negative feedback - how thick to lay it on

There are very many kinds of system in which the `output` information is supposed to be proportional to the `input` information. Linear systems, we cal I them. Most of them are however not quite linear. A power amplifier, for example, can noticeably distort the signal waveform and even add signal-unrelated information (such as `hum`). Faced with such misbehaviour, the casual designer simply lays on the `negative feedback`. It is all so simple: feedback reduces gain and unwanted products; the extra gain needed to offset the reduction of sensitivity is easily and cheaply obtained; end of unwanted output. This article is intended for the casual designer who has already burnt his fingers trying that approach. The rest of you, more knowledgeable . (or more experienced!), may read on for their own amusement - and at their own risk! The following has only one pretension - to be anything but a textbook approach.*