We found this circuit in Radio Electronics Special Projects from 1992. The circuit turns on the power when the microphone plug is inserted into the input jack.
The integrated circuit used is a voltage reference from Motorola. This configuration was obtained in...
This circuit is from a Radio Electronics from October 1970. The circuit uses transistors from that...
This circuit was obtained from a 1977 magazine, but can still be mounted using BC548 for TR1 and...