Negative feedback Amp=more faithful reproduction?

Edwyun,

Love your post and reside on your side of the fence. Curious, Have you ever listened to SET amps (hopefully with the proper speaker)? Pass is my favorite brand of ss amps.

fwiw, I don't think there is a correct side of the fence. We have our bias and whatever design gets our attention wins at least for the time being (audiophiles have been known to change their mind).

One of my amps has a variable feedback dial that goes from 0-12 db. I hear the bass firm up when I dial it in but it loses something in the overall sound that I bought the amp in the first place for.

Dracule1, I glanced over article and it seems to cover pretty much everything. I will read it in detail.

Stereophile also conducted experiment with adjustable feedback amplifier and they liked sound at minimum feedback. It doesn't mean that feedback at minimum was zero. It is virtually impossible to make SS amp without any feedback since even emitter resistors are form of feedback. The issue is not to use too much feedback. It comes to good very linear design to start with. Testing with sine waves doesn't show real picture (presence of TIM). You can have two amplifiers that measure identical but one is sounding very harsh/bright. Often amplifier that measures better sounds the worse. In early 70's before TIM was discovered SS amplifier's had huge negative feedback and THD in order of 0.001% (absolutely no need for that). In cases like that TIM can get so bad that output transistors choke on big overshoots (charge trapped at the junction) creating small gaps in music. Our brain fills them up but it makes us tired. I agree with Elizabeth that ZNFB is a catch phrase since amplifier with some amount of feedback will most likely sound better. NFB is a valuable tool that should not be used to cover poor design, cheap components etc.

Dracule1 it was not my intent to condescend when calling the model that you used "simplistic", so please do not take it that way. We agree to disagree, and that's just fine. If you feel that this is not forwarding the conversation, I am happy to bow out.

When I posed the example, I meant I was making it easy because it would be unlikely to find such an obvious example in a real environment, distortion spectra being much more complex than what I posited. Not that it needed dubming down for any of the respondents.

Square waves are used because they contain multiple freqencies. Time and frequency response are related. You can even read the frequency response of the DUT by looking at the top of the square wave backwards.

"Curious, Have you ever listened to SET amps (hopefully with the proper speaker)?"

Onemug, I have listened to some SET amps and OTL amps, all operating in Class A (oh no, another amp design principle!). In my setup at the time, I didn't feel they had the overall extension at both extremes or bass slam I like. Perhaps I should have tried more expenses tube amps. =) But they were very good in the midrange and presence. I have since gone to a bi-amp system and eventually may use some SETs or OTLs amps for their benefits in the M/H frequencies (currently using Aleph 2s, which do have some SET characteristics)) and use SS amps for their bass slam in the L frequencies. It's all a balancing act.

I am by no means a technical expert and have enjoyed both NFB amps and ZNFB designs, but I did want to note the perhaps it is a good idea to bring the human brain into this conversation (I am a neuroscientist, so I can't resist). Namely, it is fine that we are able to measure amps on the bench, but we also need to acknowledge that our ultimate enjoyment of an amp-speaker combo is based on how our brains process the signals that reach our ears. Psychoacoustics plays a major role that can't be overlooked, such as determining what frequencies we can hear most acutely and which order of distortion is more noticeable.

Also lurking in each individual brain are personal preferences. Nelson Pass' First Watt line of amps is a great example of a wide variety of design choices that are intended to both give a good match with certain types of speakers and to provide different flavors to account for different listener preferences.