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Boy, You Opened Up a Can of Worms.... [-;

There is a small group of engineers who thinks Matti Otala was a fraud, and negative feedback is always an essential part of amplifier design. While SM is correct that the output impedance of modern solid-state devices is very low, it is *not* exactly zero, and if the speaker driven is of relatively low impedance and has a sizable "motor structure" (a massive woofer/voice coil), the motor could potentially generate enough current (from its momentum) to excite a global feedback loop.

One can do the math- If the impedance ratio between speaker and output device is low enough, there will be considerable excitation of the (global) feedback from the back EMF of the speaker. (The speaker becomes the "source", the amp becomes the "load".)

But then again, as long as there is feedback in every stage *except* for the output stage, the issue of feedback-back EMF interaction becomes moot.
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