What is wrong with negative feedback?

I have read Roger Modjeski address this issue, and his opinion seems to be that negative feedback got a bad name as a result of designers who had no formal training in electronics misusing and not being competent to properly implement negative feedback. In the right hands, it is a good thing. I think it would sort of be like a chisel in the hands of an artist versus a non-artist. The artist makes great things with the chisel, and the non-artist cuts his hands.

I listened in a group setting to a Berning amplifier with adjustable feedback: No feedback, low feedback, and high feedback. We all agreed that the low feedback setting was the best, followed closely by no feedback, and distantly by high feedback. The latter setting was the only setting I would consider unlistenable. The no feedback setting was a little too soft and mellow for my tastes, but I could see someone enjoying that type of sound, and I would not kick it out of bed. For me the low feedback setting provided the best of both worlds - detail, controlled bass, without being irritating.

There are good sounding components using feedback and no feedback, which is simply more proof you need to listen to the component, because the component really is an extension of the skills and philosophy of the designer, and there are good skilled designers employing both methods.

"There are good sounding components using feedback and no feedback, which is simply more proof you need to listen to the component, because the component really is an extension of the skills and philosophy of the designer, and there are good skilled designers employing both methods."

I think this is the bottom line practically for most.

The caveat is you cannot listen to a single component alone, only a system with all the required components (source, amp, speaker/room) together. A single listen can only tell you what each component is capable of, not how good or bad each piece is or sounds. To sort it all out requires doing your homework and listening to as many combos as you can over time.

Mapman - Moderation is the word. Instead of feedback or no feedback we can settle for moderate feedback. Sound coloration comes from dynamic nonlinearity of the system with the feedback. Amplifier itself is far from being first order low-pass filter and feedback creates loss of stability - hence dynamic nonlinearity. Part of the problem is speaker - being complex load. That would suggest to me that things are really complicated and listening instead of reading will bring better results. Speaker choice and synergy with amplifier appears to be very important.

Roger Modjeski has some interesting design philosophies in general. Topics like feedback certainly stir the hornets nest within him. Just don't get him going on cables. At that point it becomes a swarm.

I have to say that the RM-10 manual is one of the best audio reads I've experienced. The amp itself is excellent too, even with 14db of negative feedback.

ULTRAFAST NEGATIVE FEEDBACK
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When an amplifier has difficulty in delivering required voltage and current many forms of distortions will occur. For example, in transistor amplifiers the increased current drawn by speakers will cause a small voltage drop across the source--i.e., the amplifier itself--which will heavily contribute to the unpleasant so-called "transistor sound.” Many transistor amplifiers use global negative feedback to reduce distortions and widen the bandwidth.

The crucial factor in negative feedback is transit time, the amount of time it takes from when an error is detected at the input until it is corrected at the output. For example, a typical transistor power amplifier has three primary sections: a low-noise high-gain differential input stage, feeding a differential-to-single-ended conversion driving a high-current output stage. Each of these three stages is designed for low distortion and noise, but those attributes typically come at the sacrifice of speed.

The typical transit time of linear amplifiers is about 2000-3000 nanoseconds, which is too slow for effective implementation of global feedback and error correction. This lagging results in ringing artifacts and enhances ODD-order harmonics which are particularly annoying to the human hearing so even the smallest amounts of these distortions are highly noticeable. Long delays in feedback also introduces transient and phase discrepancies, susceptibility to transient overload and vulnerability to disturbances at the output such as reactive speaker interactions.

In contrast, many switching amplifiers don't use low-distortion circuits. Instead, they use much faster digital logic circuits. For example, the Spectron Musician III transit time is much less then 200 nanoseconds. Such an ultra-short transit time allows the amplifier to correct for many small errors; and the control loop can follow the input much more accurately. These characteristics result in a more detailed, transparent sound with less noise and louder yet cleaner musical reproduction.