This two-transistor circuit was found in the September 1971 issue of Radio Electronics magazine. The sensor is an NTC and sensitivity adjustment is via R1.
The purpose of this circuit is to eliminate RF picked up by a turntable. The circuit is from a...
This circuit synchronized by the power grid can be used as a shield. We found it in an 80's...
This is a very simple version in which we simply fit the jacks, plugs with red and green LEDs,...