This Vox or sound activated relay was found in an American documentation from 1975. Equivalent transistors can be used, and the SCR can be a TIC106. The relay is according to the supply voltage.
Using an operational amplifier, the figure shows how to convert the waveform to low frequency...
This is the power step of the previous circuit. Output transistors must be mounted on good heat...
The UM3562 integrated circuit (not very easy to find) synthesizes three types of sound that...