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 circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
This configuration was obtained in the SGS manual of linear integrated circuits of 1982. The...
This useful inductance bridge was found in a Radio Electronics from September 1963. The...