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Good thread on diyaudio.com

119.72.193.241

Posted on August 2, 2015 at 04:12:41
kuribo
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http://www.diyaudio.com/forums/solid-state/277914-global-feedback-huge-benefit-audio.html

Some of the self-professed "scientists" and audio preachers might do well to check it out...

 

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Rod Elliott's treatise has available for years , posted on August 2, 2015 at 05:01:25
Feanor
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The crux of the matter is that negative feedback, in practice, causes high-order harmonic distortion. HOHD has be recognized as unpleasant sounding since Pythagoras.

Probably if feedback were truly instantaneous, no such distortion would be introduced. Rod Elliott's argument essentially relies on feedback be effectively instantaneous. However feedback is NOT quite instantaneous and the longer the loop, i.e. global vs. local, the longer delay and -- very likely -- the more distortion that results.




Dmitri Shostakovich

 

RE: Rod Elliott's treatise has available for years , posted on August 2, 2015 at 06:07:52
A.Wayne
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Disagree , Pythagoras was more concerned with output transformer hysteresis and its added colorations ..

 

RE: Rod Elliott's treatise has available for years , posted on August 2, 2015 at 07:10:07
rick_m
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"if feedback were truly instantaneous, no such distortion would be introduced"

You've nailed it. If the amplifier had infinite GBW (gain-bandwidth) then there would be no residual distortion products (well, except for imperfections in the passives...). But since that's an unachievable limit why not just simplify the dream and directly specify 0% distortion? It's every bit as achievable.

Fortunately the ear-brain system also has finite resolution and bandwidth so audio systems don't really have to be perfect, merely good enough that we don't notice the residual distortions.

Rick

 

Did so long ago, posted on August 2, 2015 at 07:47:27
E-Stat
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Pretty funny guy

Measurements of high order behavior found here.






 

Calvin said it best..., posted on August 2, 2015 at 07:51:13
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A huge benefit for...

 

RE: Good thread on diyaudio.com, posted on August 2, 2015 at 10:23:08
Palustris
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"Some of the self-professed "scientists" and audio preachers might do well to check it out."

It makes sense for anyone who is curious about the effects of feedback on a circuit to investigate for themselves. Build a circuit and employ different types and levels of feedback to understand the technique. That's what the hobby is about, searching for one's own "audio truth."

Those who simply want to deal in absolutes (feedback is good; feedback is bad) are nothing but trolls. There are numerous ways to implement feedback and each circuit topology reacts differently to the various types of feedback. Any assertion that feedback is "good" or "bad" reveals the lack of technical understanding of the individual making the assertion. Engineering deals with variables and when the subject of feedback is raised there are many many variables; any talented audio engineer is perfectly aware of this and employs the techniques necessary to reach his goals.

 

RE: Good thread on diyaudio.com, posted on August 2, 2015 at 14:30:04
triamp
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It's true that negative feedback is not INSTANTANEOUS. It takes about 0.00000000007 sec for the signal to propagate through the loop, give or take 0.00000000002 sec. And you think you can hear that....

Negative feedback might have positive or negative effects on sound quality, it all depends on how it is applied. To make a blanket statement that "negative feedback is bad" is ill-informed.

There is ONE blanket statement that can be made about zero-feedback amplifiers - they are trendy right now. They are the Kim Kardashians of audio :-)


One technique that has been used by several well-regarded amp builders is to use a very linear output stage - class A is often employed- but then to avoid all negative feedback around that stage. This imparts a "tube like" harmonic profile to the residual distortion, which many find "involving" or "musical" in the resulting sound. This is not so much avoiding the "bad sound of negative feedback," as it is a way using a design that ADDS EUPHONIOUS COLORATION. It is- in essence- like a TONE CONTROL. If you want an amplifier that is a tone control, that's great. For a guitar amp - where the amplifier is part of the instrument- that might be highly desirable. For playback system electronics, not so much.

I've seen this method used with solid state designs where the output stage is designed and built to be VERY VERY linear without any negative feedback, and so the residual distortion is really very slight. This takes some doing- very careful design and close matching of parts. It's not a bad choice- a very low distortion amplifier where the designer opts for a less objectionable form of residual distortion. That's not so much a "tone control" or purposeful introduction of euphonious distortion as it is a rational design choice.


Science doesn't care what you believe.

 

Bingo! Couldn't agree more....nt, posted on August 2, 2015 at 14:57:25
kuribo
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Nt

 

RE: Good thread on diyaudio.com, posted on August 2, 2015 at 15:17:53
E-Stat
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Any assertion that feedback is "good" or "bad" reveals the lack of technical understanding of the individual making the assertion.

Agreed as it is a matter of degree, if found necessary. Minimal amounts of local feedback can provide circuit stability and lower output impedance.

On the other hand, high levels have been long proved to be disastrous for sound quality. There were many designs in the 70s that sounded horrible (yet measured great) using high levels of corrective feedback.

Does anyone know of an current amp which uses high levels of feedback (to correct inherently non-linear behavior) that sounds like music?

