HS Wiring with 3-Way and Push-Pull for Series/Parallel

[aotmr]

I'm happy to share a wiring scheme for an HS guitar (one humbucker, one single coil) with an open-frame three-way switch and a push-pull pot. My goal was to create a close-to-stock wiring scheme that offers a good selection of hum-cancelling sounds (denoted by asterisks) with a single additional switch usable as a "rhythm/lead switch". The selections are:

	Parallel	Series
1	Bs + Bn*	Bs x Bn*
2	Bs + Bn + N	Bs x (Bn + N)*
3	N	Bs x N*

With the push-pull in, the three-way selects between the neck coil, the bridge coils in parallel, or both. With the push-pull out, the three-way selects between three hum-cancelling series options which place the south bridge coil in series with the neck coil, the north bridge coil, or both in parallel.

Note: Schematic is currently unverified and untested

I don't know how to properly draw a three-way open frame switch but the center position in the schematic does denote that both are connected in the center position. If the image should become unavailable in the future, the gist is that the series/parallel switch either grounds the neck and north bridge coils or puts them in series with the south bridge coil; it also places the bridge coils in parallel. This scheme is reasonably flexible, limited mostly by the three-way switch. For example, it would be easy enough to wire the tone control as a series blender, shunting the south bridge coil in series mode.

I intend to use this scheme in a Squier Baritone Cabronita Telecaster with a CALIG model P91 neck pickup and P94 bridge humbucker replacing the two factory single coil P90 soapbar pickups. I will be sure to check back in once I install the modification and with any further changes should I make them.

[newey]

aotmr-

Hello and Welcome to G-Nutz2!

Dec 21, 2020 20:17:51 GMT -5 aotmr said:

I don't know how to properly draw a three-way open frame switch but the center position in the schematic does denote that both are connected in the center position.

No one else knows how to properly draw one either, there really isn't any standardized schematic symbol for a SPDT On-On-On switch. ChrisK, one of our founding members here, used to draw one like this:



Which is probably as good a representation as any.

Your schematic looks correct to my eyes. A few points to make, however. First, any combination of 3 coils, whether in series, parallel, or any combination thereof, can only be partially hum-cancelling- meaning it will be quieter than a SC pickup alone, but not as quiet as the two coils of a HB. Second, whether the N X BS combo at position 3 in the series mode is humcancelling or not will depend upon the polarities/winding of those coils- the neck pickup will be RWRP with respect to one or the other HB coil, but you haven't specified which one. If it is opposite of the BS coil, then yes, it will be hum-cancelling.

[aotmr]

Thank you for the welcome; I've been lurking for a while and I'm looking forward to sharing some of my own ideas as well. And you're right, I could afford to be more explicit with my pickup winding directions.

As for hum cancelling three (or I suppose any odd number) of coils, I believe three in series-parallel as I've shown (or, A x (B + C) where A is of the opposite winding and polarity as B and C) should cancel. Unless I'm wrong, two identical coils in parallel produce the same amount of hum as a single coil: twice as many windings but half of the hum is shunted through the other coil's DC resistance.

[newey]

Dec 21, 2020 23:42:05 GMT -5 aotmr said:

Unless I'm wrong, two identical coils in parallel produce the same amount of hum as a single coil: twice as many windings but half of the hum is shunted through the other coil's DC resistance.

Well, we'll throw this one up for discussion, but I don't believe that is correct. Hum-cancellation doesn't work by "shunting hum through the other coils's DC resistance", it works because the string signals of the two coils are in phase (because one is RWRP), while the noise signal (which is induced in the windings via the environment, not the vibrating strings) is out-of-phase and cancels with the opposite coil.

[aotmr]

No, I don't disagree with you. My assertion is that two identical coils with the same hum-polarity in parallel produce the same amount of hum as one--because half of the hum (and indeed, signal as well) is lost through the other coil. Then, those parallel coils will cancel with a series coil with the opposite hum-polarity. This doesn't occur with series-connected pickups, and two pickups with the same hum-polarity connected in series will produce twice as much hum.

[newey]

Even in a HB, hum cancellation is not perfect. I have several HB-equipped guitars with switches to put the HB coils in either series or parallel. By your theory, I should notice a difference in the noise level by switching the coils to parallel (there is of course an obvious difference in output and in tone), but I've never noticed a difference in the noise level when switching from series coils to parallel. Granted, HBs are fairly quiet to start with, but if it was as you suggest, I should hear a difference.