If you have the skills and can get your hands on SMD components, you can assemble this small amplifier. We found it in the Radio Electronics Experimenter special edition from 1990.
This automatic control for recording signal level was found in a Radio Electronics from September...
This switched-mode circuit was found in the April 1976 issue of Radio Electronics magazine. The...
This circuit, from a 303 Circuits from the 90s, uses a telephone pickup coil as a sensor to...