This circuit is from 2005 documentation. The integrated amplifier circuit must be mounted on a good heat sink and the speaker must be able to withstand the full power of the circuit.
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...