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.
A circuit for controlling the temperature of a heating element was found in a Mullard transistor manual...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...