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#41
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Output classes A and AB
On Oct 24, 10:48 am, John Byrns wrote:
Technically correct stuff snipped. John: I agree with what you say inasmuch as it is *absolutely* technically correct. But the amplifier you posit is still a Class AB unit and/or a unit that has been modified to make only Class A - and therefore NOT a Class AB unit anymore - and as a 'modified' A not really all that hot- sh*t an A either? Point being that the GM V8 remains a V8 even though it is *capable* of operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW ratio. And it could also be modified with a suitable network of controls to remain in either 4 or 6 cylinder mode at all times - and therefore *technically* be described as a 4 or a 6. It is certainly not anyone's idea of a V8 anymore - nor what should be a good idea of a 6 or 4. Which, of course, would be a 100% marketing ploy, wouldn't it? To call it a 4 or a 6 by virtue of the modifications? As a purpose-built 4 or 6 would be a much better solution, wouldn't it? And that same purpose-built 4 or 6 could be made with the same displacement, potential output HP and torque as a V8, couldn't it? And that would, of course, cost a pretty penny - more than a similar displacement & output V8? Large output Class A (tube) amps tend to be costly, right? So, an amplifier *may* operate in Class A mode for some range based on its design. But it cannot, must not, nor should it be classified as a Class A amp if it does not operate in Class A at all ranges. Otherwise, what we have is a marketing ploy because as previously stated: Class A = Good Class AB = Not So Good All classes of amplifiers are equal, some are more equal than others. Unless similar Orwellian terms apply, then the principle of the excluded middle applies. Can't have it both ways. I am not trying to be simplistic, just clear on what is meant and what is implied. As things look from the discussion here, only Patrick is discussing this with Douglas on equal terms. And I have a sense that they agree more than they disagree. Andre has a bug up his butt - as always - and therefore cannot discuss much of anything on any reasonable terms. He really should step out of it and enjoy the discussion as it is being pursued by his betters - I am certainly watching it with interest. And the side issue of all this is that between George, Bret and Andre, the atmosphere in this NG has been pretty toxic of late. Maybe all three of them should take a rest and let the air clear... although I do have my doubts as to George being a discrete individual and not a sock-puppet. Peter Wieck Wyncote, PA |
#42
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Output classes A and AB
In article .com,
Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? The "invention" of Class AB as a hi- fidelity amp is what spurred part of a Olsen's work on perception; before it wasn't known that odd harmonics are proportionately much more disturbing than even harmonics. It seems to me that AB amps with largish parts of their output in Class A is a relatively modern trend, possibly related to ever less-sensitive speakers. I'm not sure I would agree with that, class AB amps were common even in the days of efficient speakers, I don't see it as "a relatively modern trend", if anything is a modern trend, I would think it is the return to "pure" class A amplifiers on the part of many audiophiles. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#43
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
In article .com,
Peter Wieck wrote: On Oct 24, 10:48 am, John Byrns wrote: Technically correct stuff snipped. John: I agree with what you say inasmuch as it is *absolutely* technically correct. But the amplifier you posit is still a Class AB unit and/or a unit that has been modified to make only Class A - and therefore NOT a Class AB unit anymore - and as a 'modified' A not really all that hot- sh*t an A either? Point being that the GM V8 remains a V8 even though it is *capable* of operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW ratio. The GM 4-6-8 is not a good analogy because it has 8 cylinders even when only 4 are operating. The class A vs. class AB amplifier is a different situation because the only fundamental difference between the two is the setting of the bias pot. If you ask nicely I might go in to some of the non essential differences between the two. I am not trying to be simplistic, just clear on what is meant and what is implied. As things look from the discussion here, only Patrick is discussing this with Douglas on equal terms. I wouldn't put Douglas, a.k.a. Multi-grid, on equal terms with Patrick. And the side issue of all this is that between George, Bret and Andre, the atmosphere in this NG has been pretty toxic of late. Maybe all three of them should take a rest and let the air clear... although I do have my doubts as to George being a discrete individual and not a sock-puppet. Who is "George", I haven't noticed anyone, "discrete individual" or "sock-puppet", by that name participating in this discussion? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#44
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
On Oct 23, 6:51 pm, John Byrns wrote:
In article . com, Multi-grid wrote: On Oct 24, 1:37 am, Andre Jute wrote: As for Dougles Multi-grid's silly insistence that signal and dissipation have nothing to do with Class A operation, thanks for the giggle, sonny, but you'd better hit the books lots more before you seek entry to this club. They don't Andre, no matter how much you claim they do. Class A, is as simple as you first stated it: ***Class A operating conditions do not permit the output device to cease conducting.*** Precisely, that is why when the operating conditions of a class AB amplifier are restricted by limiting the applied input voltage the amplifier is able to put out class A power at a level that is lower than the maximum available class AB power. It should get the addition that remote cut off behaviour is not included. Most real world tubes display remote cut off behaviour as the plate curves become distinctly compressed in the high voltage low current quadrant. I guess that rules out the possibility of any tube amplifier operating class A. In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. Any amp can be driven out of class by excessive signal voltage. That clown Poopie Stevenson has overreached himself again; Dougles Multi-grid is an ignorant (and impertinent) troll of a kind well known on RAT; poor Witless Wiecky is just another know-nothing garage trader who wantst to move up to repair hack status. This whole affair is nuts. We're wasting our time arguing with people who will say anything to put someone down, regardless of the known facts of physics. I've always known that Poopie and Worthless are ineducable on any timescale less than glacial. Dougles Zero-sound is clearly another veeeeery sloooow learner. The stubborn lack of sophistication in his ignorance makes me nostalgic for Pasternack, who at least sometimes said something interesting as he twisted this way and that in the web of his lies; at the very least Plod never would have been dumb enough to attempt lying about something as simple as operating classes. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ One has to laugh. The alternative is unthinkable... 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 |
#45
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
John:
Please note the interpolations: On Oct 24, 1:53 pm, John Byrns wrote: The GM 4-6-8 is not a good analogy because it has 8 cylinders even when only 4 are operating. The class A vs. class AB amplifier is a different situation because the only fundamental difference between the two is the setting of the bias pot. If you ask nicely I might go in to some of the non essential differences between the two. Mpffff... of course. But you postulated the series of zeners and so forth so as to make an as-designed AB into a pure Class A amp. From that, all else follows. Many things can be done - the question is whether they should be done to that amp and if done would the results be better/worse/as-good as if purpose-designed from the ground up. Otherwise, one is forcing the proverbial square peg into the legendary round hole. I wouldn't put Douglas, a.k.a. Multi-grid, on equal terms with Patrick. Discussing on equal terms - not necessarily on equal terms overall. Who is "George", I haven't noticed anyone, "discrete individual" or "sock-puppet", by that name participating in this discussion? Middius, and not necessarily in this discussion, but certainly part of the general miasma. Fly poop on the right, pepper on the left. Peter Wieck Wyncote, PA |
#46
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. The dissipation in the output tubes is very considerably lower than that in Class A. Graham |
#47
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. Any amp can be driven out of class by excessive signal voltage. Overdriving to cut-off is merely gross abuse and a complete red herring / irrelevance. You really should constrain yourself to talkind about stuff you understand. Which would seem not to be very much going by your posting history. Graham |
#48
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
flipper wrote: Eeyore wrote: Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. Any amp can be driven out of class by excessive signal voltage. Overdriving to cut-off is merely gross abuse and a complete red herring / irrelevance. It's not a 'red herring' when you clearly stated "under any signal condition." Do you normally operate amplifiers into gross distortion ? I was trying to avoid the '360 degree' terminology which kind of implies for its part, sinewave only use. Do please, if you desire, change it to 'any valid signal condition for which the amplifer is rated'. Graham |
#49
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Output classes A and AB
On Oct 24, 6:29 pm, Andre Jute wrote:
Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. . - Show quoted text - Well Andre, you've stepped in it this time... AB operation cannot effectively cancell *ANYTHING*. Odd sums anyway. Not second HD( or the even of any order ) because each phase is biased where the characteristics are changing too rapidly with plate current. This is the rest of the Class A definition that is implied, the finals are biased so that the change in characteristic for the opposing phases approximately cancells( and thus the even HD ). It is why the AB amp can't be labled A while both phases of the finals are conducting( or that that single definition is not enough to describe Class A ). The x power in A, and XXX power in AB is just serving notice that marketing had its way with the ad copy. AB was an obvious means of minimizing cross-over distortion and maximizing power. It works just as well for directly heated triodes with no NFB as it does for pentodes like the KT88 running a lot of it... cheers, Douglas |
#50
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Output classes A and AB
Please note the interpolations.
