Partial Coil Split / Frequency Split - Theory

moosie

Doctor of Teleocity
Silver Supporter
Joined
Jul 18, 2010
Posts
19,800
Age
65
Location
Western Connecticut
There was a wiring thread a few days ago that got me thinking about how difficult it is to get a balanced sound out of one single coil, and one humbucker.

Problem:
The full series-wired HB is overpowering, and splitting to one of the coils suffers a noticeable volume drop requiring a volume adjustment in both directions. Also the split coil often doesn't sound great.

Solutions:
There are two choices better than a plain split. The PRS style partial split with a resistor. And this new partial frequency split, with resistor and cap. So far I like the 6K2 resistor and .005 uf cap method best.

PRS coil splits are known for their natural sound, and little to no volume change. Their method is just to split via a small resistor. Some of the dumped coil is thus retained, boosting the output a bit. The resistance value doesn't seem overly sensitive. For my Duncan Seth Lover, I found that 6K2 was the best, but anything 2K either side of that would be fine. I read that PRS uses 1K2, and 2K2, but read elsewhere that someone (can't remember who) uses 7K - 15K.

It's a bit of a tradeoff, though, because the more you boost, the more you lose chime and brightness. We want it louder than a plain coil split, but also better-sounding. I had some good results with a series bass-cut cap applied to the coil that's being kept. The cap value is pretty sensitive. So far .005 µf sounds best. That's a bigger cut than I expected to like. I predicted that a .02 µf would be in the best range, but that was hardly noticeable. Smaller, at .003 µf, begins to sound artificially bright and shallow.

I'd still like to revisit the cap value, with fresh ears. I wasn't expecting such a large bass cut to sound best.

Screen Shot 2020-04-26 at 10.09.16 PM.png


In all my testing, I chose to split to the south / screw coil, dumping all or most of the north. That means connecting the split wire to hot, not ground. I think it sounded best simply because the screws are adjusted a bit higher, and staggered, on that pickup.

The top figure is easy, right? The north coil shorts to hot. Gone.

The middle fig. is a partial split, where some of north is retained.

The bottom figure builds on that idea. Remember, the more resistance, the more output, but also the darker it gets. To have both worlds, a good boost, without the darkness... I can't add treble, but I can cut bass...

Just for kicks, and because they were too much work to never see the light of day, here are the three test harnesses I made to test all this. Because they're just for testing, there's no tone pot, one of the harnesses has a position #5 that's just a dead spot, etc. It was a lot of wiring for a 20-minute test each time, but I had to be able to hear all the variations back to back.

Screen Shot 2020-04-26 at 11.58.55 PM.png



This was to test splitting with resistors from 1K to 6K, and compare to no split, to plain split, and even to coils wired in parallel.



Screen Shot 2020-04-27 at 12.18.21 AM.png




Next, I wanted to test some higher value resistors. I'd heard enough of the parallel wiring, so I dumped the super switch. I like parallel, but I'm familiar with it, so I don't need to keep comparing it.

In addition to testing different resistor values, I had this idea to try a capacitor alongside (parallel to) the resistor. The cap alone is what I've called the Fat Tap in the past, and what Gibson has used for a (not very good) faux coil tap. Fender also used it in the 60th Ann'y Strat, but with a larger cap.

Alone, the cap (usually .01 - .02 µf, Fender used .05) imparts a woody tone. It did the same here, and was not what I wanted. Good to know.



Screen Shot 2020-04-27 at 02.05.42 AM.png



The final harness kept the same higher value resistors as before, but dumped the parallel cap idea, and introduced the bass cut. Ultimately I tried four cap values, .001 µf, .003 µf, .005 µf, and .01 µf.



Finally, here's a snippet of how to wire up this splitter on a toggle or push pull.



Screen Shot 2020-04-27 at 02.13.03 AM.png
 
Last edited:

moosie

Doctor of Teleocity
Silver Supporter
Joined
Jul 18, 2010
Posts
19,800
Age
65
Location
Western Connecticut
So which version do you like best?

Hmm, was I too confusing? I edited a bit, trying to be more clear.

There's really only the one version. I was just showing the development of the idea, from plain split, then a PRS-inspired split, to the final outcome with resistor and cap. I like the resistor and cap.

