In the figure we have the basic configuration of an operational amplifier for audio signals. The circuit is from a Radio Electronics from the 90s. The power supply must be symmetrical.
This circuit was found in an old American publication. The integrated circuit used is no longer easy...
Using a transconductance operational amplifier, this circuit was found in July 1983 Radio...
This battery-powered emergency light circuit was published in an April 1962 Radio Electronics...