On Oct 24, 3:42 pm, flipper wrote: This is what I meant. People seem to be losing track of who said and meant what. I am not so sure that losing track is the correct description of what is going on. It more-or-less started with a statement that a Certain Amp was a Model for various reasons amongst which was an apparent broad Class A operational range before it went to AB. So, an amplifier *may* operate in Class A mode for some range based on its design. I may have missed something but as far as I can tell *that* is the 'argument'. I don't think anyone would disagree even for a hummingbird heartbeat that some AB amps have some range of A operation before they go AB. It is how one would describe and represent the amp overall that is at issue. But it cannot, must not, nor should it be classified as a Class A amp if it does not operate in Class A at all ranges. I haven't seen anyone claim that a Class AB amp is 'actually' a Class A amp, or should be 'classified' as an 'A' something, or any variation of the theme. Otherwise, what we have is a marketing ploy because as previously stated: Class A = Good Class AB = Not So Good I think you're worrying about something that no one in here is guilty of and, near as I can tell, the 'argument' revolves around the claim by Multi-grid: "That both tubes are conducting does not mean it is A. Have some respect... AB amps don't have any A power, that is why there is a separate classification." It would seem to me that with your comment above saying "an amplifier *may* operate in Class A mode for some range" that you are disagreeing with Multi-grid. I do not necessarily agree with Douglas. I just find the rebuttals to his statements mostly either technically inept (as from Andre) or technically elegant (as from John) but beside the point. Btw, just as a matter of discussion, I see where you're trying to go with the V8 analogy but I don't think it holds, as given, because 2, 4, 6, and 8 cylinder operation is not a 'natural' consequence of the 'engine class V8' while 'A' and 'B' (loosely defined) are for 'Class AB'. Actually, it was John that postulated a series of controls on an AB amp that would force it (hold it in) to A class only. So, the analogy of an 8 held to 4 or 6 cylinders only holds under that description. I think a closer, albeit still 'stretched' quite a bit, analogy would be if we defined 'engine classes' 4, 8 and "4-8," and then pondered if a 'Class 4-8' engine was operating 'Class 4' during the times when only 4 of the cylinders were firing. If the definition for 'Class 4' was "4 cylinders firing" then one might say it was, despite some differences, since 4 cylinders are firing under those conditions; Akin to 'Class A' being the tubes conducting 360 degrees, a situation that occurs in Class AB amps under certain conditions. Oh, the entire engine analogy is stretched more than taffy on a hot day in Atlantic City. But for all that, it is as valid as any other points made along the line in this particular thread - again excepting the direct contributions from Patrick which are right into the nitty- gritty of the situation. And one might wish to talk about under what conditions the 'Class 4-8' engine makes the transition from 'Class 4' to 'Class 8' operation because if it did so at the slightest hint of needing more power it might make for 'zippy' performance at the expense of fuel efficiency while a 'Class 4-8' engine reluctant to do so might be more efficient at the expense of 'zippy' throttle response. But, IMO, saying "it's Class 4-8, period, there is no Class 4 power" simply serves to obscure it's operation for no useful purpose. Well, it ain't nohow a "4-only" and it ain't nohow an "8-only", so it must be something else. The only accurate label would be a "4-8". That it operates in either mode is a function of its design. But it belongs to neither unique class. It might also be useful to point out, as you did, that 'Class 4' operation of a 'Class 4-8' engine is not '100% equivalent' to 'Class 4' operation in a true 'Class 4' engine (depending on how well designed each is) because you're dragging along dead cylinders, a necessary consequence of it being a 'Class 4-8' engine, and, by the same token, 'Class A' operation in a Class AB amp is not '100% equivalent' to a true Class A amplifier (depending on how well designed each is) for the same reason: the 'Class A' region of a Class AB amp is compromised by the necessities of it being a Class AB amp. Yep. And that is contributory to the point but not critical to it. However, there's nothing in the 'Class' definitions that speaks to 'optimal', 'well designed', or 'equivalencies'. Amen to that! There is quite a bit of ineffable crap out there. Some of it is very expensive and uses very expensive boutique-type tubes for no other reason than that they are expensive boutique tubes - certainly not for the quality of the signal coming out of them. Why, even their makers and defenders will wax poetic about how these amps "add coloration" to the signal that makes them an "instrument in their own right" and such twaddle. It is those sorts who will wax poetic about that little bit of "Class A" operation in an AB-designed amp as some great virtue. In point of fact, this would necessarily require that the AB operation of the same amp is somehow faulty. Otherwise a properly designed amp would be A only and t'h*ll with the headroom. Once again, unless we are dealing in an Orwellian world, it just isn't necessarily so. Peter Wieck Wyncote, PA |
#51
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
In article . com,
Peter Wieck wrote: It is those sorts who will wax poetic about that little bit of "Class A" operation in an AB-designed amp as some great virtue. In point of fact, this would necessarily require that the AB operation of the same amp is somehow faulty. Otherwise a properly designed amp would be A only and t'h*ll with the headroom. I don't see how the one follows from the other, could you please explain the logic you used in arriving at this conclusion? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#52
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GM V8-6-4 (was Output classes A and AB)
In article .com,
Peter Wieck wrote: Point being that the GM V8 remains a V8 even though it is *capable* of operating in 4 or 6 cylinder modes - albeit at much a much reduced PtW ratio. And it could also be modified with a suitable network of controls to remain in either 4 or 6 cylinder mode at all times - and therefore *technically* be described as a 4 or a 6. It is certainly not anyone's idea of a V8 anymore - nor what should be a good idea of a 6 or 4. Which, of course, would be a 100% marketing ploy, wouldn't it? To call it a 4 or a 6 by virtue of the modifications? I'm not sure it was a pure marketing ploy, especially given that I have seen ads for a current model car that uses this same idea today, unfortunately I forget what car it is, it might even be a Cadillac, although I would think they would be too gun shy to try it again. At any rate the reason I started this sub thread was to ask if anyone more knowledgeable about engines than you or I knows the theory of the 8-6-4 engine and how it was supposed to improve gasoline mileage, which as I remember it was what the hype said it was supposed to do? The only potential efficiency gain that I can see is that it would presumably reduce throttling losses a bit, but there must be more to it than just that, does anyone know? I guess I should ask Google. As a purpose-built 4 or 6 would be a much better solution, wouldn't it? Better solution for what problem? And that same purpose-built 4 or 6 could be made with the same displacement, potential output HP and torque as a V8, couldn't it? Yes, but a 4 cylinder engine with the power of a V8 might be a little rough for many Cadillac buyers. And that would, of course, cost a pretty penny - more than a similar displacement & output V8? I would expect that a V8 would cost more than a 4 of similar displacement, simply based on the parts count, but what do I know. The 4 would probably require some more expensive drive train parts than the V8, at least in manual transmission applications. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#53
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
In article .com,
