Switch Single Coil to Screw Coil on Neck Humbucker Only?

[mongopotamus]

Hi All,

I recently rewired a Charvel DK24 with two Seymour Duncan humbuckers, a 3-way switch, one push/pull volume pot (neck coil split), and one push/pull tone pot (bridge coil split) according to the diagram below.

Everything works great, but I'd like to modify the wiring so that only the neck humbucker uses the screw coil (closest to the neck) when I pull the volume pot out to go into single coil mode.  (24 fret neck, so already losing real estate)

Right now, both pickups use the slug when they are in single coil mode (neck uses bottom coil and bridge uses top coil).

1) Which wires do I swap on the volume push/pull to make this happen?

2) I don't want to change the bridge pickup, do I need to worry about phase issues?

Thanks in advance for any guidance, appreciate the help!

Here are the hardware details:

Neck Pickup:     Seymour Duncan SH-6 Duncan Distortion Humbucker

Bridge Pickup:   Seymour Duncan TB-6 Duncan Distortion Trembucker

3-Way Switch:   920D Custom Original USA Spec 3-Way Blade Selector Switch By CRL

Volume Pot:   500k Pots for Guitars, Push Pull Guitar Pots, Bourns Potentiometer, Short Split Shaft, Audio taper, The Art of Tone

Tone Pot:  500k Pots for Guitars, Push Pull Guitar Pots, Bourns Potentiometer, Short Split Shaft, Audio taper, The Art of Tone

Capacitor:  .022uf 200v Orange Drop 715P Tight Tolerance Polypropylene Guitar Tone Capacitors Small Size

Jack:  Pure Tone Multi-Contact 1/4 inch Mono Output Jack

[newey]

mongopotamus-

Hello and Welcome to G-Nutz2!

Look at your wiring diagram. Notice how the red/white pair for both HBs are connected to the center lug (the common lug) of the push/pulls? Pulling up then connected that red/white pair to the ground, shorting one coil to itself, thus leaving you with the other coil alone, i.e., your coil split. With SD pickups, the black wire is (usually) the "hot" output, and the white wire is the other end of that coil (the slug coil, as you note). Pulling the switch up grounds the white, giving you that coil alone. The red wire is likewise grounded, but so is the other end of the coil, as the green is permanently wired to ground, so the screw coil is shorted.

Sorry for being so basic with the above, but I wasn't sure how much of this you may already understand, and I didn't want any confusion as to what you will be doing here. If this is old nesw to you, I apologize.

So, if we want the other coil instead (for the neck HB), we need to ground the slug coil and connect the screw coil to output- just the opposite of whqat you now have. There are 2 ways to do so. The easiest way is to disconnect the black ground wire that runs from the bottom lug of the neck push/pull to the back of the volume pot, and instead connect it to the output, by wiring it to the 5-way switch's upper right-hand lug, which then is connected to the volume pot and output. This will then short the black and red wires together, shorting the slug coil, while the screw coil's red wire will now be connected to output, the green is still grounded, so we hear the screw coil instead.

The above way is the "down and dirty" method. It works fine, but there are those who claim that shorting coils to the hot may alter the sound a bit. I've been doing coil splits the above way for years and have never noticed any difference, but some would prefer the second method, which is to wire the HB "inside out", (as our member wolf refers to it, member ashcatlt calls it "restacking the coils", which is probably more accurately describing this). To wire the HB inside out, the black/green wires get soldered to where the red/white pair is now connected to the push/pull, the red gets connected to output and the white is grounded to where the green wire currently goes. This method is a bit more work, but it is the more elegant solution.

[stevewf]

Jun 13, 2024 1:10:23 GMT -5 mongopotamus said:

2) I don't want to change the bridge pickup, do I need to worry about phase issues?

The methods described by newey carefully avoid creating phase problems*

Swapping the split coil of only one of the the humbuckers might cause more hum, though, when splitting both pickups with the 3-way in the middle position. Often, guitar makers purposefully select the single coils to cancel each other's hum; odds are that your guitar is like that. If so, then swapping one coil split will not only defeat the hum-canceling, but it'll actually add the two hums together. I'm mentioning the above in case the guitar tends to be played where there's lots of 60Hz noise around.

If you change your mind and swap the bridge split as well, then the hum-canceling will probably be maintained.

There are other effects of switching coils splits, too. Generally, the slug coil gets a stronger signal from the strings because the slugs convey more magnetism to the strings. So people use the slug coils to get a louder sound. And then there's the brightness/thinness of the bridge pickup's outer coil compared to its inner coil. Just a couple other things to bear in mind when choosing coil splits.

*if there were no phase issues before the mod, it won't add any; but if there were issues before the mod, then they will remain. Kinda opposite of the hum scenario; if before the mod there was hum-canceling, that will be lost; but if there was hum-adding before the mod, you'll get cancelation.

[reTrEaD]

Jun 13, 2024 1:10:23 GMT -5 mongopotamus said:

Everything works great, but I'd like to modify the wiring so that only the neck humbucker uses the screw coil (closest to the neck) when I pull the volume pot out to go into single coil mode.

This is actually a very good plan. SD makes pretty drawings but they are poorly thought-out. Having the Neck split to the south (screw) coil and the Bridge split to the North (slug) coil will provide hum-canceling when both split pickups are combined together. That doesn't happen in the SD version. Also, it's better to bypass the unused coil when splitting, rather than shunting it. There's no good reason shunt in this particular scheme, so I've made a change there, too.

Jun 13, 2024 1:10:23 GMT -5 mongopotamus said:

1) Which wires do I swap on the volume push/pull to make this happen?

2) I don't want to change the bridge pickup, do I need to worry about phase issues?

The changes are shown in the drawing below. There won't be any phase issues.

[mongopotamus]

To wire the HB inside out, the black/green wires get soldered to where the red/white pair is now connected to the push/pull, the red gets connected to output and the white is grounded to where the green wire currently goes. This method is a bit more work, but it is the more elegant solution.

Thank you so much newey, appreciate the basic explanation (I need it!).

I am going to try the "elegant solution" and will add the bypass method suggested by reTrEaD.

Thank you stevewf for the details, helps me understand what is actually going on.

Really appreciate all the guidance, I will report back some time in the next week or so.

And now... I have some soldering to do!