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.
We found this circuit in a 1973 publication. The circuit lets frequencies below 480 kHz pass...
We found this source in documentation from the 1980s. The power transistor can be the BD137 and...
This circuit was suggested by Linear Technology in a 1980s documentation but can be implemented with...