This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and has its gain adjusted by the voltage at the gain input.
This 45 to 90 Hz hum elimination circuit was obtained from a 1980s documentation. The operational can...
The resistors R1 and R2 consist of 8 220 ohms x 2 W resistors connected in parallel. The...
Found in 90's Electronic Engineering this circuit can be used to measure phase angles between two...