This amplifier with gain control was obtained in a documentation from Signetics of the 80's. Transistors are of power and operational amplifiers are not common nowadays.
This circuit is interesting for experiments and can be part of the bench in the form of a module. The...
Constant currents from 10 mA to 1 A can supply the load, depending on the selection made by S1. Q1...
In the figure we have the transmitter and the receiver for an optical audio link via infrared. The...