Basically, we can influence three parameters with the values of the two components:
• The voicing of the single-coil emulation (governed by the cap’s value).
• Hum-cancelling effectiveness (governed by the cap’s value).
• Voicing of the cap’s uncoupling range (governed by the resistor’s value).
So as not to bore you with analog-system theory, I’ll simplify some explanations that aren’t critical to this mod. One common question is about the order used to connect the cap and the resistor in series. Actually, it doesn’t matter, but from a theoretical point of view, electromagnetic compatibility (EMC) states the cap should be connected to ground as shown in Image 2.
I’m using the Seymour Duncan humbucker color code for this illustration. If you have a humbucker with a different color code, this should be easy to transfer. Of course, you can only split a humbucker when it has 4-conductor wiring that provides access to the start and finish of each of the two coils. If you have a humbucker with the standard 2-conductor wiring, you’ll have to convert it to 4-conductor specs. Have this done by a qualified guitar tech or simply buy a new humbucker that comes stock with 4-conductor wiring. Let’s see what happens when you tinker with the values of the two components.
Resistor. Fender’s 1.5k resistor creates a little hole (about -5 dB) in the mids, at around 2 kHz. Depending on the pickups and the amp, this can sound good. But when using Fender blackface amps, this isn’t as desirable because of their inherent scooped midrange. Increasing the resistor value to 3.5k will eliminate the little hole in the mid frequencies. My personal favorite value is 3.9k ohm, which yields absolutely no mid hole. If you want more choices, you can wire a switch with two different resistors (for example, 1.5k and 3.9k) or use a 5k linear pot for a stepless control of this factor.
Capacitor. The cap’s capacitance lets us influence two factors, and we can deduce a relationship between them:
1. The smaller the capacitance, the better the hum-cancelling feature.
2. The higher the capacitance, the better the single-coil emulation.
Here’s a way to understand the cap’s function in this wiring: As the cap’s value drops to zero, it’s effectiveness is reduced. Zero capacitance is the same as using this wiring with no cap at all. With very high capacitance values, the coil will be shorted out more and more, until it is completely shorted, leaving only one coil still active.
A good range of cap values is from 0.01 µF up to 0.1 µF. You can use these—and everything in between—to balance the relationship between hum-cancelling and tone. The Fender value of 0.1 µF will result in maximum single-coil-like tone with a bit of hum cancelling—still much more than without the additional RC network. A 0.01 µF cap will result in a very high hum-cancelling ability (almost 40 dB), but with a tone that’s quite fat and closer to a humbucker than a single-coil (think P-90 through a warm tube amp).
Explore these cap values, combined with resistor values from 1.5k up to 5k ohm, to dial in the midrange behavior. This will keep you busy for hours! For even more flexibility, you can implement a rotary switch with several cap values and a switch to turn the complete RC network on or off.
All this can be applied to our Fender wiring. Its stock values guarantee maximum single-coil emulation, but the downside—perhaps not for you—is less hum-cancelling and a tone that exhibits a midrange scoop. I think changing the values to a 3.9k resistor with a 0.047 µF cap will result in an authentic single-coil-like tone with no midrange cut, but with the benefit of greater resistance to hum and noise. In the end, it’s about finding the right compromise, so experiment with the values of these two components to find a tone you love.
I’ll be back with another project next month … until then, keep on modding!