Multi-grid wrote: Well Andre, you've stepped in it this time... AB operation cannot effectively cancell *ANYTHING*. Odd sums anyway. Thanks for that clarification. Not second HD( or the even of any order ) because each phase is biased where the characteristics are changing too rapidly with plate current. This is the rest of the Class A definition that is implied, the finals are biased so that the change in characteristic for the opposing phases approximately cancells( and thus the even HD ). That's a bunch of nonsense and drivel, if the cancellation were simply the result of "the finals are biased so that the change in characteristic for the opposing phases approximately cancels", then the amount of odd order distortion could also be changed by PP connection. The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. Check your High School Trigonometry book to understand why the even harmonics cancel while the odd ones don't, it's a simple bit of math that doesn't depend on bias, only that the two sides of the PP circuit are identical. IIRC even PP class C amplifiers cancel even order distortion, this was made use of in early FM broadcast transmitters to minimize interference with high band VHF Television stations, without the need for a harmonic filter in the output of the FM transmitter. It is why the AB amp can't be labled A while both phases of the finals are conducting( or that that single definition is not enough to describe Class A ). It isn't obvious by what logic you arrived at that conclusion? The x power in A, and XXX power in AB is just serving notice that marketing had its way with the ad copy. You aren't by any chance one of Peter Wieck's sock-puppets are you? AB was an obvious means of minimizing cross-over distortion Class AB simply moves the crossover notch up to a higher amplitude point on the signal waveform, if you really want to minimize the crossover notch you should have Patrick design and wind you an OPT designed specifically to minimize the crossover notch, or go with a McIntosh design. and maximizing power. Class B operation would be even better for maximizing power. It works just as well for directly heated triodes with no NFB as it does for pentodes like the KT88 running a lot of it... Yep, it sure is great stuff! Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#54
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
On Oct 24, 10:48 am, John Byrns wrote:
In article .com, Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Well, yes, but who would want a strictly Class B tube amp? It'll be harsh and nasty and the THD will be grim. On the other hand, there was an urgent demand (possibly only from the marketing department, possibly from speaker manufacturers -- these things are very rarely consumer-led) for more output than available from SE or even Class A triodes. Class AB, a natural for the new multi-grid tubes, was for the time a perfect compromise between the "waste" of Class A and the (at the time) incredible power available from push-pull operation of beam tubes and pentodes, *and* Class AB had a lower NFB requirement than Class B, all others things being equal of course, and thus better stability margins. All of this happened at the same time ever-lower THD numbers became the chief marketing tool; it followed in turn that the THD should be attacked where it was most vulnerable and where it would give the biggest fix in the least time for the lowest cost, and that was at the second harmonic. So, you don't want Class B because it is crude, you can't have Class A because it is too expensive for the power you want, you must have a lot of stable power with low THD, bingo, Class AB saves your butt. You have to look at the entire package of elements that drove the general swing towards Class AB. Having looked, from a closer vantage point than ours, at the package of elements, Langford-Smith himself tells us in the RDH4 (Newnes 1997) on p 545 that: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." In Langford-Smith's eyes, therefore, it seems that what drove the choice of Class AB was the ability to retain most of the power available in Class B while reducing THD a very big chunk, without the instability that would follow on the heels of the amount of NFB to achieve the same task in Class B. The "invention" of Class AB as a hi- fidelity amp is what spurred part of a Olsen's work on perception; before it wasn't known that odd harmonics are proportionately much more disturbing than even harmonics. It seems to me that AB amps with largish parts of their output in Class A is a relatively modern trend, possibly related to ever less-sensitive speakers. I'm not sure I would agree with that, class AB amps were common even in the days of efficient speakers, I don't see it as "a relatively modern trend", if anything is a modern trend, I would think it is the return to "pure" class A amplifiers on the part of many audiophiles. Sure, Class A1 amplifiers, as in SE 300B amps, are big since say the mid-80s. But I think if you go into the history of how much of the total power of typical Class AB amps at every period was available in Class A, I think you will find that in the days of sensitive speakers, when the first watt truly was everything that mattered, the Class A benefice was quite low, a handful of watts perhaps. It is only in fact since the 1950s that it was known to specialists that third and higher odd harmonics are disproportionately more disturbing than the even harmonics; you can still see the willful resistance, arising from ignorance, to my practice of designing amps to shape the residual harmonic artifacts so that the odd residuals are miles below the fractional remaining second harmonic. Again, those tubes like 807s when operated in triode were naturals for Class AB, with a naturally beneficial harmonic spectrum; these things fell out naturally without the obsessive thought we put into the tiniest detail these days, bedevilling retrospective analysis. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ Of course I could be wrong. I wasn't there, I don't have twenty-twenty hindsight, and the few amps whose histories I know about are not exactly in the mainstream. One has to read very carefully between the lines to understand what someone like Langford-Smith tell you when he speaks of motives driving commercial choices rather mere engineering facts: his milieu and assumptions were very far from ours. 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 |
#55
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Eeyore wrote:
Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. I've already demonstrated several times that your words "under any signal condition" make your definition grossly inaccurate. I have already told you, Poopie Stevenson, three times that your definition is grossly inaccurate and why. Worse, you, Poopie Stevenson, have already admitted that your definition should be rewritten as I told you to rewrite it, three times in all: ****** Poopie wrote: Do please, if you desire, change it to 'any valid signal condition for which the amplifer is rated'. ****** Nah, Poopie, we don't only desire it, we demand it, because this kind of ignorance that you display so stubbornly reflects badly on all of us. Any amp can be driven out of class by excessive signal voltage. Overdriving to cut-off is merely gross abuse and a complete red herring / irrelevance. Precisely. That is what I explained to you, three times in all, plus once more from Flipper, before you finally understood and stopped following along behind Dougles Zero-sound like a fat little lost lamb. You are a very slow learner, Poopie. You really should constrain yourself to talkind about stuff you understand. Which would seem not to be very much going by your posting history. Me? Come on, Poopie, I'm not the one who claimed for several days that a Class A stage is one in which "the output device(s)never cease conducting *under any signal condition*." You're the one who committed that stupidity, and so many others. *You* really should constrain yourself to talking about stuff you understand -- which would seem not to be very much going by your posting history. Graham 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 |
#56
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Output classes A and AB
Poopie Stevenson aka Eeyore
wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." You're a fool, Poopie. You should have taken a tip from John Byrns and asked a question rather than made a statement you cannot back up. The dissipation in the output tubes is very considerably lower than that in Class A. You're blowing smoke out of your arse, Poopie. I'm clearly talking about output power but you try to muddy the water with "dissipation in the output tubes". You're not only a clown, you're a transparent clown. Or are you perhaps, in line with the ignorance generally displayed in your posting history, trying to claim that more output power is available from Class A than from Class AB? That would be a new nadir of stupidity even for a man who just claimed that Class A devices should conduct 360 degrees "under any signal condition". Graham Andre Jute The trouble with Poopie Stevenson is not what he doesn't know, but what he knows for certain that isn't true. --- with apologies to Mark Twain |
#57
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Output classes A and AB
