This sound meter or sonometer was found in a Popular Electronics from the 80's. The circuit can be easily implemented today, and the microphone is made of electret or ceramic.
The purpose of this circuit is to measure the intensity of audio signals. We found it in the...
This circuit is from an American 80's documentation. The transistor is general purpose,...
This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and...