This 50 Hz rejector or notch filter was found in a 1975 documentation. Other frequencies can be obtained by changing components. The filter uses a Wien network and must use a symmetrical power supply.
This treble and bass control drains some milliamperes from a 12 V supply and can be used with any...
This circuit was obtained from Dutch documentation from 1967. It uses transistors of the time...
This circuit was found in a 1980s documentation for amateur radio. The circuit is for 9 MHz...