The circuit in the figure uses two operational amplifiers: an LM101A and an LM102. Diodes admit equivalents and resistors do not have to be accurate. The power supply must be symmetrical.
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...