This interesting multi-channel circuit was found in the August 1988 issue of Radio Electronics magazine. It monitors the signal from 4 sound channels simultaneously.
Found in old American documentation, this circuit can use crystals between 27.5 and 33 MHz...
This circuit was found in a Popular Electronics from the 90's. The circuit can be used to convert...
Found in 90s documentation from Analog Devices, this circuit employs operational amplifiers of the time....