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.
Found in American documentation this circuit uses transistors of the time. The circuit can be made...
The TAA300 integrated circuit is not common today. In fact, the circuit shown is from a Dutch...
This circuit was found in a 1980s documentation. Q1 and Q2 can be BC548 and SCR a TIC106. The...