 

You seem quite lucid , posted on August 2, 2015 at 16:01:25
E-Stat
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for being 512 years old as your profile indicates. :)

 

What does "sounds like music" mean? That is entirely subjective..., posted on August 2, 2015 at 16:07:25
kuribo
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Many have found the Putzeys designs excellent and he has stated his position on feedback clearly. Of course he has also stated that first one designs the amp to be as linear as possible-not a common practice among designers in the "distortion wars". A common oversight among those who like to generalize.

 

RE: You seem quite lucid , posted on August 2, 2015 at 16:08:04
triamp
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Science doesn't care what you believe.

 

That's what, posted on August 2, 2015 at 16:27:03
E-Stat
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512 year old guys do, right? :)


 

Are there any, posted on August 2, 2015 at 16:29:21
E-Stat
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speaker companies that use the Putz amp to demonstrate their product at shows?

 

Do your homework... Google Kaluga, veritas, astah, etc. nt, posted on August 2, 2015 at 16:43:49
kuribo
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Nt

 

Maybe you're not understanding the question, posted on August 2, 2015 at 17:21:46
E-Stat
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Kaluga is one of Mr. Putz's designs.

Veritas is mid-fi Klipsch.

Astah? Hmmm. Google doesn't find them.

Would you like to clarify your post a bit with actual data? :)

 

I find your reference to Bruno as "Mr. Putz" disrespectful and immature..., posted on August 2, 2015 at 17:37:39
kuribo
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I see no point in continuing this dialog any further. Grow up.

 

What I was looking for is, posted on August 2, 2015 at 17:45:08
E-Stat
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something like this:

Wilson and VTL

Nola and Audio Research

Usher and Pass Labs

 

RE: Good thread on diyaudio.com, posted on August 2, 2015 at 19:18:32
Caucasian Blackplate
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"Those who simply want to deal in absolutes (feedback is good; feedback is bad) are nothing but trolls."

Not every person with an opinion should be considered a troll.

Designing without GNFB is an added challenge on top of what might otherwise be much easier. I would say that the real trolls are those who hide behind their measurements in defense of their election to just keep using negative feedback until the measured performance in various aspects ceases to improve.

 

RE: Good thread on diyaudio.com, posted on August 2, 2015 at 20:15:11
hahax@verizon.net
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It's usually easy on amps to tell which amps use lots of NFB. They're the ones with very high damping factors which is usually needed to get high damping factors. I'll add it's interesting to know damping factor at both middle and extreme frequencies. If it's much worse at the extremes that means the open loop response(without NFB) is poor and the NFB is being used to make a poor amp seem good.

 

RE: negative feedback , Static and low self esteem , posted on August 2, 2015 at 21:26:59
A.Wayne
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Class-D amplifiers in relation to negative feedback and its application of is not the same when compared to conventional amplifiers, can't see why lunchbox is attempting to deride Bruno Putzeys, a very accomplished designer by any measure.

Anyway , which amp manufacturer uses soundlab speakers to demonstrate their wares? I cant recall seeing them anywhere ...


Regards

 

RE: What I was looking for is, posted on August 3, 2015 at 01:25:14
morricab
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I have heard the mola mola at a couple of shows with Lansche Audio speakers (they use a plasma tweeter) but not to great effect. The sound was quite unsatisfying considering how good Lansche speakers are. I have also heard Lansche speakers with a pair of Kronzilla stereo amps (bi-amped) and it was gobsmackingly good. Not the same effect from the mola molas...no surprise there really either.

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 01:34:00
morricab
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what exactly in your opinion makes Bruno an accomplished designer?? Have you heard his latest efforts? Mediocre I would say. His early Hypex UcDs?? Horrible...unlistenable. If this is what qualifies as "accomplished" then I will take an "unaccomplished" designer anyday.

Soundlabs are hard on amps with a lot of negative feedback...tend to make the amps unstable because of the very high capacitance and back EMF (nearly 100% of what goes in comes back out...albeit pretty scrammbled up). Also, the large impedance swings (from very low to very high) makes many trnasistor amps sound thin on such speakers because the midband is where the impedance is high so it gets emasculated. OTLs are promising but they can be unstable too because they usually use feedback (some that don't work well on big Electrostats).

I had big Acoustats and two different OTLs, neither of which was happy and one actually oscillated so badly I had to rush to shut them off before something bad happened.

So, they are not the ultimate tool for demoing with most manufacturers amplifiers because of these issues. With the right amps though there is not much out there that is better...maybe nothing.

 

RE: What does "sounds like music" mean? That is entirely subjective..., posted on August 3, 2015 at 01:39:43
morricab
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"Of course he has also stated that first one designs the amp to be as linear as possible-not a common practice "

That is not really what he is doing. He has an amp that actually won't even function properly without negative feedback and then loads it up with as much as the design can take...this is not "designs the amp to be as linear as possible".

A designer who has to choose each part and signal path layout and power supply transformer and circuit design choice with an eye for interactions that lead to higher distortion and to minimize those without just wrapping it all up in negative feedback is doing what Putzey's claims.

THis is what many the best SS and tube amp designers do and then they find that adding negative feedback actually DEGRADES the sound, despite what the test bench says. This belief that the test bench tells the truth is misleading. It tells a truth devoid of human input but it does not tell a Human truth, which is the only one that truly matters...at least to humans.

