How close to the real thing?

Atmasphere, I noticed that the output impedance of one of your amps is about 4 ohms, and I assume that impedance is not perfectly linear across all ten octaves. So, isn't that high output impedance going to affect the audible frequency response of the amp-speaker combination, and in ways that vary with every different loudspeaker's impedance curve?

Mapman says:

"Well, the whole negative feedback issue has been beaten to death pretty thoroughly already in other threads.

My conclusion is that it is just one of many design and execution factors that affect results depending on how well it is executed."

I couldn't agree more.

Atmasphere, unfortunately the way you present the concept of feedback with the term "propagation delay" helps to 'propagate' (sorry, couldn't help it ... :-) ) a misconception about negative feedback. Yes, "negative feedback is always lagging behind" but it is still able to "correct the signal it was supposed to". If it ends up lagging by 180 degrees, half a wavelength, with gain still happening, then you have positive feedback, and an oscillator, and fried tweeters!

So, the feedback ALWAYS lags, even by some tiny amount, but that is just part of the understood design of any working circuit. You can easily buy one of those "terrible" opamps with much more global feedback then a typical audio power amp, that is working comfortably at microwave frequencies, that is, beyond 1,000,000 kHz -- not bad for such a "mediocre" part!

Global feedback in an audio device, on the other hand, with discrete components is typically rolled off (because it has to be for stability, remember the oscillator!) to become non-existent at the higher frequencies, where it is most necessary, and where the ear is most sensitive to distortion -- that is part of the real problem. Also, that is why nearly all gear has rising distortion at higher power, and higher frequencies; in other words, it is not the presence of feedback that's the problem but that at the very time it is most needed, it's done a bunk ... :-) !!

Frank

Frank ,

The time smearing can be significant, this is what Atmasphere was alluding to, I do believe this is so if one get's carried away with NFB. Most SS designers today understand such and dont drink from the NFB pond in excess. The only way to eliminate it's usage is to design amplifiers which are very stable( matching transistors goes along way here) I do Believe Nelson Pass has made an even bigger step and acquired some pretty interesting devices, so we will see.

Tube amplifiers also use less NFB than there SS counterparts, so if NFB is really,really, bad then.....:):)

IMO output stage Bias is also very important in creating "that sound" associated with SS amps, how you balance the 2 ( Bias amt/NFB) when attempting to reduce distortion gives the amp that certain SS "character".

Regards,

Sorry Weseixas, re ".. can follow along ...". My earlier comment was just firstly agreeing with Kirkus that a lot of people have had special listening moments without it quite making sense why, and secondly, that my answer is to be fussy, fussy, fussy, just like people who make and look after aircraft are, which is why flying is so relatively safe, ie. equivalent to audio sounding "real".

Frank