Amplifier Feedback Good or Bad?

[Gmoney]

Bruno Putzeys, leading amplifier designer and expert in feedback circuits. Designer of some of the best performing amplifier circuits in existence.

Never hread of this dude, thanks for posting this up going Research him right now. I’m old school out side of Dr. Harman and Dr. Tool the two that I idolize
well 3, Gene comes in a close 3rd he may move up to #2,only because Dr. Harmon passed away.

 

[Gmoney]

I reluctantly voted 2 because 1 is clearly false. If no feedback is used you are going to have distortions that are likely going to exceed the threshold of audibility, period.. My only issue with 2 is, the words "best sounding" always bother me, as it is subjective by nature. If those two words are deleted, I would have voted happily instead reluctantly.

PENG No! it’s #1 bro! Harman/Kardon I believe always Advertise low negative feedback! So less is best!! joke.

 

[Gmoney]

Well, for some designs it is good but too much is too much, right?

I see you and Pogre, playing it safe, come on guys! Commit! What we got to lose? Gene going to prove all of us wrong anyways. I’ve been on Genes AH forum for close to 7 year’s now and never have I seen Gene post up anything false or Proven wrong.

 

[Pogre]

playing it safe uh Pogre? I picked #1 because I read that low negative feed back was good, better or great. You should know by now Gene aka Master Yoda loves to trip us up with loaded or Trick questions just to test knowledge of his Forum members. I know first hand cause Gene, has/likes to Pimp out some of us on his YouTube channel. Anyone remember his Article on his YouTube on where Gene goes “Freedom”. from Braveheart? I’d Volunteer to be a test subject just to be noticed on his YouTube channel, would a Honor in my book.

Not really playing it safe, it's true. This subject has never really made it on my radar before. I'm learning about it right now.

 

[highfigh]

I reluctantly voted 2 because 1 is clearly false. If no feedback is used you are going to have distortions that are likely going to exceed the threshold of audibility, period.. My only issue with 2 is, the words "best sounding" always bother me, as it is subjective by nature. If those two words are deleted, I would have voted happily instead reluctantly.

Depends on the goal- some guitar amps had a Presence control, which varied the NFB; low Presence setting used high NFB and high Presence setting used almost no NFB. Obviously, for a hifi amp, none may be OK if it's not being pushed but the difference in sound would need to be tested in order to make an informed decision about the sound quality.

 

[PENG]

Never hread of this dude, thanks for posting this up going Research him right now. I’m old school out side of Dr. Harman and Dr. Tool the two that I idolize
well 3, Gene comes in a close 3rd he may move up to #2,only because Dr. Harmon passed away.

Both Speedskater and I have previously posted links to his (this dude) papers on negative feedback. Those are good reads too, in additional to the one on this thread.

Links in post#9

TIM Distortion, High Speed Transistors & the AU-X1

Tony is working on a Sansui AU-X1 (unfortunately his example is in pretty rough condition internally). I thought some members here might enjoy the technical aspects of this video: This is what my originals looked like on one of the heatsinks when they were re-set during restoration. This...

forums.audioholics.com

To save you time:

https://www.edn.com/negative-feedback-in-audio-amplifiers-why-there-is-no-such-thing-as-too-much/

https://www.edn.com/negative-feedback-in-audio-amplifiers-why-there-is-no-such-thing-as-too-much-part-2/

 

[PENG]

Depends on the goal- some guitar amps had a Presence control, which varied the NFB; low Presence setting used high NFB and high Presence setting used almost no NFB. Obviously, for a hifi amp, none may be OK if it's not being pushed but the difference in sound would need to be tested in order to make an informed decision about the sound quality.

Thanks, but I really don't care much (actually I do, but only to point, just not much) about what others say about what sounded good or bad to them. We have all different taste. That's why I rely mostly on what I hear, specs, and measurements.

 

[Swerd]

I once met Bob Cordell, an EE with some experience in audio amplifier design. I should add that Bob Cordell is the only amplifier designer I know .

Cordell says that "when it is used properly, negative feedback vastly improves an amplifier, both sonically and in measurement".

He published an article in Audio magazine in February 1980 at the height of the controversy surrounding Transient Intermodulation (TIM) Distortion and its relationship with negative feedback. The article discusses the origins of TIM and the transient nature of music that can bring it on. It points out that amplifiers with inadequate slew rate margin are the ones prone to TIM. Moreover, the article demonstrates that large amounts of negative feedback, when properly applied, do not in any way contribute to TIM. The bad rap that negative feedback gets to this day is largely a result of that misconception.

You can find links to that article here:

CordellAudio.com - Another View of TIM

www.cordellaudio.com

http://www.cordellaudio.com/papers/another_view_of_tim.pdf

http://www.cordellaudio.com/papers/another_view_of_tim_II.pdf

 

[Gmoney]

Not really playing it safe, it's true. This subject has never really made it on my radar before. I'm learning about it right now.

Me to, but I believe I did read way back that low negative feedback was better but don’t Quote me on that cause I’m no audio Engineer either. But I was just needling you on the choice thing. joking wasn’t making fun of you personally cause god knows my working Knowledge isn’t anywhere’s near PENG, HD, and you I’m just a peon who likes to have fun in here sometimes.

 

[Gmoney]

Both Speedskater and I have previously posted links to his (this dude) papers on negative feedback. Those are good reads too, in additional to the one on this thread.

