What to do with unused coil when coil splitting a humbucker?

[wayfaerer]

Hello, first time poster here.

I'm good with wiring and have seen and understand diagrams for coil splitting. For example, check out the "Coil-cut" diagram from StewMac here. This scheme involves both ends (green and red) of the unused coil being grounded when in coil split mode. Obviously, one end (white) of the used coil is also grounded in this case.

Here's my question: Is there any difference in terms of noise, tone, mojo, magnetic field, magnetic pull of the strings, or anything else, between the following scenarios:

1. Both ends of the unused coil are grounded, as in the diagram above
2. Both ends of the unused coil are not connected to anything except each other
3. Both ends of the unused coil are not connected to anything at all
4. One end of the unused coil is grounded, the other is not connected to anything
5. One end of the unused coil is hot (connected to the output), the other is not connected to anything

The reason I ask is that I'm going to wire my guitar up in kind of a non-standard way and just want to understand this better before I finalize the pickup switching scheme.

 

[beaubrummels]

Re: What to do with unused coil when coil splitting a humbucker?

I believe 4-5 have the potential to be a noise antenna. The others are fine.

 

[wayfaerer]

Re: What to do with unused coil when coil splitting a humbucker?

I believe 4-5 have the potential to be a noise antenna. The others are fine.

That's my intuition as well.

I found this forum post which seems to suggest there's more to it than that, but I got kind of lost reading it. It seems like they're talking about the difference between the ends of the unused coil being connected to each other or not, moreso than whether they are grounded (although that's mentioned later in the thread). If I understand it all correctly, the take-home message is that it's better to leave both ends of the unused coil fully removed from the circuit, not connected to ground or each other. If so, I'm not sure why or how much it matters, though.

 

[Artie]

Re: What to do with unused coil when coil splitting a humbucker?

I believe 4-5 have the potential to be a noise antenna. The others are fine.

Actually, 3 & 5. #4 is the normal way any pickup is connected when it isn't being used. Having said that, shorting the coil out is definitely the preferred way.

 

[wayfaerer]

Re: What to do with unused coil when coil splitting a humbucker?

Actually, 3 & 5. #4 is the normal way any pickup is connected when it isn't being used. Having said that, shorting the coil out is definitely the preferred way.

It's conceivable that there is a theoretical downside to #4 (one side grounded, other side floating), but that the pickups are spaced far enough apart to minimize/negate it.

I agree, shorting both sides of the unused coil in a coil-split humbucker to ground does seem to be preferred way. I'm just wondering if there's a reason for that, or if it's just done out of convention or the convenience of wiring a switch this way.

 

[eclecticsynergy]

Re: What to do with unused coil when coil splitting a humbucker?

It'd be cool to employ the unused half as a dummy coil for noise reduction - too bad you can't simply turn off magnetism.
Could a humbucker be made with slots in the baseplate so that one coil could be physically shifted away from the bar mag?
It'd give a new, more literal meaning to the term splitting coils...

 

[GuitarDoc]

Re: What to do with unused coil when coil splitting a humbucker?

Any of those switching options will result in the same thing. There will be no negative consequences to any of them. Which way you choose to do it will only be because of convenience. I've actually used all of those schemes in my guitars...they all work perfectly fine.

All 5 of those will take the unused coil completely out of the circuit. It's not like the unused coil has its own separate/additional magnet, so physically moving it away from the active coil will make no difference.

 

[Artie]

Re: What to do with unused coil when coil splitting a humbucker?

All 5 of those will take the unused coil completely out of the circuit.

Hey Doc . . . I would only disagree with item #5. This will cause the coil to be hanging on the hot side, and acting as a noise antenna. In some environments, like a home studio or such, it probably wouldn't be a problem. But in a club, with florescents and maybe some neon's, it could be a problem.

 

[RayBarbeeMusic]

Re: What to do with unused coil when coil splitting a humbucker?

In practice, leaving either end unterminated is not a problem. Don't worry about it.

 

[Artie]

Re: What to do with unused coil when coil splitting a humbucker?

In practice, leaving either end unterminated is not a problem. Don't worry about it.

At the risk of sounding like a dick. . . a guitar pickup is a signal generator. It can generate the signal you want, from the strings. Or the signal you don't want, from the air. It must be terminated properly to work in the hostile environment of a cheap club. Or anyplace else where it makes noise. Yes . . . don't "worry" about it per se. But if it makes noise, then terminate it properly. It isn't difficult.

 

[RayBarbeeMusic]

Re: What to do with unused coil when coil splitting a humbucker?

