We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
This traditionally configured power supply provides +12, -12 V and 5 V voltages for operating and...
This simple circuit for headphones or small speakers was found in documentation from the 90s. The...
The operational amplifier used is not common today, but the circuit can be implemented with modern...