 

RE: +1 nt, posted on August 3, 2015 at 01:40:42
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nt

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 02:16:21
A.Wayne
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Morri,

Just because you dont care for the sound of class-D doesn't make BP less of a designer and the last time i looked Ohms law did apply to both tooby amps as well as SS and as you know , toobs are subjected to Frequency aberration at their outputs due to speaker load and phase angles more so than SS .


The reason I dont have ESL's anymore is because I'm no longer a fan of the Big "capacitor "sound, I'm sure my decision doesn't make the Sound Lab designer "stupid" or an ESL speaker bad , just makes it not my cup of tea , it would be easy for me to say i prefer the near perfect resistor load of a pure Ribbon , but that kind of generalization would lead to Static type conclusions .


Regards

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 05:31:33
morricab
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Since sound quality is all that matters in the end if I think BPs amps don't sound good then I think he is not a great designer because he has fundamental flaws in his approach to amp design, IMO. He is obviously a clever designer to get that crap to work, but being clever is not what makes one great...getting great sound makes one great in this field. There have been a lot of clever guys making interesting circuits that simply were a big fail in the sonic department (Halcro for example??). You guys define greatness simply if the guy in the here and now has a bit of a name for himself. If someone is talking about him or his designs in 30 years then maybe he was on to something.


" last time i looked Ohms law did apply to both tooby amps as well as SS and as you know , toobs are subjected to Frequency aberration at their outputs due to speaker load and phase angles more so than SS"

Sorry, A. Wayne, I thought you were more sophisticated than this. You are stuck in the kindergarten of sound if you believe this is the main reason the two types of products sound so radically different.

I can apply equalization to a tube amp to make it measure exactly like the SS amp and they will still sound nothing alike. What does this tell me?? That the FR of an amplifier is largely UNimportant. It is not the main driver of the character of the amps sound.

I have demonstrated this many times with speakers but the same holds true for amps. FR is not terribly important, non-linear distortions are. Make two speakers measure the same in-room and still have totally different sounds. Same is true for amps. A digital eq (digital in and digital out) is quite useful for such experiments.

"i prefer the near perfect resistor load of a pure Ribbon , but that kind of generalization would lead to Static type conclusions "

For sure a resistive load will be kinder to all amps, even if it is somewhat low impedance. However, if you were not mating the right kind of amp to your electrostats that might explain why you were not smitten with the sound. Once I hooked up no negative feedback amps to electrostats they sang like angels. No negative feedback means no back EMF corruption of the signal through the feedback loop and no amp stability issues. One just has to make sure that the amp can supply the current needed.

As I said I have heard Scintillas sound amazing with a tube amp tailored to deliver power into 1 ohm. It had no negative feedback as well and drove the Scintillas to more than acceptable levels while sounding great. Into the much easier to drive Studio Grands it was outclassed by a KR Audio VA350i, which could not get more than a whisper from the Scintillas (no surprise but we tried anyway for fun).

 

Exactly!, posted on August 3, 2015 at 05:41:18
E-Stat
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... which is usually needed to get high damping factors.

Those are the ones I avoid. :)

 

Actually, posted on August 3, 2015 at 05:52:31
E-Stat
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Also, the large impedance swings (from very low to very high) makes many trnasistor amps sound thin on such speakers because the midband is where the impedance is high so it gets emasculated.

While that may be true of single transformer designs like Quad, Sanders, ML, etc., such is not the case for Sound Lab where it is highest in the bass.

 

Yeah, posted on August 3, 2015 at 05:58:21
E-Stat
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I found the same also to be true of the Halcro amp as you observed. Clearly, Putzeys like Candy is committed to using high levels:

"And if you get to very large amounts of feedback, the result is just supersmooth. So that is why I say that it is normal for an experimenter to experience that if you take a good-sounding zero-feedback amplifier and add 6dB of feedback, the result sounds worse. They heard that right. But had they been in a position to add 60dB, well then, suddenly they would have been confronted with a sound that is little short of magical."

60 db of correction? Otay!

Soundstage! interview

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 06:19:13
E-Stat
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Anyway , which amp manufacturer uses soundlab speakers to demonstrate their wares?

There are few companies I suspect largely because of size and cost. The amplifiers that are happy driving reactive loads are relatively few.

Ralph Karsten has used them with his amplifiers before as did Ray Kimber when he wanted to showcase his Isomike recordings. He used six and quad pair versions for years at RMAF and at CES using Pass Labs amplification, a natural match. Early Threshold amps were frequently used with Dayton-Wright electrostats in the 70s.

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 07:25:47
A.Wayne
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Morri,

You are putting words in my mouth , i responded to your " kindergarten logic" about impedance swing and SS by pointing out to you toobs are the ones most affected by speaker impedance and phase, you were the one who brought it up ...

The Apogee scintilla may have been 1 ohm but the impedance and phase is pretty close to a pure resistor , mostly their low sensitivity is what makes them a amp breaker and with matching transformer their is no huge current demand from toob or SS amp , only DC Amplifiers will have this issue of current supply , of course output transformers bring other issues to the table ...


