ABSTRACT
Most of this book deals with the actual power amplifi er itself, and its immediate ancillary circuitry such as power supplies, overload and DC offset protection, control of fan cooling, and so on. It is quite feasible to take one or more such amplifi ers and put them in a box with no further complications. Such a product was the much-loved Quad 303 power amplifi er, which had no controls at all unless you count the mains voltage selector. However, amplifi ers are very often also provided with input circuitry that gives a balanced input, gain control, fi ltering, level indication, and so on. This wholly new chapter deals with these subsystems, defi ning the amplifi er input system as any part of the signal path before the actual power amplifi er stage.
