This 100 Hz filter was found in the August 1993 issue of Electronics Now. The components can be modified to operate at other frequencies.
Found in a 1990s Popular Electronics, this circuit produces a tone on a small speaker. The keyer...
This second amplifier is based on the integrated LM108 and has a differential input. The resistor...
This 80's circuitry decodes stereo signals used in analog TV at the time. The circuit can be used...