"Maybe you made the perfect Amp?"
Not hardly. It's the 120 I was simulating. LTSpice was showing harmonic distortion only 80dB down right at the output of the voltage source. Model is a perfect source; no internal impedance. So, less than perfect generation is what I was seeing. I bet they have their reasons. I have 16 bit 48K generators unless anyone can lead me to a Freeware generator that does better than that. Although I don't expect to rely on simulation, it is part of learning what can be done and where to look. Same with the noise simulation. I see them as a place to get a hint.
I am still convinced we can measure the differences. It is likely to be a dynamic problem , masking problem, and preferences all rolled up so there is not a number that will always be "better". A set of differences, not the traditional bench tests. I think that is established. What set is the question.
In my limited understanding, BJT's are a bit more linear. JFETS have the advantages you mentioned, plus the ability for the nifty trick John came up with on his input design. Quite clever as symmetry is the goal, not an absolute. Wonder what the schematic of my "new" C5 Nak looks like. I guess it is all FET as it is a Pass design. Seems to work quite well.
I only need good enough to convince my wife to stay in the room when I am playing Harry James or Copland.
Not hardly. It's the 120 I was simulating. LTSpice was showing harmonic distortion only 80dB down right at the output of the voltage source. Model is a perfect source; no internal impedance. So, less than perfect generation is what I was seeing. I bet they have their reasons. I have 16 bit 48K generators unless anyone can lead me to a Freeware generator that does better than that. Although I don't expect to rely on simulation, it is part of learning what can be done and where to look. Same with the noise simulation. I see them as a place to get a hint.
I am still convinced we can measure the differences. It is likely to be a dynamic problem , masking problem, and preferences all rolled up so there is not a number that will always be "better". A set of differences, not the traditional bench tests. I think that is established. What set is the question.
In my limited understanding, BJT's are a bit more linear. JFETS have the advantages you mentioned, plus the ability for the nifty trick John came up with on his input design. Quite clever as symmetry is the goal, not an absolute. Wonder what the schematic of my "new" C5 Nak looks like. I guess it is all FET as it is a Pass design. Seems to work quite well.
I only need good enough to convince my wife to stay in the room when I am playing Harry James or Copland.
No, don't worry, I don't (would that life were so simple!). On his and other meter-reader terms, his designs are successful.
What is interesting, perhaps, is how DS alternates between, in essence, declaring that he's wrapped things up and the rest of us don't need to bother (for example his "blameless" adjective freely applied, almost always to his own stuff [although he granted Stochino kudos for the latter's non-slewing amps]), and then deciding to share some new thing of his that represents, in his opinion, an advance.
Brad
Agree, that was stunning to me too. And their logic and experimental support of this seems unassailable, although I need to devote serious study to the piece and not just the enthusiastic but necessarily brief perusal. I'm going to do some poking around among some of my friends (one whose PhD is specifically in psychoacoustics) to get their read, if they can be persuaded to devote the required attention.
Unfortunately, as many know from bitter experience or by observing it, many academics or former academics are as lazy and stubborn as the "rest of us", and a consequence of this is to resist genuinely new information and theories, unless recommended by a respected colleague. As well remember that in academia, to be found wrong is considered to be shameful and career-limiting, despite how many times one has gotten it "right".
Having said that, there's plenty of "crank" stuff out there and it often is sent to academics. The UCLA Astronomy reading room used to get such all the time, as well as other professors there, particularly those with something approaching popular notoriety (George O. Abell for example, who wrote a widely-adopted textbook and cataloged clusters of galaxies and planetary nebulae, thus has an ongoing presence. They often misspelled his name, naturally, a "bad sign" for openers). When I see this stuff (I collected it when people tossed it out for a while) it seems as if it's easy to recognize, and yet saying that is a bit along the lines of the famous statement about not being able to define "pornography", but being sure one knows it when one sees it.
Although this material is not, by any means, as earth-shattering as Einstein's early work, there have been some recent discussions about whether or not, in today's climate of referreed journals, Einstein would have ever gotten published.
Brad
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I confess I was somewhat apprehensive when Samuel was working on that paper, which began as a review as it were for Linear Audio, but wound up on his website, as I didn't know how well DS would respond to criticism. But we were pleasantly surprised that he was supportive, even appreciative. This is another reason why I mentioned "mellowing".
