Fan control:

Most domestic amplifiers are cooled solely by convection, but it may happen that a standard heat exchanger does not provide adequate cooling for a certain output amplifier. In such a case other means must be used, normally a fan or fans. The circuit described in this article provides a temperature-dependent, proportional control for such a cooling fan. It enables the turn-on threshold and the control characteristic to be set as needed within a given range. It also provides over-temperature indication which may be used to actuate the protection circuit of the amplifier.