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Modifying An Electric Guitar

My older son Mitch had some success modifying an electric guitar - I helped him replace a pick guard and change a pickup.  That made him want to undertake a more extensive modification of a different guitar.  He bought a Fender MIM Telecaster

 

on Ebay and picked up a bunch of components from several online sources, including new pickguard, locking tuners, string tree, a piezoelectric bridge, an electronic preamp and new output jack, a dual concentric potentiometer for combined tone & volume, a switch to select the standard magnetic pickups and/or the new piezo pickups and a battery box to hold the 9 volt battery to power the preamp.

He also wanted to swap one of the pickups for a Gold Lace Sensor pickup that had come from the guitar he had previously modified.  I'm a pretty competent electronics experimenter, and in fact had worked as a technician and circuit designer years ago, so I felt confident I could handle the wiring.  I was a little worried about attacking an expensive guitar body with woodworking tools, but I agreed to help.

The modifications required stripping the guitar down to the body, routing out a rectangular hole in the back for the battery box, drilling a hole for running the battery wires to the control cavity, drilling new mounting holes for the bridge, replacing the output jack and the tuners, & then wiring the whole thing up.  The first operation we undertook was to make the recess for the battery box.  Mitch had purchased a router template along with the box, but it didn't come with any instructions.  We selected a location for the battery box on the back that would be near but not overlap the control cavity on the front and traced the outline.  I mounted a scrap of 1/2" plywood to the face of the guitar with carpet tape to give us a level surface and to protect the guitar's finish.

 

The cavity was supposed to be 1-5/16" deep, 1" wide and 2-1/2 inches long.  We took the guitar to the drill press and used a 7/8" fostner bit to rough out the opening to about 1-1/8" deep.

 

After the first hole was drilled, we knew there was no turning back.  The next step was to mount the template on the guitar over the rough opening.  We had to elevate it a bit with some shims so it would clear the string ferrules.  I had intended to use a 1/2" pattern bit to rout the recess, but the bit I had wasn't long enough to get the depth we needed.  I tried a 3/8" upcut spiral bit with a template guide, but again couldn't get the depth I needed, and when I made a shallow test cut I found the opening was a bit too small for the box.  I finally ended up using a 1/4" solid carbide upcut spiral bit and a 17/64" id, 5/16" od template guide.  The tiny clearance between the bit & the steel guide worried me, but by taking light cuts to minimize deflection of the bit, it worked out OK.  And this seemed to be the right combination, since the box was a perfect fit.  We don't have any pictures of this because Mitch said he was too freaked out by what I was doing to take them.  Too bad.

The next step was to drill a hole for the battery leads.  I hadn't really thought about how I was going to do that before I started.  Sometimes you get lucky, though.  I was able to use a long (aircraft) 5/16" bit in my cordless drill, introduced into the existing mounting hole for the output jack in the side of the body. The angle was just right to connect the control cavity to the new battery compartment.  If I had put the recess for the battery in a slightly different location this wouldn't have worked.  I'm not sure I would have been able to come up with another way to do this, and that could have been a real disaster.

With the scariest part of the woodworking done, the next step was to drill new mounting holes for the bridge.  The paper template that came with the bridge made this a pretty straightforward operation.  Then we needed to drill the control panel for the new selector switch.  We centered it between the existing holes for the volume & tone controls.  Again we got really lucky, because when it came time to install the new preamp, which was mounted on the back of a  new volume control, there was only a tiny bit of clearance between the circuit board and the switch.

Wiring up the new components should have been pretty straightforward, but the instructions that came with the new parts were pretty sketchy.  We only had a few incomplete pictorials and no schematics.  The color codes & number of wires from the magnetic pickups didn't match the instructions, either.  Also, one section of the new dual concentric potentiometer that  was to function as a volume control for the mag pickups and as a tone control was the wrong value - we needed a dual 250k pot but all we could find was a 250k/500k.  A 470k fixed resistor wired across the 500k section took care of that.  We got it all wired up & got the rat's nest stuffed into the existing cavity without too many problems, bought a 9 volt battery, put on one string & plugged it into the amp. The new pickup sounded terrible and the magnetic pickups didn't work at all.  Mitch was pretty bummed out, but I wasn't that surprised.  In fact, I had suggested we only put one string on the guitar for the test, in case we had to take the whole thing apart.  I opened up the control cavity, adjusted the trimmer on the preamp for the piezo pickup and found I had left out one wire - from the mag pickup volume control to the toggle switch.  Soldered that wire on & tried again.  Much to my surprise, everything worked, and after stringing and tuning, the guitar sounded great.  Looked good, too.

The whole thing took about 5 or 6 hours.  I guess if we had to do it again we could cut that time in half.  Hey, maybe this could be a new business venture for us.

You can send questions or comments to Mitch by clicking here.

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