BELOW: the stock OE20 schematic is an unusual mixture of 1950s and Modern that connects the center taps of the volume/tone pots with a cap from #1 lug tone lug to ground. This keeps the volumes independent from each other allowing a more balanced center-toggle sound. It also raises a good question about whether a cap should go before or after the resistive wiper in the tone pot. My personal feeling is that the cap should go after. This is because a tone control is a variable low-pass filter which filters out high frequencies and lets low ones pass. In loudspeakers a 6db lowpass crossover always places the resistance first in the + path while a cap goes after to ground. So despite the schematic looking like an anomaly I believe OS was correct in choosing this method.

Standard potentiometers use terminal 1 as the ground, terminal 2 as the input, and terminal 3 as the output. Yet its common in the guitar world to break the rules and run the signal backwards through terminal 3 and ground the terminal 2 to the pot at times. Each method works and can subtly change tonality and interactivity. Fun stuff. There was nothing wrong with the stock pots but I suspected that some cost cutting had been done. The holes in the guitar top were small making CTS pots shafts too large as replacements.

I installed a set of "Shen Zhen JD Moon Science and Technology" long-shaft split pots. I can't find much about this company other than they make some after-market parts for guitars online. The pots had quality machining and a firm smooth action and averaged 467-483K ohms at max and about 5 ohms at minimum which is within 20% tolerance. The case diameter is larger than stock and the shafts have a 8mm x .75 thread. Stock values were A500K on the tones and B500K on the volumes. I decided to keep those tapers.

According to Bourns: "Standard guitar potentiometers have a rear metal cover that is used as the ground. The rear cover is actually grounded to the metal bushing and the metal shaft".

This means the proper way to ground a pot is a ground lug on the shaft or by mounting its shell against a circuit board. Yet a decades old practice is to solder a ground wire across the tops of the three of the four pots. Skipping one pot makes no sense because completing the circle and looking like a loop or antenna doesnt actually mean it is one. An electric guitar is a passive device: the pickup sends out millivolt AC signals when a string passes over it like a dynamic microphone. As long as all the negative leads electrically connect to each other its grounded. The only way you get an audible ground loop is on an active circuit like an amplifier where you have different gain stages.

Single pickups can be prone to noise but there isn't a valid reason with humbuckers to keep skipping a pot other than it creates a vintage look. Acknowledging this in 1977 (45+ years ago) Gibson stopped using pot ground wires and began installing a metal plate to ground everything to a single plane. In 2008 Gibson went a step further and began using a drop-in PCB and quick-disconnect jacks.

SOLUTION: To create my own backplate I used several layers of copper foil under the pots and on the volume pots I soldered the #1 tabs to the cases. The result is a tight, minimalist hybrid with the back-plate grounding the pot circuit to itself. At this point there was no need for a clunky ground wire across the case tops. The expected result is a dead quiet soundfield with zero hum or noise.

Folklore is that bumblebees, tropical fish, or paper-in-oil caps are needed to get that 'original' sound'. Yet prior to the 1980s capacitors were poor quality and not considered by the industry to have a "sound". As a result manufacturers for decades chose the cheapest parts available. As a result if you open up audio equipment from the 1950's up through the 1990s you'll see circuit boards filled with cheap ceramic, tantalum, and paper caps. Even in the early 1980s when when audiophiles discovered the sonic benefits of film capacitors it took several more years for manufacturers to grudgingly start using them. Today, its still rare to see audio-grade parts consumer audio equipment. Modern tolerances are 2% or better while 10-20% was typical for parts in the 1950-60s.

Below is the accepted sonic order for film capacitors in the audiophile community. This takes into account real-world specs such as ESR and pulse response. Teflon, polystyrene, and polypropylene have extremely low resistance and excellent high frequency response which is why they are used in audio, sample and hold equipment and critical timing circuits. Polyester is widely used in mainstream audio equipment but is considered by some a lesser choice. Tantalum, ceramic, and paper have poor frequency response and aren't suitable for audio. Yes, this means that the higher on the list you go the list the "better" the sound quality. My OE20 came with a generic green polyester .047uf film cap on each tone pot. I decided to go rogue and replace them with two NOS Russian K71-7 .047uf 250V 0.5% polystyrene capacitors. I have used the Russian K series in other equipment and like their sound and tolerances.

	Teflon Polystyrene Polypropylene (and metallized) Polyester (and metallized) Mica Tantalum Ceramic Paper

The stock tuners were adaquate and stamped "BY". I decided on Gotoh as replacements and the Gotoh catalog has a large number of styles, but finding and buying them was a challenge. Each tuner is available with different features, finishes, and up to 18 different knob styles. So what looks like an easy item to order online could arrive in my mailbox in literally dozens of different configurations. It doesn't help that Gotoh doesn't sell to the public.

After lots of measuring I went with a set of "Gotoh Large Schaller-style tuners". Part number AN0903. They were identical bolt-ons, no issues. In the photo below the stock tuners are on the left and the Gotohs on the right. The result is my guitar now stays in tune even after heavy playing and I hear a more solid tonality in chords.

