This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
This configuration is suggested by Mullard (Philips) in an old manual of 555 integrated circuits....
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
Found in a 1980s documentation, this amplifier features high common mode rejection. The operating...