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 high Q “rejector” or notch filter rejects signals whose frequencies are in the range...
This circuit was found in documentation from the 90's, having an LC compensation network. The...
This two-transistor circuit was found in the January 1994 issue of Electronics Now magazine....