Brad
Having the simulator show the generator with distortion only 80 dB down is pretty strange and disturbing, but probably obvious if one knew the details of the software.
Something I've done when Circuitmaker refuses to run fourier analysis is to lay down a series of notch filters (bootstrapped twin-t) at the fundamental, and sometimes as well at low-order harmonics, and observe their outputs (and sometimes merely adding these to the schematic allows fourier to run!).
Broad-brush, without a long list of proper references, and neglecting lots of other effects:
BJTs: relatively high transconductance for a given operating bias current and collector-emitter voltage. Relatively high output impedance at the collector even at rather low collector-emitter voltages. High gm means that local feedback will reduce the distortion of a single common-emitter stage without as large a resistor (compared again to other devices). But that distortion is mostly due to the exponential function that properly describes this transconductance, and which is associated with all manner of distortion. One of the more successful (measurements now folks) strategies is to "predistort" the signal at the base with another nonlinear device, usually another transistor often "diode-connected"; Barrie Gilbert has made something of an industry out of various clever approaches in this connection, even to the point of the now-eponymous Gilbert multiplier.
JFET or DMOS: Often described as square-law devices. Modern low-noise parts depart from the simplest models when the details are considered (see, for a recent brief discussion Scott Wurcer's mic preamp piece in Linear Audio Vol. 1; for more detailed discussions Ed Oxner's book is excellent). Real devices also have some contact resistance, which means that even a common-source stage with no external resistance in the source will have a little local feedback. Were these parts truly square-law alone, and had very high drain impedance in saturation, in principle they would generate second harmonic distortion and sum-and-difference-frequency IM distortion.
FET transconductance for a typical bias current will be lower than for a bipolar (roughly speaking, similar device area yada yada). As a result the strategy of linearization via local feedback will be less effective than for bipolars.
Tubes (!). Well, to the extent a triode conforms to the first-order Langmuir-Child theory, the product of transconductance and plate resistance, "mu", is constant over a useful range of operating currents/voltages. Loading on the plate spoils this, but not too quickly. With ideal L-C triodes and no plate load, triodes are distortionless (but of course we have to have some sort of load).
For all three device types, operation in a long-tailed pair (Brit influence excuse me) will, with perfectly matched devices driven differentially and deploying outputs differentially, cancels even-order distortion. So will "push-pull" operation, except that P and N type devices are never all that well-matched, and tubes that use electrons-only require transformers. Boyk and Sussman seemed quite surprised and delighted that push-pull JFETs were IM-distortionless, but their IM distortion paper uses ideal devices for their modelling.
Brad
Wife's critical ear testing results are in:
She still prefers the RB 951 to the HCA 1200ii playing my Paradigm studio 20's. Even well over 3dB louder, the trumpet blair on track one of The King James Version (Sheffield) is "smoother." When I played my Julian Bream, I thought the nylon strings kept the metallic edge away too. In highly subjective terms, When I compared the DH 120; RB 951 and 1500, I thought the 1500 to be , "clinically open". A level of detail that I thought maybe was not natural. So for our preference, with my current speakers and current CD's, we prefer the Rotel.
Now, on my woofers, the 1200 is VASTLY better than the DH-220 I was running. Slam dunk, Tex Avery eyeball pop, amp going on e-bay.
If I were to guess, the more limited bandwidth of the Rotel's may be masking bad things the tweeters are capable of doing. However, I tried a passive LP filter on the crossover and it did not help. We will repeat the tests again in the distant future after I build some Revealtor or Excel based speakers.
Denon S-Audio CD player, Nak CA-5 preamp for those wondering. No need to make judgement on fractions of a percent matching. Whatever this is, it is a simple good/bad and is not very sensitive to level. Level was enthusiastic and above speech, but not loud.
If someone would like to donate , oh say a Aragon, Krell, or Levinson, I would gladly see if our preference really is in favor of a deficiency, or just in favor of some design choices over others.
