Amplifier Feedback Good or Bad?

[highfigh]

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?

Psychoacoustics has nothing to do with EE- it's dealt with in acoustics and audiology, though. The objective results matter to the engineers, sound matters to the people with the money (or want the money from it). If the engineers happen to be in that group or have an interest in it, then it matters to them but EEs had nothing to do with discovering psychoacoustics.

 

[highfigh]

Should only marry Yamaha’s. Might last longer.

But which brand should someone cheat with?

 

[highfigh]

I think “amp neg feedback” is something only amp designers care about. The rest of us just want the final product - great sound and reliability.

If you look at what NFB does, it isn't just what amp designers care about- it removes some distortions and noise from the output and if less distortion is a goal for the end users (which may or may not be audible anyway), then someone will decide that the lowest is another goal (damned competitive types!) and the marketing department gets involved.

I found this link- the EEs can digest it and report on its value & accuracy (I'm not an EE, but I know many)-

Negative Feedback and Gain

Amplifiers, explained with the minimum of maths. Amplifier design, Amplifier Classes A to H, NFB, Circuits, Power Amplifiers, Op amps.

learnabout-electronics.org

 

[Bruno P.]

(...) then someone will decide that the lowest is another goal (damned competitive types!) and the marketing department gets involved.

That ain't how it works exactly though. Marketing departments the world over have successfully convinced a large chunk of the market, not just that measurements don't matter but also that good measurements are a bad sign. That has allowed them to print money in the high end market without needing an actual engineering department. The result is that now, trying to sell an amp based on the fact that it has low distortion (achieved using lots of feedback) is practically suicide. No marketeer would take that job on.

Mind you I get the impression that the AH bunch are quite level-headed compared to the audiophile fringe. I might be preaching to the choir here.

 

[highfigh]

That ain't how it works exactly though. Marketing departments the world over have successfully convinced a large chunk of the market, not just that measurements don't matter but also that good measurements are a bad sign. That has allowed them to print money in the high end market without needing an actual engineering department. The result is that now, trying to sell an amp based on the fact that it has low distortion (achieved using lots of feedback) is practically suicide. No marketeer would take that job on.

Mind you I get the impression that the AH bunch are quite level-headed compared to the audiophile fringe. I might be preaching to the choir here.

I have worked in consumer electronics for over 45 years- the marketing departments are some of the worst things about it.

The mythology isn't new- about 35 years ago, a regular shopper (he was far too into the high end to actually buy anything from us) came into the first store where I worked and asked if I had Cramolin. I told him that I did, at home. He told me to put it on my AC plugs and I slowly asked "whhhhhyyyyyy?"- he said it cleans the tangs and contacts in the receptacle, lowers the background noise and tightens the bass. I said "Get out", he said "No, really!" and I then said "No, I meant, leave!". This is the predecessor of using hospital-grade receptacles and stupidly expensive power cords, gold-plated fuses and other things that completely ignore the power grid and house wiring. Maybe we should market audio rhinestones for volume controls.

The marketing department licks their finger, checks for wind direction and acts accordingly. They play with words, to make people act on impulses that are based in ignorance but seem plausible to the reader. Audio magazine had a short article called 'The Greening of CDs', referring to using a green magic marker on the edge of the discs and how it makes several improvements. That was the last time I read that rag.

I grew to dislike high end audio fans and that segment of the industry a long time ago and it has only gotten worse. I don't know if you ever worked in retail audio, but that specifications race in the late-'70s/early-'80s was a royal PITA. People who read the audio mags and comprehended none of it would come in, with their brand new copy of the magazines that had specific passages highlighted, to pick our brains and find out if we knew what we were talking about. Where I worked, we had the benefit of a few people who were EEs or on the way to becoming that, so we could ask before proudly taking an erroneous stance on something when we weren't familiar with it. "What's the damping factor?": is something that was far too common when Sansui started showing it. "Is it Direct-coupled?" was another. We didn't sell Sansui, but we sure did repair a lot of it- their R-series was a car crash wrapped in a train wreck, wrapped in a ship wreck.

Speaking of marketing without needing an engineering department, what's your take on cables that have batteries and a little LED? Every EE I have asked has looked at me like I had three heads and a horn coming out of each forehead.

