Wow! This is one industrial, epic, intensely cool blog for y'all! You see, for years now I've been hearing rumors about how the high-end PRS 58/15 pickups perform something strange instead of the typical shutting off one coil to go into single-coil mode. What I saw on several blogs were refrences to one coil being partially shut off via a resistor. I had heard the pickups and certainly I agreed that they did NOT sound at all like ANY split humbucker I had EVER heard! Generally, when one coil is shut off on a humbucker, what's left is an anemic, sharp, piercing single coil sound ... very low output (it IS only HALF a pickup, of course) and VERY harsh/bright because of it's very low wind count.
low-wind count pickups tend to be brighter because there are fewer electrons scraped off or jumping layers due to parasitic capacitance. Generally, a relatively large wire (in pickup terms) of 42 gauge when only traversing ONE of the two bobbins of a humbucker has a LOT less lost electrons on it's comparatively short trip around only the single coil.
Okay ... but ... the "single-coil" sound of a Paul Reed Smith 58/15 is actually quite DARK and lifeless ... quite the opposite of the normal split humbucker. It IS still quite low output compared to the full humbucker, but not even as bright as, say, a darker sounding Strat pickup ... just kinda' like a low-output (and non hum-cancelling) version of the pickup when in full humbucking mode ... which is also quite dull and lifeless.
So what the heck IS going on inside that pickup?
Well, fate brought into my shop a semi-hollow "Special 22" that was a BEAUTIFUL Private Stock instrument gifted to a top Nashville player who is a member of a very well known band. But dude just couldn't get into the dull, dead, dark, lifeless tone of the 58/15's ... and wanted my "Vaughn's Custom Holy-Grail PAF" set installed to have both great PAF humbucker tome AND good solid single-coil tone on all 5 positions of the selector switch.
The Semi-hollow Special 22 has a middle mini humbucker in between the neck & bridge pickups, but it is NEVER used on it's own ... it's ONLY there to mix in with the neck and bridge for those Strat position 2 & 4 tones. and it does a fine job of that, so we left the center pickup alone!
Now comes the good part!
Each pickup was wired with standard 4-wire (black, white, green, red, plus bare ground/shield) and ... When I removed the stock 58/15 set I noticed the individual single-coil switches were like nothing I had ever seen, VERY unusual! Here is a pic of the switches and a quick sketch I made:
So that required some extra digging ... and dig I did, first I measured until I came up with resistance and induction across all conductors, I made a quick diagram, here it is:
So the only thing left to do was tear into one and see if my suspicions were right.
There were a couple of unusual bits. It was potted TO DEATH, the (copper??) baseplate was topped with fiber board, (never seen that before), and the spacer was a cheep plastic piece, and the magnet apeared to be a standard cheapo cut-n-polished Alnico V. Also, the connections were not really "terminated" they were just taped up with the coils... ugg! the leads simply spilled out the side between the baseplate and cover. soooo ugly! Makes me wonder if this was a prototype??
At any rate, I confirmed that both coils terminated to the black lead .... actually, all THREE coils did. Wait ... uh, what?? Yep, three coils! I discovered that the slug side bobbin actually had TWO separate coils wound on it (one on top of the other) one which finished into the white lead was a traditional 4k match to the 4K screw side bobbin, but there was a SECOND coil wound on that poor little slug-side bobbin that read 6K and was terminated to the green lead.
So the IDEA here was that in humbucker mode, both coils had a matched resistance of about 4K, and in single-coil mode the entirely separate 6K coil on the slug side was the only part active, and 6K is a fairly normal value for a single-coil pickup. This all (sorta) makes sense until you think about what wire had to be used to put both the 6K and 4K coils on that one tiny bobbin. Humbuckers (and most single-coils) generally use 42 gauge wire, some overwound sets use one gauge smaller, 43, to get a coil up to about 7K resistance ... but to get 10K around that bobbin ... it had to take 44 gauge, at least on the 6K tap. That's some TINY wire, and that's also VERY significant tonally! Because as the wire gauge gets smaller, the tone gets darker as more and more electrons find it impossible to make it through that tiny pipeline all the way to the other side ... resulting in a dark and dead tone, especially given the heavy wax bath and the relatively low gauss reading from the non-magnetic pole-pieces (as opposed to actual Alnico magnet pole-pieces in a Fender design.. In other words, this pickup sounds EXACTLY like it's design would suggest, dark, dull, dead, lifeless.. Case closed. So now we all know what Paul's engineers were TRYING to do, and why it could never actually sound good.
One last little bit of strangeness for those of you who have made it this far.
Notice something REALLY strange in the single-coil switch diagram above ? Look close! Got it yet??? Look again:
Yep, the phase is reversed!
On the neck pickup in single-coil mode the green (6k start) is grounded and black (all finishes) is hot, and thew Bridge is the other way around! And in humbucker mode, white is grounded and red is positive output on the neck pickup and the opposite is true on the bridge pickup! And, to make this work and NOT be out of phase, the magnet was reversed on the neck pickup and the pickup itself was ALSO reversed so the SLUG coil was outward (closest to the fingerboard).
Holy crap that was a lot of experimental weird crap, and produced some of the worst pickups I've ever heard.
All the photos I could find of the back of PRS 58/15 pickups showed one old-world braided shield over cloth strand lead, and an additional white lead ... I assume with this wiring, the old-world lead is the "standard" 4k per side humbucker, and the white lead is the finish on that second 6K tap on the slug-side. So, simply solder the braided shield to ground and then switch from the cloth wrapped wire to the individual white lead to go to "single coil" mode. That's actually a pretty cool and elegant way of pulling off this weird contraption ... but I'm sure they still sound like crap. Sorry Paul.
I hope y'all enjoyed this blog, it was a heckuva lotta work!