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I have always thought that there was a fundamental difference between negative feedback (nfb) and error correction (ec) in an amplifier loop1). But it's more subtle than that. Error correction is, in my view at least, more elegant than negative feedback. In the article I give some equivalent conceptual circuits that show the embedded positive feedback loop within a H.ec loop. At a cursory glance that may give the impression that there is infinite loop gain. However, that is only the case if the forward gain would be zero which is not a realistic condition. In fact, it can be shown that the loop gain varies directly in proportion to the forward gain error (thank you Mike). Thus, when the latter would be zero, there would be no feedback at all.
Negative feedback relies on excess gain in the main amplifier (forward) loop. By returning a part of the output signal to the input, the amplifier gain becomes much smaller, but also distortion becomes much smaller. Output impedance becomes much smaller, and input impedance becomes much higher. In other words, the amp becomes much more ideal. So this is a kind of trade-off: we give up most of the large (open loop) amp gain to get a much more linear and ideal result. Sounds pretty neat, but what about that (very) large open loop gain we need to make nfb work? That in itself can be a source of problems.
Nfb is quite old, it was invented by Harry Black (see pic) in 1934. If you are interested in how this works in more detail, heres his original paper.
จาก Jan Didden เวป linear audio
http://www.linearaudio.nl/pax-1.htm
