This circuit lets through the 300 Hz to 3kHz range that corresponds to the human voice. We found it in the Radio Electronics magazine of February 1990. The circuit uses both parts of the LM381.
This circuit is from the Motorola Linear Databook published in 1990. The circuit for 1 kHz can be...
This circuit uses one of the first commercial transistors, availble in 1958, year of the...
This stage circuitry for amplifying microphone signals makes use of germanium transistors as indicated...