Found in a 90’s 303 Circuits, this circuit uses components that are still common and has a common LED as indicator.
This microphone amplifier operates on battery voltage. The output is in an earphone. The...
This low power amplifier circuit for speaker or phone is from the Philips Databook of 1990. The...
This circuit is from a Radio Electronics from August 1992. The transistor used allows the control of...