Here’s a great reference image, which clearly shows the differences between the typical A (audio/log), C (reverse audio/log), B (linear), and W (s curve) tapers. Less common are the K, D, and G tapers.
Here’s another excellent article on guitar pickups, courtesy of Pete Biltoft at Vintage Vibe Guitars. Thanks Pete for the permission to post this here!
August 2011
DC resistance measurements are widely used as a gauge of the “output” of passive magnetic pickups. This use of DC resistance is both technically incorrect and often misleading; to find out why, read on…More
A reader recently asked me a question about the low pass filter in a guitar tone circuit:
Will a 250k tone pot with a .02uF capacitor sound the same as a 500k pot with a .01uF capacitor (all else being equal)?
This is an interesting thought experiment, and the answer is simultaneously obvious and non-intuitive.
At first glance, you might be tempted to look at this standard low-pass filter schematic (borrowed from the LPF wiki), and the associated formula for cutoff frequency as 1/2piRC, and conclude that the two circuits would behave identically (since 250k*.02uF is the same as 500k*.01uF). However, the problem there is that the R in the formula is not the tone pot! That R is really the internal resistance of the guitar, or the resistance of the pickup.
In the tone circuit, the pot actually sits above the capacitor C, but below the branch to the output Vout, as shown at left. So, the formula for the cutoff frequency is more complex. In this analysis by a guitarist/mathematician named Bill, he suggests a formula for the cutoff frequency as follows:
How’s that for insanely non-intuitive?! Bill points out that the lower square root term only works with tone resistances less than about 20k (since otherwise the value would go negative producing imaginary numbers in the square root), thus explaining the often limited useful range of tone pots, and why log taper pots are more useful for tone than linear. Nevertheless, this seems to be an over-idealized formula, since in practice, I do see more variation in the tone pot even at higher resistances. This formula doesn’t seem to capture the full complexity of the reactive network made up of pickup inductor, and overall circuit resistance and capacitance (including cable capacitance).
Ok, so math is clearly the wrong way to think about this!! Too complicated! Back to the original question. Let’s think of it more simply. Imagine you turn both pots down to zero- you’re basically eliminating the variable resistance pot and wiring the cap directly to ground. Of course, the larger capacitance .02uF will sound darker than the .01uF. So they’re obviously not equivalent circuits.
Next up, experiment! Grab a couple pots, caps and some alligator leads and try it out! You’ll find that they do indeed sound quite different. The larger capacitance with the smaller pot resistance sounds darker, no matter how you slice it, when compared to the 500k pot and .01uF cap. Even with both pots up full, the larger capacitance with the smaller pot sounds a bit darker.
This all begs the question, why do guitar manufacturers often pair a 250k tone pot with a .047uF cap, versus the .022uF cap with 500k pots? The former will produce a darker sound both because of the larger capacitance but also because of the increased load on the pickup from the smaller resistance. “Double whammy” as Bill points out at the end of his paper.
Following last year’s All About Pickup Magnets, here’s another excellent article on guitar pickup magnets, courtesy of Pete Biltoft at Vintage Vibe Guitars. Thanks Pete for the permission to post this here!
In this article, Pete consolidates his own expert research on pickups, along with a bunch of information from the Wikipedia magnet entries and Magnet Kingdom, to give us an overview of magnets in general, as well an in-depth look at AlNiCo magnets for guitar pickups.More
Ok, I admit it. I was seduced by the low low price. This Ktone travel guitar, found cheap on ebay, is apparently a knockoff of the Hofner Shorty. The Shorty gets reasonably good reviews, so I took a chance on this one. After a few minutes with the Ktone, it became very clear that the flaws in workmanship and detail far outweigh the price savings.
Turns out, sometimes you get exactly what you pay for… So, I’m now turning my attention to the significantly more expensive, but undoubtedly waaaay better Traveler Guitar Escape EG-1 Vintage. I had a chance to play it at a local GC, and this one looks to be a winner.
Here’s some pictures of the Ktone guitar, which start off promising and then go downhill fast:
As you can hear in my recent video review of the Vox SSC33, the Vox CoAxe pickups sound amazing. They’re dynamic, noiseless in all modes, and most importantly offer up a wide range of incredible sounds.
With the two blades sandwiching the pole pieces, you can see right away that these aren’t your typical humbucker, single-coil or P90…
Curious for more details on these mysterious creations, I got in touch with the man behind the magic- the inventor of the CoAxe pickup: Eric Kirkland, Chief Designer at VOX Guitar Development (G-Rok), in Novato, California. Read on…More
I recently had a chance to play the new Vox SSC33, and it’s a thing of beauty. This is the mid-priced 33 series guitar, in the single cutaway, teaburst finish, with an ash top, mahogany body and neck, and rosewood fretboard. It’s an incredible value when you consider it shares the same MaxConnect aluminum bridge, CoAxe pickups, and super-smooth tuners as Vox’s higher end 55, 77 and Virage guitars. And it comes with a really nice padded gig bag.More
Let’s take a look at push/pull potentiometers. Shown here are three specimens- Bourns PDB183-GTR01-504A2, Gibson PPAT520, and AllParts EP 4286-000. These are all 500k audio taper pots with knurled split shafts. The EP4286 has a longer 3/4” shaft, while the others have the standard 3/8” or “short” shaft. This Bourns has the highest torque of the bunch– it’s the hardest to turn, while the Gibson is the easiest, and the AllParts has just a touch of mechanical graininess to the feel.
A push/pull pot is just a potentiometer sitting on top of a DPDT switch. The switch actuator is the shaft of the pot itself, which drives down right into the switch. When you pull the shaft up, you are moving the switch actuator to connect the top half of the switch, and when you push the shaft down, you are moving the switch actuator down to connect the bottom half of the switch. There’s no built-in electrical connection between the pot and the switch – if you want the switch to control the pot’s behavior, you need to connect up some wires (as in the example described at the end of this article).
