Spin-a-split wiring questions

Tex Mexico · September 2023

Hi guys,

https://www.seymourduncan.com/blog/latest-updates/guitar-wiring-explored-the-spin-a-split-mod

This is a spin-a-split wiring mod I'm planning to use on a single-pickup cabronita project, but instead of full split with the pot at 100% I want it full humbucking with the pot at 100%.

Do I just wire ground to the left lug instead of the right?

In the existing diagram I'd need a no-load pot to achieve full humbucking, would I still need a no-load if I reverse it?

ICBM · September 2023

Tex Mexico said:

Hi guys,

https://www.seymourduncan.com/blog/latest-updates/guitar-wiring-explored-the-spin-a-split-mod

This is a spin-a-split wiring mod I'm planning to use on a single-pickup cabronita project, but instead of full split with the pot at 100% I want it full humbucking with the pot at 100%.

Do I just wire ground to the left lug instead of the right?

In the existing diagram I'd need a no-load pot to achieve full humbucking, would I still need a no-load if I reverse it?

That's what it gives - full humbucker at 10, split at 0. If you wire it the other way you would need a reverse Log pot, or it will basically act like a switch. You do need a log (or at worst audio taper) pot to give a useful range of partial split sounds, a linear won't.

You can use a no-load if you want, but in practice a standard 250K or 500K pot has enough resistance at full up that there's no difference.

Funkfingers · September 2023

Tex Mexico said:

a single-pickup cabronita project

Is the pickup a Filter'Tron clone of some description?

TBH, that type of pickup will have so much treble as to render a coil split for tonal variety redundant.

There is an argument for trying a passive bass cut. This would preserve noise-cancellation at all times.

CasperCaster · September 2023

Firstly, sorry for the long response - the first paragraph may actually provide all the information you need. My comments aren't specifically based on a Filtertron type humbucker, more my experience with PAF and hot PAF pickups.

The easy solution would be to use an off the shelf 250K no-load or blender pot, which will definitively be full humbucking at '10' since the coil junction is lifted and can't see earth at '10' due to the no-load aspect. If this works for you, and you get the results you need then feel free to ignore the subsequent paragraphs. However, it's unlikely that you'll start to hear any change until you turn the pot down to around '5' or '6', because the majority of the interesting partial split sounds occur below those resistance values (crudely, I'd say single coil sounds with increasing body and warmth from 1K to about 10K; in-between sounds in the 10-20K range; and humbucking sounds with decreasing amounts.of single coil character as you progressively go above 20K).

For me, I'd consider using a smaller value log pot and adapting it to no-load (it's quite easy - I think there's a video on Six String Supplies, or Google it). A log 100K pot, or even 50K pot (particularly as its converted to no-load) is plenty for a spin-a-split. And with CTS 450 series pots it's easy to swap wafers, so if you find a solid shaft pot of the correct value, you can swap the wafer into a splined pot 'carcass' if that's what you require. The steeper the taper the better (no more than 10%, ideally 5% if you can find one). The reason for this is because most of the interesting variation occurs below about 25-30K, so you want plenty of resolution in the sub 25K range, but enough additional resistance to ensure it is full humbucking at '10', hence the no-load mod. This is why a typical 250K pot will only really start to provide any interesting sounds below the mid-way point, hence all the interesting split sounds would be crammed into the last half of the rotation of the pot, and if you particularly like single coil sounds they will be in the last 10-15% of the rotation of the pot - the solution is using a 100K or 50K converted to no-load rather than 250K.

As a final comment, if you don't like the fully split sound then you can additionally wire in a fixed value series resistor to set a 'minimum' value for the pot*. For example, if the split sounds below 1.5K are too thin, then wire in a fixed resistor of 1.5K in series with the pot. This means the zero position for the pot will always give you a great split sound since there will always be 1.5K of resistance due to the fixed resistor. Additionally, you effectively increase the resolution of the pot in the low resistance range. This mod is probably something to try after you've lived with the spin-a-split for a while.

*As an aside, this fixed resistor trick can also be used with tone controls - for example, it is one aspect of Fenders Grease Bucket circuit (for want of a better description a variable additional series capacitor is the other aspect, which raises the corner frequency of the filter as more cut is applied, but to my mind Fender made really bad capacitor choices, but that's another story!).

Tex Mexico · September 2023

Thanks so much guys, as usual very high-quality and extremely helpful answers on TFB!

I've got my stuff on the way for this project so will do some experiments when it gets here and let you know how it turns out. Thanks again!

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