This common circuit using operational amplifiers was found in the 1993 issue of Radio Electronics Special Projects. The circuit is sandwiched between the pickup and the amplifier input.
This oscillator configuration with the operational 741 was obtained in a European documentation from the...
The LED frequency flashes depends on the value of the capacitor tested according to the table. We...
Found in the September 1972 issue of Radio Electronics magazine, this signal injector is based on the...