Andre Jute
December 6th 05, 07:14 PM
Sander deWaal wrote:
> Just look what Arny had to say to one of your posts about the use of
> NFB ....the original was posted to RAO by our friend Brat Ludwig :-)
Ludwig is a thief. The material is copyright and clearly marked for use
on RAT only.
As for Arny, I read every one of his literal-minded misunderstandings
in the hope of learning something. I wasted my time. The kicker is in
Arny's remark that:
> If NASA listened to Jute, the Rusians would have beaten us
> to the moon.
Arny is welcome to listen to Russian hi-fi, hundred per cent negative
feedback, total silence on an airless surface, if he believes that
suits the closed-circuit aridity of his mind.
I'll stick to hi-fi which plays music.
Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"an unbelievably comprehensive web site" -- Hi-Fi News & Record Review
PS: Interestingly, Arny kicks the bejeezus out of his own organ
grinder's monkey, Pinkerton, who was the one who came up with the
ignorant 50dB feedback suggestion, in this passage:
(Jute:)
> > Before I even finished the design of the KISS 300B it was
> > forcefully suggested by a wannabe guru that with only
> > 50dB more gain (about seven times as much as is likely to
> > be in the actual design) I can apply 50dB of negative
> > feedback to linearize my amplifier.
(Krueger:)
> Good example of Jute's ignorance of feedback. It's highly
> unlikely that one could apply 50 dB loop feedback to a power
> amp with an output transformer and still have acceptable
> stability.
Yeah, I know, Arny. As should be clear from the text even to an
illiterate engineer, I wasn't the one who made the silly 50dB
suggestion; your accolyte Stewart Pinkerton came up with it; that is
why I told Pinkothicko to **** off back to you and stop pretending he
was my guru.
Here's Arnie's letter as forwarded by Sander:
> - begin long quote -
> Arny Krueger said:
>
> > The Ultrafidelista view of Negative Feedback
> >
> > by Andre Jute
> >
> > Negative feedback is the paradigm of modern electronic
> > design. It is mother's milk to an electronics engineer.
> > He learns to say '100dB of NFB,' in his sleep before he
> > finishes his first week at the most humble polytechnic.
>
> Good example of Jute's ignorance of the engineering
> education process. Feedback is usually taught as it relates
> to automatic control systems. Last time I looked courses
> like these generally fit into the junior or senior years.
>
> In short the idea that "He learns to say '100dB of NFB in
> his sleep before he
> finishes his first week at the most humble polytechnic" is
> sheerist BS.
>
> > Before I even finished the design of the KISS 300B it was
> > forcefully suggested by a wannabe guru that with only
> > 50dB more gain (about seven times as much as is likely to
> > be in the actual design) I can apply 50dB of negative
> > feedback to linearize my amplifier.
>
> Good example of Jute's ignorance of feedback. It's highly
> unlikely that one could apply 50 dB loop feedback to a power
> amp with an output transformer and still have acceptable
> stability.
>
> > Negative feedback, shorthanded as NFB, is the instant
> > response of the audio engineering fraternity to all ills,
> > real, perceived, non-existent. They don't even ask if
> > there is a problem, they swing the club of NFB
> > regardless. NFB has become a reflex axiom of mainstream
> > audio design. An audio engineer with his negative
> > feedback is like a policeman who runs out into the street
> > with his stick and starts beating a confession out of the
> > first housewife he sees. The difference is that the
> > policeman is relieved of duty to await punishment and the
> > audio engineer gets away with it. In the case of the
> > policeman it is unacceptable behaviour, in the case of
> > the audio engineer so much the expected norm that no one
> > except the ultrafidelista notice. I guess that if one in
> > ten million audio amplifiers does not have negative
> > feedback added, it will be a lot...
>
> No amount of rediculous posturing can counter the fact that
> NFB can be made to work very well and to great advantage,
> thank you.
>
> > No one asked if my KISS Amp requires linearization. The
> > presumption by all except those already of the
> > ultrafidelista persuasion was that I would welcome
> > suggestions about A Good Thing.
>
> If the kiss amp has less than 0.05% nonlinear distortion
> with any power level or any frequency or combination of
> frequencies 20-20 KHz, then its fine as is. I doubt it is
> that good.
>
> > In the face of such overwhelming acceptance by qualified
> > engineers, why do we as ultrafidelista not take the same
> > easy path of negative feedback? Especially considering
> > that superficially NFB is easy to understand and apply.
>
> > How does negative feedback work?
>
> > Negative feedback is simply a negative voltage fed back
> > from the output to the input amplifying device to offset
> > part of the harmonic distortion which is present as a
> > positive voltage.
>
> This is a highly incomplete explanation. In fact the voltage
> fed back offsets not only the distortion but a goodly part
> of the basic signal. Therefore, NFB generally reduces an
> amplifier's gain for both the basic amplfied signal and also
> the distortion.
>
> > It costs nothing except a loss of gain
> > and a few side effects such as phase shift and possible
> > instability which are well known in the mathematical
> > literature and more or less easily guarded against
> > depending on the level of NFB.
>
> In fact NFB properly applied reduces, not increases an
> amplifier's phase shift.
>
> > 'Wow!' those meeting NFB for the first time will now say,
> > 'Something for free! I'll grab some of that for my amp.'
