This variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3 general purpose op-amps like the 741 and must use a symmetrical source.
This circuit was taken from recent English documentation. The circuit uses a 500 uA microammeter as an...
Found in Popular Electronics from the 90s, this circuit uses a reed switch on the rails as a...
This filter for scratch and rumble noises that occur on turntables was found in the February 1995...