She still prefers the RB 951 to the HCA 1200ii playing my Paradigm studio 20's. Even well over 3dB louder, the trumpet blair on track one of The King James Version (Sheffield) is "smoother." When I played my Julian Bream, I thought the nylon strings kept the metallic edge away too. In highly subjective terms, When I compared the DH 120; RB 951 and 1500, I thought the 1500 to be , "clinically open". A level of detail that I thought maybe was not natural. So for our preference, with my current speakers and current CD's, we prefer the Rotel.
Now, on my woofers, the 1200 is VASTLY better than the DH-220 I was running. Slam dunk, Tex Avery eyeball pop, amp going on e-bay.
If I were to guess, the more limited bandwidth of the Rotel's may be masking bad things the tweeters are capable of doing. However, I tried a passive LP filter on the crossover and it did not help. We will repeat the tests again in the distant future after I build some Revealtor or Excel based speakers.
Denon S-Audio CD player, Nak CA-5 preamp for those wondering. No need to make judgement on fractions of a percent matching. Whatever this is, it is a simple good/bad and is not very sensitive to level. Level was enthusiastic and above speech, but not loud.
If someone would like to donate , oh say a Aragon, Krell, or Levinson, I would gladly see if our preference really is in favor of a deficiency, or just in favor of some design choices over others.
the psychoacoustic testing literature is very firm on the level matching requirement - at several dB differences Loudness curves change perceived frequency balance, nonlinear hearing effects
Katz implies he can use these perceptual effects to set set levels "by ear" between recording venue, mastering studio monitors to better than ~ 1dB - but he does measure SPL in both for "ground truth" for this claim
but Clark's ABX curves shows that 0.1 dB level matching is required for level alone to have "no discernable" statistically significant perceptual effect
obviously many "clearly audible" differences don't require such strict level matching to identify - but you can't rule out a priori that level differences below 1 dB as being "the real" cause for any unqualified claim of "audible difference"
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And I wanted to append to the generalities that I'm not implying that any specific characteristic translates into the BIG question and answer. And saying that, I'm not, for the most part, withholding insights or even most theories about that. Some of the woolier ones are not suitable for publication as yet. When it comes to wild surmises on a peak in Darien, for the moment I'll side with Wittgenstein in his Tractatus.
This gets to be particularly sticky when loudspeakers are being compared, since significant differences in frequency response are common, and attempts to level-match with pink noise drive as measured by a microphone are in some ways fundamentally imprecise.
I contracted to design a precision attentuator to allow signal gain presets to be used when speakers were being compared (there's an AES preprint from 1997; the system described was never completed, as it was going to take another 20k and require that a secretary be let go, and I think they fell back on some commercial equipment from Audio Authority
). It would have pleased meter-readers. But the basic difficulty of setting required levels to begin with is still a problem.Brad
Yea, yea, yea. You need to see what I said. Her preference was clear over a wide range of levels. As close as I can set a test tone on the terminals (.02V) and well over three dB above and below. For her, the problem is not close. It is yes/no. I am not making claims on WHAT the difference is, or if your ears would agree. If it were what I THINK I am also hearing, it is subtle enough that I would agree with all the precision controlled test procedures. When I was listening to guitar music the other night, I can only say for sure I think the strings were more correct, but that I forgot to listen as I wound up listening to the recording not the amp. I did not with either of the others. I am stating a preference, no absolutes.
Applying Physics Makes Auditory Sense
Hello KSTR and forum members,
About Heerens and de Ru careful analysis of the auditory pathway experiments that were executed by Wever and Lawrence [16],
a remarkable experiment in 1950:
Ernest Glen Wever and Merle Lawrence:
The acoustic pathways to the cochlea, JASA July 1950, 22: 460-467
experiment:
• They (Wever and Lawrence) removed the cat eardrum and ear-bone-chain.
• Brought in a tube around the round window.
• Stimulated with pure tones as follows:
only on oval window.
only on round window.
on both windows different in phase from 0 ° - 180 °.
• Recorded the cochlear microphonics, [CM]
• signal which corresponds to signal to the brains.
Results in CM changes:
• Windows separately with the same signal: CM: equal changes
• Both windows simultaneously in the same direction: CM: no change
• Both windows in the opposite direction [180 ° or pi]: CM: maximum change
• Maximum is 6 dB higher than the two stimuli separately. (Recorded by Wever and Lawrence)
Conclusions Wever & Lawrence:
• Both paths provide identical signal in auditory nerve.