That's a bunch of nonsense and drivel, if the cancellation were simply the result of "the finals are biased so that the change in characteristic for the opposing phases approximately cancels", then the amount of odd order distortion could also be changed by PP connection. The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. So then John, when one is cut off, what is cancelling? and on this: "The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. And how are two tubes 'the same' when one is in the traditional AB bias piont? Further, as one starts cutting off( not far from its idle point ), how is this remotely like what is going on in the other phase? I'll give you a hint.....nah, you'll get it eventually. Do try and keep your answer out of the Nonsense&Drivel category. cheers, Douglas Check your High School Trigonometry book to understand why the even harmonics cancel while the odd ones don't, it's a simple bit of math that doesn't depend on bias, only that the two sides of the PP circuit are identical. No kidding. Where would one get these magical identical tubes? Getting a class A amp to cancel its 2nd HD is not a trivial exercise. I suggest you try it on your AB amps, just for kicks. cheers, Douglas |
#58
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GM V8-6-4 (was Output classes A and AB)
At
any rate the reason I started this sub thread was to ask if anyone more knowledgeable about engines than you or I knows the theory of the 8-6-4 engine and how it was supposed to improve gasoline mileage, which as I remember it was what the hype said it was supposed to do? Internal combustion efficiency is determined by the compression ratio. High-vacuum conditions reduce the effective compression ratio. Going to smaller displacement( through de-activating cylinders) meant operation at higher manifold pressure, and thus higher compression( from a given cam timing and combustion chamber geometry). Unfortunately, you were dragging along other cylinders. There were a few means of reducing the pumping losses, some worked better than others. Also, the inactive cylinders were rotated in order to maintain operating temperatures. There's more to it, but those are the broad strokes. cheers, Douglas |
#59
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Output classes A and AB
In article .com,
Multi-grid wrote: That's a bunch of nonsense and drivel, if the cancellation were simply the result of "the finals are biased so that the change in characteristic for the opposing phases approximately cancels", then the amount of odd order distortion could also be changed by PP connection. The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. So then John, when one is cut off, what is cancelling? The even order spectral components of the distortion products produced in each of the two tubes, including cutoff effects. and on this: "The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. And how are two tubes 'the same' when one is in the traditional AB bias piont? Both tubes must be at the same bias point, be it "traditional AB" or whatever other bias point floats your boat. Further, as one starts cutting off( not far from its idle point ), how is this remotely like what is going on in the other phase? Because both tubes are doing exactly the same thing over a complete cycle, except out of phase. I'll give you a hint.....nah, you'll get it eventually. No, I don't think I will ever get "it" unless you give me a hint. Do try and keep your answer out of the Nonsense&Drivel category. Done. Check your High School Trigonometry book to understand why the even harmonics cancel while the odd ones don't, it's a simple bit of math that doesn't depend on bias, only that the two sides of the PP circuit are identical. No kidding. Where would one get these magical identical tubes? To the extent that you can't get magical identical tubes you will have to settle for less than complete even order distortion cancellation. Getting a class A amp to cancel its 2nd HD is not a trivial exercise. It's easy enough, trivial even, to adjust the differential bias so a single even order harmonic is canceled, even with non-identical tubes. I suggest you try it on your AB amps, just for kicks. My amp operates class A. Are you saying that getting a class A amp to cancel its 2nd HD is more difficult than getting a class AB amp to cancel its 2nd HD, or vice versa, or neither? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#60
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Output classes A and AB
Andre Jute wrote: Eeyore wrote: Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. I've already demonstrated several times that your words "under any signal condition" make your definition grossly inaccurate. But you're an ignorant **** and what you say is a load of ********. "In a Class A circuit, the amplifying element is biased so the device is always conducting to some extent" http://en.wikipedia.org/wiki/Electro...lifier#Class_A You're confusing cause and effect but your brain is too addled to understand the difference. Graham |
#61
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Output classes A and AB
Andre Jute wrote: Eeyore wrote: You really should constrain yourself to talkind about stuff you understand. Which would seem not to be very much going by your posting history. Me? Come on, Poopie, I'm not the one who claimed for several days that a Class A stage is one in which "the output device(s)never cease conducting *under any signal condition*." You're the one who committed that stupidity, and so many others. And * so many others* too eh ? Ever consided we might actually be right ? You're a ****ING CRETIN Joot. Go back to the miserable hole you crawled out of. Graham |
#62
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Output classes A and AB
Andre Jute wrote: Poopie Stevenson aka Eeyore wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A** push-pull output stage will do that too. AB operation has NOTHING to do with distortion cancellation. Your problem is that you don't understand what you'r reading so you quote out of context as a result of your utter IGNORANCE. Graham |
#63
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Output classes A and AB
On Thu, 25 Oct 2007 10:26:32 +0100, Eeyore
wrote: Andre Jute wrote: Poopie Stevenson aka Eeyore wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A** push-pull output stage will do that too. AB operation has NOTHING to do with distortion cancellation. Your problem is that you don't understand what you'r reading so you quote out of context as a result of your utter IGNORANCE. Graham Graham, please just killfile the idiot like most of us have. His dribbling meanderings are just as irritating at second hand as they are when they have dropped fresh from his rear end. d -- Pearce Consulting http://www.pearce.uk.com |
#64
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GM V8-6-4 (was Output classes A and AB)
"John Byrns" wrote in message ... In article .com, Peter Wieck wrote: Which, of course, would be a 100% marketing ploy, wouldn't it? To call it a 4 or a 6 by virtue of the modifications? If not a rhetorical question, then this is a straw man argument, as the relevant products are still called V-8s by the marketing people. I'm not sure it was a pure marketing ploy, especially given that I have seen ads for a current model car that uses this same idea today, unfortunately I forget what car it is, it might even be a Cadillac, although I would think they would be too gun shy to try it again. AFAIK, the technology is being used in current production GM and Chrysler cars. I have friends who drive them. At any rate the reason I started this sub thread was to ask if anyone more knowledgeable about engines than you or I knows the theory of the 8-6-4 engine and how it was supposed to improve gasoline mileage, which as I remember it was what the hype said it was supposed to do? A cylinder in a gas engine uses more energy if it is only partially in use than if it is turned off. Some losses stay about the same, but other losses are vastly reduced if you partially turn the cylinder off by means of significantly altering the valve timing. AFAIK, the spark plug still fires but no fuel is injected, and the amount of air that the cylinder pumps is vastly reduced. As a purpose-built 4 or 6 would be a much better solution, wouldn't it? Better solution for what problem? Better than operating with a very tightly closed throttle. The engines that receive this treatment are relatively large and powerful. They are agressively throttled back most of the time. And that same purpose-built 4 or 6 could be made with the same displacement, potential output HP and torque as a V8, couldn't it? Approximately yes. Engines are built with as many cylinders as possible to smooth the noise and vibration. They are built with as few cylinders as possible to reduce production costs. But, varying the number of cylinders has secondary effects, such as the torque curve, etc. Yes, but a 4 cylinder engine with the power of a V8 might be a little rough for many Cadillac buyers. Cars with very large 4 cylinder engines have been built. One was built on half of a V8. It was rough and noisy, not to mention being on the heavy side. These days most larger in-line 4 cylinder engines have a balance shaft to cancel out some of the secondary shaking motions. And that would, of course, cost a pretty penny - more than a similar displacement & output V8? A really big 4 would be cheaper to build, all other things being equal. I would expect that a V8 would cost more than a 4 of similar displacement, simply based on the parts count, but what do I know. You would be right. The 4 would probably require some more expensive drive train parts than the V8, at least in manual transmission applications. I don't know about that. For one thing, we haven't said which configuration 4 this is. IME flat 4s put out a lot of low end torque for their displacment, and require beefed-up drive trains that can handle it. In-line 4s and V6s and V8s seem to be lower on low end torque for a given displacement and stroke/bore, and can probably get by with less beef in the clutch, tranny, differential, and CV joints. |
