Found in a 1992 book, this circuit is intended for operation with audio signals. Equivalent operational amplifiers can be used. The optical coupler is an unusual type today.
This circuit was obtained in an American documentation translated in the 80's. The circuit can be...
This circuit is from a 1998 Electronics Now and can be easily assembled since it uses a common...
This circuit was suggested by National Semiconductor in its Linear Application Handbook. The...