Internal GK-5 Install (part 3)

I flipped her over and am ready to locate the tone control pot’s hole. Since it’s the most rearward, I can work from that point to optimize the location of the rest.

I got it right at the edge of the cutout for maximum forward room for the other pot and the switches.

I managed to scribe the approximate center of where the shaft was.

I located the hole for the volume pot, traced the outline of the cutout for reference, and then drilled both undersize. I used a reamer to get two perfectly round holes that were just big enough for the pots to push through them.

Some cheap copper foil tape for shielding (I got it at Lidl for like $2.99 for 60 ft).

Squeegee it into place and then use a straight edge and razor knife to score and peel the excess away.

All done, ready for the next, final steps.

I mounted the pots and knobs, seated myself with the instrument in playing position, and used an awl to mark the ideal location for the pointer for each control.

then used a hand drill to get both holes about .002 under size for the Luminlay rod.

I put a drop of cyanoacrylate (CA) glue on the stick and worked it into the first hole, cut it flush with nippers, and repeated the process for the other hole. The dots will look great once I wet sand the pickguard to a uniform sheen.

Back to the body. I need to get shielding paint in there and give it time to dry before I assemble anything.

I prefer the StewMac shielding paint, but mine was dried out (12 years old) and they didn’t have it in stock. Fortunately, an e-bay vendor had some okay stuff at a decent price (shielding paint is pretty pricey). According to the label, it’s for professionals, but I used it and got fine results regardless.

While the paint dried, I wet-sanded the control plate with 600…

Then 800…

And finally some 1200 to get a low-gloss look that better matches the satin black finish of the Synapse. The dots look like they were always there.

Drilling brass (especially 1/8” (3.5mm) plate) can be tricky. I needed the thickness for two reasons:

• Strength: a pair of jacks with cables in them can really wrench something if you, say, step on a cable

• The added thickness moved the ends of the panel jacks further from the internal surfaces inside the body cavity.

What makes brass tricky for drilling is that large diameter drill bits can ‘grab’ and deform/mangle the piece right as you break through the far side, and in my experience, this is a bigger issue when you start (as you should for practically any other metal) with a pilot hole. I read a lot of wisdom from various machining message boards, and decided to drill to full size (no pilot) and to go a bit easy on the chuck tightness so that when the bit grabs the brass, it will simply stall instead of mangle.

I started with a pair of punch marks, hoping they might influence the web of the drill as it made first contact. I should have drilled, like, 1/8” diameter shallow dimples from those punch marks instead. Well, it worked fine for one, but not the other, so the holes ended up on a slightly different plane, but it was actually a serendipitous thing I later discovered.

So there are two 15/32 holes now. Not aligned the way I wanted, but close enough. I traced them onto the steel jack plate and then tried to remove as much as I could from the circles (it’s a very interrupted cut once you get to about a 1/4” hole) with a step bit. I then very laboriously filed them the rest of the way with a round file.

Hopefully these pictures will help you smell what’s cooking…

I hit part of the hemispherical rout with a burr to get just a little more clearance for jack solder lugs if needed. The grounds are the longest lugs, so likely not really an issue if they hit the shielding paint— which should be ground as well. The sleeve lug of the TRS looked kinda close, so I played it safe.

there’s about an 1/8 of an inch (3.5mm) of leeway. Plenty.

I put some shielding paint on the freshly milled wood, installed the jack plate with the TRS jack, and then soldered the 2-conductor 22AWG shielded pigtail onto it. Since those holes in the brass weren’t on the same plane, I was able to install the jack plate mounting screw next to the TRS jack with it already screwed in tight. I put the other jack plate screw in, and then used my ace-up-the-sleeve tool to get the TS jack torqued in.

The secret weapon to tighten the jack from the inside? “Jack the Gripper”

It’s an ingenious tool from Frank Ford of Frets.com. Somewhere on frets.com’s ‘machining’ pages, you can see a step-by-step walkthrough of Frank making them with his lathe. You can buy them through StewMac. Totally worth it. A real problem solver.

Getting ready to solder my TRS pigtail to the lugs on the plastic TRS jack mounted to the GK-5 PCB. Plenty of big lugs on there to piggyback from for a non-destructive ‘mod’. I considered making a short TRS cable to run from the GK plug to the back of the new jack, but after about a millisecond, I decided that solder is simpler and superior in every way, mechanically and electrically— no finnicky connector surfaces to need de-oxidation a decade from now; just continuous, molecularly bonded metal all the way from the circuitry to the jack.

And there they are— permanent, unless I heat them up and pull them off to return the unit in original condition.

Time to tuck all of it in and see where we land…

With plenty of room for the board, it was time to make my GK-5 burrito. Ever wonder what that amber film they put between PC boards and cases and such is? It’s Kapton. If you decide to insulate your electronics with some, be sure to get the kind that’s rated as an insulator. Some varieties have conductive coatings for shielding, so be cautious when selecting and ordering.

It’s fairly resistant to bending and creasing (mine is 5 mil), but that will help me in this case…

About 4 wraps around total, and the whole assembly fits in there perfectly and is completely isolated from the conductive paint, etc. The PCB itself weighs a few grams, so with just the tension of that thick Kapton rolled around it, it’s totally stationary, even if you shake the guitar.

When I originally planned an internal installation for the GK, I had all sorts of notions about anchoring the PCB— a 1/4” dowel into the jack, and then sink the dowel into a hole in the solid part of the control cavity wall, or maybe some tiny, long screws with plastic tubing for standoffs and a few other elaborate, overkill ideas.

But just rolling it up in a dielectric film was way better and simpler than any of those. Glad I didn’t overthink it for too long.

All the wiring has been tidied-up, and the back plate is back in place. The double jack config is looking kind of mysterious now that it’s put in the final visual context. It also almost looks like it was meant to be there— which it most certainly was not. Either way, thanks for just enough extra room back there Mr. Steinberger. Awesome design!

And finally, I have the pickup and volume/tone controls where I prefer.

Will I be able to run the GK and magnetic outputs at the same time?

Will the plugs fit in there side-by-side?

Yes, I can and…

Yes, they do.

I doubted it from the get-go, but a part of me suspected there could be some high-speed data noise (‘hissing') in the analog output if I ran them at the same time, inside the same control cavity, but there is zero audible interference, noise, etc., even with preamp gain cranked to the maximum setting and a boost pedal fully boosted. I think the digital signal is orders of magnitude weaker than the magnetic pickup signals, and their inherent impedance differences are far too great for any noticeable crosstalk.

All in all, everything works as expected, no wart on the outside of the instrument, and the controls are in a better location.

Mission(s) complete.

And that concludes the GK-5 install and long-postponed control relocation for one of my Synapse baritones. I hope you learned something.

At the very least, I hope you learned that a vision and the determination to make it reality are 95% of what’s needed to create something that no one else (probably) has.

Make stuff happen. Don’t be afraid of failure. Don’t obsess about perfection, don’t get wrapped-up in planning and preparation— Obsess about completion. Get your projects done.