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.
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.
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!
Founder, Acme Guitar Works
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The Oregon-based company extends their line of sustainably sourced models with an inventive new bracing system and a wallet-friendly price tag.
Myrtlewood grows in Oregon along a 90 mile stretch of the Pacific Ocean coast. It is Breedlove’s favorite tonewood for backs and sides. In addition to its highly varied color patterns extenuated by the thin Burnt Amber Burst finish, myrtle delivers surprising energy and extraordinary tonal balance. To further boost the high-energy sound, we chose a European maple neck—which is denser than mahogany—and an Ovangkol fretboard and bridge. Of course, the top is European spruce for responsive, powerful projection. We spared no detail, including brass inlays, Fishman Flex Plus-T Electronics, and a travel-ready hardshell case.
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Learn Guitar With The Gibson App
The Gibson App is more than a pocket-sized guitar teacher, it’s loaded with an archive of exclusive content and original programming from its premium and accessible award-winning online network, Gibson TV, featuring music icons telling their best guitar stories, with more episodes and installments added regularly. Users can watch Black Sabbath’s Tony Iommi share insights and tales from his decades-long career on the series “Icons,” dive into Joe Bonamassa’s assortment of legendary Les Paul guitars on “The Collection,” or see how Gibson’s iconic instruments are made in their Nashville factory from body to binding on “The Process.” There’s even a series called “The Scene” that focuses on backstage stories from hallowed music venues from coast to coast like The Troubadour and Grand Ole Opry.
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This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl and smooth sustain saturation when pushed into overdrive.
Belltone Guitars, as part of their Custom-Select System curated offering of pickups, has partnered McNelly pickups to create a one-of-a-kind retro-vibe P-90 pickup in the standard Filtertron size format. This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl, and smooth sustain saturation when pushed into overdrive.
The McNelly P-90 Foil-Coil comes housed in a ‘raw’ nickel outer casing with a dull nickel foil face with metal mount screw gromets to complete the ‘new-vintage’ aesthetic, making it a perfect choice for your signature Belltone custom build. Available exclusively through Belltone Guitars.
Check out the Custom-Select System belltoneguitars.com to preview the McNelly P-90 Foil-Trons and all our standard and selectable components available to create your own signature Belltone. Then visit the Dream Lab on our website and select either model B-Classic ONE with its top binding or B-Classic TWO with its arm and body contours select your body color from our wide range of offerings, select your neck profile of either standard ‘C’ or thicker ’59 Round Back and either Maple or Rosewood fingerboard followed by your tuners, pickguard, and strings. Finally, review our curated custom-designed, and unique pickup selection to locate the McNelly P-90 Foil-Trons to complete your signature build.
Builds start at just over $2,300.00 with a custom case and shipping included.
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