• Over much of the frequency range:
Oscillations in phase on oval and round window: minimum
Vibrations in antiphase on oval and round window: maximum
Similar research Voss, Rosowski, Peake (1996):
• Differential pressure oval - round window: signal.
• Signal Components: DC [DC] AC [AC]
Heerens and de Ru conclusions:
• Signal to arise in the brains by: moving the perilymph.
• Two identical stimuli moving opposite, (as in the experiments that were executed by Wever and Lawrence ), supplies total movement: 2 times as large.
But electric signal is not: 2 but 4 times as large.
6 dB (10.log 4 = 6.0).
For: 6 dB = 10 × 10log 4
Yes we are talking about "change in potential".
And we're not talking about the "ever-present potential".
It is namely the change of the present potential, which increases by a factor of 4, if the perilymph speed increases by a factor of 2.
Still according to the mathematical relationship that 6 dB = 10 × 10log 4.
This results in:
The signal generated in the auditory nerve is proportional to the square of the perilymph velocity.
Our hearing differentiates and squares.
So far Heerens and de Ru careful analysis of the auditory pathway experiments that were executed by Wever and Lawrence [16],
But then immediately the question:
Is there in physics such a mechanism? Answer: yes: have long known:
The Bernoulli's law.
Published in 1738.
Heerens and de Ru:
Bernoulli's law in "Applying Physics Makes Auditory Sense" is applied under quasi-static conditions.
About:
Applying Physics Makes Auditory sense
presentation:
Here is a Prezi online: prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
http://prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
After verifying the sound experiments mentioned in their book
and after verification of the experiment
http://www.a3ccm-apmas-eakoh.be/pcbwp/experiments.htm
I believe that this - "Applying Physics Makes Auditory Sense" - theory is representative of the operating principle of the human ear and the cochlea.
Besides that: a former colleague of W. Chr. Heerens, a highly skilled senior professor in applied physics, who reviewed the booklet during a contribution procedure for a scientific journal, quite recently gave the verdict that he fully agreed with the arguments and statements of Heerens and de Ru and he urged the editor to make a full scientific discussion possible for their views. He also warned the authors Heerens and de Ru that to be in right is not the same as to be put in right.
It’s part of the way messengers or designers of new paradigms are encountered by the mayor supporters of the competing one. Of course the scientific reputation rankings of so many scientists are involved and in danger in case a paradigm shift is happening.
The only issue that counts is that scientific arguments from both sides brought in discussion, verified and weighted in a careful way must turn the balance. Ignoring irrefutable arguments because they form a thread for the ranking of a scientist has always been contra productive for the progress in a field of science. History shows many of such examples. One of the most salient among them certainly is the Copernican revolution.
So, You find the arguments in a Prezi online presentation here:
http://prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
Sincerely,
Vincent Cynric Yaw
Hello KSTR and forum members,
About Heerens and de Ru careful analysis of the auditory pathway experiments that were executed by Wever and Lawrence [16],
a remarkable experiment in 1950:
Ernest Glen Wever and Merle Lawrence:
The acoustic pathways to the cochlea, JASA July 1950, 22: 460-467
experiment:
• They (Wever and Lawrence) removed the cat eardrum and ear-bone-chain.
• Brought in a tube around the round window.
• Stimulated with pure tones as follows:
only on oval window.
only on round window.
on both windows different in phase from 0 ° - 180 °.
• Recorded the cochlear microphonics, [CM]
• signal which corresponds to signal to the brains.
Results in CM changes:
• Windows separately with the same signal: CM: equal changes
• Both windows simultaneously in the same direction: CM: no change
• Both windows in the opposite direction [180 ° or pi]: CM: maximum change
• Maximum is 6 dB higher than the two stimuli separately. (Recorded by Wever and Lawrence)
Conclusions Wever & Lawrence:
• Both paths provide identical signal in auditory nerve.
• Over much of the frequency range:
Oscillations in phase on oval and round window: minimum
Vibrations in antiphase on oval and round window: maximum
Similar research Voss, Rosowski, Peake (1996):
• Differential pressure oval - round window: signal.
