This circuit with the LM741 operational amplifier can be applied to other operational amplifiers. We found it in the September 1989 Radio Electronics magazine.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...