Links in post#9

TIM Distortion, High Speed Transistors & the AU-X1

Tony is working on a Sansui AU-X1 (unfortunately his example is in pretty rough condition internally). I thought some members here might enjoy the technical aspects of this video: This is what my originals looked like on one of the heatsinks when they were re-set during restoration. This...

forums.audioholics.com

To save you time:

https://www.edn.com/negative-feedback-in-audio-amplifiers-why-there-is-no-such-thing-as-too-much/

https://www.edn.com/negative-feedback-in-audio-amplifiers-why-there-is-no-such-thing-as-too-much-part-2/

Thanks PENG, will Definitely give it a read. Like I just posted up to Pogre, I’m needling you guys, what I know? about what negative feed back, is it really good, bad or great to have more? or none at all? I just posted up that Harman/Kardon Advertisers or advertised low negative feedback I just took their word that, that was a goid thing. Hey they the Experts. Guess it’s like that dam Dampening factor thing. lol They just Advertise all that stuff just to trip us up make us think we get more for our money when it’s really less most of the time. Half joking here PENG. Oh one thing, I got 19 more postups to go to reach 1000 post. I’m tried of being a “Chief” never liked being a Chief, it always got me in to much trouble on AH. Newbies and youngling’s joining up on AH, hit me up a lot they think I know a lot. I don’t want to be that Famous on AH.

 

[PENG]

Me to, but I believe I did read way back that low negative feedback was better but don’t Quote me on that cause I’m no audio Engineer either. But I was just needling you on the choice thing. joking wasn’t making fun of you personally cause god knows my working Knowledge isn’t anywhere’s near PENG, HD, and you I’m just a peon who likes to have fun in here sometimes.

Me neither, I am not an audio electronic engineer, though I am sure if there is such a degree option. My final year options for my EE degree was in Control and power system. "Control systems" means the syllabus would include feeback, feed forward theories, and lots of Laplace, Z, Fourier transforms, infinite series kind of math. Just because someone is an EE, doesn't mean one has in depth knowledge in audio electronics, though one usually would have/or should have the basic knowledge.

 

[Zaskarx]

Didn’t Dr. Harman Publish an article about negative feedback? Phase lock?

You might be thinking of Dr. Matti Otala, who performed the initial research on TIM and helped HK design a series of low negative feedback amplifiers in the early '80's. I hadn't heard that his work had been discredited until I read this article, I'd be interested in links to more information/studies on this subject.

Nelson Pass has an interesting article on feedback in amplifier design, worth reading and makes a strong case that negative feedback should be used sparingly to avoid introducing complex distortions to the signal.

I guess you could call me a proponent of low feedback amplifiers, obviously this is very subjective, but the best sounding amplifiers I own are an HK PM660 and a Nakamichi PA-7, both of which incorporate low global feedback circuits based on designs by Otala and Pass.

 

[Auditor55]

Me neither, I am not an audio electronic engineer, though I am sure if there is such a degree option. My final year options for my EE degree was in Control and power system. "Control systems" means the syllabus would include feeback, feed forward theories, and lots of Laplace, Z, Fourier transforms, infinite series kind of math. Just because someone is an EE, doesn't mean one has in depth knowledge in audio electronics, though one usually would have/or should have the basic knowledge.

Shouldn't one also be astute or learned in the field of psychoacoustics? How would you know one way or the other absent listening test?

 

[Gmoney]

You might be thinking of Dr. Matti Otala, who performed the initial research on TIM and helped HK design a series of low negative feedback amplifiers in the early '80's. I hadn't heard that his work had been discredited until I read this article, I'd be interested in links to more information/studies on this subject.

Nelson Pass has an interesting article on feedback in amplifier design, worth reading and makes a strong case that negative feedback should be used sparingly to avoid introducing complex distortions to the signal.

I guess you could call me a proponent of low feedback amplifiers, obviously this is very subjective, but the best sounding amplifiers I own are an HK PM660 and a Nakamichi PA-7, both of which incorporate low global feedback circuits based on designs by Otala and Pass.

Thank you Sir! I’d Rather be half right then half wrong. But I also could be thinking of another article also.
I had received a email from Harman/Kardon umm around 2011 or 2012, I had called into their service department and the person who picked up my phone call, he and I where discuissing the amp of the two channel 3490 . His word not mine, that the amp was of a Analog design and “warm” just an Analogy the warm thing, was because of it’s low negative feed back.

 

[PENG]

Shouldn't one also be astute or learned in the field of psychoacoustics? How would you know one way or the other absent listening test?

Of course, the founder of Audyssey, Dr. Kyriakakis, an EE studied both.

 

[Gmoney]

Thanks, but I really don't care much (actually I do, but only to point, just not much) about what others say about what sounded good or bad to them. We have all different taste. That's why I rely mostly on what I hear, specs, and measurements.

Ditto!! I’ll read, read and read some more than if I’m still not sure I’ll find as many post ups as I can of the Most Trusted members on AH.

 

[mtrycrafts]

.... I am sure you know why I mention him right?

Please, tell us, don't be shy.

 

[mtrycrafts]

Now you

What a fascinating topic. I chose option 3 for the poll.

can change it.

 

[Pogre]

Now you

can change it.

Not yet, I'm still reading up on it!

 

[mtrycrafts]

I want straight wire with gain.

What- someone had to say it.....

Well, it has lots of straight wires in it and gains. Although some may bend a bit.