PRS has obvious benefits over plain, because of the volume drop. But I felt constrained by the trade off between retaining enough of the other coil, and getting darker, losing single coil chime. Hence the addition of the bass cutting cap applied to one coil.


On the other hand, if you're asking which of the harness diagrams, none. They're just testers.

If you're asking about the final pic, and do I prefer splitting to the screw or slug coil... it depends on context. Not really the point of all this. Just showing how to do it both ways, because with the addition of the cap, which side of the resistor it goes on depends on which coil is being removed.

But in general, if a bridge humbucker, I'll split to the slug (north) coil, because it sees more string movement. In other scenarios, like phase switching, I'd want to split to the coil that remained hum cancelling in the given conditions.
 
Last edited:

moosie

Doctor of Teleocity
Silver Supporter
Joined
Jul 18, 2010
Posts
19,800
Age
65
Location
Western Connecticut

eallen

Friend of Leo's
Gold Supporter
Joined
Jul 30, 2013
Posts
2,855
Location
Bargersville/Indianapolis, Indiana
Cool work thru!

The key to humbuckers single mix is a comparable henry humbucker to the single. I do them all the time with no volume drop and level blending of the mix.

I am a Lawrence wilde guy so I use a L90 2.0 henry in the neck mixed with an L48 in the bridge. Sweaaaat. Beck Lawrence turned me on to the mix years ago & it has been a winner. A little hotter single I would go to 2.8h, and contine up in henry as needed to match.

Eric
 

overt

TDPRI Member
Joined
Jan 21, 2021
Posts
13
Age
35
Location
Spain
I would like to thank you for the coil split idea! It sounds great! I tested every coil split idea in the past (only cap, only resistor, both, etc) and I never really liked them. Your mod has low end at the same time it has those chimming highs, at the same time the volume drop is really small.
 

overt

TDPRI Member
Joined
Jan 21, 2021
Posts
13
Age
35
Location
Spain
Hello

I did this mod on a HH guitar. I used a 4pdt to split both pickups at the same time. On the neck position it activates the South Coil and on the bridge pickup it activates the North coil. I don´t know why but I am hearing pop noises both when activate the 4pdt switch and also when I change the position on the pickup selector (which is ok because I only hear the pops on coil split mode). I seens like the capacitors retains charge or something. I recorded a little video. I aprecciate any help. The split sound awsome!

 
Last edited:

moosie

Doctor of Teleocity
Silver Supporter
Joined
Jul 18, 2010
Posts
19,800
Age
65
Location
Western Connecticut
Hello

I did this mod on a HH guitar. I used a 4pdt to split both pickups at the same time. On the neck position it activates the South Coil and on the bridge pickup it activates the North coil. I don´t know why but I am hearing pop noises both when activate the 4pdt switch and also when I change the position on the pickup selector (which is ok because I only hear the pops on coil split mode). I seens like the capacitors retains charge or something. I recorded a little video. I aprecciate any help. The split sound awsome!


I'm not sure. If you're right, and it is cap discharge, running a high value (1meg) resistor in parallel to the cap should kill the pop.

The signal will still go the easiest way - through the cap. But when it can't, and the cap would load up a charge, the resistor path is better than nothing, and the charge will bleed off.

I think that's how it should work... :rolleyes:
 

overt

TDPRI Member
Joined
Jan 21, 2021
Posts
13
Age
35
Location
Spain
Solved! Thank you. I soldered two 1.5m resistor in parallel with the capacitors (one on each) No pops now. I can´t tell you if it changes the tone or how does it compare to the previous version, but for now it sounds good.

 

sandman1952

TDPRI Member
Joined
Jun 30, 2021
Posts
4
Age
36
Location
usa
Hello

I did this mod on a HH guitar. I used a 4pdt to split both pickups at the same time. On the neck position it activates the South Coil and on the bridge pickup it activates the North coil. I don´t know why but I am hearing pop noises both when activate the 4pdt switch and also when I change the position on the pickup selector (which is ok because I only hear the pops on coil split mode). I seens like the capacitors retains charge or something. I recorded a little video. I aprecciate any help. The split sound awsome!


hi
what value did you use for the resistor on the neck and bridge, what humbucker are you using
thanks
 




Top