#65
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Output classes A and AB
"Eeyore" wrote in message ... Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. Agreed. Any amp can be driven out of class by excessive signal voltage. Overdriving to cut-off is merely gross abuse and a complete red herring / irrelevance. Agreed. Jute seems to be addicted to excluded-middle arguments. Kick out those and the straw men, and he's hardly have anything to say. ;-) You really should constrain yourself to talkind about stuff you understand. It would save a lot of bandwidth. Which would seem not to be very much going by your posting history. Jute is mostly about hyperbole. In real life he makes Walter Mitty look like a world-class adventurer. ;-) |
#66
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GM V8-6-4 (was Output classes A and AB)
On Thu, 25 Oct 2007 05:56:37 -0400, "Arny Krueger"
wrote: A cylinder in a gas engine uses more energy if it is only partially in use than if it is turned off. Some losses stay about the same, but other losses are vastly reduced if you partially turn the cylinder off by means of significantly altering the valve timing. AFAIK, the spark plug still fires but no fuel is injected, and the amount of air that the cylinder pumps is vastly reduced. In the huge diesels that routinely turn off multiple cylinders, the valve gear is uncoupled so the valves remain closed. That way no air is pumped and the losses drop to negligible levels. You really don't want to be shifting air, even if there is no combustion, if economy is your objective. d -- Pearce Consulting http://www.pearce.uk.com |
#67
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Output classes A and AB
On Thu, 25 Oct 2007 06:00:25 -0400, "Arny Krueger"
wrote: "Eeyore" wrote in message ... Andre Jute wrote: In the halflight dreamworld inhabited by Dougles Zero-sound, Poopie Stevenson and Worthless Wiecky, SE amps would be impossible, Class A1 amps would be impossible, and all other classes would produce zero music -- in fact all other classes would produce 100 per cent pure noise by being operated at all sonic peaks at either max current and zero voltage or zero current and voltage plate overvoltage. All of that follows logically from Poopie's absurd redefinition of Class A as a Class in which "the output device(s)never cease conducting *under any signal condition*," (emphasis added). It's ludicrous. It's actually the only accurate definition. Agreed. Any amp can be driven out of class by excessive signal voltage. Overdriving to cut-off is merely gross abuse and a complete red herring / irrelevance. Agreed. Jute seems to be addicted to excluded-middle arguments. Kick out those and the straw men, and he's hardly have anything to say. ;-) Can you overdrive a class A amp to cutoff? In my experience what happens when you overdrive a class A amp is that one device saturates, and the other sticks with its normal bias condition. There is no circumstance in which I have ever managed to put a class A amplifier output device into cutoff. d -- Pearce Consulting http://www.pearce.uk.com |
#68
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Output classes A and AB
"Don Pearce" wrote in message ... On Thu, 25 Oct 2007 10:26:32 +0100, Eeyore wrote: Andre Jute wrote: Poopie Stevenson aka Eeyore wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Or bits of silicon, or whatever amplification device is being used. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." No such thing in the RDH4 at hand. It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A** push-pull output stage will do that too. Agreed. AB operation has NOTHING to do with distortion cancellation. Agreed. Your problem is that you don't understand what you'r reading so you quote out of context as a result of your utter IGNORANCE. Seems like Jute has his own private translation of the RDH4 that adds errors to what the original authors wrote. Graham, please just killfile the idiot like most of us have. His dribbling meanderings are just as irritating at second hand as they are when they have dropped fresh from his rear end. The guy who manipulates the Jute sockpuppet is an attention-hound, pure and simple. |
#69
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GM V8-6-4 (was Output classes A and AB)
"Don Pearce" wrote in message ... On Thu, 25 Oct 2007 05:56:37 -0400, "Arny Krueger" wrote: A cylinder in a gas engine uses more energy if it is only partially in use than if it is turned off. Some losses stay about the same, but other losses are vastly reduced if you partially turn the cylinder off by means of significantly altering the valve timing. AFAIK, the spark plug still fires but no fuel is injected, and the amount of air that the cylinder pumps is vastly reduced. In the huge diesels that routinely turn off multiple cylinders, the valve gear is uncoupled so the valves remain closed. Thats about the same as what they do in the cars I mentioned. That way no air is pumped and the losses drop to negligible levels. Agreed. You really don't want to be shifting air, even if there is no combustion, if economy is your objective. That seems to be how the technology works. I am informed by my friends who have cars that implement this strategy, that there are consistent and significant real-world fuel economy gains, as measured by modern car computers that display dynamic fuel economy measures. |
#70
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Output classes A and AB
Andre Jute wrote: On Oct 24, 6:57 am, flipper wrote: On Wed, 24 Oct 2007 13:44:13 +0100, Eeyore wrote: Patrick Turner wrote: Eeyore wrote: Multi-grid wrote: maxhifi wrote: Stating that "the amplifier is Class A until XXX watts", really, is telling you how hot the tubes are biased relative to the two extremes of pure class A (full dissapation), and pure class (cut off).- Hide quoted text - Class A has nothing to do with dissipation either. Just because some marketing group noticed that class A means something good, does not make it right either. Just because it seems to make sense is no reason to *******ize the definition. Find some other way to describe it. The definition of Class A is very simple. It requires that the output device(s) never cease conducting under any signal condition. It means slightly more than this because tubes don't cut off as sharply as other devices. I see what you're saying but I do believe that the definition is unchanged. Obviously avoiding any region of significant non-linearity is preferable but that in its own right doesn't change the definition. People are talking semantically past each other with some speaking of the definition of the 'amplifier' class while others are speaking of it's behavior under a restricted set of operating conditions; and it is useful to observe that under an appropriately restricted set of conditions the output tubes conduct 360 degrees as in 'Class A' operation. "Useful", indeed, Flipper. Thanks. But I would go further and say that the signal and dissipation restriction is part of the definition, as you go on to imply: For example, if maximum power, or efficiency, were the primary concern then one might bias more to the 'B' side of the equation while if fidelity were the primary concern one might bias more to the 'A'. Precisely. Both Class A operation and Class B operation are inherent in the nomenclature and definition and their relative importance is clearly intended to be in the designer's discretion. Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. The "invention" of Class AB as a hi- fidelity amp is what spurred part of a Olsen's work on perception; before it wasn't known that odd harmonics are proportionately much more disturbing than even harmonics. It seems to me that AB amps with largish parts of their output in Class A is a relatively modern trend, possibly related to ever less-sensitive speakers. He he, No, The largish % of class A power in an "AB" amp is a very very rare trend these days. I cannot think of a single PP amp which has a large % of class A power. ARC and CJ and most others are locked into a stupid desperate war of watts, where they try to extract a maxima of class AB watts and to hell with class A, and reliability. Who is going to buy a class AB amp with 2 x 6550 per channel that puts out a "parsimonious 50 watts" when the guy down the road is making a similar amp which puts out 75 watts? Hell, may as well try for 100 watts. The Chinese meanwhile are dumping absolute crap onto the market which falls apart or burns out sooner rather than later and distracts buyers from spending on ARC and CJ who of course have prices which are 15dB higher than the Chinese amps. To try to snare sales though, the big US brands try to extract more power, its like they can't bare to be seen to make 40 watt amps with a pair of 6550 and then be seen to charge the 15dB more. What the big makers do, ARC, CJ and many others around the globe is just raise the B+, and lower idle current, and then lower the RLa-a and presto, you have a raw PA amp around which you run about 12dB max of GNFB, and call it hi-fi, but your lucky if there is 5 watts of class A before the amp lurches into class AB for the majority of the power ability of 75 watts which BTW will NEVER get used. Amp manufacture has, like 1,001 other products become a marketting exercize, not any thing else. Certianly not an exercize in providing maximal fidelity with a minimum of NFB. One might also observe that's likely why it's called Class AB and not Class insert unique letter. There is in fact a class between Class A and Class AB with a unique description: "Limiting Class A1", which is set up so that the crossover happens when one valve just reaches current cutoff and the other simultaneously reaches zero bias. It makes for an amazingly smooth sound but it is a bitch to set up and keep tuned if you want to keep your circuits simple. I was therefore rather interested in what Patrick said elsewhere in this thread (in more general sense rather than specifically about LImitiing Class A1) about within 10 per cent of conduction angle being imperceptible... Limited class A is the correct term, not limiting, which can mean something else. All PP class AB amps are capable of producing class A power only and never moving into class AB. And I meant what I said about defining the class A. Class A in a PP amp is where the anode current is *always* at leasst above 10% of the idle current. So where you have 50mA of idle current in each of the PP tubes, and an Ia swing of +/- 45mA, each tube is working in PURE class A, and thus the pair are ALSO said to be working in pure class A. Suppose you have a pair of tubes, fixed bias, B+ = +500V, and a swing of +/- 350Vpk on each tube. There is 700Vpk a-a, = 500Vrms. Let us say the Ia change at each anode = + or - 45mApk, then the RL seen at each anode while working in pure class A = 350V / 0.045A = 7.78k. Effectively, the OPT places these loads in series, and you have a load RL a-a = 2 x 7.78k, or 15.6k. With 500vrms across 15.6k, you get 16 watts of pure class A. The idle pda for each tube = 500V x 0.05A = 25 watts, so for 2 tubes its 50 watts. Efficiency maximum = 16 / 50 = 32%. We would be describing approximately the outcome with a pair of pure class A KT88 in triode. So what happens when we use a 5k load on the same amp? The same idle current flows, and the same range of Ia variation 0f +/- 45mA will define the class A **current** swing, ( where the **current** wave THD 5% and mainly all 2H ). So the class A load on each tube = 1/2 x 5k = 2.5k, so the maximum class A V swing at each anode = 2,500ohms x 0.045A pk = 112.5Vpk = 225pk from anode to anode, or 159vrms across 5k, giving 5 watts of class A. But the load value allows for a much larger increase in Ia than the 50mA of maximum decrease in Ia. This also means that once the Ia travels below 10% of the idle value, the gm of the tube cutting off has diminished to such a low value the other tube turning on harder is providing virtually all the Ichange x Vchange across the available load, and is the only device coupled through only 1/2 the OPT primary to the load, so the RL seen by this tube turning on hard has reduced to 1/2 its class A load, or 1/4 of the nominal RL a-a, and in this case its 1.25k. The load is the same as that for a class B amp. Load lines will describe it all far better at my website. But you would find that triodes in AB with Ea = 500V, and load of 5ka-a can make a peak Emin = 220V, so swing = 500-220 = 280V, and at this point peak Ia = 220mA approx on each output tube, and this operation is at the limit of operation without being hindered by grid current. So pk a-a sw = 560V pk = 396vrms, and this means you get 31 watts of class AB power into 5k. 5 watts of pure class A is possible, then the operation ***gradually*** changes from impure class A to AB, where one tube cuts off gradually, and the other tube turning on reaches a peak current several times the idle value. if the current waves in each tube are examined, with a 5k load the waves are seen to have about 5% mainly 2H when making 5 watts into 5k, but at 31 watts, the current THD becomes over 20% with lots of harmonics. Most don't reach our ears because of the complementary action of the two tubes. Pentodes and beam tetrode amps have less gradual change than triodes when passing from class A to class AB, and in fact generate far more dirty sounding "switching" harmonics higher than 2&3H in what is called the "switching zone" or "crossover region". McIntosh became renowned for producing 50 watts from a pair of 6L6 running them in low bias current class AB, and applying a total huge amount of local and global NFB to get the Rout and THD/IMD low. ARC use 16 x 6550 in their reference 600 amps to make 600 watts. This means there is 75 watts coming from each pair of PP output 6550. Not much class A power though. I have just completely re-engineered and re-wired an ARC VT100, made in 1996. It has 4 x 6550 per channel. I found that when there was 8 ohms connected to the 0-8 outlet, you'd get about 125watts of AB power, but very little class A because the tubes were being pushed hard into class AB1. 8 ohms was the load where maximum PO is available. I found that using an 8 ohm load connected to the 0-4ohm outlet gave less maximum PO, about 75 watts but a much higher % of class A po before class AB PO begins. The speakers I have to test this amp for any remaining bugs have 8 ohm woofers for 20Hz to 250Hz, and a pair of 6 ohm SEAS midranges in series for 250Hz to 3.2kHz and a dome 6 ohm SEAS tweeter for above 3.2kHz. The speaker Z is thus well above 8 ohms in the main power band for music, and when cranked loud, the amp's new green-red LEDs which indicate Idc at the cathodes do not change from the correct pale green to red. There is plenty of class A power AND GREAT NATURAL FIDELITY available. Some folks would insist in using "4" ohm speakers with dips in the main power band to 2 ohms, and connect to the 0-4 ohm outlet **which really should be labelled 0-8**. The 0-8 outlet should be re-laelled 0-16 ohms. The use of speakers with Z = average 3 ohms instead of 10 ohms like I have means that the THD/IMD will be approximately 3 times as high for the same PO as with 10ohms, class A power is reduced to near nothing, and the damping factor is hopeless. Class AB PP amps have a varying Rout which is lowest while the amp works in class A, but which doubles when in class AB at extremes of wave points. This unfixed Rout translates to compression, massive 3H, and lots more IMD than while working in class A. Anyway, the quad of 6550 while working in class A with a 10ohm load connected across the mis-labelled 0-4 ohm outlet do sound VERY well. Those wanting a schematic of what have done may ask as I have a .gif available. Its much simpler than the original, and I won't beak ARC rules by handing out free copies of their abominable concoctious junk. The reformed ARC VT100 can make 23Vrms into 8 ohms at its 0-4 ohm outlet, = 66 watts, or about 24Vrms into 10 ohms = 57 watts, which is completely plenty! The 0-8 ohm outlet should ***never be used*** unless you have genuine 16+ ohm speakers, or perhaps ESL where the Z is high below 1kHhz down to 100Hz, and you simply need a large voltage drive. One may always have a high Z midrange ESL across the 0-8 ohm outlet, and a lowZ woofer across the 0-4 ohm outlet. The other config available is the 4-8 connection. This amount of never-spoken-about-section-of-winding is equal to 0.293 x the whole secondary winding turns, which is a theoretical match for 16 ohms, but should have been for 32 ohms. The 