 

[AcuDefTechGuy]

If you look at what NFB does, it isn't just what amp designers care about- it removes some distortions and noise from the output and if less distortion is a goal for the end users (which may or may not be audible anyway), then someone will decide that the lowest is another goal (damned competitive types!) and the marketing department gets involved.

I found this link- the EEs can digest it and report on its value & accuracy (I'm not an EE, but I know many)-

Negative Feedback and Gain

Amplifiers, explained with the minimum of maths. Amplifier design, Amplifier Classes A to H, NFB, Circuits, Power Amplifiers, Op amps.

learnabout-electronics.org

No, what the End-users have been caring about from the beginning is the actual measurements of the amps - THD+N, SNR, Crosstalk, FR, etc.

Which amp would you choose REGARDLESS of the negative feedback?

1. Amp with THD of 0.008%, SNR 132dBA, Crosstalk 94dB, FR 20Hz-20kHz +/- 0.1dB

2. Amp with THD of 0.8%, SNR 90dBA, Crosstalk 60dB, FR 20Hz-20kHz +/- 1.0dB.

So who really cares about negative feedback at the end of the day as long as the amp has great measurements, has good power output, sounds great, looks great, and is reliable?

 

[Gmoney]

Should only marry Yamaha’s. Might last longer.

LMAO!!! You do have your Moments Andrew, I didn’t see that one coming.

 

[Gmoney]

No, what the End-users have been caring about from the beginning is the actual measurements of the amps - THD+N, SNR, Crosstalk, FR, etc.

Which amp would you choose REGARDLESS of the negative feedback?

1. Amp with THD of 0.008%, SNR 132dBA, Crosstalk 94dB, FR 20Hz-20kHz +/- 0.1dB

2. Amp with THD of 0.8%, SNR 90dBA, Crosstalk 60dB, FR 20Hz-20kHz +/- 1.0dB.

So who really cares about negative feedback at the end of the day as long as the amp has great measurements, has good power output, sounds great, looks great, and is reliable?

All those specs are what anyone who wants a good amp should look for and should at least have some working knowledge of what they mean and why those specs are important. Not all Manufacturers post up every spec and detailed reason why. Take low negative feed back how often is that even mention? or slew rate? here’s one that’s off Subject, Speaker’s, On axis off axis, back in the 70’s 80’s you would see that mention most of the time, today you’d be lucky if they even mention the order of the XO. So yeah I’m very Interested about negative feedback good or bad. But is it something I really need to worry about when choosing a amp? Maybe or maybe not I’d say depends on what build of a amp I want. Class A class A/B class D amps do I need to know if the Class of a amp has anything to do with negative feedback if it does or not would bad feedback be better to have with a class H amp? All that I just posted up are just my Simple analogies of my take on negative feedback good or bad. Gene’s Editorial of this Subject should be very Interesting in my book and I’m looking for it to get my learn on.

 

[highfigh]

No, what the End-users have been caring about from the beginning is the actual measurements of the amps - THD+N, SNR, Crosstalk, FR, etc.

Which amp would you choose REGARDLESS of the negative feedback?

1. Amp with THD of 0.008%, SNR 132dBA, Crosstalk 94dB, FR 20Hz-20kHz +/- 0.1dB

2. Amp with THD of 0.8%, SNR 90dBA, Crosstalk 60dB, FR 20Hz-20kHz +/- 1.0dB.

So who really cares about negative feedback at the end of the day as long as the amp has great measurements, has good power output, sounds great, looks great, and is reliable?

An amp that only does 20-20KHz within .1dB isn't really that good, is it? Many amps from the '70s tested +0dB/-.1dB to 100KHz or 200KHz and all they show now is 20K? That tells me the FR has lost importance.

NFB also improves linearity in some designs, so I don't think it's accurate to say it's not important.

I couldn't hear the difference between -90dB SN and -132dB SN if my life depended on it- it's just not audible from the listening position unless the speakers are insanely sensitive and these days, sensitivity isn't as important as it was when amplifiers topped out at 15W-25W.

 

[Mikado463]

Being a Nelson Pass fan for decades I simply trust his judgement when it comes to amplifier design ...........