>
> Just just contrdicted the first phrase in the previous
> paragraph that says that NFB has a price in the form of a
> loss of gain.
>
> > Hey, I said it, and I am a professional intellectual, by
> > definition an infinite skeptic. NFB is a thing of beauty
> > that will draw you in. It is like an electronic Marxism
> > which admits of no contrary arguments because it has
> > subsumed them all into The Holy Measurements. To question
> > The Measurements is to commit heresy.
>
> Jute's mistake here is that its not heresy to question
> measurements, and people have been doing that for decades,
> even in such conservative journals as the JAES.
>
> >You need to be of
> > strong mind to resist the blandishments of such a
> > universal panacea and of strong stomach to withstand the
> > hysterical assaults of the lesser engineers defending
> > their holy grail. (And when you do get hold of a superior
> > engineer to explain NFB to you, you need to be high-domed
> > indeed because suddenly NFB can turn very intricate.)
>
> It is true that some advanced course work in calculus can be
> of great help when designing systems with feedback. This
> automatically disqualifies a great percentage of basement
> geniuses and high end chief engineers, writers and
> reviewers.
>
> > Unfortunately NFB doesn't come without a price. It levies
> > a cruel charge on the perceived quality of the sound.
> > Negative feedback is what gives all those 'blameless'
> > transistor and big PP tube amps their chillingly
> > unnatural sound.
>
> Strange that these supposedly unnatural-sounding amplifiers
> can pass a straight wire bypass test, and so many low-NFB
> power amps can't.
>
> > Then how did NFB come to be such a panacea in amplifier
> > design?
>
> Because when applied with reasonable care by competent
> engineers, NFB works. NFB got men to the moon. NFB makes
> your car idle and run. NFB keeps your water heater from
> exploding. It keeps your house and oven at the temperature
> you set on your thermostat. NFB makes cell phones work.
> etc., etc.
>
> > Your guess is as good as mine. Hi-fi design is not
> > prestige work for engineers, or highly paid. The most
> > talented and best qualified engineers go into automobiles
> > or military hardware or big construction projects or
> > computer design.
>
> All areas where NFB is highly depended on, and it works.
>
> >The left-overs design amplifiers in the
> > time they have to spare from writing up specs for
> > requesting a CE mark for a new electric kettle. Lemmings
> > storming en masse over a cliff come to mind; such people
> > don't see the necessity of original thought, or have the
> > mental equipment for it. The exceptions to this rule are
> > normally audio enthusiasts in charge of their own small
> > audio manufactories with niche markets; those who grow
> > larger from this base follow the mainstream mantra of
> > "mo' NFB give lowa' THD" because the marketing channels
> > demand it from them if they wish to grow. At this point
> > they usually cease to offer anything different, only the
> > exclusivity of a very high price. (I know, because a
> > sub-board I designed for a supplier to the trade turns up
> > in so many very expensive amps with so many different big
> > names neatly silkscreened on it... it strikes me as the
> > sort of detail a real designer, as distinct from a
> > marketer, would take under his own control.) Those very
> > few makers who will sell you an ultrafi amp without any
> > NFB operate even tinier shops, usually one man and a cat,
> > just hanging on.
>
> Usually the cat knows as much if not more about calculus
> than the man,
>
> > The mechanism by which NFB wrecks your sound
>
> NFB wrecks the sound the same way NFB makes your water
> heater explode: as a rule it doesn't.
>
> > Negative feedback at first acquaintance sounds good
> > enough to take to bed and cuddle. It isn't. It isn't even
> > as simple as a superficial acquaintance may suggest.
> > Follow the steps with me, from the theory as she is
> > received to what arrives at your brain as music:
>
> > 1. In theory NFB reduces all harmonic distortion equally,
> > without discrimination.
>
> Nope. NFB is often dependent on frequency. As a rule it
> reduces higher harmonics less.
>
> >Strictly in theory it does not
> > reshape harmonic distortion by reducing the most
> > objectionable third and higher order odd harmonic
> > distortion to a greater extent than the relatively
> > harmless 2nd harmonic.
>
> Actually, any order of nonlinear distortion, even Jute's
> beloved order 2 can wreck the sound of music.
>
> > Thus NFB at its theoretically most
> > benign is already useless in terms of psychoacoustics, as
> > will become clear at point 4. If you disregard
> > psychoacoustics, as many audio engineers do, NFB is
> > brilliant in reducing total harmonic distortion to a
> > number as tiny as you want. You just pile on more NFB.
>
> This paragraph really says nothing.
>
> > 2. In real life, as distinct from simplified theory, NFB
> > adds artifacts of its own. Remember, it is a loop. The
> > signal starts at the input and is amplified by devices
> > until it reaches the output. From the output a part of
> > the signal called the negative feedback is fed back to
> > the input. Here a loop is completed and the combination,
> > less distorted, reaches the output again, a part of the
> > combination is fed back, endlessly. The artifacts we want
> > to consider here are created by the fed-back residue of
> > harmonic distortions adding to both the fundamental and
> > the distortions already created by the amplifier, then
> > some portion of the sum of the original and the feedback
> > distortion is fed back again and added on, until the
> > ooh-ah bird flies up its own fundament. It looks
> > marginally less disgusting as a recursive mathematical
> > formula with lots of nested parenthetical parcels of
> > noise being loaded onto your music.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
> > But it is a monkey on
> > the back of your sound, with a smaller monkey on the back
> > of the first monkey, a still smaller monkey on the back
> > of the second monkey, and so on ad infinitum. These
> > additive artifacts are all higher harmonics and the more
> > dominant ones are all odd. Suppose, for the sake of
> > simplicity, a superbly designed ultrafidelista amp with
> > some second harmonic and zero odd harmonics before NFB.
