This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
This circuit was found in an American publication from the 50's. The transistors are made of...
The circuit shown is an amplifier for medium impedance headphones including bass and treble...
This circuit for an optical audio link using LED or LASER was found in a 90s QST magazine. The circuit...