Another device that you occasionally see in guitars is something called a varitone.  It is a rotary switch that runs the signal across one of several selectable capacitors (one position usually lacks a capacitor, and is therefore a bypass).  This drops out different frequencies to give you several interesting starting points for your sound.  Usually people have a 5 or 6 position switch, for example in B.B. King's "Lucille" or some of the over-the-top B.C. Rich guitars from the '80s.

My experience
I originally had a 5-position version in a strat.  Because of the torque required to switch between positions you normally see these with a "chicken-head" knob (again, see "Lucille") which will screw onto the shaft and hold it firmly in place.  That just never looked great on a strat, so I spent a lot of time modifying the switch to accommodate a standard strat knob.  I cut the shaft down and pulled apart the switch to reduce the resistance between the positions, but I was never satisfied with it, so the switch itself was seldom used in spite of the cool sounds.

Currently I have another version one ready to be wired into another project that I haven't gotten to yet (although the schematics are already drawn and the components all purchased).  The cheapest rotary switch out there is a 12 position model available at Radio Shack for about $1.  Why not go with still more options?  This time I'm using it in a guitar that doesn't look so bad with the chickenhead since it is a bit of a frankenstein.

Note: Interestingly, a varitone will provide completely different results with different pickups because each pickup's voice has a signature set of frequencies for the caps to operate on.

A varitone of your own
There is a varitone available as a kit through Torres Engineering and another one at Griblin Engineering (they also have a "super varitone" with extra sounds from switching the range).

The values of the capacitors can vary, but the tables below provide a good range of tonal color.  Feel free to experiment.  However, the Griblin model was the best in my experience.  Results will no doubt depend on the pickups in your guitar.  Some values will produce a muddy signal, others will brighten your tone, other still will fall somewhere inbetween to give you a glassy sound.

My little monster
At left is a varitone I built with on a rotary switch with a "chicken head" knob. This one has 11 capacitors (the 12th position being the bypass).  Details can be found below.

To build your own, below are a few recipes.  Capacitor values are expressed in both microfarads (uF) and picofarads (pF) since many of these components are found with value expressed in either unit.

6-position varitone (Griblin model)
100,000 pF = 0.1 µF
50,000 pF = 0.047 µF
39,000 pF  = 0.039 µF
10,000 pF = 0.01 µF
2,200 pF  = 0.0022 µF
0 pF  = 0 µF (bypass)

6-position varitone (Gibson's "Lucille" and Blueshawk models*)
220,000 pF = 0.22 µF
30,000 pF = 0.03 µF
10,000 pF = 0.01 µF
3,000 pF = 0.003 µF
1,000 pF = 0.001 µF
0 pF = 0 µF (bypass)

*This is according to a couple schematics I found on the web.  Supposedly there are also resistors included in the circuit to balance the output level of the signal, but I don't believe they are required.

Incidentally, I tried the B.B. King model in the store on a couple occasions and did not find the effect to be as dramatic (or as useful) as with the Griblin version.  Of course, as with everything else in the search for the perfect tone, this all depends on the type of the pickups, your amp, effects, and the alignment of the planets!

12-position varitone (my own recipe)
220,000 pF = 0.22 µF
100,000 pF = 0.1 µF
47,000 pF = 0.047 µF
22,000 pF = 0.022 µF
15,000 pF = 0.015 µF
10,000 pF = 0.01 µF
4,700 pF = 0.0047 µF
1,500 pF = 0.0015 µF
1000 pF = 0.001 µF
330 pF = 0.00033 µF
100 pF = 0.0001 µF
0 pF = 0 µF (bypass)

Finally: How it's wired!
The whole thing is going to be connected in parallel, so you should not have to take apart any of the original wiring except to physically substitute another (e.g., tone) control for the varitone.
  Here are the steps:
  • The capacitors are all soldered on consecutive lugs on the rotary, preferably in increasing order of capacitance.  If it isn't obvious which position is which, probe it with a continuity tester.
  • Solder together the free ends of the capacitors (i.e., the ends not soldered to the switch).
  • Run a wire from the merged free ends to the hot lug on the master volume (or, alternatively, directly to the jack; electrically it's the same thing).
  • Run a wire from the common lug (most likely near the center of the bottom) on the rotary switch to any place in the ground side of the circuit.
  • Play guitar!

An option included on many guitars with varitones is to include a small inductor* on the ground side of the circuit.  This retains the high frequencies, whereas without it, everything is lost below a certain point and the varitone behaves more like a conventional tone knob or low-pass filter (albeit with a different profile from either in most cases).

*The blue thing.  I don't know the value, sorry.

Note: The jack was from when I used this one to make a varitone box.  Normally you wouldn't see it connected exclusively to the jack like so.

Varying your Varitone
A potentiometer can also be added to vary the level of effect of the varitone.  Just place it between the varitone and the rest of the circuit.

Further reading

Copyright Alexplorer.