This balance indicator for stereo amplifiers was found in an 80's Elektor. The components used are common. Zeners are 1.8 V or close to that value.
This is a diagram of a 1958 commercial receiver. The circuit was found in documentation at the...
This circuit was found in the September 1974 issue of Radio Electronics magazine. It consists of a...
This circuit is in the SGS manual of linear integrated circuits of 1982. The integrated circuit is of...