He's quoting 100W, not 50W. Anyway, after some searching I think that the 0.01% THD20 plot I was referring to earlier was for a version which used the MJ802/MJ4502 connected as a CFP.
As for the 50W/8R 'Blameless' with MJ802/MJ4502 in a plain double EF performance, here it is:
Attachments
Piercarlo,
The time delay is a huge and fundamentally insurmountable problem. There´s every reason to doubt the accuracy of time delay and phase correction techniques.
Global feedback lowers the measured distortion by transforming (multiplying) harmonics into high frequency dirt, safely outside the measurable range, thus it`s essentially about distortion redistribution. It also inevitably introduces new distortions. The result is an adverse harmonic spectrum, tones deprived from their harmonic content, a tangle of phase relationships, a clean but unpleasurable sound.
The problems with global feedback are serious enough even if properly used, noticed by many audiophiles, those who use their ears.
The time delay is a huge and fundamentally insurmountable problem. There´s every reason to doubt the accuracy of time delay and phase correction techniques.
Global feedback lowers the measured distortion by transforming (multiplying) harmonics into high frequency dirt, safely outside the measurable range, thus it`s essentially about distortion redistribution. It also inevitably introduces new distortions. The result is an adverse harmonic spectrum, tones deprived from their harmonic content, a tangle of phase relationships, a clean but unpleasurable sound.
For one part of circuit topologies this is true (namely, those with two voltage gain stages in the feedback loop), but not for an other part of circuit topologies with only one voltage gain stage in the loop such as the AD797, the AD797 clone and other cascode based variations)
However, I still watch too strong generalization of the term "NFB" respectively "global feedback".
The global feedback on its own istn't the problem, actually. The proof is simple, the Pass-ZEN variations and even Andrea Ciuffoli's "power follower" also uses "global feedback" (even if it does not appear by the "power follower" after first look - here is a serial NFB in use and by the ZEN variation's a parallel as customary in inverting mode). which means automatically, that the kind of circuit topology is the actual problem.
By the way - amplifier circuits without NFB I have never found until this day, even not in so called "NFB-free" tube amps.
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What means Class-B in this case?
No idle current through the MJ802/MJ4502 like Quad 405 (pure Class B/current dumping) ?
Or a low value of arround 20 - 50mA (Class AB)?
This both values of idle current would produce completly different THD plots because the "Blameless" isn't a current dumping.
Lumba,
You have managed to summarize most of the misconceptions about negative feedback in one place. I guess you have not been reading all the info on this thread over the last few years.
In particular, you appear to be one of the many folks who have mis-interpreted and mis-applied Baxandall's results. You are not the only smart person who has done this.
Cheers,
Bob
Hi Andrew, yes, Self uses the term optimized-bias class B where just about everyone else uses the term optimized-bias class AB. Of course, the fact that there is a fuzzy line between low conduction and no conduction opens the door to such semantic battles. The term class AB was well established many years ago in reference to properly-biased vacuum tube amplifiers.
Cheers,
Bob
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I'm one of the confused. I read Lumba's post and it makes sense to me - in that the use of nfb reduces THD but it doesn't do so perfectly. Firstly, there is the issue of phase change from input to output which is now inside the nfb loop. We all know we have to pay attention to this in order to have an amplifier rather than an oscillator. It seems reasonable that feedback which has a significant phase error compared with the input will not be as effective. So why would Lumba be incorrect in regards the timing/phase issue ?
Also, from what I understand, Baxandall has shown how nfb whether local or global, increases higher order harmonics in non-linear systems. So what we see from the application of nfb is lower THD which shows up particularly well in terms of reduced low order harmonics, but we also introduce more high order harmonics. One could describe this as a redistribution from low order to high order. I'm not saying this is a bad thing, but isn't this correct and also consistent with what Lumba posted ?
