Partial coil split advice

djspecialist

My guitar already has coil splits on both pickups, selected via push-push switching tone pots. The problem is that activating the split results in a significant volume drop; I'd like to get a single coil-ish sound, but at a level closer to the full humbucker.

I have heard that one way to do this is to modify the wiring so that instead of completely removing one coil, its level is reduced instead. So here I am, soldering iron at the ready, trimpots (4k2 and 10k2, since I don't yet know what value will sound best) ... but where do I put them?

I think the photos below show the wire which, when the split is activated, shorts one coil to ground - in which case I need to splice the pot in series into that wire. Right?





Can anyone tell me whether that's the right place?

djspecialist

jellybelly

I put a Rothwell 'Cool Little Knob' in my brothers Fat Strat that sounds incredible and is highly variable. Lots of fat, clean tones, and from a Seymour Duncan Invader no less!! Highly recommended.

ICBM

djspecialist said:

Can anyone tell me whether that's the right place?

That will work, yes.

Or if it's easier to mount the trimmer, connect it between the two coloured wires and the switch - you can use the top terminals on the switch (currently not used for anything) to help support the trimmer, ie solder the two outer connections of the trimmer to the two rows of pins and the centre connection of it to the coil split wires.

djspecialist

ICBM said:

djspecialist said:

Can anyone tell me whether that's the right place?

That will work, yes.

Or if it's easier to mount the trimmer, connect it between the two coloured wires and the switch - you can use the top terminals on the switch (currently not used for anything) to help support the trimmer, ie solder the two outer connections of the trimmer to the two rows of pins and the centre connection of it to the coil split wires.

Haven't yet managed to get around to this, but planning to shortly.

So I understand that I could solder both the outer two lugs of the trimmer to the top row of terminals.  Then would I unsolder only the red wire from the middle row of terminals, and solder that instead to the centre lug of the trimmer?

Is that electrically equivalent to inserting the trimmer into the black wire which leads from the bottom row of terminals to ground?

My head is hurting from trying to turn those pictures into a circuit diagram.  The only reference I have is this one - but it shows the push pot being on the volume, whereas mine is on the tone.

steamabacus

djspecialist said:

My head is hurting from trying to turn those pictures into a circuit diagram.  The only reference I have is this one - but it shows the push pot being on the volume, whereas mine is on the tone.

It makes no difference which pot the push switch is on - a push-pull pot is essentially two entirely different components (a potentiometer and a switch) that are physically joined. Just think of the switch contacts entirely separately from the pot contacts.

If it's still doing your head in (and I do understand, it does my head in trying to visualise this stuff based on written/verbal descriptions) might I suggest a different approach to the trim pots?

I've actually done this very mod on my Ibanez Artist just last week and I find it much easier to just have a few different single resistors on and around the PRS recommended values (I've never found the values need to be more than one or two of the standard resistor values above or below those used by PRS).

Make up (or buy) a couple of short wires with small crocodile clips soldered on either end (these are useful for other mods/repairs so keep them somewhere handy) - about 20cm is more than enough length for these. On a strat-style scratchplated guitar you need enough length to trail out from under the 'plate so you can experiment with the plate fitted. Les Paul style rear cavities are much easier to work on.

Then snip the black wire to ground (in your original pics), connect a crocoldile clip lead to each side and then try out various resistors held between the two remaining clips (effectively inserting the resistor into the wire as shown.

When you have found the best value, solder the resistor between the two parts of the snipped black wire.

On my Ibanez Artist I ended up with pretty much the same values as PRS - 1.0k on the neck and 2.2k on the bridge.

djspecialist

@steamabacus, thanks for your reply.  The tip about making up extension leads with croc clips is nice - I'll definitely follow that.

It's good to hear that you've also done this mod.  Are you happy with the effect on the tone of your Ibanez Artist?  Do you know what the resistance of your pickups are (one coil, and two coils in series)?

