Notes on Electronics

Potentiometers

Guitars with humbucking pickups typically use 500K-ohm potentiometers (pots), and guitars with single coil pickups typically use 250K-ohm pots. There are several exceptions here, and in some cases, other pot values are used. A couple of examples are: Gretsch guitars typically use 500K-ohm pots regardless of pickup type. Gibson uses 300K-ohm pots in many guitars.

When a volume or tone pot is turned to “10”, a small amount of the guitar’s signal is still passing through it to ground. Because of this, it still has an effect on the guitar’s tone. Our ears perceive this loss of signal to ground as being mostly the “high end” or high frequencies. The lower the value of the pot, the more of the high frequencies seem to be lost to ground. The higher the value, the lower the loss.

Guitars with single coil pickups, such as most Fenders, use the lower 250K-ohm pots, sending more of the over-abundant high frequencies to ground, making for a more pleasing tone than if it were otherwise. Guitars with humbucking pickups, such as most Gibsons, use the higher 500K-ohm pots, sending fewer of the less plentiful high frequencies to ground. Even with this pot value “manipulation” of the signals, guitars with single coil pickups typically output more, and higher, high frequencies than guitars with humbucking pickups. This is just the nature of the beast. The phenomenon that reduces hum in humbucking pickups also reduces some of the pickup’s high frequencies.

Tone Capacitors

The value of the capacitor (cap) connected to the tone pot will have an effect on the tone as well even when the tone pot is on “10”. Many players can hear this, some cannot. Most of us can hear the difference in cap value when the tone is turned down towards “0” from “10”. The tone control’s cap value is something that you may wish to experiment with to “dial in” your desired tone. The lower value cap will pass the highest frequencies to ground. As the cap value is increased, the “gate opens wider”, allowing additional, lower high frequencies to pass to ground as well. For a guitar that seems overly bright, try installing a higher value tone cap. For one that is overly dark, try a lower value cap. Again, the effect is very subtle.

“Treble Bleed” Capacitors

Quite often, when a volume pot is turned down, our ears perceive the treble frequencies being reduced in a disproportionately high amount as compared to the bass frequencies. To counter this phenomenon, a “treble bleed” or “treble bypass” capacitor is sometimes used. The treble bleed cap is typically soldered across the “signal in” and the “signal out” legs of the volume pot. (See our Tele ^® Wiring Diagram and our Strat ^® Wiring Diagram for examples.) The common value for this cap is .001µF (microfarads). You may wish to experiment with this if you are experiencing a noticeable treble loss as you turn down your volume control. Some guitar and amp combinations do not really output much, if any, of the treble frequencies in question to begin with. If this is the case, or if you do not use your volume control, this issue is of no concern.