Regards

 

RE: negative feedback , Static and low self esteem , posted on August 3, 2015 at 07:36:21
A.Wayne
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If using Output transformers then i prefer the amp to be toob than SS . You are wrong about BP , I have spoken privately to many known amd rated designers who think he is doing fantastic work in the his area of expertise , many themselves are looking very closely at what he does , mostly it seems , the next real break thru will be with the SMPS and associated noise.


A pity your dogma keeps you from looking outside your box ..

 

RE: Good thread on diyaudio.com, posted on August 3, 2015 at 08:05:55
b.l.zeebub
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So in dB how much is 'minimal' feedback and how much would you say is a lot?

 

You may (inadvertantly?) be onto something., posted on August 3, 2015 at 08:29:30
rick_m
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"I would say that the real trolls are those who hide behind their measurements in defense of their election to just keep using negative feedback until the measured performance in various aspects ceases to improve."

First, let me be very clear: Anyone who eschews measurements on a philosophical basis is a lame brain in my opinion. OK! That being said I ALSO believe that anyone who clings to measurements past the point where they correlate with final performance is spinning their wheels.

THD is a veeeeery old measurement and in it's day had a decent corrolation with perception because the ol' tubes and transformers didn't have much oomph so the output power before clipping was pretty important. THD was essentially a way of quantifying where clipping began as unscrupulous marketeers would measure their output power when all that was left of the signal was a square wave. On top of that it was easy to measure, it just took an oscillator, a passive twin-tee notch filter and a voltmeter.

Ahhh, tradition! But time and technology march on and now we have many new and improved ways to generate, measure, fudge and argue about distortions. Perhaps the most lasting legacy of THD is that it's ensconced in many specifications and standards and of course the hearts and minds of audio fanciers. If we did nothing more than only count the odd-order products (easy in the FFT age) it would prolly be a big help....

Rick

 

Judgement call, posted on August 3, 2015 at 08:45:00
E-Stat
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I would say 60 db of global is a lot! I can think of several designs using 10-15 db.

 

RE: Judgement call, posted on August 3, 2015 at 10:04:58
b.l.zeebub
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10-15dB is a bit less than Nelson Pass uses in his designs.

 

agreed, it IS the time domain smear that marrs the clarity in a recording venue... via Global feedback..., posted on August 3, 2015 at 10:32:21
Cleantimestream
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and to a lesser extent, local feedback.

Fast Fourier analysis clearly shows this happening.

The guys with inefficient speakers and huge amps {most using feedback} simply cannot hear this because the resolution is inferior.

Make no mistake, the signal slogging through a passive crossover is just as bad, hence electronic crossovers being superior.

Lastly, the room is the most vital and influential factor for Music.
The Mind has No Firewall~ U.S. Army War College.

 

RE: agreed, it IS the time domain smear that marrs the clarity in a recording venue... via Global feedback..., posted on August 3, 2015 at 11:26:31
A.Wayne
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Inferior resolution to what, live music ...? Agree

 

Some local, yes, posted on August 3, 2015 at 11:46:06
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No global feedback is used.

 

RE: Some local, yes, posted on August 3, 2015 at 12:01:22
A.Wayne
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Depends on design goals , one thing for sure ypu can't pour tons of feedback on an unstable amplfier , open loop gain has to be stable to pour on NFB like that ..

Regards

 

Sorry, posted on August 3, 2015 at 12:11:03
E-Stat
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My ears don't buy his Kool Aid.

Nor do many other designers for that matter.

Enjoy the sterile results. :)

 

RE: Some local, yes, posted on August 3, 2015 at 12:11:09
b.l.zeebub
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You know Nelson is a member at diyaudio and participated in the thread linked to.

 

I'm delighted to see he joined the conversation, posted on August 3, 2015 at 12:40:07
E-Stat
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after the OP. And has some wise words to add:

" The more linear the amplifier, the better feedback works, but also the less need for it. Basically Bart Locanthi's point back in 1966. "

Indeed, the more linear the amplifier, the less the need for it. And he applies it locally to a single stage as opposed to globally across cascaded stages as is typically done.

Don't know about you, but I find a big difference between 15-20 db and 60 db - a hundred times more so! :)

 

RE: Sorry, posted on August 3, 2015 at 13:09:27
DrChaos
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The meaning and consequences of feedback are completely different in a class-D architecture.

I wouldn't necessarily extrapolate experience from AB amplifiers. From the descriptions the class D systems are much more like nonlinear dynamical control systems, where proper modeling and control law dynamics is very important.

 

And yet, posted on August 3, 2015 at 13:18:13
E-Stat
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The meaning and consequences of feedback are completely different in a class-D architecture.

I hear the same manifestations using that approach with either design as does Brad. The Halcro being a perfect example of an AB design that sounds like a switcher. Smooth and *detailed* perhaps, but harmonically sterile and unnatural sounding to these ears.

To each his own.

 

RE: I'm delighted to see he joined the conversation, posted on August 3, 2015 at 13:31:58
b.l.zeebub
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Indeed.

Personally however I couldn't care less about feedback and I have no idea how much my amps use.
All I care about is that they are the most transparent ones I've come across so far.

