This circuit allows the listening of undersea sounds using a special transducer. Operational amplifiers can be of any type. The circuit was found in a Popular Electronics from the 90s.
This 2000 circuit can work with one of the many infrared remote-control transmitters described in this...
This receiver for listening on the phone was found in a Japanese magazine in 1967. The circuit uses...
The circuit shown in the figure is suggested by Intersil (www.intersil.com) and makes use of the...