> > Add NFB and the second harmonic will be lowered but the
> > recombinant new loop now contains newly added
> > intermodulation effects between the fundamental and the
> > residual second harmonic, and that is third harmonic. In
> > the next cycle a small but nasty dose of fifth harmonic
> > that wasn't there before is added by interaction between
> > the still residual second harmonic and reduced newly
> > added third harmonic.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
> > In short, the artifacts NFB adds to
> > the distortion mix are all of the most harmful kind. But,
> > say the proponents of NFB, so what? Every time the loop
> > cycles the added artifacts are smaller, even if there are
> > more of them... The whole affair starts to smell of
> > trying to argue with a Marxist who simply declares any
> > inconvenient truth 'an anomaly'. (If this sounds like a
> > mess from which you should run a mile, you have come to
> > the right conclusion. Start running now. It gets worse.)
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
>
> > 3. We thus arrive at a situation where distortion has
> > been lowered by NFB but where the most disturbing odd
> > harmonic distortions are still present to some measure,
> > with the added disadvantage that new and extremely
> > disturbing artifacts of higher harmonic distortions have
> > been created by the very process of using negative
> > feedback to lower distortion.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
>
> > Regardless of the absolute
> > level of THD, or the volume setting, the mix of harmonics
> > has been adversely affected and now includes a higher
> > proportion of third and higher harmonics than before NFB.
> > Let me say that again: after NFB, third and higher
> > harmonics will make up a greater part of the distortion
> > than before.
>
> But, all orders of distortion will be greatly reduced.
>
> > 4. Low volume levels perforce accounts for 99 per cent of
> > audiophile listening because we all have families or
> > neighbours, and we would like to keep our ears.
> > Unfortunately for the lowest common denominator of hi-fi
> > designer, the one who specifies NFB as a conditioned
> > response much like Pavlov's dogs slavered when the bell
> > rang, human physiology and psycho-acoustic response is
> > such that odd harmonics are disproportionately more
> > disturbing at lower than at higher listening levels. This
> > inescapable effect is independent of definition of
> > 'listening level.' At the 110dB in-room SPL (only 14dB
> > louder than an automatic riveter!) advocated by the
> > already deaf Transient Overload Elite known on newsgroups
> > as the Borg, this poisonous concoction of original
> > distortions and NFB recombinant artifacts will be least
> > disturbing (and soon not heard at all!). At any lower
> > level perceived interference of this harmonics cocktail
> > with the music will increase in inverse proportion to the
> > volume level. At low volume levels the artifacts
> > generated by NFB will by their nature as higher harmonic
> > distortions be disproportionately far more disturbing. At
> > these normal listening levels 0.75 per cent of second
> > harmonic distortion may be below the threshhold of
> > perception for sophisticated listeners, whereas tiny
> > amounts of third and higher odd harmonic distortions
> > grate.
>
> NFB reduces distortion at all output levels, large or small.
>
> > And they still use Negative Feedback? Are they stupid?
>
> No, they are wise.
>
> > No, they are not stupid. Most of them march to the drum
> > of a cost accountant on whom we wouldn't spit if he were
> > alight. NFB is as cheap in money terms as it is expensive
> > in terms of perceived quality of music. We shall come to
> > those who claim to be sympathetic to high-fidelity but
> > insist on devices which do not work without NFB, who have
> > another devious answer. Here, meanwhile, for you to keep
> > in mind, is a single-sentence summary of a complicated
> > interdisciplinary argument:
>
> > The case against NFB is that for 99 per cent of listening
> > the NFB cure is worse than the disease.
>
> In fact the inverse is true.
>
> > But surely we don't have to do anything so stupid?
>
> What's really stupid is avoiding NFB because of Jute's
> senseless claims.
>
> > It follows from the argument above that ultrafidelista
> > should choose an intrinsically linear topology and device
> > which does not require added negative feedback to
> > 'linearize' the output.
>
> In fact good designs with NFB start out with circuits that
> have as low distortion as is practical before the addition
> of NFB. See Self's blameless power amp circuit for many
> examples of this.
>
> > The intrinsically linear device
> > is the thermionic tube in either its triode form or as a
> > pentode hogtied to work as a triode, which can be a most
> > pleasing alternative both economically and sonically.
>
> In fact triodes have built-in NFB.
>
> > The
> > topology is often single-ended operation, chosen also for
> > several other reasons described elsewhere in these
> > articles, including KISS; if the chosen topology is
> > push-pull operation, which is more difficult but far from
> > impossible to arrange without NFB, operation should be
> > specified as Class A1. Inside the argued case above lies
> > too the overwhelming reason to accept the potential small
> > disadvantage that may accompany the preferred topology in
> > comparison to the discarded alternatives. The
> > disadvantage is of course the potential for a residual
> > second harmonic that measures high by transistor or NFB
> > tube standards. (Note the word potential. With a
> > conservatively designed DHT amp the potential problem
> > should not arise.)
