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 was obtained in an Electronic Design from the 80's. It has the adjustment of the gain...
This circuit was obtained in a 1977 magazine, but it can still be easily assembled, as the...
This circuit uses only passive components and must be tuned to the operating range. The circuit is...