At the risk of sounding like a dick. . . a guitar pickup is a signal generator. It can generate the signal you want, from the strings. Or the signal you don't want, from the air. It must be terminated properly to work in the hostile environment of a cheap club. Or anyplace else where it makes noise. Yes . . . don't "worry" about it per se. But if it makes noise, then terminate it properly. It isn't difficult.

Having done this and things far, far more complicated, and exposed those things to lots of stray emf, I stand by exactly what I said.

In theory, there is no difference between practice and theory, but in practice there is.

 

[freefrog]

Re: What to do with unused coil when coil splitting a humbucker?

I found this forum post which seems to suggest there's more to it than that, but I got kind of lost reading it. It seems like they're talking about the difference between the ends of the unused coil being connected to each other or not, moreso than whether they are grounded (although that's mentioned later in the thread). If I understand it all correctly, the take-home message is that it's better to leave both ends of the unused coil fully removed from the circuit, not connected to ground or each other. If so, I'm not sure why or how much it matters, though.

So, for the fun of this Sunday morning (at least for mine), I've redone these tests from Guitarnutz with a different methodology and testing gear.

I've applied the experiment to a P90 sized HB's with two symmetrical rows of screw poles and I've tested it split, with the 2d coil...
1-totally open,
2-totally closed,
3-connected to hot only,
4-connected to ground only...
5-totally grounded.

Conclusions ?

-About NOISE: nothing new. I won’t waste our time by repeating what our fellow members said above.

-About FREQUENCY RESPONSE: Yeah, I've noticed a slight difference in the behavior of the active coil, depending on how the 2d coil is silenced…
But it’s subtle and would probably be washed out by any variation in pots resistance or wiring capacitance.

Below is the response of the HB that I mentioned, once split and with its unused coil wired in different ways.

Firstly, here is its SIMULATED response while its unused coil is totally open or closed on itself (it has been generated thx to a 5spice model including the same LRC specs than the real pickups).



Now, here is the MEASURED response of the active coil with the unused second coil open then closed on itself:



I had to use a linear scale to make the effect really visible. "Negligible" difference, apparently (in this case at least).

That said, it would/should/could/might/may become more noticeable with asymmetrical coils, exhibiting different LRC specs and physical architecture + a different coupling factor.


Now and just to be clear:

1-in my tests, the worst scenario WAS with the unused coil closed on itself without being grounded.

BUT…

a-it’s not as if people would wire it like that in most cases;
b-whatever the topic on Guitarnutz appears to suggest, the problem with an unused coil closed on itself is NOT the slightly different frequency response. According to my measurements, the detrimental effects of this topology would rather be in added noise and distortion + squashed dynamics (but again, these differences are subtle in this case of pickup with two identical rows of poles).

2)Modeling a humbucking pickup like a transformer remains a good idea IMHO/IME, since it takes in account coils coupling (like in my first screenshot above). BUT it would be MUCH more useful to apply it to other things like... DiMarzio Dual-Resonance. He, he... ;-)

FWIW (2 cents of useless geekiness, obviously. LOL).

 

[beaubrummels]

Re: What to do with unused coil when coil splitting a humbucker?

I think the most common Duncan scheme is one not mentioned, both ends of the unused coil to hot. I believe this is what the triple shots do and is how splitting is shown in most Duncan diagrams. I thought this is where the discovery of the “antenna” problem came from and was the genesis of the argument to ground out the unused coil?

 

[Artie]

Re: What to do with unused coil when coil splitting a humbucker?

All the Duncan diagrams I've seen, split to the stud coil by taking red/white to ground. That means that three wires, red/white/green, all go to ground. The Triple Shots are an exception. Since they can split to either coil, you take red/white to ground for the stud coil. And red/white to hot for the screw coil. And, of course, anytime you want to split to the screw coil, you'd short red/white to hot. But that's not really the norm.

Or, you can reverse the order of the wires, and use red for hot, white for ground, and then short the black/green series connection to ground for the screw coil to be active. Both ways work.

 

[wayfaerer]

Re: What to do with unused coil when coil splitting a humbucker?

Conclusions ?

-About NOISE: nothing new. I won’t waste our time by repeating what our fellow members said above.

-About FREQUENCY RESPONSE: Yeah, I've noticed a slight difference in the behavior of the active coil, depending on how the 2d coil is silenced…
But it’s subtle and would probably be washed out by any variation in pots resistance or wiring capacitance.

Thanks, I really appreciate the data you collected! That's exactly what I was looking for and I think it's useful to know.