Where I disagree with Lumba is that nfb is bad. I'm thinking that nfb is the greatest thing since sliced bread for reducing distortion from non-linear amplifier elements which all of our amplifiers have inside of them. Where I see the problem is that some people are rather too nervous, not making a bold decision between ultra low feedback and lots of feedback. They then end up in the middle ground and generate a host of horrible high order harmonics that are too high in relative magnitude. It seems to me that many amplifiers fall into this category. Perhaps it's a case of 'go big or go home' with nfb. Using lots of nfb isn't easy, it gets tricky. The 'easy way out' is to use a middling level of nfb which Baxandall has shown us is the worse of both worlds.
What am I missing ?
This I know everything.
I want to know the according idle current value through the output buffer of 'Blameless' device from GK "50W/8R with MJ802/MJ4502" describt about post #362 (to the frequency dependend THD plots there)
Please note - that was my actually question about post #366 !!!
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Yes, they can be "swept under the carpet".
To start with, you are as usual confusing time and frequency domains. There is nothing (like energy) to conserve by "shifting" spectral components in the frequency domain, when the loop is closed.
rather than answering the quoted words, syn08 go in a personnal
volontary misunderstanding of lumba , streching the words used by
the latter, as usual...
distorsion products are relegated to high frequencies, in a wide range,
as far as the amp has intrinsical gain more than 0db....
these high frequency noise are not counted in distorsion measurements,
although the total energy can be several times the distorsion specified in a
20/20khz bandwith...
volontary misunderstanding of lumba , streching the words used by
the latter, as usual...
distorsion products are relegated to high frequencies, in a wide range,
as far as the amp has intrinsical gain more than 0db....
these high frequency noise are not counted in distorsion measurements,
although the total energy can be several times the distorsion specified in a
20/20khz bandwith...
that is not a question I could see.
You asked if it was conventional ClassB outputs switching off at quiescent or ClassAB passing 20 to 50mA.
Self sets up his Blameless by Vre not by Ire/Ib.
Re=0r1, 21.3mVre
Re=0r22, 23.1mVre
Re=0r33, 23.8mVre
Re=0r47, 27.4mVre
I'm not sure why he came up with that high value of 27.4mVre for Re=0r47.
Most commentators say it should be <26mVre and some say reducing as Tj rises.
Pure audio ideology, as I've yet forecasted. I regret of this, but any further talking with you is completely useless from a technical viewpoint. Simply lost time. You prefer ideology and audio "newage culture" instead of science (even if you need again to cheat yourself masquerading your twaddlings with a mimic of a technical knowledge that you don't really own). My tastes are on the exactly opposite way, sorry...
Goodbay
Piercarlo
This argument I always get to hearing, when I suggest to make measurements of IM by 200 KHz + 199KHz and THD measurements between 100 KHz and 500 KHz.
But it is not true. It is true that one above approx. 20 KHz hear nothing (not even the THD products there).
On the other hand everyone knows that the traditional THD/IM measurements (10KHz THD and IM 19/20KHz) nothing said about the audible results in sound quality of each amplifier.
This means, solutions must be found, to measure an amplifier so that everybody know about character in sound, without one have heard the said amplifier for ourselves.
That is not to create for 100%. But if we perform an amplifier IM investigating by 200 KHz+199KHz resp. THD measurements between 200 KHz and 500 KHz with passable low values, the probability is very high to achieved nearly perfect sonic transmissions (resp. very unlikely that such amp sounds bad - except for the low frequency aera - recognize there are different rules).
Sine wave signals and complex signals of music are completly different, and for more accordance between measurement THD/IM values and sonic results the selecting of higer (at best RF-) sine wave frequencies is the only way - so I think.
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He's incorrect in attributing this problem to the feedback itself instead to the BAD USE of feedback. Timing problems are out of worries from at least a 40 years, as planar devices become largely available on market.
Lumba Ogir, as many others, don't know - or forget to know - that if most higher frequency we can ear is about 20 kHz, then we can't ear time slices shorter than of the corresponding period. Actually appear that real abilities in detecting time slices of human ears are at most limited to the frequency band where its sensitivity peaks - 2-3 kHz, roughly equivalent to a 0.5 ms... when typical throughtput timing of transiting signal in not exceptional audio electronics are AT LEAST 500 times shorter! Time is not anymore a problem in audio electronic, either analogical or digital (the so called "jitter problem", in the form as often publicized in audio reviews, is a not problem at all...).