• Signal Components: DC [DC] AC [AC]
Heerens and de Ru conclusions:
• Signal to arise in the brains by: moving the perilymph.
• Two identical stimuli moving opposite, (as in the experiments that were executed by Wever and Lawrence ), supplies total movement: 2 times as large.
But electric signal is not: 2 but 4 times as large.
6 dB (10.log 4 = 6.0).
For: 6 dB = 10 × 10log 4
Yes we are talking about "change in potential".
And we're not talking about the "ever-present potential".
It is namely the change of the present potential, which increases by a factor of 4, if the perilymph speed increases by a factor of 2.
Still according to the mathematical relationship that 6 dB = 10 × 10log 4.
This results in:
The signal generated in the auditory nerve is proportional to the square of the perilymph velocity.
Our hearing differentiates and squares.
So far Heerens and de Ru careful analysis of the auditory pathway experiments that were executed by Wever and Lawrence [16],
But then immediately the question:
Is there in physics such a mechanism? Answer: yes: have long known:
The Bernoulli's law.
Published in 1738.
Heerens and de Ru:
Bernoulli's law in "Applying Physics Makes Auditory Sense" is applied under quasi-static conditions.
About:
Applying Physics Makes Auditory sense
presentation:
Here is a Prezi online: prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
http://prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
After verifying the sound experiments mentioned in their book
and after verification of the experiment
http://www.a3ccm-apmas-eakoh.be/pcbwp/experiments.htm
I believe that this - "Applying Physics Makes Auditory Sense" - theory is representative of the operating principle of the human ear and the cochlea.
Besides that: a former colleague of W. Chr. Heerens, a highly skilled senior professor in applied physics, who reviewed the booklet during a contribution procedure for a scientific journal, quite recently gave the verdict that he fully agreed with the arguments and statements of Heerens and de Ru and he urged the editor to make a full scientific discussion possible for their views. He also warned the authors Heerens and de Ru that to be in right is not the same as to be put in right.
It’s part of the way messengers or designers of new paradigms are encountered by the mayor supporters of the competing one. Of course the scientific reputation rankings of so many scientists are involved and in danger in case a paradigm shift is happening.
The only issue that counts is that scientific arguments from both sides brought in discussion, verified and weighted in a careful way must turn the balance. Ignoring irrefutable arguments because they form a thread for the ranking of a scientist has always been contra productive for the progress in a field of science. History shows many of such examples. One of the most salient among them certainly is the Copernican revolution.
So, You find the arguments in a Prezi online presentation here:
http://prezi.com/ahuqkgq4lajr/applying-physics-makes-auditory-sense/
Sincerely,
Vincent Cynric Yaw
Hi,
Audacity? Cooledit/Adobe Audition?
Sure. I am still convinced that the dream of lasting peace, of world citizenship, of the rule of international morality may be attained by humankind. Yet when I look around me, everywhere is war. War in the east, War in the west, War up north, War down south - War - war - Rumours of war*, preparation for war, the rattling of nuclear sabres.
So I normally concern myself less with possible dreams of a possible future and concern myself with the same grimy, boring old present. And unless we change the minds of people here in the present, the rest is not worth a rat's rear end.
I agree. It cannot really be a static problem, as under those co nditions any of the Amp's you play with are way past good and evil and should all be "blameless". However, as I found when I build the "Blamless" Amp, it was indeed blameless, you could for example never blame it for providing good sound quality or increasing my musical enjoyment over japanese generica featuring STK "Chip Amp's"...
BJT's have "better linearity" in a sense that parallels "lower THD" and only in some cases.
Looking at the section titled "5. VAS Distortion" in Samuel Groners Commentray on Self's Amplifier Book illustrates that Transistors behave very differently and that at least some FET's have better overall linearity as well as reduced high order distortion.
If it is a Nak CA-5 (not C-5) like this:
The MC Stepup is a single 2SK170 in common gate. I have the service manual if you would like it.
Ciao T
* Adapted from Bob Marley "War"
Audacity? Cooledit/Adobe Audition?
Sure. I am still convinced that the dream of lasting peace, of world citizenship, of the rule of international morality may be attained by humankind. Yet when I look around me, everywhere is war. War in the east, War in the west, War up north, War down south - War - war - Rumours of war*, preparation for war, the rattling of nuclear sabres.