4-8 connection gives a match to 1.37 ohms, if we considered the two labelled 4 and 8 as right. In fact, the VT100 would give superlative fidelity into 2.7 ohms if a speaker of 2.7+ ohms was connected between the 8 and 4 output posts. I have set up the VT100 so it has separate bias adjust pots for each tube, and Ia+Ig2 at idle = 39mA measured at the cathode. VT100 is a UL amp with OPT with ct speaker secondary which is optimistically a match for 16 ohms, and each end applies some local CFB to the output tubes. I have Ea at +430V, so Pd at idle for each 6550 = 17 watts only. One can only barely keep a hand on the mesh cover over the tubes even with such a low Pd at idle. I sure don't need to run the 6550 any hotter than they are now. The amp may be played very loud, and music does not unbias the amp badly. The total Pd = 67 watts, and if UL class A efficiency max = 45%, then maximum possible class A from this amp = 30 watts, AND THIS IS PLENTY!!! I have also fixed an ARC Reference One preamp to use with the VT100. One of its EI-6922 had gone noisy. Its complicated circuit has been left alone except for lifting the OV rail from the case and re-connecting via 22 ohms. The VT100 had a true horror for a PSU and after fitting a CLC B+ filter and re-locating earth paths, I finally got hum&noises to be less than 1mV with preamp gain at max with open cd input. The ARC Reference one preamp is a fully balanced design except that the balanced output isn't from a floating secondary of a transformer. It should be, but ain't. Gain max is 12dB, and because there are 8 x 1/2 6922 triodes used in each channel, with an easily possible open loop gain of 1,000 at least, I would suppose that the level of global NFB used around the totally balanced LTP type stages amounts to about 40dB at least. Its bandwidth = 1Hz to 680kHz, and noise is low, and it is a superbly measuring preamp. But I would get similar sound using 2 triodes instead of 8 in a line stage, and have no need for balanced at all. The ARC preamp does seem to be sonically neutral as one would expect from a totally pure class A amp with a shirtload and bootful of NFB. I am amused at those who would say that changeing from say Sovtek 6DJ8/6922 will change the sound from say Siemans NOS 6DJ8. I would always suggest that the high amount of NFB must blind the listener to sonic variations, since any artifact or sonic signature is cancelled away by the NFB action. For a lot more about class A and AB in power amps, go to the educational/diy pages at my website. http://www.turneraudio.com.au Patrick Turner. 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 |
#71
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
John Byrns wrote: In article .com, Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Class AB was found to be more efficient and cheaper per watt to produce, and give better sonic performance than the SE amps of 1935. Once anyone needed more than 3 watts, PP was considered, and the bonus was to banish high THD/IMD of the SE amps of the day. The SE radio amps using a lone 6V6 in beam tetrode mode with no NFB were often used, and had mainly 2H, but many OTHER H, and sounded lousy over a whisperish level. HOWEVER, in the misplaced zeal to banish 2H and settle for the clean PP sound, especially when you had a pair of output 2A3, designers would labour away to force an input triode to feed and IST to drive the PP outputs with a two phase secondary. SUN amps are a classic example. Typical primary voltage needed at the 1:2 IST = 50Vrms. So the bloomin input driver tube was making lots of 2H and there was NO net betterment in the sonics except that because the power ceiling was slightly higher. More thoughtful PP amps were designed in the late 40s by leak, Quad, Radford etc, where ALL distortion was considered bad, and where the driver stages were designed to produce far less THD/IMD than the output stage. The Williamson is a classic example. It can be used with 300B in the output, and NFB needn't be used, and THD/IMD will remain low enough, and the 28 watts AB1 will be enough for most folks even now with insensitive speakers. With sensitive speakers of the 50s, the 28 watts of AB triode power was the equivalent of having 112 watts today on average. But very very fine SE amps can be built, and the 2H is low, along with other H, and not much NFB need be used. Patrick Turner. The "invention" of Class AB as a hi- fidelity amp is what spurred part of a Olsen's work on perception; before it wasn't known that odd harmonics are proportionately much more disturbing than even harmonics. It seems to me that AB amps with largish parts of their output in Class A is a relatively modern trend, possibly related to ever less-sensitive speakers. I'm not sure I would agree with that, class AB amps were common even in the days of efficient speakers, I don't see it as "a relatively modern trend", if anything is a modern trend, I would think it is the return to "pure" class A amplifiers on the part of many audiophiles. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#72
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Multi-grid wrote: On Oct 24, 6:29 pm, Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. . - Show quoted text - Well Andre, you've stepped in it this time... AB operation cannot effectively cancell *ANYTHING*. Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. The two non linear current waves in the tubes of the AB pair are summed, and the VOLTAGE total is substantially linear, with a small fraction of the THD of each tube's current wave. Its magic, but it works for most ppl. Odd sums anyway. Depends on the phase of the harmonics relative to fundemental. Its possble to have the 3H of the driver stage acting like compression, and the 3H of the low bias current output stage with 3H acting like expansion, and then there is the transformer 3H etc..... Nothing is general, generic, or simply explained for all occasions, he, he. Not second HD( or the even of any order ) because each phase is biased where the characteristics are changing too rapidly with plate current. This is the rest of the Class A definition that is implied, the finals are biased so that the change in characteristic for the opposing phases approximately cancells( and thus the even HD ). It is why the AB amp can't be labled A while both phases of the finals are conducting( or that that single definition is not enough to describe Class A ). Ah, but all AB amps start off with at least a bit of pure class A before beginning to work in AB. Even transistor amps with miniscule bias currents, and acting very close to pure class B amps. There is always some little bit of class A power where the I swing +/- is less than the idle current. That's class A. Its not the most wonderful class A, but its still class A. The x power in A, and XXX power in AB is just serving notice that marketing had its way with the ad copy. AB was an obvious means of minimizing cross-over distortion and maximizing power. Indeed it was, and still is. It works just as well for directly heated triodes with no NFB as it does for pentodes like the KT88 running a lot of it... cheers, Douglas Purists don't like impurity like the Pope don't read Penthouse. Class AB triodes are NOT much used because the 3H is considerable, and for a given % of 3H, its 9/4 times worse than the same % of 2H. Some say its 27/8 times worse. But its never the THD itself that bothers, because music is mainly all harmonic which are related except for some notes which ain't related and the transients; drum beats etcs. Its the resulting IMD that really grates, and the sum and difference frequencies produced when a zillion F are in the amp at the same time dynamically adds up to unwanted grunge as background noise better abandoned if possible, except abandoning 2H, 3H etc is not so easy as dropping off an unwanted child at the orphanage. You gotta cancel it out, not so easy, or feedback it, or prevent it happening in the first place by using all class A to cover the whole dynamic range. So many purists will go for an SE triode operating right in the middle of its most linear curve, then use only a small part of the curve, which is nearly straight, so the music sounds fine. Horns and SET were made for each other. I would say that the IMD products produced by an amp with low 2H is probably nowhere near as objectionable than the same amount of IMD products made by a PP amp. A PP amp which is into AB transition during average levels isn't any better sounding than the SET... Patrick Turner. |
#73