 

RE: "harmonically sterile", posted on August 3, 2015 at 13:36:27
b.l.zeebub
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What does that even mean?

To me it reads as 'lacking euphonic distortion' but that can't be it, can it?

 

RE: "harmonically sterile", posted on August 3, 2015 at 13:41:20
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I can think of many (unamplified) instruments that have a rich and characteristic harmonic envelope.

A piano. A cello. A French horn.

The best audio gear is able to replicate that complex harmonic structure in its entirety.

Those that cannot sound sterile and lacking in realism to these ears, regardless of how *clean* the sound may be.

 

RE: "harmonically sterile", posted on August 3, 2015 at 13:52:33
b.l.zeebub
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So there are amps which fail to amplify certain parts of the input voltage?

 

You got me, posted on August 3, 2015 at 13:54:18
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I'm telling you what I hear.

 

Comparative numbers, posted on August 3, 2015 at 14:15:40
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The MC450 reports a DF of 400 which falls into the moderate camp in terms of SS amps.

By comparison, the Mola Mola Kaluga's is 4,000 and the Crown Studio Reference is a whopping 40,000!

 

RE: Sorry, no one is selling ..., posted on August 3, 2015 at 14:40:38
A.Wayne
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Are you Buying something .... ?

 

RE: I'm delighted to see he joined the conversation, posted on August 3, 2015 at 14:43:44
A.Wayne
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after the OP. And has some wise words to add:

" The more linear the amplifier, the better feedback works"

- E-Stat



I just told you that to correct your instability statement made before .....

 

RE: And yet Halcro , posted on August 3, 2015 at 14:47:22
A.Wayne
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I don't get this Halcro , Halcro , strawman argument , if you look at Halcro bench measuremts there are issues , so bad argument against ..


Distortion is present in everything we hear so distortion onto itself is not our only target , if zero feedback was the answer no one would be using it , fact is , one mans Euphoria is another's anathema , there is no one answer for all ...

Regards

 

RE: And yet Halcro , posted on August 3, 2015 at 14:57:50
E-Stat
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... if you look at Halcro bench measuremts there are issues

Interesting. That's certainly not John Atkinson's opinion:

"As I have come to expect from Bruce Candy designs, the dm88 offers superb measured performance."

What do you find problematic?

Here's the data.

 

RE: Good thread on diyaudio.com, posted on August 3, 2015 at 14:58:12
SETdude
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Arm chair geniuses. :-)

 

RE: And yet Halcro , posted on August 3, 2015 at 15:04:25
A.Wayne
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There are issues , obvious issues glossed over by John , poor psu is one , i will review again and put up for discussion ...

 

We will look forward to your, posted on August 3, 2015 at 15:09:41
E-Stat
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providing some substance.

 

RE: And yet Halcro , the ultimate strawman , posted on August 3, 2015 at 15:23:16
A.Wayne
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D1.
The dm88's voltage gain was a higher-than-average 29.4dB into 8 ohms via the unbalanced Voltage Mode input; unusually, it dropped by 6dB, to 23.4dB, using the balanced jack.


2. The unbalanced Voltage Mode input impedance was a little higher than usual for a solid-state design, ranging from 25k ohms at 20Hz to 22k ohms at 1kHz, though it dropped further, to 17.5k ohms, at 20kHz. The balanced input impedance was exactly twice the unbalanced, as expected. However, the Minimal Path input had a very low impedance of 650 ohms across the audioband. As well as explaining the slightly lower voltage gain via this input, this low input impedance will be incompatible with many preamplifiers, especially those using tubed output stages.


3. The measured output power at 1% THD+N was greater than specified, at 295W into 8 ohms (24.7dBW) and 525W into 4 ohms (24.2dBW). The dm88 is less happy driving 2 ohms, however, clipping at 266W (18.2dBW).


Theres more but who has the time to keep feeding your strawman , you should read the review sometime , the Halcro has only low thd going for it , IMO it was never a good Sota amplifier, in actuality , its a toy ...

Regards

 

???, posted on August 3, 2015 at 15:33:25
E-Stat
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1. So the gain dropped using a balanced connection. And?
2. Actually, there are many SS amps with higher impedance. That's good. Don't use the minimal path input for the stated reason. And?
3. It's horrible when the output is higher than specified. And?

JA would simply shake his head and smile. Like I'm doing now.

 

RE: ???, posted on August 3, 2015 at 15:38:57
A.Wayne
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Lol,

Obvious why you keep pushing your circular arguments , you are clueless , have poor comprehension and full of Dogma ....



Go play somewhere else , not interested ,

 

RE: "harmonically sterile", posted on August 3, 2015 at 16:02:48
mkuller
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...these tend to be solid state amplifiers which emphasize the transient attack of the note but cut off its decay and the harmonic overtones with it.

While tubed amps may have more low level harmonic distortion, they don't cut off the decay and instruments have more of the realistic harmonic "bloom".

Which is what many people familiar with live, unamplified music prefer.

Neither is free of distortion - as I've described,the distortions just manifest themselves differently to the ear.

