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 stable 20 MHz oscillator was suggested by the National Semiconductor's Linear Applications Handbook...
This buffer and driver is from the integrated circuit manual itself, the Linear Technology LT1206. The...
The transistors in this 1978 circuit can be BC548 and 1N4148 diodes. The electrolytic capacitors can be...