Components: Potentiometers
A potentiometer is a resistor with a movable tap, turning a fixed resistance into an adjustable one — it's the component behind every knob on a pedal. This chapter covers linear vs. audio (logarithmic) taper, the three-lug wiring convention, and why the wrong taper is the most common reason a control feels bunched up.
A potentiometer — a “pot” — is a resistor with a movable contact called a wiper, and it’s the part behind every knob on a pedal’s enclosure. Turning the knob physically slides the wiper along a strip of resistive material, changing the resistance between the wiper and each end of that strip. Every gain, tone, volume, rate, and depth control you’ve ever turned on a pedal is a potentiometer doing exactly this.
The resistive ruler mental model
Picture a ruler made of resistive material with a fixed total resistance end to end — say, 100kΩ. A pot’s wiper is a movable contact that can touch anywhere along that ruler. Measure from one end to the wiper and you get a resistance that changes as you slide the contact; measure from the wiper to the other end and you get the complement of that value. A pot always has three connection points, called lugs: the two outer lugs connect to the fixed ends of the resistive strip, and the center lug connects to the movable wiper. Rotating the shaft moves the wiper’s position on that ruler, which is exactly what “turning up the gain” physically does inside the enclosure.
Linear taper vs. audio (logarithmic) taper
Not every pot changes resistance at a constant rate as it turns — and this is the single most consequential spec choice for how a control actually feels to use. A linear taper, marked with a “B” prefix on the part body, changes resistance at an even, constant rate across the full rotation, and shows up mainly in blend/mix controls and some tone and rate controls. An audio (logarithmic) taper, marked with an “A” prefix, changes slowly at first and then rapidly toward the end of the rotation, and is the standard choice for volume and gain controls. The difference isn’t cosmetic: human hearing perceives loudness logarithmically, not linearly — a doubling of actual signal power doesn’t sound twice as loud, it sounds like a modest bump. An audio-taper pot’s resistance curve is deliberately shaped to compensate for that, so that turning a volume knob feels like it increases loudness evenly across its rotation. A linear-taper pot used in a volume control instead feels like almost nothing happens for the first half of the turn and then loudness rockets up in the second half — a classic symptom of the wrong taper, not a wiring mistake.
The standard three-lug wiring convention
Most pedal controls use all three lugs: the two outer lugs connect across a resistor or capacitor network (so the pot’s full resistance range is always in the signal path in some proportion), and the wiper (center lug) taps off the point in between and feeds that tapped value into the next stage. Some simpler wiring only uses two lugs — one outer lug tied to the wiper — which turns the pot into a simple variable resistor (a rheostat) rather than a proportional divider. Which convention a given control uses is specified by the schematic, and getting a lug wrong doesn’t damage anything, but it does mean the knob’s sweep won’t behave the way the schematic’s designer intended.
Common mistake: installing a linear pot where an audio-taper pot belongs
Linear and audio-taper pots are physically identical in every way except the internal resistive curve, and the taper is marked only in small print on the pot’s body (commonly a “B” prefix for linear, “A” for audio/log) — easy to miss when ordering or sorting parts. Installing the wrong taper doesn’t break a circuit; it makes the control feel unnatural, with most of the perceived change crammed into a narrow part of the knob’s travel. If a gain or volume control on a finished build feels like “nothing happens until the last quarter-turn,” a swapped taper is the first thing worth checking, ahead of any deeper troubleshooting.