>
> Push-pull operation is in fact a great way to make power
> amps more linear prior to the application of feedback.
>
> > The ultrafidelista, who are as keen on silent amps as
> > anyone else, accept this small potential difficulty
> > because it is the lesser evil compared to NFB.
> > Unbelievers (largely unwashed, according to reports)
> > sneer that ultrafidelista like this approach because of
> > the 'added euphonics', which is bow-wow techie talk for
> > the warmth a big chunk of second harmonic lays on a zero
> > negative feedback single-ended amplifier. But competent
> > design can easily reduce the level of second harmonic to
> > below the level of perception without the need for NFB
> > and its deleterious after-effects. In any event, it is
> > your amplifier. You paid for it. You have a right to tune
> > it as you please. The key thing is to get rid of NFB and
> > to understand why you did it.
>
> If you did it because of Jute's posturing, you're an old
> kind of fool.
>
> > Can we prove any of this scientifically?
>
> Hard to do because Jute's so-called scientific claims are
> bogus.
>
> > We have already.
>
> LOL!
>
> > All of this is the technical subtext to
> > my longtime contention that what the ultrafidelista hear
> > and love is not a directly heated triode sound as is
> > claimed by many enthusiasts but a Class A1, ZNFB sound.
> > (Admittedly, as we have seen above, the right sound is
> > virtually guaranteed with a ZNFB DHT SE amp of
> > conservative provenance but may have to be developed the
> > hard way with more economical or higher-power
> > contenders.) In comparative ABX tests conducted over a
> > number of years, I found that professional musicians,
> > certified golden ears, choose the triode-linked Class A1
> > PP ZNFB EL34 whenever it is present in the test over all
> > other contenders including SE 300B and 'blameless'
> > high-NFB silicon.
>
> Show us your level-controlled, bias-controlled listening
> tests, Andre.
>
> > Science also proceeds by pure reason.
>
> Actually, science proceedes by both pure reasoning and
> practical experience.
>
>
> >Ultrafidelista have
> > long doubted whether what engineers insist we measure
> > (the absolute level of distortion, THD) predicts success
> > in audio gear. This is the full circle, because I have
> > just proven by logical, individually uncontested steps
> > that what matters, once a certain modest level of silence
> > is assured to an amplifier, is not the absolute level of
> > disharmonics but their composition. The same proof
> > demonstrates that a more beneficial distribution follows
> > instantly from doing without NFB.
>
>
> NFB lowers all relevant forms of distortion. Distortion is
> one of those things where less is more.
>
>
> > But transistor amps won't work at all without NFB!
>
> Absolute BS. Transistor amps without NFB were built in the
> early days, before the refinements that enable the use of
> NFB are possible.
>
> > That is not our problem. Those who choose inefficient
> > speakers and consequently are forced to accept monstrous
> > amps made possible only by gigadeciBels of NFB, will
> > receive our sympathy - and the music they deserve.
>
> Seneseless posturing.
>
> > Engineering hangers-on of transistor attempts at high
> > fidelity, where the measure of success is vanishing THD
> > rather than sonic hedonism, pretend to be enthusiasts for
> > NFB. To make it work for them, they have attempted to
> > change the rules so that we won't hear what their
> > treasured NFB does to our sound. They sneer that low
> > level listening, which 99 per cent of us prefer and where
> > NFB does most to wreck the sound, is 'easy listening' and
> > therefore not permissible. According to them we should
> > all be forced to listen at the high volume level which
> > suits NFB amps, which they call 'realistic'. This is a
> > contemptible circular argument, only too characteristic
> > of a fascist mentality in a part of the audiophile
> > spectrum which wants to prescribe their arid vision
> > without regard for our enjoyment.
>
> More senseless posturing.
>
> > We can recommend a good tailor to them. It hurts every
> > time you wear his suit. No pain, no gain, fellers!
> >
> >
> >
> > In summary
> >
> > Almost everyone listens at low level most of the time.
>
> And, SS high feedback amps are what they use as a rule.
>
> > NFB wrecks everybody's sound at all levels but most
> > wretchedly at normal listening levels.
>
> Wrong. NFB can work well at both low and high levels.
>
> >e started out
> > with a contemptible circular argument and we have met
> > another along the way. We can now put both in context:
> >
> >
> >
> > An 'engineer' who designs an amplifier which does not
> > work perfectly without negative feedback is like a tailor
> > cutting the suit incompetently and then demanding that
> > you walk like a cripple to make it fit, so that everyone
> > can admire the brilliance of your tailor.
>
> The joke is that Jute prizes triodes, which are just
> pentodes with NFB added back in.
>
>
> > Negative feedback is a bodge. That is why it is
> > despicable to the ultrafidelista.
>
> If NASA listened to Jute, the Rusians would have beaten us
> to the moon.
>
> - end long quote -
>
> --
>
> "Audio as a serious hobby is going down the tubes."
