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250k volume pot coil-split mod, retains 500k for humbuckers [diagram included]

Alex C

Inspired
I'm the proud owner of a Carvin/Kiesel DC727 that I received about two years ago and I've been very pleased with it. I ordered it just before the Lithium humbuckers were available, but I was able to get a late prototype version of them, which I'm also pleased with and which are still in this guitar even though I have a Crunchlab/Liquifire set laying around.

I ordered the guitar with individual coil-split toggle switches, and my only minor issue has been that the split single coil sounds can be a bit harsh in the upper mids and treble frequencies because the 500k volume pot is still in place when the coils are split (whereas most single-coil setups use a 250k volume pot, which rolls off some of that high end). To address this, I performed the following modification.

The spare pole on each DPDT coil-split toggle is used to switch in a fixed 470k resistor to ground at the output of each pickup, so that when a split pickup is selected the 500k volume pot has a ~500k resistor in parallel with it, which is roughly equivalent to a 250k pot. When a pickup is not split, the 470k resistor is not connected, so in humbucking mode the 500k pot is retained. Below is a diagram illustrating this.




This has really smoothed out some of the "bright honk" and "bite" of the split-coil sounds, making them a bit more Strat/Tele-like, and I can now switch seamlessly from humbucker to single coil mode without adjusting the guitar's tone control or the Axe-Fx BMT or presence.

Are there any production guitars with coil-splitting that implement something like this?
 

brianv4

Fractal Fanatic
I think Fender is doing something similar to achieve to same result. It may be a dual pot for HSS guitars. It's been a while since I've read up on it though. Anyway, thanks for the diagram! very cool
 

GM Arts

Power User
Yes, this is a good mod. The main effect of lower pot values is to reduce the height of the upper resonance peak, which admittedly, sounds similar to "rolling off the top end".

Of course, with both switches set to single coil, you'll have a pot value of approx 160K, but that's fine with both pickups connected.

I recommend connecting the tone cap to the connection between selector switch and volume pot instead of the pot wiper.
 

Alex C

Inspired
I recommend connecting the tone cap to the connection between selector switch and volume pot instead of the pot wiper.

Good catch. That's an error in my diagram; the circuit is wired with the cap on the third lug of the volume pot.
 

Matt_B_77

Power User
Thanks for sharing. I've read about this mod before and it interests me. I split humbuckers a lot and they're bright to begin with (PAFs) and I like 500K volume pots.
 

Rex

Legend!
IIRC, PRS does something like this on some of their models.

I'm putting together an Ibanez 540S-QM that does something similar. It's got an HSH configuration, and I'm using an S-1 four-pole push/push switch to handle the resistor switching across all pickup positions with a single stroke.
 

666was999

Power User
There exist dual pots with 2x250k or 2x500k and also with push/pull switching. That's even better when you often play around with volume and tone.
Most people let them turned all the way up and never touch tone at all...the fixed value is just perfect for them anyway.
 

Julian_J

New Member
Hi everyone,

I know I'm a bit late to response to this thread but as I currently set up a 2x humbucker (with coilsplitting) telecaster myself I was also a bit disturbed by the harsh sound of the single coil setting - especially the neck pickup. It doesn't sound bad but it's way to harsh/modern/whatever compared to a original telecaster singlecoil.

My wiring diagram looks slightly different from yours, that's why I'm not completely sure if I would get the same effect by placing an additional 470k resistor at the spot marked with the red arrow ... ?

WIRING_2_J.jpg

Many thanks,
Julian
 

Rex

Legend!
Hi everyone,

I know I'm a bit late to response to this thread but as I currently set up a 2x humbucker (with coilsplitting) telecaster myself I was also a bit disturbed by the harsh sound of the single coil setting - especially the neck pickup. It doesn't sound bad but it's way to harsh/modern/whatever compared to a original telecaster singlecoil.

My wiring diagram looks slightly different from yours, that's why I'm not completely sure if I would get the same effect by placing an additional 470k resistor at the spot marked with the red arrow ... ?

View attachment 75411

Many thanks,
Julian
You’re right. That’s not the same thing.
 

666was999

Power User
Hi everyone,

I know I'm a bit late to response to this thread but as I currently set up a 2x humbucker (with coilsplitting) telecaster myself I was also a bit disturbed by the harsh sound of the single coil setting - especially the neck pickup. It doesn't sound bad but it's way to harsh/modern/whatever compared to a original telecaster singlecoil.

My wiring diagram looks slightly different from yours, that's why I'm not completely sure if I would get the same effect by placing an additional 470k resistor at the spot marked with the red arrow ... ?

