to properly weight the importance of simply being upstream in the signal path. Always. When you find the time, please elaborate on points 3, 4 and 5. 6. Loud voices will say that everything (that doesn't include the dreaded vacuum valve, scourge of nations) sounds the same. This has recently been expanded to include transistor amplifiers from the early 1970's, by certain especially vocal ideologes, in another thread, this very week. Against such a religious fervor, nothing can stand. This relates back to points 1 and 2, where for judgement has been substituted the belief that when the master tape is reproduced with under-x per cent of THD, the engineer has faithfully performed his service. In human terms, elevating a single measure of goodness so high is inspired by fear, a desire to control events (can't let a bunch of arty-farties substitute taste for what engineers "know"), which is also a form of fear, and of course the largest fear-reflex of them all is religion, the defense against fear of the unknown darkness. Modeling and analysis are essential; but the map is not the world. Actually, the only °essential* is having some method of deciding where you want to arrive. High fidelity went wrong long before Mr Leak's inspired marketing terminology (Point One) became an engineering article of faith, but that set the seal on the decline. Which conclusion? That "triodes sound better" or that "there must be an electrical explanation"? Strong agreement with the former; That's why we are here. strong disagreement ('cause that ain't science!) with the latter. Eh? Surely a thermionic valve is nothing but a bunch of electrical impulses created by vacuum, wire and electricity? Whatever happens in there, regardless of whether we can see it or not, regardless of what we call the result, *must* perforce have an *electrical* explanation. °That* is science. Anything else would make me uncomfortable -- and me a certified witchdoctor! "Take the money and run" -- Len Deighton And also... who? Bob Segar? Somebody like that, anyway. Woody Allen. From of an early movie about a hapless bank robber. Len Deighton, one of the best novelists ever to work in the thriller genre, was referring to a novelist's relationships with "moom pitcher pipple". Much thanks, as always, Chris Hornbeck Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
#37
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Sander deWaal wrote: Eeyore said: As for the effect of the order of the distortion, does anyone recall who wrote that thesis about it and the weighting thereof ? Hamm? He wrote that joke of a paper purporting to compare tubes and transistors. It's something quite recent I have in mind. Daniel Cheever: http://www.next-power.net/next-tube/...b_menu_item=99 Thanks Sander. That's the one. Graham |
#38
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Andre Jute wrote: This relates back to points 1 and 2, where for judgement has been substituted the belief that when the master tape is reproduced with under-x per cent of THD, the engineer has faithfully performed his service. What master tape ? There's sod all tape used these days ! Graham |
#39
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Stuart Krivis wrote: What's so sadly wrong with the story is that the US military went through the whole exact same hand-wringing back 100+ years ago in the Phillippines, leading to the adoption of, wait for it, the .45 caliber. Theoretically, they can use hotter loads in the 9mm because all of the pistols are newer. But I still prefer the 45 ACP. :-) Me too : ) Why use two rounds when you only need one? Bob H. |
#40
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On 26 Sep 2006 18:57:28 -0700, "Bob H." wrote:
Stuart Krivis wrote: What's so sadly wrong with the story is that the US military went through the whole exact same hand-wringing back 100+ years ago in the Phillippines, leading to the adoption of, wait for it, the .45 caliber. Theoretically, they can use hotter loads in the 9mm because all of the pistols are newer. But I still prefer the 45 ACP. :-) Me too : ) Why use two rounds when you only need one? A major justification for the larger calibers in modern personal confrontations is simply the size of the bore; anybody who's ever looked at the receiving end of a pistole seems to remember (and mentally inflate) the bore. And, worst case, ya still gotta knock the ****er down enough to allow ya to do some serious kicking. Real people don't just lay down and play dead like in the movies. What a gruesome topic. Who started this? Much thanks, (I think, Arf!) Chris Hornbeck |
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