Digital recorder ISD1016 (CB7963E)

Found in a Popular Electronics from the 90s, this digital recording circuit uses an unusual integrated circuit today.

Optical Gain Control (CB6324E)
This simple circuit controls the signal amplitude through a photoresistor optical coupler. The...
Light Activated AND Gate 2 (CB5318E)
This circuit can be implemented with standard photodiodes consisting of a two input optical AND gate....
Operational audio amplifier (CB21109E)
In the figure we have the basic configuration of an operational amplifier for audio signals. The...