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.
The transistors of this old circuit from the 60s can be the BC548, in a current version. The...
This filter, found in an old manual, has characteristics of reduced overvoltage given by the graph...
The selected circuit is from the Texas Instruments optoelectronics manual. With it you can receive...