View attachment 75411

Many thanks,
Julian

In your wiring diagramm one humbucker gets split the usual way, by switch the inner wires of the humbucker to the ground. That way you hear the inner/mag coil of the humbucker. (Usually).

The other humbucker gets split different. You switch the inner wires of the humbucker to the 3 way switch. So start and end if one coil are connected to the same point and it shortcut. That way you get the outer/ screw coil of the humbucker (Usually). It sounds different.

If it was my stuff I'd put lower values between 1k to 3k there where you marked it with the arrow, 470k is so high, it would unsplit the split it in a way.
 

guitarnerdswe

Fractal Fanatic
Hi everyone,

I know I'm a bit late to response to this thread but as I currently set up a 2x humbucker (with coilsplitting) telecaster myself I was also a bit disturbed by the harsh sound of the single coil setting - especially the neck pickup. It doesn't sound bad but it's way to harsh/modern/whatever compared to a original telecaster singlecoil.

My wiring diagram looks slightly different from yours, that's why I'm not completely sure if I would get the same effect by placing an additional 470k resistor at the spot marked with the red arrow ... ?

View attachment 75411

Many thanks,
Julian
Your diagram is what's called a partial split. Meaning the normally shunted coil is still active, but not as much as it usually is. PRS often do this.

The upside to this is that it's not quite as noisy as a full split. How much of the second coil is active is determined by the value of the resistor. As been previously stated, 470k is waaay to big for this purpose.

The original post was about loading down the signal so that the singles see a 250k vol pot and the humbucker sees the full 500k. Totally different thing, and a much more subtle difference than when comparing a full split to a partial split.
 

mr_fender

Fractal Fanatic
One downside to using a parallel fixed resistor is that it will change the taper of the volume pot. To avoid this, you can use a dual gang stereo 500k pot and switch that in parallel. That will halve the pot value and maintain a logarithmic taper.
 
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guitarnerdswe

Fractal Fanatic
One downside to using a parallel fixed resistor is that it will change the taper of the volume pot. To avoid this, you can use a dual gang stereo 500k pot and switch that in parallel. That will halve the pot value and maintain a logarithmic taper.
Downside to that is that they're most often awkward to turn. Stiff etc. I can't really say I've ever felt that using a load resistor changes the taper, nor heard about it. I fail to see why from a theoretical standpoint. But granted, I'm not an authority on the subject matter.
 
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Julian_J

New Member
Thanks a lot for all your answers! That leaves me two questions:

1) Which method will me get closer to a real single coil sound? Full Split or Partial Split (with the right amount of kOhm)? I guess I'll simply try it myself this weekend, just curious for your opinions and haven't really found any coherent statements to this topic so far.

2) If I decide to partial-split both pickups, where would I have to place the resistor adressing the initial topic of this thread. Does someone maybe has a wiring diagram for this scenario? 2xhumbucker (both partially splitted), 1xpush-pull-vol

Oh and any changes to the taper of the vol pot are fine to me as I actually rarely use it.
 

guitarnerdswe

Fractal Fanatic
Thanks a lot for all your answers! That leaves me two questions:

1) Which method will me get closer to a real single coil sound? Full Split or Partial Split (with the right amount of kOhm)? I guess I'll simply try it myself this weekend, just curious for your opinions and haven't really found any coherent statements to this topic so far.

2) If I decide to partial-split both pickups, where would I have to place the resistor adressing the initial topic of this thread. Does someone maybe has a wiring diagram for this scenario? 2xhumbucker (both partially splitted), 1xpush-pull-vol

Oh and any changes to the taper of the vol pot are fine to me as I actually rarely use it.
Totally depends on your pickups. There are basically 3 "easy" ways to split a humbucker.

1. Full split
2. Partial split (resistor)
3. Partial split that varies with freq. (resistor + capacitor)

There are more ways to do it by introducing an inductor into the circuit, but now we're heading into advanced territory. No 1 is the thinnest, no 2 is semi-humbucking were the partially shunted coil is constant over all frequencies. No 3 is the most advanced of these, but probably also the most authentic (to a strat or tele) single coil tone.

What you're basically doing is leaving the pickup fully humbucking in the lower frequencies, but gradually split in the midrange, and fully split in the the top end. The problem with fully split humbuckers is often that they lack low end compared to a strat/tele pickup. Splitting it with a resistor and cap gives you a bigger/fuller low end, and retain the chime and sparkle in the highs. Plus, you eliminate the 60 cycle hum. There will still be high frequency hiss though.

I assume you already know how to do method 1. No 2 you can find in the PRS support section. No 3 is sometimes called the Bill Lawrence split. It's wired exactly the same way as the PRS one, but there is also a capacitor in series with the resistor going to ground. Good values to start with is a 47nf cap and a 3.6k resistor.
 
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