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Varitone Switches?


al heeley
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Has anyone tried putting in one of those varitone switches which has about 5 rotary positions switching thru different values of capacitors, to give the tone different ranges? Is this one of those big knobs you get on the Gibson Lucille-type guitars? I wondered if it had any merit adding in to a new build to give a greater number of tone options. Maybe a simple mini switch bringing in 2 or 3 different caps, attached across the tone pot lugs?

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Yes, a varitone switch is one of those big knobs found on various Gibson guitars. It does switch between different capacitor values, but it is not attached to the tone pot. The tone pot is just a plain old simple tone pot and is independent from the varitone.

There is an inductor in series with the varitone caps. This creates an LC circuit that passes various bands of midrange to ground. Sort of like having a selection of notch filters.

Position 1 disconnects the circuit. Position 2 connects the circuit and has the smallest capacitor and the least effect. It mellows out the upper midrange without making it muddy. Positions 3 through 6 go through progressively larger caps giving the sound different notch frequencies. Position 6, with the largest cap gives a pretty good single coil imitation.

On the Gibson varitone, there is a 100K resistor that gets switched in. This drops the volume too much so I always replace it with a straight piece of wire.

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You get a high cut, but with a boost at the frequencies just below...
You mean an "apparent boost", or resonant peak, right? Since a passive filter can only attenuate, there's never a boost without a battery.

Surprisingly, it can really be a boost - and theres no rules of physics broken here! The capacitor and the inductance of the pups form a resonant circuit at a frequency dependent on their values. Responce at this frequency is greater, after which it falls sharply at higher frequencies. This is a voltage boost - of course there is no power boost (that would defy energy conservation), but it is voltage that the amp is reacting to, so you get a greater signal at this fequency.

There are lots of mechanical analogies where putting a small input into a spring/mass system, at the resonant frequency, causes a larger response- which builds up over several cycles. Who ever bounced up and down on a car with no shock absorbers?

John

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OK, I misunderstood what you meant - so you're not actually boosting anything by using a smaller cap, you're simply increasing the center frequency of the natural 6dB resonant peak to make it more musically useful. You say tomato, I say lycopersicum berry - I suppose it could be considered a midrange boost, as opposed to a standard setup with a larger cap, which would then be a bass boost. :D

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