> - Howard Ferstler, 25/4/2005
> Just look what Arny had to say to one of your posts about the use of
> NFB ....the original was posted to RAO by our friend Brat Ludwig :-)
Ludwig is a thief. The material is copyright and clearly marked for use
on RAT only.
As for Arny, I read every one of his literal-minded misunderstandings
in the hope of learning something. I wasted my time. The kicker is in
Arny's remark that:
> If NASA listened to Jute, the Rusians would have beaten us
> to the moon.
Arny is welcome to listen to Russian hi-fi, hundred per cent negative
feedback, total silence on an airless surface, if he believes that
suits the closed-circuit aridity of his mind.
I'll stick to hi-fi which plays music.
Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"an unbelievably comprehensive web site" -- Hi-Fi News & Record Review
PS: Interestingly, Arny kicks the bejeezus out of his own organ
grinder's monkey, Pinkerton, who was the one who came up with the
ignorant 50dB feedback suggestion, in this passage:
(Jute:)
> > Before I even finished the design of the KISS 300B it was
> > forcefully suggested by a wannabe guru that with only
> > 50dB more gain (about seven times as much as is likely to
> > be in the actual design) I can apply 50dB of negative
> > feedback to linearize my amplifier.
(Krueger:)
> Good example of Jute's ignorance of feedback. It's highly
> unlikely that one could apply 50 dB loop feedback to a power
> amp with an output transformer and still have acceptable
> stability.
Yeah, I know, Arny. As should be clear from the text even to an
illiterate engineer, I wasn't the one who made the silly 50dB
suggestion; your accolyte Stewart Pinkerton came up with it; that is
why I told Pinkothicko to **** off back to you and stop pretending he
was my guru.
Here's Arnie's letter as forwarded by Sander:
> - begin long quote -
> Arny Krueger said:
>
> > The Ultrafidelista view of Negative Feedback
> >
> > by Andre Jute
> >
> > Negative feedback is the paradigm of modern electronic
> > design. It is mother's milk to an electronics engineer.
> > He learns to say '100dB of NFB,' in his sleep before he
> > finishes his first week at the most humble polytechnic.
>
> Good example of Jute's ignorance of the engineering
> education process. Feedback is usually taught as it relates
> to automatic control systems. Last time I looked courses
> like these generally fit into the junior or senior years.
>
> In short the idea that "He learns to say '100dB of NFB in
> his sleep before he
> finishes his first week at the most humble polytechnic" is
> sheerist BS.
>
> > Before I even finished the design of the KISS 300B it was
> > forcefully suggested by a wannabe guru that with only
> > 50dB more gain (about seven times as much as is likely to
> > be in the actual design) I can apply 50dB of negative
> > feedback to linearize my amplifier.
>
> Good example of Jute's ignorance of feedback. It's highly
> unlikely that one could apply 50 dB loop feedback to a power
> amp with an output transformer and still have acceptable
> stability.
>
> > Negative feedback, shorthanded as NFB, is the instant
> > response of the audio engineering fraternity to all ills,
> > real, perceived, non-existent. They don't even ask if
> > there is a problem, they swing the club of NFB
> > regardless. NFB has become a reflex axiom of mainstream
> > audio design. An audio engineer with his negative
> > feedback is like a policeman who runs out into the street
> > with his stick and starts beating a confession out of the
> > first housewife he sees. The difference is that the
> > policeman is relieved of duty to await punishment and the
> > audio engineer gets away with it. In the case of the
> > policeman it is unacceptable behaviour, in the case of
> > the audio engineer so much the expected norm that no one
> > except the ultrafidelista notice. I guess that if one in
> > ten million audio amplifiers does not have negative
> > feedback added, it will be a lot...
>
> No amount of rediculous posturing can counter the fact that
> NFB can be made to work very well and to great advantage,
> thank you.
>
> > No one asked if my KISS Amp requires linearization. The
> > presumption by all except those already of the
> > ultrafidelista persuasion was that I would welcome
> > suggestions about A Good Thing.
>
> If the kiss amp has less than 0.05% nonlinear distortion
> with any power level or any frequency or combination of
> frequencies 20-20 KHz, then its fine as is. I doubt it is
> that good.
>
> > In the face of such overwhelming acceptance by qualified
> > engineers, why do we as ultrafidelista not take the same
> > easy path of negative feedback? Especially considering
> > that superficially NFB is easy to understand and apply.
>
> > How does negative feedback work?
>
> > Negative feedback is simply a negative voltage fed back
> > from the output to the input amplifying device to offset
> > part of the harmonic distortion which is present as a
> > positive voltage.
>
> This is a highly incomplete explanation. In fact the voltage
> fed back offsets not only the distortion but a goodly part
> of the basic signal. Therefore, NFB generally reduces an
> amplifier's gain for both the basic amplfied signal and also
> the distortion.
>
> > It costs nothing except a loss of gain
> > and a few side effects such as phase shift and possible
> > instability which are well known in the mathematical
> > literature and more or less easily guarded against
> > depending on the level of NFB.
>
> In fact NFB properly applied reduces, not increases an
> amplifier's phase shift.
>
> > 'Wow!' those meeting NFB for the first time will now say,
> > 'Something for free! I'll grab some of that for my amp.'
>
> Just just contrdicted the first phrase in the previous
> paragraph that says that NFB has a price in the form of a
> loss of gain.
