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Replace your pickup selector switch with a panpot

 

by Craig Anderton

 

I've tried several designs over the years to be able to do a continuous pan between the bridge and neck pickups, like how a mixer panpot sweeps between the left and right channels. This isn’t as easy as it sounds, but if you’re in an experimental mood, this mod gives you a wider range of colors from your axe without needing outboard boxes like equalizers.

 

However, there are some tradeoffs. A pickup selector switch has no ambiguous positions: it’s either neck, bridge, or both—end of story. A panpot control has two unamibiguous positions at the extremes of rotation, but there's a whole range of possible sounds in between. These variations are subtle, but while it's more difficult to dial in an exact setting than with a standard pickup selector switch, in return there are more possibilities.

 

ABOUT THE SCHEMATIC

 

This circuit uses a standard potentiometer for volume, a dual-ganged potentiometer to do the panning, and an SPDT (single-pole, double-throw) switch with a third, center-off position. Although you won’t need to drill any extra holes if you guitar has a selector switch/volume/tone control combination, the dual gang pot is thicker than standard pots; this could be a problem with thinner-body guitars.

 

 

 

Due to all the variables in this circuit, I recommend running a pair of wires (hot and ground) from each pickup to a test jig so you can experiment with different parts values. To avoid hum problems, make sure the metal cases of any pots or switches are grounded. If you end up deciding this mod’s for you, build the circuitry inside the guitar.

 

The dual-ganged panpot (R3) provides the panning. Ideally, this would have a log taper for one element and an antilog taper for the other element but these kinds of pots are very difficult to find. A suitable workaround is use a standard dual-ganged linear taper pot and add "tapering" resistors R1 and R2. If these are 20% of the pot's total resistance, they’ll change the pot taper to a log/antilog curve.

 

The panpot value can range between 100k and 1 Meg, which would require 22k and 220k tapering resistors respectively. Higher resistance values will provide a crisper, more accurate high end while lower values will reduce the highs and output somewhat. A 100k panpot with 22k tapering resistors will cause noticeable dulling and a loss of volume unless you use active pickups, in which case lower values are preferred to higher values; however, some people might prefer the reduced high end when playing through distortion, because this can warm up the sound. The volume control (R4) can be a 250K, 500K, or 1 Meg log (audio) taper control.

 

The three-position switch provides a tone control designed specifically for this circuit, and connects a capacitor (C1) across one pickup, the other pickup, or neither pickup (the tone switch's center position). I was surprised at how switching in the capacitor can change the timbre at the panpot's mid position, and this definitely multiplies the number of tonal options. The optimum capacitor value will depend on the pickups and amp you use, but will probably range from 10 nF (0.01 uF; less bassy) to 50 nF (0.05 uF; more bassy). For even more versatility, you could connect the switch center terminal to ground, and wire different capacitor values from each switch terminal to its corresponding pickup.

 

Two final notes: adjust the two pickups for the same relative output by adjusting their distance from the strings. If one pickup predominates, it will shift the panpot's apparent center off to one side. Finally, switching one pickup out of phrase provides yet another bunch of sounds; also note that removing the tapering resistors may produce a feel that you prefer, particularly if one of the pickups is out of phase.

 

 

 

Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.

 

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afrozaon  |  September 10, 2014 at 11:10 pm
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