What Are Potentiometers?

Posted on by Stephen Smith

YJM PotAs guitar players we’re familiar with the volume and tone controls on our guitars. Potentiometers (pots) – or variable resistors – have been used for decades on guitars, effects and amplifiers. There are two distinct types of potentiometers that we typically use for these applications: linear (often abbreviated as “lin”) and logarithmic (“log” or “audio”). Each of these types of potentiometers are used for specific applications, but first let’s break down what a potentiometer is, and how it works.

A potentiometer is a resistor that can be adjusted to control the amount of voltage running through a circuit. The most common construction uses three contact points: the middle sliding contact is called a wiper, and the other two ends contact to a fixed resistor called a track. The wiper is moved via a rotating shaft across the track to affect the resistance. The variable potential or voltage is obtained at the wiper contact as it is turned. It is a fraction of the fixed potential found across the track.

Linear potentiometer graphed out

Linear potentiometer graphed out.

Linear potentiometers (like the name suggests) works in a linear way. The amount of resistance between ends of the track and the wiper goes up and down at a constant rate. If you were to map out the rate on a graph it would be represented in a straight line. This sort of potentiometer works fine for a tone control, but for volume controls linear pots can feel a little “off.”

The human ear perceives volume in a logarithmic way, but what does this mean? A logarithm is a mathematical term, so for those of you who finished school a long time ago like me, lets get a definition from Wikipedia.

“The logarithm of a number is the exponent to which another fixed value, the base, must be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: 1000 = 10 × 10 × 10 = 103.”

Logarithmic potentiometer graphed out.

Logarithmic potentiometer graphed out.

So using a linear pot as a volume control would appear to have large obvious changes at low volume, and very little apparent change over the rest of the range.

Logarithmic pots are perfect for volume-type applications as they give the impression of a linear adjustment of volume, even though on paper they don’t. If they were to be graphed out the line would be curve, showing the exponential rate in which the resistance changes.

Seymour Duncan offer a range of high quality potentiometers. These potentiometers are high quality items custom-crafted by Bourns® to exact Seymour Duncan specifications. These audio taper potentiometers are perfect to use for volume or tone controls, and come in 250K versions for single coil equipped guitars and 500K for humbucker equipped guitars.

Also available are the Liberator solder-less pickup wiring system the amazing Blackouts Modular Preamp. These two products also have the same quality Bourns® crafted potentiometers built into them, providing smooth turning and rugged construction, ready to withstand whatever a guitar player throws at them.

Written on March 23, 2014, by Stephen Smith

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  • David Gaskin

    This is about the first page of a ten (or more) page article, isn’t it?

  • Patrick Durham

    What if you had no pots but just p’up straight into jack? Would you get monster output or just meh?

    • david

      no Patrick you wont. Pots, cables and tone filter capacitor are part of a system which acts as a resonator enhancing some frequencies and lowering others. You can tune that system by changing some parts. try to go straight into the amp with a patch cable and listen to the difference, both with full volume or let say half volume, then switch to a normale cable . can you ear the mid boost? have fun.

  • Brett Husebye

    You get more output. You also get less tones. There are many ways to wire pickups, the issue being how original do you wish your guitar to be. I have a 69 Fender Thinline Reissue, I am changing the capacitor to . 022 from a .05. Other than that I dont wsnt to poke holes all over the guitar putting on various switches or extra knobs.

  • DR

    While the discussion about perception of volume and log tapers may apply to any audio amplifier, I contend that the same does not apply to guitars.

    A “volume” knob on a guitar behaves differently than a volume knob on an audio amplifier.

    Plug into a responsive/overdriven tube amp (eg. tweed deluxe), roll up the volume knob for full breakup and roll it back for a clean tone while preserving much of the volume. A linear pot will produce a full useable sweep and large range of tones while a log pot changes too much in only a short sweep acting more like an on-off switch.

    Not all log tapers are the same too… an 80/20 log taper is far different than a 60/40 log taper. In fact the latter is more similar to a linear taper which is 50/50.