>
> > Hey, I said it, and I am a professional intellectual, by
> > definition an infinite skeptic. NFB is a thing of beauty
> > that will draw you in. It is like an electronic Marxism
> > which admits of no contrary arguments because it has
> > subsumed them all into The Holy Measurements. To question
> > The Measurements is to commit heresy.
>
> Jute's mistake here is that its not heresy to question
> measurements, and people have been doing that for decades,
> even in such conservative journals as the JAES.
>
> >You need to be of
> > strong mind to resist the blandishments of such a
> > universal panacea and of strong stomach to withstand the
> > hysterical assaults of the lesser engineers defending
> > their holy grail. (And when you do get hold of a superior
> > engineer to explain NFB to you, you need to be high-domed
> > indeed because suddenly NFB can turn very intricate.)
>
> It is true that some advanced course work in calculus can be
> of great help when designing systems with feedback. This
> automatically disqualifies a great percentage of basement
> geniuses and high end chief engineers, writers and
> reviewers.
>
> > Unfortunately NFB doesn't come without a price. It levies
> > a cruel charge on the perceived quality of the sound.
> > Negative feedback is what gives all those 'blameless'
> > transistor and big PP tube amps their chillingly
> > unnatural sound.
>
> Strange that these supposedly unnatural-sounding amplifiers
> can pass a straight wire bypass test, and so many low-NFB
> power amps can't.
>
> > Then how did NFB come to be such a panacea in amplifier
> > design?
>
> Because when applied with reasonable care by competent
> engineers, NFB works. NFB got men to the moon. NFB makes
> your car idle and run. NFB keeps your water heater from
> exploding. It keeps your house and oven at the temperature
> you set on your thermostat. NFB makes cell phones work.
> etc., etc.
>
> > Your guess is as good as mine. Hi-fi design is not
> > prestige work for engineers, or highly paid. The most
> > talented and best qualified engineers go into automobiles
> > or military hardware or big construction projects or
> > computer design.
>
> All areas where NFB is highly depended on, and it works.
>
> >The left-overs design amplifiers in the
> > time they have to spare from writing up specs for
> > requesting a CE mark for a new electric kettle. Lemmings
> > storming en masse over a cliff come to mind; such people
> > don't see the necessity of original thought, or have the
> > mental equipment for it. The exceptions to this rule are
> > normally audio enthusiasts in charge of their own small
> > audio manufactories with niche markets; those who grow
> > larger from this base follow the mainstream mantra of
> > "mo' NFB give lowa' THD" because the marketing channels
> > demand it from them if they wish to grow. At this point
> > they usually cease to offer anything different, only the
> > exclusivity of a very high price. (I know, because a
> > sub-board I designed for a supplier to the trade turns up
> > in so many very expensive amps with so many different big
> > names neatly silkscreened on it... it strikes me as the
> > sort of detail a real designer, as distinct from a
> > marketer, would take under his own control.) Those very
> > few makers who will sell you an ultrafi amp without any
> > NFB operate even tinier shops, usually one man and a cat,
> > just hanging on.
>
> Usually the cat knows as much if not more about calculus
> than the man,
>
> > The mechanism by which NFB wrecks your sound
>
> NFB wrecks the sound the same way NFB makes your water
> heater explode: as a rule it doesn't.
>
> > Negative feedback at first acquaintance sounds good
> > enough to take to bed and cuddle. It isn't. It isn't even
> > as simple as a superficial acquaintance may suggest.
> > Follow the steps with me, from the theory as she is
> > received to what arrives at your brain as music:
>
> > 1. In theory NFB reduces all harmonic distortion equally,
> > without discrimination.
>
> Nope. NFB is often dependent on frequency. As a rule it
> reduces higher harmonics less.
>
> >Strictly in theory it does not
> > reshape harmonic distortion by reducing the most
> > objectionable third and higher order odd harmonic
> > distortion to a greater extent than the relatively
> > harmless 2nd harmonic.
>
> Actually, any order of nonlinear distortion, even Jute's
> beloved order 2 can wreck the sound of music.
>
> > Thus NFB at its theoretically most
> > benign is already useless in terms of psychoacoustics, as
> > will become clear at point 4. If you disregard
> > psychoacoustics, as many audio engineers do, NFB is
> > brilliant in reducing total harmonic distortion to a
> > number as tiny as you want. You just pile on more NFB.
>
> This paragraph really says nothing.
>
> > 2. In real life, as distinct from simplified theory, NFB
> > adds artifacts of its own. Remember, it is a loop. The
> > signal starts at the input and is amplified by devices
> > until it reaches the output. From the output a part of
> > the signal called the negative feedback is fed back to
> > the input. Here a loop is completed and the combination,
> > less distorted, reaches the output again, a part of the
> > combination is fed back, endlessly. The artifacts we want
> > to consider here are created by the fed-back residue of
> > harmonic distortions adding to both the fundamental and
> > the distortions already created by the amplifier, then
> > some portion of the sum of the original and the feedback
> > distortion is fed back again and added on, until the
> > ooh-ah bird flies up its own fundament. It looks
> > marginally less disgusting as a recursive mathematical
> > formula with lots of nested parenthetical parcels of
> > noise being loaded onto your music.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
> > But it is a monkey on
> > the back of your sound, with a smaller monkey on the back
> > of the first monkey, a still smaller monkey on the back
> > of the second monkey, and so on ad infinitum. These
> > additive artifacts are all higher harmonics and the more
> > dominant ones are all odd. Suppose, for the sake of
> > simplicity, a superbly designed ultrafidelista amp with
> > some second harmonic and zero odd harmonics before NFB.
