This is a traditional 741 configuration with gain close to 100. We found it in the December 1972 Radio Electronics magazine. The power source must be dual.
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...