High-power AF amplifier (2)

EE June 1986 26 HIGH-POWER AF AMPLIFIER 2 After last month"s discussion of the power output boards and associated power supply, this concluding article details the design and construction of the bridge/stereo preamplifier, driver stage power supply, soft turn-on and protective circuitry, as well as an effective fan control section. In addition, a variety of illustrative material is offered as an aid to understanding the amplifier"s mechanical construction. Driver stage power supply The circuit diagram of the combined ±90 V and +12 V supply unit originally given on page 63 of last month"s issue of Elektor Electronics unfortunately contains a small error and a correct version of it is, there- fore, reproduced here. The ±90 V driver stage supply is quite straightforward; it is capable of supplying up to 2 x 100 mA. The open-circuit voltage of this section is about +100 V. The +12 V supply is so conventional as to make any descrip- tion of it unnecessary. Preamplifier In order that ...