> > Add NFB and the second harmonic will be lowered but the
> > recombinant new loop now contains newly added
> > intermodulation effects between the fundamental and the
> > residual second harmonic, and that is third harmonic. In
> > the next cycle a small but nasty dose of fifth harmonic
> > that wasn't there before is added by interaction between
> > the still residual second harmonic and reduced newly
> > added third harmonic.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
> > In short, the artifacts NFB adds to
> > the distortion mix are all of the most harmful kind. But,
> > say the proponents of NFB, so what? Every time the loop
> > cycles the added artifacts are smaller, even if there are
> > more of them... The whole affair starts to smell of
> > trying to argue with a Marxist who simply declares any
> > inconvenient truth 'an anomaly'. (If this sounds like a
> > mess from which you should run a mile, you have come to
> > the right conclusion. Start running now. It gets worse.)
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
>
> > 3. We thus arrive at a situation where distortion has
> > been lowered by NFB but where the most disturbing odd
> > harmonic distortions are still present to some measure,
> > with the added disadvantage that new and extremely
> > disturbing artifacts of higher harmonic distortions have
> > been created by the very process of using negative
> > feedback to lower distortion.
>
> This is for all practical purposes, total BS. The bottom
> line is that a power amp with a properly designed NFB loop
> has far lower distortion of all relevant orders because of
> the NFB.
>
>
> > Regardless of the absolute
> > level of THD, or the volume setting, the mix of harmonics
> > has been adversely affected and now includes a higher
> > proportion of third and higher harmonics than before NFB.
> > Let me say that again: after NFB, third and higher
> > harmonics will make up a greater part of the distortion
> > than before.
>
> But, all orders of distortion will be greatly reduced.
>
> > 4. Low volume levels perforce accounts for 99 per cent of
> > audiophile listening because we all have families or
> > neighbours, and we would like to keep our ears.
> > Unfortunately for the lowest common denominator of hi-fi
> > designer, the one who specifies NFB as a conditioned
> > response much like Pavlov's dogs slavered when the bell
> > rang, human physiology and psycho-acoustic response is
> > such that odd harmonics are disproportionately more
> > disturbing at lower than at higher listening levels. This
> > inescapable effect is independent of definition of
> > 'listening level.' At the 110dB in-room SPL (only 14dB
> > louder than an automatic riveter!) advocated by the
> > already deaf Transient Overload Elite known on newsgroups
> > as the Borg, this poisonous concoction of original
> > distortions and NFB recombinant artifacts will be least
> > disturbing (and soon not heard at all!). At any lower
> > level perceived interference of this harmonics cocktail
> > with the music will increase in inverse proportion to the
> > volume level. At low volume levels the artifacts
> > generated by NFB will by their nature as higher harmonic
> > distortions be disproportionately far more disturbing. At
> > these normal listening levels 0.75 per cent of second
> > harmonic distortion may be below the threshhold of
> > perception for sophisticated listeners, whereas tiny
> > amounts of third and higher odd harmonic distortions
> > grate.
>
> NFB reduces distortion at all output levels, large or small.
>
> > And they still use Negative Feedback? Are they stupid?
>
> No, they are wise.
>
> > No, they are not stupid. Most of them march to the drum
> > of a cost accountant on whom we wouldn't spit if he were
> > alight. NFB is as cheap in money terms as it is expensive
> > in terms of perceived quality of music. We shall come to
> > those who claim to be sympathetic to high-fidelity but
> > insist on devices which do not work without NFB, who have
> > another devious answer. Here, meanwhile, for you to keep
> > in mind, is a single-sentence summary of a complicated
> > interdisciplinary argument:
>
> > The case against NFB is that for 99 per cent of listening
> > the NFB cure is worse than the disease.
>
> In fact the inverse is true.
>
> > But surely we don't have to do anything so stupid?
>
> What's really stupid is avoiding NFB because of Jute's
> senseless claims.
>
> > It follows from the argument above that ultrafidelista
> > should choose an intrinsically linear topology and device
> > which does not require added negative feedback to
> > 'linearize' the output.
>
> In fact good designs with NFB start out with circuits that
> have as low distortion as is practical before the addition
> of NFB. See Self's blameless power amp circuit for many
> examples of this.
>
> > The intrinsically linear device
> > is the thermionic tube in either its triode form or as a
> > pentode hogtied to work as a triode, which can be a most
> > pleasing alternative both economically and sonically.
>
> In fact triodes have built-in NFB.
>
> > The
> > topology is often single-ended operation, chosen also for
> > several other reasons described elsewhere in these
> > articles, including KISS; if the chosen topology is
> > push-pull operation, which is more difficult but far from
> > impossible to arrange without NFB, operation should be
> > specified as Class A1. Inside the argued case above lies
> > too the overwhelming reason to accept the potential small
> > disadvantage that may accompany the preferred topology in
> > comparison to the discarded alternatives. The
> > disadvantage is of course the potential for a residual
> > second harmonic that measures high by transistor or NFB
> > tube standards. (Note the word potential. With a
> > conservatively designed DHT amp the potential problem
> > should not arise.)