So I normally concern myself less with possible dreams of a possible future and concern myself with the same grimy, boring old present. And unless we change the minds of people here in the present, the rest is not worth a rat's rear end.
I agree. It cannot really be a static problem, as under those co nditions any of the Amp's you play with are way past good and evil and should all be "blameless". However, as I found when I build the "Blamless" Amp, it was indeed blameless, you could for example never blame it for providing good sound quality or increasing my musical enjoyment over japanese generica featuring STK "Chip Amp's"...
BJT's have "better linearity" in a sense that parallels "lower THD" and only in some cases.
Looking at the section titled "5. VAS Distortion" in Samuel Groners Commentray on Self's Amplifier Book illustrates that Transistors behave very differently and that at least some FET's have better overall linearity as well as reduced high order distortion.
If it is a Nak CA-5 (not C-5) like this:
The MC Stepup is a single 2SK170 in common gate. I have the service manual if you would like it.
Ciao T
* Adapted from Bob Marley "War"
Attachments
Hi,
Analysing the schematics of JC's Parasound designs I found them to use very high amounts of negative feedback. I queried this with JC who suggested that Parasound have specific commercial reasons to demand very low THD, so he leaves them running at "Max Feedback" against his personal experience. In my estimation somewhere in the 60dB++ region for models with Mosfet Drivers, 50dB+ for the ones with BJT Drivers.
By comparison the RB951 I estimate at 30dB NFB.
This together with a number of other factors that for your wife at least (as for myself) the inverse of the amount of global looped feedback forms an indicator of quality. You might try this by adjusting the open loop gain of HCA-1200 so that you have only 10 - 20dB Global loop feedback.
Or you might want to try an HK Amp. Seems they have stuck with their "low feedback" philosophy even in their latest models, the HK-990 (which measures totally horroshow# for an amp with only around 14dB NFB, as shown in the Stereophile review). Many earlier ones (the whole range measured by Dejan) also have less than 20dB looped feedback.
Why bother with that overpriced, underperforming and generic sounding crud?
I see nothing in the Revelator or Excel Dome tweeters to recommend them over any number of 1 USD/pcs (@ 1KU) Chinese OEM Softdomes.
Aragon and Krell look more similar than different, Levinson look more different than similar. IME non of them are worth the bother. In general I find most "American Muscle Amp's" quite amusical sounding and tend to prefer certain European and Japanese designs, if we must use solid state.
Try a Goldmund Mimesis 8 or 9 or a top of the range DNM Amp, or one of the dpa (UK) ones. These are IME among the best solid state I have had the chance to hear.
An outside bet, if you can find them are the Zeck (Germany) Bi-Mos range Pro-Amp's, but they must be "domesticated" (cut out all the Op-Amp balanced input circuitry and ratchet up the quiescent current a fair bit), this one I remember as uncommonly good sounding, I even used them at times at home to drive HiFi Speakers, specifically a Zeck A-402... Some of the Yamaha PA-Amp's where also quite good.
Ciao T
Analysing the schematics of JC's Parasound designs I found them to use very high amounts of negative feedback. I queried this with JC who suggested that Parasound have specific commercial reasons to demand very low THD, so he leaves them running at "Max Feedback" against his personal experience. In my estimation somewhere in the 60dB++ region for models with Mosfet Drivers, 50dB+ for the ones with BJT Drivers.
By comparison the RB951 I estimate at 30dB NFB.
This together with a number of other factors that for your wife at least (as for myself) the inverse of the amount of global looped feedback forms an indicator of quality. You might try this by adjusting the open loop gain of HCA-1200 so that you have only 10 - 20dB Global loop feedback.
Or you might want to try an HK Amp. Seems they have stuck with their "low feedback" philosophy even in their latest models, the HK-990 (which measures totally horroshow# for an amp with only around 14dB NFB, as shown in the Stereophile review). Many earlier ones (the whole range measured by Dejan) also have less than 20dB looped feedback.
Why bother with that overpriced, underperforming and generic sounding crud?
I see nothing in the Revelator or Excel Dome tweeters to recommend them over any number of 1 USD/pcs (@ 1KU) Chinese OEM Softdomes.