The nut on my OE20 appears to be plastic. My neck is very slim at the nut and after careful measuring I determined that there's isn't a replacement nut that fits the OE20. The E to E distance on the Gibson and offshore Epiphone nuts is 1-2mm too wide which would put my strings on the edge of the frets. I spoke directly to a couple of replacement nut companies but neither could supply one that fit the OE20. They suggested I buy a blank and cut my own which I thought was a poor answer considering all the obscure guitar models that have replacement nuts. Rather than mess up the factory balance I decided to leave the stock nut in place.

My toggle was quiet but the middle position had a lot of play. On inspection it was a generic lightweight, rectangular switch with a tiny circuit board. I replaced it with a Switchcraft short body version. The Switchcraft is a nicely machined, heavy switch. I also removed the round plastic rhythm/treble switch plate which I never liked it on a Les Paul. Imagine if a Strat had a label on its pickup switch how odd it would look

OS oddly provided a flat plate instead of rounded style to fit the contour of the body. Replacements were nowhere to be found because the stock plate has 23mm screw centers while every single plate on the market was 25 or 25.4mm. Rather than drill new holes in the body I went the easier path. I put the flat plate in boiling water for a couple of minutes then curved it to fit. I added black screws which look great.

OS did something odd. For the bridge anchors they used M6 instead of the common M8 size. The post threads were sloppy causing bridge tilt I didnt like. So I searched obsessively for over a week but couldn't find a single company that made replacement anchors in M6. To make things trickier I discovered that instead of using standard profile guitar anchors OS used similar "steel rivet nuts". Rivet nuts have different spline profiles, are inexpensive, and are used as sheet metal and wood fasteners. I understand using rivet nuts to save costs but why they chose M6 instead of the standard M8 is a mystery. Finding stainless rivet nuts in M8 was also a challenge. I ended up buying a cheap offshore bridge just to get a pair. Replacing them was super-easy. I made a puller out of a short collar of PVC pipe and large washer with a M6 bolt through the center. With a soft cloth underneath the PCV I was able to use a spanner to crank out the rivet nut in 30 seconds. Zero fuss. I simply pressed the new bushing back in by hand.

Rivet nut on left and guitar
anchor on the right

The stock tailpiece was heavy with M8 anchors. But I noticed when turning the studs they would grind and bind on the bottom of the tailpiece, caused by a jagged seam cast into the bottom. In looking for replacements I found that OS had gone rogue again and used a proprietary tailpiece with a narrow 80mm stud-to stud measurement: everyone else uses 82 or 82.5mm in width. I did some brainstorming and came up with an interesting solution.

STEP ONE: I left in the stock M8 tailpiece anchors.
STEP TWO: I bought a Gotoh GE101Z tailpiece in zinc chrome at 82mm width.
STEP THREE: I installed TonePros M8 locking studs. The tiny top posts let me slip the tailpiece on with no interference.
STEP FOUR: To counter stud tilt I used stainless 8 x 1.25 jam nuts on both the bridge and tailpiece studs.

BELOW: My final setup uses an Agile BM-003 bridge (73.5mm spacing) and Gotoh tailpiece. The jam nuts remove slop and tilt and provide very solid coupling to the body. This may not be conventional but the thin width fits perfectly and I like the stainless patina.

Incidentally, I have had trouble with the string action templates found online. I find them difficult to see and the measurements don't seem accurate in some cases. Feeler gauges come covered with messy oil. So I use the old-school method of using a nickel (1.95mm) on the 12th fret of the bass E, and a dime (1.35mm) on the treble E. Setting the bridge height this way gives me a fast, clean action.

As a final step I replaced the stock pickups with Seymour Duncan '59 humbuckers. Fabricated to mimic the original PAF sound they are wound on one of the original Gibson machines (very satisfying). I went with nickel covers and a single wire configuration and bought them directly from Seymour Duncan to make sure I got authentic ones.

Humbuckers with metal covers are made in long-leg (1/2") and short leg (1/4") styles. Seymour Duncan only makes '59s in the long version despite comments online that a short version exists. I found the corners of the squared legs touched the neck cavities slightly. I didnt want to introduce microphonics by having the legs touch the body. So I used wire cutters to clip the corners off the long-legs to reshape them. A simple and satisfying fix.

The OE20 pickups sounded fine but the '59s were immediately better. More musical, powerful and dynamic I could hear nuances that had been obscured. The overtones took on a more harmonically correct sound. Very pleasing. NOTE: The stock pickups measured 6.8K on the neck and 17.9K on the bridge. The '59s are 7.6K on the neck and 8.2K on the bridge. The stock short-leg bridge pickup is below.

My project replaced all the stock wiring with OFC, a new toggle switch and polystyrene caps, simplified the grounding scheme, added quality tuners, heavily coupled the bridge & tailpiece, and added new pickups. After setting the intonation notes pop out of an inky-black background, tones and dynamics are far more musical and revealing than before. Sustain is HUGELY improved due to the increased coupling of the bridge & tailpiece. With the instrument unplugged the increased coupling results in the OE20 sounding like an acoustic guitar the ringing is so strong.

That the OE20 was so highly regarded in factory-form even with average quality bridge/tailpiece and tuners is a real testament to its design. I like the unusual tone circuit, as it reveals that OS built this guitar with intent rather than copy age-old designs. Externally my OE20 looks the same and I was able to accomplish everything without a scratch. Now I can concentrate on technique without feeling like any shortcomings are the guitar's fault. Fun stuff.