Mar 142019

Fig. 1: DuoTone control circuit

The Tone Control hasn’t changed much over the years. It’s a capacitor in series with a potentiometer, and these connect between the volume control’s hot (or middle) terminal to ground. Removing the gray capacitor (5 nF) shown in Fig. 1 produces the traditional circuit, though the potentiometer may be a different value (and the remaining capacitor will probably be 20 nF, or 0.02 μF).

In their quest for “better” tone, many players make changes to the capacitor, the potentiometer or the wiring. To my ears, most of these mods don’t necessarily make a guitar’s tone better, just different. However, that difference may be better for the way you play, your pickups or your musical tastes.

The studio offers many opportunities to change guitar tone. Before going into amp sim distortion, I usually use an EQ plug-in rather than the guitar’s tone control to reduce highs, because it allows me to choose the EQ’s frequency and rolloff more precisely. But unlike a plug-in, a guitar’s tone control interacts with the pickup to accent particular resonances. That’s a difficult effect to obtain solely with EQ.

The DuoTone control shown here rewires the guitar’s tone control to provide two different resonances along with the traditional high-frequency rolloff. The tone control’s capacitors have smaller values than usual, so the tone isn’t quite as dark (see Fig. 2). The 500k linear-taper potentiometer takes the caps out of the circuit when centered; turning it clockwise brings in one tone, while spinning it counter-clockwise brings in the other.

Fig.2: Frequency response curves: The red line is response with tone control disconnected. The pink line shows response with a 10 nF capacitor, and blue shows it with a 5 nF capacitor.

To find the capacitor values you prefer, temporarily disconnect your tone control and get two leads with alligator clips. Attach one lead to the volume control’s hot terminal and the other lead to ground. Now clip the remaining lead ends to different capacitors and pick the values that produce your two favorite tones. For me, they were 5 nF (0.005 μF) and 10 nF (0.010 μF). Then rewire your tone control as shown in Fig. 1 to accommodate the extra capacitor. You can also wire the tone control’s middle terminal to the volume control’s middle terminal for “vintage” wiring, or to the volume control’s hot terminal for “modern” wiring.

Modding the mod. The pot’s value is a compromise. A 250k pot lets you dial in tone with more precision, but it dulls the sound somewhat, even with the pot centered. A 1 Meg pot makes no detectable difference to the sound when centered, but the control acts more like a switch when it’s turned, because the range over which you can hear a tonal change is small. A 500k pot gives a smoother action and produces only the slightest dulling (you may not even notice it).

Another mod involves using a pot with a push-pull switch to disconnect the tone control and remove any possible loading. Insert the switch between the tone control’s middle terminal and the volume control, or between the junction of the two capacitors and ground. This is helpful if you use a 250k pot but probably unnecessary for the other values, making this mod even easier!

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Tech Support: Tone Control
Source: Guitar Player