Found in a 1967 Electronics World, this preamplifier uses an integrated circuit from that time, difficult to obtain today. The maximum frequency is 15 kHz.
This stage circuitry for amplifying microphone signals makes use of germanium transistors as indicated...
This circuit was suggested by Philips in 1967 documentation. The circuit receives modulated light and has...
This circuit is from an English magazine of 1974, but can still be assembled with the replacement of...