Phase problems are instead still again between us... BUT NOT as a charge of guilty for negative feedback ITSELF but only for its heavy misuse acted in the past from many electronic builders which, instead of FIRST design very linear amplifiers and SECOND apply to them an adeguate feedback amount to stabilize their perfomarces, applied directly HUGE amounts of NFB, which require an equally huge amount of compensations that turned an originally frequency linear circuit in an integrator that actually need to be linearized by feedback itself.
The goal of this misuse is, obviously reduce design costs skipping any optimization phase: the consequences are poor performance amplifiers which steem directly from poor design practice. Is the same difference existing, as you may figure out, among a well trained athlete and a merely steroid boosted one. The first play its work well, the second quickly turn itself from boosted to busted!
.That Lumba Ogir miss (abusively because is not a fact which agree with his ideological viewing of NFB as "universal evil") is just the difference between NFB and its abuse, attributing to the former the guilts of the latter. Not a little miss, indeed...
It should be more consistent if Lumba don't missed again a key factor for judging this event: ITS MAGNITUDE. If its true that NFB spread up the spectral population of distortion, its also true that the total amount distortion is WELL lowered (and often lowered well deep into noise floor).
But is not this the real missed point. That really matter when distortion sink below noise floor is its ability to change meaningfully the "color" of the noise floor itself: if this remain in his composition substantially "white" not with pure measuring tones but with the true complex riddles of effective audio signal, then we can consider distortion essentially wiped out from the acoustical scene.
This is the true reason what, sometime, manage some strumentally deficitary amplifiers to "sound better than" of other REALLY (I well underline this word: REALLY) instrumentally better amplifiers: simply when mixed down to listening, their features of noise floor, spectrum of distortion manage to form with music a "syndrome" that hear more "pleasurable" (essentially because SIMPLER THAN, and thus less fatiguing than original audio signal) of the the same music played by a better system which, more clean and detailed of the former, may appear just "more fatiguing" or "unpleasureable" of it because of increased amounts of details to be processed by brain listeners. That Lumba is not able to recognize because of its bias about his alleged "superhearing capabilities" is what some problems of "unpleasanteness" don't steem from technical sources but just fron PSYCHOACOUSTICAL sources. In other words problems are inside the ears of Lumba (and any else human being of course), NOT in amplifier itself that, symply... amplifies. Amplifiers have not enough brain to create so sophisticated artifacts that Lumba claim for them! ;-)
The real problem with very high performance circuits of many amplifiers available on market is that they unmask unpitiously that in the rest of amplifiers (and also in the rest of audio chain) remain unoptimized. Power supplies play a big role in this especially if we take in account some unavoidable fact: amplifiers are connected to other electronics not only by mean of direct signal connection but also by main grid supplying the floor that effectively connect all systems toghether, especially at higher frequency where SVRR, often heavily based on high NFB ratios only, is yet compromised. This is especially true with digital sources (sometimes also radio receivers) where the normally employed "EMI-RF filters" on the mains are of little aid because they miss the near ultrasonic band of frequencies (roughly from 20 kHz to the low end of Long Wave radio broadcast band).
In this scene the "defects" of audio electronics is, simply, their having a "too good" passband that permit them to work in regions of spectrums where NFB has become uneffective and their intrinsic linearity (different from low frequency linearity) is plainly doubtful. Again, these are not problem caused by NFB but, in fact but its EFFECTIVE ABSENCE. A problem related with excessive amount of NFB is that may realize a condition where, in the same amplifier but in different region of audio band, cohabit too different working modes.
Just one point at the end. However you use NFB more or less intensively, you obtain EVER a distortion REDUCTION. If you act your playings in the way of obtaining very linear amplifier YET IN OPEN LOOP STATE, you obtain a well breed amplifier just with moderate amounts of NFB, Baxandall or not Baxandall. NFB may change the distribution of EXISTING nonlinearties but it CAN NOT INVENT nonlinearities (either dynamical or static) not yet presents in circuit. This is another key point that Lumba Ogir miss... Of course!
Hi
Piercarlo
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