The varitone circuit is an RLC notch filter that can be added in the guitars main circuit.
It utilizes a variety of capacitors to achieve a reduction in frequencies at set points within the overall bandwidth. As the varitone is rotated from (position 1) to (position 6), the center frequency (f0) of the filter shifts from higher to lower frequencies.
The key point in order to get the most effective results of this RLC circuit is the adjustment of its characteristics according to the guitars main circuit specs (pickups, pots, capacitors, cable types).