As for which wire to snip - I can see that @ICBM's suggestion would allow me to immobilise the trimpot.  But I'm wondering whether that's necessary - it's pretty small, so could it just "float", spliced into that black wire?  I guess in that case I'd want to use some heatshrink to ensure that all the contacts were insulated.

steamabacus

I'm very happy with the mod - it gives the split sound just a touch more 'body', enough to make the sound a little fuller and more musical. The pickups are Seymour Duncan Alnico II Pros, so a 'vintage' wind (not sure of the exact dc resistance). I've also done this mod with a SD Screamin' Demon (around 10k or so) in the bridge position in another guitar. For that, I think I settled on a 1.8k resistor.

imalrightjack

I know that the info provided by @ICBM for me (the PRS DGT mod, I think) worked terrifically well.

djspecialist

Tonight I realised I already had some leads with croc clips as @steamabacus described.

So I snipped those black wires and used the croc clips to splice in a 0-4.7k trimpot.  Doing that on each pickup in turn allowed me to find values I like the sound of (2.4k for the bridge, 1.5k for the neck). Next time I'm near Maplin I'll pick up some resistors close to those values and solder them in.

djspecialist

Resurrecting this thread, due to a change of pickups, and a problem ...

I recently bought a pair of Oil City HBs, plus new pots (2 x 500k volume, 2 x 500k tone w/ push-pull).  I also bought a pair of new tone caps and a pair of resistors (1.5k) for partial coil splitting.  The only other control on the guitar is a standard 3-way pickup selector.

I took all this to a tech for installation, but it seems to have been wired wrongly:
https://photos.app.goo.gl/CyoxscyNAvpeyaJ86

The coil split resistor has been wired in series with the volume pot  

The volume now has almost no effect from 10 down to about 2, then suddenly drops to nothing.  The coil split has a larger than expected volume drop, presumably because there is no resistor in the connection to ground when the tone pot is pulled out.

So, I need to take it back to the tech.  Does anyone have a (link to) a good wiring diagram for my setup?

ICBM

Your tech clearly doesn’t understand what he’s supposed to be doing. The resistors simply go between the coil split switch and ground (or hot, if that selects the coil you want).

What he’s done has effectively bypassed the volume pots.

The diagram you need is exactly the same as for normal coil splitting, but with the resistors in the split connection.

djspecialist

ICBM said:

The diagram you need is exactly the same as for normal coil splitting, but with the resistors in the split connection.

The problem is that I can't find even the no-resistor version of that diagram.

This is the closest I could find (Googling "2 humbuckers 2 volume 2 tone wiring"), but the split is on the volume pot:
https://i.pinimg.com/originals/5d/94/55/5d945562fc919a369b6a2677eddb02e0.jpg

ICBM

It makes no difference which pots the switches are on.

To be honest, if a tech can’t wire up a standard coil split circuit and add a couple of resistors in the right places, I’m not sure a diagram will help...

OilCityPickups

As @ICBM says, the switch can be seen as totally separate from the volume and tone controls ... all that needs done is the white and green series link wires need to be soldered together, then soldered to one end if the resistor. The other end solders to the switch and is shorted to ground when the pot is pulled out. For any sort of competent tech, hardly rocket science ... 
Two more resistors will be on the way to you before the weekend, but I'd seriously consider changing your tech before he buggers them too! :-)  

ICBM

I would actually put the resistors between the switch and ground - a little neater, and saves needing to use a wire for that - but electrically it’s no different and either will work.

OilCityPickups

ICBM said:

I would actually put the resistors between the switch and ground - a little neater, and saves needing to use a wire for that - but electrically it’s no different and either will work.

I usually push the wired up resistor and the link wires into some clear shrink tube and zap it ... so I have a nice stiff resistor wire to solder into the switch ... six and two threes really.

Funkfingers

This is how a Paul Reed Smith S2 Series circuit does it. (Note the different resistor value for each pickup position.)

https://i.imgur.com/lfMlaR4.jpg?1