Personally, I can't listen to music with what I hear as solid state distortion long term.

 

If you'd like to engage John Atkinson, posted on August 3, 2015 at 16:43:58
E-Stat
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over the "obvious issues glossed over by John , poor psu is one"

He can be reached readily over at Critics Corner.

 

RE: If you'd like to engage John Atkinson, posted on August 3, 2015 at 17:42:26
A.Wayne
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Thanks for the tip, i did like toobs on my Soundlabs , it did help to add meat to its thinny sound and lack of percussive energy . after much effort it was just not delivering the goods , maybe the newest ones are less colored , i should ask John ...

 

Do ask him , posted on August 3, 2015 at 17:52:16
E-Stat
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about his "glossing over obvious issues" with the Halcro measurements.

 

RE: Do ask him , posted on August 3, 2015 at 23:41:33
A.Wayne
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Sure , no problem and you ? Best to remind him about your views on BP and class-D , write all you know , your last thesis on amplifiers barely filled the back of a business card ...

 

RE: Do ask him , posted on August 3, 2015 at 23:47:48
A.Wayne
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Take 2 business cards , ask him about this one dont forget to mention your thoughts on BP...


I am always leery of measuring class-D amplifiers—their performance can be, shall I say, idiosyncratic. But no excuses need be made for MBL's Corona C15. This is an impressively well-engineered amplifier.—John Atkinson

 

RE: You may (inadvertantly?) be onto something., posted on August 4, 2015 at 01:58:36
morricab
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"THD is a veeeeery old measurement and in it's day had a decent corrolation with perception because the ol' tubes and transformers didn't have much oomph so the output power before clipping was pretty important"

This is not really true. The correlation with THD is not too bad when there is no negative feedback applied to the amplifier and the circuitry from the amps on test are similar. Back when SET was about the only game in town then it was somewhat meaningful. Add push/pull (which partially cancels out the even harmonics) and add negative feedback and the correlation with the total breaks down. Power is not at issue and clipping sounds bad no matter what amp (although duration of clipping and recovery from clipping ARE important).


"If we did nothing more than only count the odd-order products (easy in the FFT age) it would prolly be a big help....
"

Look at what was proposed by D.E.L Shorter in the 1940s where he weights each harmonic to be progressively more important. Even that was found not to be sufficient by Cheever and others who have found the ear/brain subjective response is far more non-linear than Shorter supposed.

BTW, just for fun I computed the impact of harmonics from Shorter's equation (as inadequate as it is) on many amps from published data (the best being in stereophile and soundstage) and found that the amps that were often the best after application of the equation were low to no feedback designs and a couple of SETs! Does it mean they sound better? I think so...

 

RE: I'm delighted to see he joined the conversation, posted on August 4, 2015 at 02:00:31
morricab
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"And he applies it locally to a single stage as opposed to globally across cascaded stages as is typically done.
"

Crowhurst demonstrated that this has the same effect in the end so it is a fallacy to assume it is better.

 

RE: Do ask him , posted on August 4, 2015 at 02:10:27
morricab
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Not that impressive...

 

RE: Do ask him , posted on August 4, 2015 at 02:16:19
morricab
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Also not that impressive. See the resonance in Figure 1 just outside the audio band? Note also Figure 2 with the measurement filter, lots of ultrasonic garbage riding on the square wave. Not also the distortion harmonics and IMD looks messy as well. The only good Theta amp I ever heard was the original Dreadnaught that was designed by Charles Hansen of Ayre fame.

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 02:43:49
morricab
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Dogma? I have no dogma. I have been about as open to trying new things as anyone on this forum...including Class A SET amps ;-). You should try it some time. How many Class D amps have you owned? I have owned three different ones (hypex based, Ice based and PS Audio). I have friends who have owned several others. I give them a listen (usually it is short because of the mediocre sound) at every show I attend.

Same for SS amps. I have had Class A, AB, H (or whatever Carver amps were), negative feedback , positive feedback, low feedback, high feedback.

Same for hybrids: Class AB, Class A, low feedback, no feedback, SINGLE ENDED!!

Had OTLs as well (two types) both were Class AB of course.

The only type of amp I haven't tried yet is single ended OTL and I only know of a couple makers out there (Transcendent Sound and Accuhorn).

In the last 4 years I have had a no global feedback Class AB SS amp (BAT VK200), a Class AB hybrid with low feedback (Einstein "The Absolute Tune"), Class D monoblocks (Hypex based with linar power supply), two Class A Push/pull triode amps (VAC 30/30, Pure Sound A30), two single ended hybrids (KR Audio VA350i and NAT Symbiosis SE), a 300B parallel SET (JJ 322) and a pair of 6C33C based parallel SETs (Wall Audio M50s).

Prior to that I was many years with KR Audio and before that with Sphinx hybrid push/pullers. Along the way some other SETS (Cary CAD572se for example).

Does that look like the resumè of someone who is dogmatic? One thing I found is that A) no feedback sounds best and B) SET sounds better than push/pull. Of course this is assuming that the amp is not in distress driving the speaker.

