Don's first prototype
Reader: Don Baker
Hometown: Tulsa, Oklahoma
Guitars: First, Second, and Third Prototypes
I’m much less a guitarist or luthier than an engineer and inventor. I came up with a neat way to wire matched single-coil pickups into humbucking circuits (U.S. Patents 10,380,986 and 10,810,987). For two, three, four, and five pickups, you get one, six, 25, and 90 distinct humbucking circuits. For three pickups, you can get six more distinct circuits with hum. For humbucking (HB mode) you just add the outer line pickup(s) to the inner line on the 6-way switch label. Hum mode shorts out the inner line pickup.
The guitar industry has shown no interest, so I’m taking the long route, like Mr. Wally Byam, the founder of Airstream Inc. He started off selling plans to make his travel trailers. I planned on making a lot of mistakes, and used Photoshop to design a versatile plywood guitar body using a minimal amount of wood. It has a bolt-on neck (Saga Music Golden Gate S-94, with an unmodified headstock), a central spine below the pickups, two arcing ribs to enclose the electronics cavities, and laminate front and back covers. I make my own round guitar knobs, and do it all in my apartment and balcony (routers are very dusty). Anyone with a decent woodshop can make one.
A closeup of the switch and knob configuration on Don’s first prototype.
The first prototype, a white guitar, has three P-90s with N, S, and N poles up, bridge to neck, tone pots for each pickup, a 6-way switch with a 2-way mode switch (HB and Hum), a preamp to equalize the output amplitudes with switching, a volume pot, a moveable middle pickup, and a power LED which lights with the preamp when the guitar cable is plugged in. The second prototype, a black guitar, has three Allparts Vintage Chrome humbuckers, phase reversal switches on the neck and bridge tone pots, pickups moveable to any place between the neck and bridge, and over 20 distinct circuits.
“I’m writing a highly illustrated DIY journal on how it is made, including most of my mistakes.”
As I build the third prototype with three fixed-place Jazzmaster pickups (with the middle pickup poles inverted to S up) and Spanish cedar veneer front covers, I’m writing a highly illustrated DIY journal on how it is made, and including most of my mistakes. (I’m trying a lot of new things.) I’m up to about 24 chapters and a few hundred images. This time I’m thinking I’ll use just six humbucking circuits with a preamp. In exchange for buying the book, I intend to grant the right to make two patented/patent-pending guitars with non-amplified switching, and then sell the preamp separately.
Don’s second prototype.
It’s going slow. Since a drunk driver nailed me in 1985 when I was 39, I got old and only have a few productive hours a day. But every day, I do a little bit more.
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.
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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.
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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