What is wrong with negative feedback?

"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.

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.

Best thread EVER.