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.
This circuit uses a JFET at the input to increase the impedance. The circuit has a gain voltage...
This simple circuit for a high impedance magnetic phone (500 ohms or more) has been found in a...
We find this circuit in American documentation from the 1980s. It consists of a frequency folder...