QUIET TURN-ON CIRCUIT FOR CARBON MICROPHONES

摘要

A preamplifier for a carbon microphone is provided at its input with a field effect transistor biased to a non-conductive state. When the microphone switch is turned on to connect the microphone to the amplifier the source of the bias is substantially cut off but an RC delay circuit is provided to maintain the bias momentarily to keep the amplifier inoperative until the rush of current through the microphone subsides so that the usual "click" sound is not heard when the microphone is turned on.