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.
This circuit was found in the National component manual which is not currently simple to obtain....
In this circuit, the current capacity doubles, but is still of the order of microamps. The...
We found this circuit in a Hands On Electronics from the 90s. However, the circuit can still be...