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 02:46:41
morricab
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"mostly their low sensitivity is what makes them a amp breaker "

It is referenced to an 8 ohm watt so it is not really as low as you are claiming as long as the amp in question can deliver sufficient current. 100 1 ohm watts are sufficient to get it quite loud without audible strain...I can attest this from experiencing it first had with a tube amp specifically designed for a 1 ohm load and 100 watts into that 1 ohm load.

 

RE: Yeah, posted on August 4, 2015 at 02:48:27
morricab
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Well, I don't know if you have heard any of Putsey's new Ncores but I have and the sound was far from "magical". An all Kondo system with top notch horns will do "magical" pretty nicely as will some large electrostats with the right amp.

 

Your opinion in in the minority....and no more meaningful than anyone else's...., posted on August 4, 2015 at 03:25:41
kuribo
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Sorry, Audio Taste Arbitor, your opinions mean ziltch....

 

Unlike here, most of the posters on diyaudio actual have practical experience and techinical knowledge..., posted on August 4, 2015 at 03:28:38
kuribo
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I value those opinions over those of the psuedo scientistics and half truth parrots seen here all too often...

 

Your opinion is valid only for you. Many others disagree, which is only natural, posted on August 4, 2015 at 03:34:31
kuribo
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since audio preferences, like all other things subjective, are a personal matter of taste. There is no universal best. Get over it.

 

You haven't a clue as to what Bruno Putzeys is doing with his amp designs...nt, posted on August 4, 2015 at 03:37:06
kuribo
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nt

 

Too bad as you seem too enchanted by tube coloration to appreciate the truth...nt, posted on August 4, 2015 at 03:38:42
kuribo
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Not everyone appreciates them but judging by the reviews coming in, they are indeed something special to many...

 

I'm having trouble locating this reference, posted on August 4, 2015 at 06:13:24
E-Stat
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would you care to cite this assertion?

What I find in the 1956 High Fidelity Circuit Design seems to suggest the contrary:

"Another feature detracting from the advantages of overall feedback is its effect on output hiss and other noises generated in all high gain amplifiers...All these disadvantages of overall feedback can be overcome by restricting the number of amplifier stages over which feedback is applied....Applying inverse feedback from the output over not more than two stages-and preferably only as far back as the driver stage-will prevent instability troubles with changes in the output load."

 

RE: Do ask him , posted on August 4, 2015 at 06:31:06
E-Stat
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Sure , no problem and you ?

I don't share your assertion JA "glossed over" anything nor provides a "straw man" argument that the Halcro measures well - at least using conventional metrics.

It does.

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 06:52:38
A.Wayne
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I was disappointed by my VK500 , SET 's limit speaker choices , but agree they are best when discussing toobs. Hypex is not NC1200, so no comments until i hear the Rowlands , i did like the Devialet setup when i heard them (400/400) the owner told me he was disappointed until he went to the full mono package ...


 

As do I, posted on August 4, 2015 at 06:56:18
E-Stat
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I enjoy reading the comments of well known designers like John Curl, Ralph Karsten and Nelson Pass.

Their products speak very well for them.

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 07:04:00
morricab
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I only heard the Devialet in stereo mode of course...most are not buying two of them. I have heard the original, the 110 and whatever the next model up is (200?). They are never disastrous like some of the Class D I have heard and if you only ever heard somewhat midfi SS or budget tube amps I can see how you might think it is the best things since sliced bread. Even against better SS and many push pull tubers I can still see the appeal. BUT, it is easily beaten with regard to getting the tone of instruments correct and that for me is the major let down. Smoothness, power, transparency etc. are there but tone is not. Instruments sound bleached out compared to the real things.

 

RE: Your opinion is valid only for you. Many others disagree, which is only natural, posted on August 4, 2015 at 07:05:36
morricab
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Many more do not...get over it preacher man!!

 

RE: Your opinion in in the minority....and no more meaningful than anyone else's...., posted on August 4, 2015 at 07:07:16
morricab
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Take a walk around the shows and you will see that it is not the case. Many more top class tube gear now than ever before, most of the Class D hype has died away...if representation at the shows is any indication.

 

RE: Too bad as you seem too enchanted by tube coloration to appreciate the truth...nt, posted on August 4, 2015 at 07:11:03
morricab
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The fact that you make such statements means you clearly didn't look closely at the MBL Corona and Theta amp using Putzey's modules. There is plenty of coloartion lurking in there...none of which is consonant with natural sounds.

 

RE: "harmonically sterile", posted on August 4, 2015 at 07:47:45
b.l.zeebub
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Despite being very familiar with live, unamplified music from working for and touring with a leading opera company, time spent in recording studios and a friends in an acoustic bands I have never heard what you describe.

On the contrary my SS amps play substantially more of the decay than tube amps due to a much better SN ratio.

However the times I have heard tube amps in a replay chain they tended to add a kind of artificial 'bloom' which does not exist in the original recording.
Great for guitar amps and such like when they are effectively part of the instrument but very annoying in a stereo system.

 

RE: You may (inadvertantly?) be onto something., posted on August 4, 2015 at 08:39:29
rick_m
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"This is not really true. The correlation with THD is not too bad when there is no negative feedback applied to the amplifier and the circuitry from the amps on test are similar."

