This circuit was found in a Popular Electronics from the 90's. The output signal can be applied to a headphone or speaker. The microphone can be a piezoelectric tweeter capsule or other type.
This voltage inverter circuit is from a Radio Eklectronics from October 1965. It was used in...
This circuit uses a 100 kHz crystal, but nearby frequencies can be obtained with appropriate...
This circuit provides 70 W at 8 ohms and 100 W at 4 ohms. We found this amplifier in a 1992...