If someone would like to donate , oh say a Aragon, Krell, or Levinson, I would gladly see if our preference really is in favor of a deficiency, or just in favor of some design choices over others.
Aragon and Krell look more similar than different, Levinson look more different than similar. IME non of them are worth the bother. In general I find most "American Muscle Amp's" quite amusical sounding and tend to prefer certain European and Japanese designs, if we must use solid state.
Try a Goldmund Mimesis 8 or 9 or a top of the range DNM Amp, or one of the dpa (UK) ones. These are IME among the best solid state I have had the chance to hear.
An outside bet, if you can find them are the Zeck (Germany) Bi-Mos range Pro-Amp's, but they must be "domesticated" (cut out all the Op-Amp balanced input circuitry and ratchet up the quiescent current a fair bit), this one I remember as uncommonly good sounding, I even used them at times at home to drive HiFi Speakers, specifically a Zeck A-402... Some of the Yamaha PA-Amp's where also quite good.
Ciao T
That is a fair amount of 'second guessing' T, I would be happy if he just adjusted the voltage across the emitters at 22 mV or so. That would be a good start. Cap bypassing could be improved with Rel polystyrene or polypropylene across the power supply rails, while removing most of what is in there at the moment.
I agree that feedback is not necessarily a 'good' thing, but without getting the circuit properly adjusted, messing with the feedback will be relatively pointless. It will just increase the measured distortion, unless you up the open loop bandwidth at the same time.
The HCA 1200 is a relatively old design, about 20 years old. It is probably in need of a good 'clean-up' as well.
I agree that feedback is not necessarily a 'good' thing, but without getting the circuit properly adjusted, messing with the feedback will be relatively pointless. It will just increase the measured distortion, unless you up the open loop bandwidth at the same time.
The HCA 1200 is a relatively old design, about 20 years old. It is probably in need of a good 'clean-up' as well.
John,
Looking at the HCA range I might be tempted to degenerate the input stage a little (it is very low distortion though as is), but it is probably not needed, the VAS has massive degeneration already, so the frontend will already be quite linear.
Using the common techniques in reducing OLG increasing OLBW is unavoidable.
In fact I would recommend for an easy try to simply add a local loop from the VAS Output to negative input, this allows changing the feedback around the output stage in a wide range of amounts and with a little ingenuity can be used to also provide some VAS Loading at the same time. The GBWP stays the same in this case, but OLG is reduced, so bandwidth must increase.
This way tvrgeek could experiment easily with a range of ratios between global loop, inner loop and completely open loop gains and find if adjusting these ratio's affect his wife's perception of the problems.
In Push Pull Tube Amplifier with large amounts of overall negative feedback I found shifting this into a mixture of degeneration (input stage) and local loops (output stage anodes to driver stage grids, DC coupled) and completely ditching the global feedback loop gave very similar measured performance (THD and broadly for Damping Factor) in both cases but subjective improvements in sound quality where large.
I will have to try how much of this is applicable to solid state amplifiers, however I suspect the parallels are quite substantial.
Ciao T
Looking at the HCA range I might be tempted to degenerate the input stage a little (it is very low distortion though as is), but it is probably not needed, the VAS has massive degeneration already, so the frontend will already be quite linear.
Using the common techniques in reducing OLG increasing OLBW is unavoidable.
In fact I would recommend for an easy try to simply add a local loop from the VAS Output to negative input, this allows changing the feedback around the output stage in a wide range of amounts and with a little ingenuity can be used to also provide some VAS Loading at the same time. The GBWP stays the same in this case, but OLG is reduced, so bandwidth must increase.
This way tvrgeek could experiment easily with a range of ratios between global loop, inner loop and completely open loop gains and find if adjusting these ratio's affect his wife's perception of the problems.
In Push Pull Tube Amplifier with large amounts of overall negative feedback I found shifting this into a mixture of degeneration (input stage) and local loops (output stage anodes to driver stage grids, DC coupled) and completely ditching the global feedback loop gave very similar measured performance (THD and broadly for Damping Factor) in both cases but subjective improvements in sound quality where large.
I will have to try how much of this is applicable to solid state amplifiers, however I suspect the parallels are quite substantial.
Ciao T
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