WELL! How dare you say something like that, especially when you're right...

I still see it as a dynamic issue however it IS more subtle than just clipping. If you look at the plate curve on your curve tracer or in a manual it's pretty easy to see where the transfer Fn. is the most linear so if you bias to that point small signals are pretty clean (If your plate-VC transformer isn't very saturated...). But as the signal increases so does the distortion.

I think it probably helps that that's a "natural" form of distortion progression as our ears themselves become more distorted with increasing SPL. Poor ol' push-pull is at it's worst just where our sensitivity is the most keen.

Rick

 

RE: "harmonically sterile" vs artificial Bloom , posted on August 4, 2015 at 09:32:10
A.Wayne
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Correct , the artificial bloom is what most enjoy , especially with SET's , most of the sterile sound associated with SS are due to poor speakers and source equipment , they are not as forgiving as their toob counterparts.


Irony is thinking any of it aproach Real , if none does , which is right ? Precisely why there are so many options , the science tells us individuals will choose whatever listening cues triggers them into believing real , everyone is different hence the many options , as to the issue with my Soundlabs , i never felt it sounding real and i still do find large panel speakers truncate instrument decay and weight , obvious when you hear them , so best to pair them with electronics which "blooms" ...


Hence the Toob Mantra



Regards

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 09:34:34
A.Wayne
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Devialet ..


Morri you heard an early version please try and listen to a current software version and mono's , everyone i spoke to even those who owned them had an issue with those ..

 

RE: "harmonically sterile" vs artificial Bloom , posted on August 4, 2015 at 09:45:08
mkuller
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...ask John Curl which sounds more like music to him.

The answer is tubes (which is why he prefers to design with j-FETs rather than bi-polar transistors).

Everyone responds to ss and tube distortion differently.

There is no "right", only personal preference.

 

RE: You may (inadvertantly?) be onto something., posted on August 4, 2015 at 10:13:38
morricab
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Interesting points. Cheever noted that the natural harmonics your ear makes change with amplitude so the amplifier in question would have to mimic these changes with different level as well.

What this means is that the sensitivity of the speaker matters because if an amp is making a constant pattern regardless of level (may or may not be true) then that pattern will be right for some levels and not for others. So an amp that is really good at low levels if made to work, even if it is not clipping, might be making a pattern that is more audible. I would guess that SETs are at their best when making a watt or two or less so a sensitive speaker with an easy load will allow them to shine. Some might actually do better though in a more demanding speaker. As the level rises though our sensitivity to these things drops as well.

"I think it probably helps that that's a "natural" form of distortion progression as our ears themselves become more distorted with increasing SPL. Poor ol' push-pull is at it's worst just where our sensitivity is the most keen.
"

Exactly, monotonic series seems to be the best (since true zero distortion doesn't seem to be an option at this point) where you get a drop in level with each progression in the harmonic series (exponential decay). If odds are equal to evens or odds dominate this is not a natural progression in nature or the ear/brain's own harmonics.

You know, I have had some pretty nice push/pull amps but there was something missing that was hard to describe once I went away from SET I had to come back again.

I recently had a Pure Sound A30, which is Class A, and in triode mode and at moderate to kind of loud levels it was very good and lives up to the reputatoin of giant killer. However, I found that for late night low volume listening and for quiet dialogue it was clouding up the sound. My JJ 322 sounds much clearer at the low volumes I often have to listen. If I was listening all the time loud I would say it was not too far behind and given the price I think it is still a great little amp.

My Sphinx Project 14 mKIII was better but still sounded broken compared to the KR Audio Kronzillas I had for review some years ago. It wasn't even close...

The VAC 30/30 was one I probably should have kept though. It was pretty darn nice sounding but still not as "whole".

 

RE: negative feedback , Static and low self esteem , posted on August 4, 2015 at 10:49:23
morricab
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Heard two more recent verions as well or did you not catch that?

 

RE: You haven't a clue as to what Bruno Putzeys is doing with his amp designs...nt, posted on August 4, 2015 at 10:52:37
morricab
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Do you honestly believe his amp is "as linear as possible" before he adds 60, 70, 80db of negative feedback?? Distortion is probably nearing 100% without it.

 

Would you care to comment on this:, posted on August 4, 2015 at 12:51:20
carcass93
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As far as reasons, potential resale value etc.

I mean, I wouldn't like to see something like this, if I'm an owner - would you?




 

Opinion of EVERYONE here is in the minority....majority is happy with a smartphone and earbuds., posted on August 4, 2015 at 13:21:07
carcass93
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With that out of the way:

Assuming you're correct (and it's not a fact), and you are with the majority within this tiny minority - why in the world would anyone care?

Is that what this all is about? Not for me, thank you.

 

RE: Would you care to comment on this and others, posted on August 4, 2015 at 14:02:34
A.Wayne
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Could be worse try buying AR stuff , its not any different from anything else in the big wallet Hi- end ...

 

RE: You haven't a clue as to what Bruno Putzeys is doing with his amp designs., , posted on August 4, 2015 at 14:05:05
A.Wayne
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Obviously not , since You cant pour on feedback if there is open loop instability ....

 

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