Premier Guitar features affiliate links to help support our content. We may earn a commission on any affiliated purchases.

The Log and Short of Tapers

How tapers in pots work, and what it means for your volume control

Last month, we started talking about the differences between audio taper and linear taper pots. If you read that column, you’ll recall that audio taper pots are designed to mimic the logarithmic (log) way in which we humans perceive changes in volume. Let’s look at some diagrams to better understand their operation.

Let’s assume we have a strip of carbon that provides 250K ohms of resistance when measured from end to end with a meter. As shown in the following illustration, if you took measurements from either end to the center, you would expect to measure half the total resistance, or 125K.

If you widened the carbon strip overall then it would provide less resistance, meaning more current would flow through it, just as more current can flow through a large wire than through a small wire. Similarly, if you narrowed the carbon strip, then resistance would be increased and less current would flow. But what if you tapered the strip, making it wide at one end and narrow at the other? As you might expect, a tapered strip would provide more resistance at one end than at the other, as shown in the following illustration.


Get WiredGet Wired

You can see that taking a meter reading from the two ends of the strip still produces a resistance of 250K, but now when you measure from the midpoint to either end, you get different readings depending on whether you’re measuring the wider half or the narrower half.

When we talk about pot “tapers”, this is what we are referring to. Back in the early days of electronics, tapering the resistive element was one way to produce a nonlinear potentiometer. Of course, a linear potentiometer wouldn’t have had a tapered element, but nonetheless the term “taper” stuck and is now used universally, regardless of whether we’re speaking of linear or nonlinear pots.

You may have noticed that in the illustration of the tapered element, 10 percent of the overall resistance (or 90 percent, depending on your perspective) is measured at the midpoint. 10 percent is the de facto standard for audio taper pots at the midpoint because it correlates to the log plot (graph) that describes human hearing. That is, at the midpoint, we want the volume to be half as loud, which correlates to a 90 percent reduction in power. So on a scale of 1 to 10 (which is usually what you’ll find on a volume knob, unless you’re Nigel Tufnel), rotating the pot to its midpoint means that the pot lowers the power from 10 down to 1, while our ears perceive a reduction in volume from 10 down to 5.


LINEAR TAPER

Get WiredGet Wired
125K READING (INPUT HALF OF A 250K LINEAR POT - SIGNAL PATH IN RED)
125K READING (GROUND HALF OF A 250K LINEAR POT - SIGNAL PATH IN RED)
AUDIO TAPER

Get WiredGet Wired
225K READING (INPUT HALF OF A 250K AUDIO POT - SIGNAL PATH IN RED)
25K READING (GROUND HALF OF A 250K AUDIO POT - SIGNAL PATH IN RED)


Tapered resistive elements are a thing of the past as far as I know; they’re certainly not used in pots that are used in the guitar industry. In fact, the carbon element used in guitar pots isn’t even logarithmic – there are tricks used in these pots to simulate a log response, but that’s a topic for a future column. Here are a couple of illustrations showing the concepts presented by the previous illustrations, but applied to guitar pots.

Cool, huh? More next month!




George Ellison
Founder, Acme Guitar Works
acmeguitarworks.com
george@acmeguitarworks.com
772-770-1919

Featuring FET instrument inputs, "Enhance" switch, and innovative input stage, this pedal is designed to solve challenges like poor feel, setting levels, and ease of use.

Read MoreShow less

Ted’s to-go kits: the silver box and the Big Black Bag.

Traveling with a collection of spare essentials—from guitar and mic cables to extension cords, capos, tuners, and maybe even a mini-amp—can be the difference between a show and a night of no-go.

Anyone who’s seen a spy flick or caper movie knows about go bags—the always-packed-and-ready duffles or attachés filled with passports, a few weapons, and cash that’s ready to grab and run with when the hellhounds are on your trail. As guitar players, we also need go bags, but their contents are less dramatic, unless, maybe, you’re playing a Corleone-family wedding.

Read MoreShow less

Firebirds came stock with a solid G-logo tailpiece, although Bigsby vibratos were often added.

Photo by George Aslaender

The author’s PX-6131 model is an example of vintage-guitar evolution that offers nostalgic appeal in the modern world—and echoes of AC/DC’s Malcolm Young.

An old catchphrase among vintage dealers used to run: “All Gretsches are transition models.” While their near-constant evolution was considered confusing, today their development history is better understood. This guitar however is a true transition model, built just as the Jet line was undergoing major changes in late 1961.

Read MoreShow less
DØVYDAS & John Bohlinger Busk in Downtown Nashville
DØVYDAS & Bohlinger Busk in Downtown Nashville Before We Give Takamine Guitar & Fishman Amp to Local

Then we give a Takamine guitar & Fishman amp to an up-and-coming Nashville musician.

Music City is always swirling with top-notch musicians performing anywhere they can, so Takamine and Fishman challenged PG's John Bohlinger to take his talents downtown to—gig on the street—where he ran into YouTube sensation DØVYDAS and hands over his gear to rising star Tera Lynne Fister.

Read MoreShow less