This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
We found this circuit in a Popular Electronics of the 90s. The MOSFET can be of any type,...
Found in a 1970s RCA documentation, this circuit uses a relay to control external loads. R1 is 150...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...