Audio distortion and feedback - Pass Labs

Audiophiles seem to revel in minor controversies – vinyl vs CD’s, tubes versus solid state, capacitor, wires, magic dots… and negative feedback. At one extreme, the position is that “feedback makes amplifiers perfect”. At the other extreme, “feedback is a … Continue reading →

www.passlabs.com

 

[Gmoney]

Being a Nelson Pass fan for decades I simply trust his judgement when it comes to amplifier design ...........

Audio distortion and feedback - Pass Labs

Audiophiles seem to revel in minor controversies – vinyl vs CD’s, tubes versus solid state, capacitor, wires, magic dots… and negative feedback. At one extreme, the position is that “feedback makes amplifiers perfect”. At the other extreme, “feedback is a … Continue reading →

www.passlabs.com

Thanks for posting up that link, just added it to my bookmark!!

 

[Verdinut]

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.

I know that all well designed amplifiers got to use some negative feedback, otherwise audible distortion and noise would have made them unsuitable for high fidelity performance.

 

[AcuDefTechGuy]

An amp that only does 20-20KHz within .1dB isn't really that good, is it? Many amps from the '70s tested +0dB/-.1dB to 100KHz or 200KHz and all they show now is 20K? That tells me the FR has lost importance.

NFB also improves linearity in some designs, so I don't think it's accurate to say it's not important.

I couldn't hear the difference between -90dB SN and -132dB SN if my life depended on it- it's just not audible from the listening position unless the speakers are insanely sensitive and these days, sensitivity isn't as important as it was when amplifiers topped out at 15W-25W.

I can't even hear beyond 16kHz, but you can hear to 200kHz?

And you would buy an amp with a SNR of 90dBA even if you could buy an amp with a SNR of 132dBA?

 

[PENG]

Thanks for posting up that link, just added it to my bookmark!!

Be careful what you read. Now you know why I mentioned him. That's one of the examples I can think of, that got taken out of context by people don't really know the basics of control theory. If you put Mr. Nelson and Mr. Putzeys in the same room, Ii highly doubt they would disagree a whole lot on this topic.

 

[Auditor55]

Psychoacoustics has nothing to do with EE- it's dealt with in acoustics and audiology, though. The objective results matter to the engineers, sound matters to the people with the money (or want the money from it). If the engineers happen to be in that group or have an interest in it, then it matters to them but EEs had nothing to do with discovering psychoacoustics.

Psychoacoustics, in my opinion, relevant whenever the question of whether something is good or bad is when it comes to designing a piece of audio gear such as amps. So is Amplifier Feedback Good or Bad? If it adversely affect sound quality, then yes it is bad. BTW, the psychoacoustic deals objective results as well, it's about what the human ear can hear.

 

[PENG]

I can't even hear beyond 16kHz, but you can hear to 200kHz?

I don't doubt some may think they could hear 16 Hz when they played a tone, but they may not realize they were hearing the harmonics (e.g. 32, 48, 64, even 80 Hz). Lots of subs would produce lots of harmonics at that frequency.

 

[AcuDefTechGuy]

I don't doubt some may think they could hear 16 Hz when they played a tone, but they may not realize they were hearing the harmonics (e.g. 32, 48, 64, even 80 Hz). Lots of subs would produce lots of harmonics at that frequency.

Yeah, last time I gave myself a self-test, I think I could only hear between 30Hz-16kHz. And that's probably stretching it a little bit. Probably more like 32Hz-15kHz.

 

[Gmoney]

Be careful what you read. Now you know why I mentioned him. That's one of the examples I can think of, that got taken out of context by people don't really know the basics of control theory. If you put Mr. Nelson and Mr. Putzeys in the same room, Ii highly doubt they would disagree a whole lot on this topic.

Thanks PENG, haven’t read it yet, but yeah I try as much as I can with the Limited expert knowledge that I don’t have to keep an open mind.

 

[Gmoney]

Yeah, last time I gave myself a self-test, I think I could only hear between 30Hz-16kHz. And that's probably stretching it a little bit. Probably more like 32Hz-15kHz.

I have 5% drop around the upper end of my hearing in my left ear. And that was back in 2007 last time I had a Real hearing test done where your in that hearing room.

 

[AcuDefTechGuy]

I have 5% drop around the upper end of my hearing in my left ear. And that was back in 2007 last time I had a Real hearing test done where your in that hearing room.

So IOW, you can't hear beyond 20Hz-20kHz since you don't have giant golden ears?

What about triple platinum ears?