Auto (Partial) Split HSS wiring

[doobiebrother]

I came across this interesting post describing a slight modification to the typical PRS style partial coil split. I was wondering if it was possible to wire a 5 way switch (or superswitch if necessary) so that it works like this:

1: Bridge HB
2: Partial Split Bridge (north coil) + middle
3: middle
4: neck + middle
5: neck

For those that don't want to click on the link, the OP essentially adds a HPF (5nf cap) to the coil that isn't being shunted so that he can tame the bass frequencies a bit.

[newey]

doobiebrother-

Hello and Welcome to G-Nut2!


This is not possible (at least as I see it) with a regular Strat-type 5-way switch. You can split the HB at position 2, just as Fender does with their HSS models. But because the Regular Strat switch shorts postions 1 and 3 at position 2, adding a cap or resistor for that position will also affect the full HB at position 1.

A Superswitch (or similar 4P5T lever switch) would do the trick, however. There is also a 2p5T "half Superswitch" which would also work.

[doobiebrother]

Happy to be here! Good to know that this is possible with a standard superswitch.

I found this diagram that's pretty close to what I want to do. Sorry for the dumb question, but what changes would I need to make to that wiring diagram to do what I want? The main difference I see is that I wouldn't need to split the neck pickup (HSS). How would I integrate that RC circuit? 

[newey]

To undo the neck split at position 4 is simple, just disconnect the two wires (red and yellow) marked "north + south finish from neck". These are soldewred to lug 4 on the upper left-hand pole of the switch. Solder those two wires together if they didn't stay soldered together when you disconnected them from the switch. Tape off the connection and just let it hang loose in the cavity.

As for the cap and/or resistor, the diagram you linked to shows one version with a resistor and another with a cap and resistor. Is the cap-and-resistor version what you want to do, or is it just the cap alone (that's all you mentioned in the end, so I'm unsure).

[doobiebrother]

That makes sense! Thanks a bunch for taking the time to help me with this.

Yep, I'd like both the resistor for the partial coil split and the cap for the bass cut. All of this of course only happens on position 2

[doobiebrother]

This is almost exactly what I want. I initially thought I'd want just the middle pickup in position 3, but am now interested in a coil split bridge + neck option. Would the resistor go in between the right position 2 lug and ground? would the cap go on the left position 2 lug? just to recap:

1: Bridge HB
2: Partial/HPF Split Bridge HB (north coil) + middle
3: Partial/HPF Split Bridge HB (north coil) + neck (am open to south coil too if that is easier, just worried that the rc circuit will make it difficult)
4: middle + neck
5: neck

[Yogi B]

May 27, 2024 15:17:30 GMT -5 doobiebrother said:

I'd like both the resistor for the partial coil split and the cap for the bass cut. All of this of course only happens on position 2

What is the actual tonal result you desire to achieve?

I ask because in the linked TDPRI thread the intent seems to be to balance the output of the split neck humbucker with the bridge single coil in their respective positions. Whereas it appears there was little to no consideration of what happens when both pickups are selected in parallel — i.e. the only circumstance you are planning to use the partial split.

The bass cut capacitor works because it's an impedance that is grows larger at lower frequencies, becoming larger than the combined parallel impedance of the tone & volume pots and the input impedance of whatever is next in the signal chain. Thus, the voltage divider to which the signal is subjected (formed from the capacitor and the following loading) results in greater attenuation for bass frequencies. The cut-off frequency of this is around 150Hz — assuming a 5nF cap, two 500k pots (with the tone at 10), and a following input impedance of 1Meg.

The blue trace in the following plot (which is the humbucker with the partial coil shunt & bass cut cap) gives a rough idea on the effect upon the frequency response. For comparison the full humbucker (green) & the humbucker with one coil completely shunted (purple) are also shown.

A potential issue comes when we place a lower impedance load after the capacitor, this raises the cut-off frequency resulting in more of the signal being removed. An example of such would be another pickup, which for low frequencies has an impedance close to its DC resistance — this is what the lower part of the following plot hopes to illustrate.

The orange traces show the combined output of both coils the (partially) shunted humbucker and the middle (or neck) single coil. The other traces show how each pickup contributes to that total: red for the humbucker & yellow for the single coil. The bright traces are for the situation with the partially shunted humbucker coil & the bass cut cap; whilst the darker traces are for 'regular' switching — the fully shunted humbucker coil (and no cap).

With the bass cut cap in place, below around 1kHz where the humbucker contributes virtually nothing to the resultant signal, with the single coil taking up the slack. The capacitor affects how the humbucker loads the single coil, as well as vice-versa. As such, there's less loading on the single coil compared to the simple parallel case, so for lower frequencies the output is as though it were just the single coil selected alone. This parallel 'balancing' is why, even though the individual coils' contributions vastly differ between the two cases, the (orange) combined responses (insofar as what the electrical circuits contribute) are so similar.

[doobiebrother]

These response curves are amazingly helpful, thanks for those!

To answer the most relevant question: I want less low end on my position 2 sound, but without volume drop. I understand there'll always be some drop, but it'd be nice to minimize the volume drop if possible. Right now, my guitar does the full split HB + middle on position 2. The tone itself is great, but there's a ton of extra low end that I end up having to dial out. This ends up negatively impacting the other pickup positions.

Are there other resistor/cap values that can allow more of the humbucker signal in so that it contributes more to the summed signal? There might also be another solution entirely that can accomplish what I'm looking for. That second figure is fascinating. I had no idea affecting the signal for the bridge humbucker would affect the middle pickup's contribution the way it does.