We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer unusual in our day. The transistor is general purpose type.
This circuit is originally recommended as hearing aid or stethoscope. The output transducer is a...
Figure Bellow shows how to interface CMOS circuitos with TTL using the 4049 or 4050 IC. The power...
This 80's circuit uses an integrated amplifier of the era, but nothing prevents it from being...