>
> Push-pull operation is in fact a great way to make power
> amps more linear prior to the application of feedback.
>
> > The ultrafidelista, who are as keen on silent amps as
> > anyone else, accept this small potential difficulty
> > because it is the lesser evil compared to NFB.
> > Unbelievers (largely unwashed, according to reports)
> > sneer that ultrafidelista like this approach because of
> > the 'added euphonics', which is bow-wow techie talk for
> > the warmth a big chunk of second harmonic lays on a zero
> > negative feedback single-ended amplifier. But competent
> > design can easily reduce the level of second harmonic to
> > below the level of perception without the need for NFB
> > and its deleterious after-effects. In any event, it is
> > your amplifier. You paid for it. You have a right to tune
> > it as you please. The key thing is to get rid of NFB and
> > to understand why you did it.
>
> If you did it because of Jute's posturing, you're an old
> kind of fool.
>
> > Can we prove any of this scientifically?
>
> Hard to do because Jute's so-called scientific claims are
> bogus.
>
> > We have already.
>
> LOL!
>
> > All of this is the technical subtext to
> > my longtime contention that what the ultrafidelista hear
> > and love is not a directly heated triode sound as is
> > claimed by many enthusiasts but a Class A1, ZNFB sound.
> > (Admittedly, as we have seen above, the right sound is
> > virtually guaranteed with a ZNFB DHT SE amp of
> > conservative provenance but may have to be developed the
> > hard way with more economical or higher-power
> > contenders.) In comparative ABX tests conducted over a
> > number of years, I found that professional musicians,
> > certified golden ears, choose the triode-linked Class A1
> > PP ZNFB EL34 whenever it is present in the test over all
> > other contenders including SE 300B and 'blameless'
> > high-NFB silicon.
>
> Show us your level-controlled, bias-controlled listening
> tests, Andre.
>
> > Science also proceeds by pure reason.
>
> Actually, science proceedes by both pure reasoning and
> practical experience.
>
>
> >Ultrafidelista have
> > long doubted whether what engineers insist we measure
> > (the absolute level of distortion, THD) predicts success
> > in audio gear. This is the full circle, because I have
> > just proven by logical, individually uncontested steps
> > that what matters, once a certain modest level of silence
> > is assured to an amplifier, is not the absolute level of
> > disharmonics but their composition. The same proof
> > demonstrates that a more beneficial distribution follows
> > instantly from doing without NFB.
>
>
> NFB lowers all relevant forms of distortion. Distortion is
> one of those things where less is more.
>
>
> > But transistor amps won't work at all without NFB!
>
> Absolute BS. Transistor amps without NFB were built in the
> early days, before the refinements that enable the use of
> NFB are possible.
>
> > That is not our problem. Those who choose inefficient
> > speakers and consequently are forced to accept monstrous
> > amps made possible only by gigadeciBels of NFB, will
> > receive our sympathy - and the music they deserve.
>
> Seneseless posturing.
>
> > Engineering hangers-on of transistor attempts at high
> > fidelity, where the measure of success is vanishing THD
> > rather than sonic hedonism, pretend to be enthusiasts for
> > NFB. To make it work for them, they have attempted to
> > change the rules so that we won't hear what their
> > treasured NFB does to our sound. They sneer that low
> > level listening, which 99 per cent of us prefer and where
> > NFB does most to wreck the sound, is 'easy listening' and
> > therefore not permissible. According to them we should
> > all be forced to listen at the high volume level which
> > suits NFB amps, which they call 'realistic'. This is a
> > contemptible circular argument, only too characteristic
> > of a fascist mentality in a part of the audiophile
> > spectrum which wants to prescribe their arid vision
> > without regard for our enjoyment.
>
> More senseless posturing.
>
> > We can recommend a good tailor to them. It hurts every
> > time you wear his suit. No pain, no gain, fellers!
> >
> >
> >
> > In summary
> >
> > Almost everyone listens at low level most of the time.
>
> And, SS high feedback amps are what they use as a rule.
>
> > NFB wrecks everybody's sound at all levels but most
> > wretchedly at normal listening levels.
>
> Wrong. NFB can work well at both low and high levels.
>
> >e started out
> > with a contemptible circular argument and we have met
> > another along the way. We can now put both in context:
> >
> >
> >
> > An 'engineer' who designs an amplifier which does not
> > work perfectly without negative feedback is like a tailor
> > cutting the suit incompetently and then demanding that
> > you walk like a cripple to make it fit, so that everyone
> > can admire the brilliance of your tailor.
>
> The joke is that Jute prizes triodes, which are just
> pentodes with NFB added back in.
>
>
> > Negative feedback is a bodge. That is why it is
> > despicable to the ultrafidelista.
>
> If NASA listened to Jute, the Rusians would have beaten us
> to the moon.
>
> - end long quote -
>
> --
>
> "Audio as a serious hobby is going down the tubes."
> - Howard Ferstler, 25/4/2005