ASK-HBS – DC Resistance Sweet Spot For Coil Splitting

ASK-HBS - DC Resistance Sweet Spot For Coil Splitting

Question

I wanted to try your partial tap resistor for my coil tap. How does DCR relate to choosing a resistor value?

Would you say the recommended 7K is a good choice for my SD Pearly Gates, because the DCR is 7.3K?

What about my Custom Custom in the Bridge Position? It has a DCR of 14.1K. It seems 7K isn’t the best choice there.

Many thanks,

Marcus

Answer

Hello Marcus, and thank you for the great question. You use a partial tap resistor because some lower output humbuckers may lose too much gain to output a useful tone when split, especially when activating the mod mid-song. Instead of turning off the second coil completely in a coil-split modification, you can reduce the cut by 25, 50, or 75 percent, to get a more usable split tone.

Unfortunately, the “usable split tone” is 100% user preference. No one can tell you how much of the second coil should remain when you split it. If the tone drops out too much, you will need a higher value resistor if you don’t notice a difference, a lower value. If you have high-output humbuckers like possibly your Custom Custom or the DiMarzio Super Distortion with its 22k DCR, you might not need the resistor at all.

Although I can’t wire it up and try it, I assume your Pearly Gates with 7.3 DCR will remain mostly full-on when split with a 7k resistor, giving you a slight change in tone without losing too much volume. However, you will notice much more of a difference with your 14.1 DCR Custom Custom as the resistor may shut off 50% of the second coil. This won’t be as dramatic a change as leaving the resistor out, which would shut off the second coil completely.

Again, it’s not about the resistor value as much as the resulting tone. In my opinion, the best way to find the value you need is to use a variable resistor to get the sound you want. After which, you can measure the resistance and install a permanent resistor with that value or leave it as is. We explain how to use a variable resistor in our Partial Tap Resistor – Advanced Techniques article, and I think that will help you.

I hope this answer helps you, and I’d love to know what values you find sound best when you choose them.

Thanks again!

Ed

REPLY FROM MARCUS

Hey, thanks for the advice.

So the choice of resistor is totally related to the DCR of the pickup. That’s cool info and would be great to see as a footnote on the  Partial Tap Resistor – Advanced Techniques page because many pickup manufacturers list DCR in their specs (or it is easy to measure directly).

For example, if I installed the 7K resistor for my 7.3K coil tap (as I was intending to do), it would have basically made my switch efforts a waste!

So based on your input, I installed a 2.2K instead and now have about 30% signal coming through my slug coil when tapped.

It sounds good enough, but I might add a second 2.2K in parallel (which according to my calculations means 1.1 K resistance / 15% signal pass).

For the Custom Custom, I ended up leaving out the resistor completely. The tone I wanted was a semblance of a Strat bridge pickup and I think I’ve achieved that sound, especially when I add in a little reverb… but IMO nothing can create that Fender twang except a Fender.

Anyways thanks for the tips!

Best regards,

Marcus

Our resident electronics wizard came by his skills honestly — first as an apprentice in his father’s repair shop, later as a working musician and (most recently) as a sound designer for film. His passion for guitar led him to Humbucker Soup, where he continues to decode the wonders of wiring and the vicissitudes of voltage. Ed has never taken his guitar to a shop — he already knows how to fix it.