Suitable for clandestine listening and in SMD assembly, this circuit was found in the Radio Eletronics magazine of August 1988. The listening is in headphones and the amplifier is electret.
This circuit indicates the volume of an audio signal in a different way. The circuit is from 1997...
This circuit was found on a Radio Elettronica (Italy) from April 1974. The circuit can be easily...
This configuration can be made based on other operational amplifiers. For other frequencies, the...