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Multi-grid wrote: That's a bunch of nonsense and drivel, if the cancellation were simply the result of "the finals are biased so that the change in characteristic for the opposing phases approximately cancels", then the amount of odd order distortion could also be changed by PP connection. The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. So then John, when one is cut off, what is cancelling? Look at the current wave in each tube. In AB or B the current wave has SEVERE distortion spectra. But the voltage across the WHOLE PP OPT primary is largely free of the horrendous THD in each tubes current wave. So its THD reduction by complementary action. Its like two men sawing a log with a long bush saw, with one man at each end either pulling or pushing the saw all the way on each stroke. This is class A, and the differences in applied forces by each man tend to cancel and a linear saw action results. In class AB, each man pulls the saw about 1/2 way across the stroke then lets go, and the other guy grabs his saw handle and pulls the saw back the other way. Each man only mainly pulls the saw in turn, and applied force is jerky, and frankly, a difficult way to work; the Union will be down soon to have a go at the boss who told the men to saw the log that way. But in electronics, we can switch things on and off with absolute ease, and there is no Triode Union to make a boss's life a misery. and on this: "The fact is that the even order cancellation is not dependent on the biasing of the tubes, beyond the requirement that the two tubes are identical and are both biased the same. And how are two tubes 'the same' when one is in the traditional AB bias piont? Further, as one starts cutting off( not far from its idle point ), how is this remotely like what is going on in the other phase? I'll give you a hint.....nah, you'll get it eventually. Do try and keep your answer out of the Nonsense&Drivel category. cheers, Douglas We all get it in the end.... Check your High School Trigonometry book to understand why the even harmonics cancel while the odd ones don't, it's a simple bit of math that doesn't depend on bias, only that the two sides of the PP circuit are identical. No kidding. Where would one get these magical identical tubes? Getting a class A amp to cancel its 2nd HD is not a trivial exercise. It mainly IS a trivial exercize and was invented about 2 days after the first triode was made. Any two tubes are never identical, but are often within 90% equal to each other. Therfore the 2H cancelation in pure class A PP is so substantial that 90% of the 2H of either tube is cancelled away leaving far far less than if the two tubes were used in SE & parallel for the same class A power. I suggest you try it on your AB amps, just for kicks. cheers, Douglas Trying to make the driver stage make distortions that will cancel the output stage's PP distortions is extremely difficult to achieve, and nobody sets out to do it. I tried it, I failed. Trouble is that PP output tube distortions change in amplitude and perhaps phase and spectra with the dynamic changes in loads connected. Speakers are not lile a simple one value resistance. One can manage to more easily exploit 2H cancelling phenomena in SE amps between SE driver and SE output tube. PP amp makers all sensibly try to make the driver linear, and output stage linear, and then not have to apply too much NFB to cancel the little amount of mainly 3H distortion.. Some think this is BS, and build a class B thing with lots of THD/IMD without any NFB. Then they apply lots more NFB than the fella using mainly all class A in his output stage. The unruly class B amp with a shirtload of NFB in the output stage McIntosh, emitter follower etc, and a bootfull of global NFB has become the natural choice of profit hungry amp makers. If you hunger for best music, you must spend more for the inefficiency costs of class A. The staus quo among all amps is 95% AB with rough working AB / near B devices switching with lots of NFB. 5% are either mainly class A, or AB tube amps, or the new PWM amps with whatever correction facilities thay can muster. In 20 years time, all the SS AB amps will have become extinct like dinosaurs. The PWM amps can sound as good as generic low bias SS amps and be far more efficient and far cheaper and lighter/smaller. Tubes will remain if the Greenhouse Police are not too zealous, and they will hold sway amoung a small minority of listeners actually willing to put their money on the sound, rather like there will always be someone who likes sailing yachts around the bay, rather than drive around the bay in a stink boat. Patrick Turner. |
#74
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Eeyore wrote: Andre Jute wrote: Poopie Stevenson aka Eeyore wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A** push-pull output stage will do that too. AB operation has NOTHING to do with distortion cancellation. But it does. There is partial cancelation of 2H currents up until cut off in one device, and in each wave of signal voltage. However, despite the very non linear **currents** in each PP device when in AB, the net voltage & current when summed in the load is substantially linear. The equivalent circuit of a PP pair is that of two non linear current generators in series with each end of the RLa-a. The summed current in Rla-a is linear. But you can also have PP action and class B where the devices are in parallel and working on a common load. There us more than one way to set up devices in PP... Patrick Turner. Your problem is that you don't understand what you'r reading so you quote out of context as a result of your utter IGNORANCE. Graham |
#75
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
Patrick Turner wrote: Eeyore wrote: Andre Jute wrote: Poopie Stevenson aka Eeyore wrote: John Byrns wrote: Andre Jute wrote: Historically, the original purpose of Class AB was to annihilate the second harmonic which before made up such a very large part of the THD, while still allowing beam tubes and pentodes to give much larger power than available before. Andre, why was Class AB necessary to annihilate the second harmonic, didn't Push Pull operation already annihilate the second harmonic irrespective of the class of operation? Yes, you are right. It does. The SOLE purpose of AB is to produce larger power outputs using the same tubes. Now this poor dumb slow learner Poopie Stevenson, an embarrassment to everyone who comes into contact with him, claims to know more than the RDH4! Yo, Poopie, in the RDH4 (Newnes 1997) on p 545 we find this nugget of authoritative information by F. Langford-Smith B.Sc. B.E. himself: "Class AB operation indicates overbiased conditions, and is used only in push-pull to balance out the even harmonics." It's the push-pull that cancels those harmonics YOU UTTER CRETIN ! A Class **A** push-pull output stage will do that too. AB operation has NOTHING to do with distortion cancellation. But it does. ONLY because AB working is by design push-pull. The same thing happens in long-tailed pairs. the distortion cancellation is NOTHING whatever to do with AB operation. Graham |
#77
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
In article ,
Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. It sounds like you have become one of Multi-grid's sock-puppets. The two non linear current waves in the tubes of the AB pair are summed, and the VOLTAGE total is substantially linear, with a small fraction of the THD of each tube's current wave. And that small fraction is very small indeed, approaching zero to be precise, for the even harmonics. Its magic, but it works for most ppl. It's not magic, it's just math. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#78
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Graham |
#79
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
On Thu, 25 Oct 2007 15:40:55 +0100, Eeyore
wrote: John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Graham Because if you add an even harmonic to a signal, you have to make it asymmetrical. You always get a peak coinciding with a trough on one half cycle, followed by a peak coinciding with a peak on the next. If you modify the signal to remove any asymmetry, you must by definition remove the even harmonics. d -- Pearce Consulting http://www.pearce.uk.com |
#80
Posted to uk.rec.audio,rec.audio.tubes
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Output classes A and AB
"Patrick Turner" wrote in message ... In class AB, each man pulls the saw about 1/2 way across the stroke then lets go, and the other guy grabs his saw handle and pulls the saw back the other way. Each man only mainly pulls the saw in turn, and applied force is jerky, and frankly, a difficult way to work; the Union will be down soon to have a go at the boss who told the men to saw the log that way. So speaks someone who obviously has no experience cutting wood with a cross-cut saw. You can pull on a saw, but pushing on it can easily cause it to bend and bind. When 2 men use a cross-cut saw, each man pulls far more than he pushes. Class AB verging on pure class B is the preferred mode of operation for a cross-cut saw. |
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