This circuit consists of a stereo audio compressor. We found it in Radio Electronics magazine from October 1968. The circuit uses an opto-coupler made with a neon lamp and LDR.
The integrated circuit used in this configuration for noise reduction on FM radios is not common...
This circuit was found in the April 1984 issue of Radio Electronics magazine. The integrated...
We found this circuit in a 1977 National Semiconductor Databook. The circuit can use other FETs...