I knew I wouldn't be able to leave this guitar alone. As a concession to the "vintageness" of this guitar, I decided to make only reversible (heh!) modifications, primarily to the circuitry. At the outset, I considered some of the original circuitry to be disposable (the Tone switch and Microphone circuit), some to be desirable, but not essential (the Decade and phase switch), and some that I'd give up very reluctantly (the bass and treble controls).

Controls Cover Plate: The first and most straight-forward task was to fabricate a replacement controls cover plate for the backside. Some of the modifications I was thinking of involved hacking into that plate and I didn't want to do that to the original plate. The plate is a very simple shape, in a single ply .1" thick black ABS plastic. It's not too difficult to make if you can find a similar piece of plastic to hack up. I didn't, and ended up using a piece of .1" thick Plexiglass. The clear thing is kinda neat, but served a more utilitarian function while I planned the modifications: It let me see how stuff was to be positioned inside (although I still mounted the switch at an odd angle). A good thing about Plexiglass is that you can paint it from the inside and it looks glossy from the outside, but without any danger of the paint being scraped off. I shielded it with aluminum tape, which also happens to keep the paint from be scraped off from the inside.

Impedance-Matching Transformer: I wanted to install an internal impedance matching transformer since it would eliminate the need to use the special impedance matching cable. Originally, I thought I'd probably never use the low impedance feature so it really didn't need to be switchable, as it is with the Les Paul Recording model. However, it's an easy modification to add via a flush-mounted slide switch on the back controls cover plate (being a set-and-forget control). The 10:1 transformer was harvested from an XLR impedance matching gizmo which looks amazingly like the Gibson one. They're not very expensive, but it's a shame to discard the housing (which probably accounts for most of the cost) for the tiny transformer inside. I constructed a more compact shield enclosure out of copper foil and soldered it to the switch.

Potentiometers: The potentiometers were the biggest problem, mainly because they involve both operational and aesthetic considerations. The pots must have a knurled split shaft to fit the original knobs, and there are at least two variations on shaft knurling (one fits, the other doesn't). It gets worse: Les Pauls sometimes require the less common long shafted pots because the pots are mounted through the wood layer, which is much thicker than the plastic of a pickguard. To get an idea of what my option were, I removed the microphone pot. I was pleasantly surprised to find that it was mounted with a brass nut with an extended threaded sleeve which went into the body. This compensates for the more common short shaft pot, and expands the variety of values from which you can choose. This can be important if you want to install circuitry which uses pots with values other than the usual 25K, 250K or 500K. Another surprise was that the pot had been shimmed against the wood with a couple of "Rhythm/Treble" pickup selector rings. Hey, souvenirs! It's unfortunate that they didn't use the more unusual "Front/Rear" rings, but I guess they were probably in shorter supply.

Unfortunately, the main controls cavity is fitted with a metal plate which increases the distance to the body face and requires long shafted pots. With the Les Paul Personal, you can't just remove the metal plate because the Phase and Tone Select switches are riveted to a specially formed section, so that they'll mount at just the right height. The plate provides some shielding, so it's a good thing, but it does make the selection of replacement pots more difficult. The original pots, with values like 1K and 2.5K, were pretty much unusable for what I had in mind.

The Plan: I only had a vague notion of what I really wanted. Minimally, I wanted the guitar to put out a kickass signal that couldn't be called "wimpy", and that could overdrive stuff. Conceptually, this would transform her into a Julie Strain-like Amazon guitar, capable of stomping any chest-thumping guitar equipped with mere Super High Output Humbuckers. (After all, she has the largest pair of pickups I've ever seen in a guitar.) I played around with my Seymour Duncan Pickup Booster again and once again decided that I wanted more than just a walloping volume boost. It's true that a really hot signal can overdrive an input, but how an input responds can vary greatly: Feed a super hot signal into some boxes and you get a raspy clipped sound. Feed it to a Twin Reverb and you get an insanely loud and clean sound. As with my Stratocaster, I decided that I wanted built-in overdrive for better control over this aspect. I considered getting Voodoo Lab's Sparkle Drive, but since I couldn't find one locally and really didn't know how I was going to accommodate the controls, I decided to use something that I was familiar with: A Boss SD-1 Super Overdrive.

SD-1 Overdrive Circuit: This time I took a picture to show where you jumper the circuit to force it to stay on. Of course, this is necessary if you want to make it mechanically switchable ("True Bypass"). This guitar has more than enough room so I didn't have to cut the circuitboard in half and fold it, like I did with my Strat. The battery box was installed in the back cover plate, and the Volume and Tone pots were removed and replaced with appropriate value resistors. I kinda wanted to keep the tone pot, but I didn't have any spare pot positions at the time and figured that I could make use of the guitar's other tone-shaping circuitry in a more global way. The Drive control leads were wired to a 1M pot located where the Microphone control had been. The input and output were wired to Position 3 of the gutted Tone Selector switch (basically, a 3-position Strat pickup selector switch. I was tempted to replace it with a 4-pole 5-position "Superswitch", but I would have had to drill out the original switch's mounting rivets and route a little wood).

I did a portion of Robert Keeley's infamous mods to the SD-1 circuit: C2, C3 & C8 were replaced with .1µF polyester film caps to improve the bass response. Bass is still a little light, but there's more than there was before. I also added the 47pF cap across the diodes (to smooth out the distortion) and increased the gain by replacing R6 with a 2.4K resistor.

Pickup Booster: That left two more positions on the switch. Since the controls cavity had a little more room, I put the Seymour Duncan Pickup Booster in there and attached it at Position 2. This worked well since switching between the two active circuits is quiet. I even managed to squeeze in the Pickup Booster's volume control so that the switching between it and the OD could be balanced. The circuit's original 25K antilog taper (oddball), short solid-shaft pot was mounted where the microphone XLR jack had been, and I made a jackplate to avoid altering the original one. It's a weird place for a control, but is actually pretty convenient. Besides, a set-screw knob could be used there without severely mucking up the guitar's original aesthetics.

Tone Controls: This is strange stuff, which has taken a lot of follow-up trial & error experimentation, accompanied by much head-scratching. Earlier in this series of articles, I mentioned that the Decade control provides a very subtle tone-shaping effect in high-impedance mode (that I had a hard time hearing). However, in low-impedance mode, the Decade Control has a very noticible and cool-sounding effect, shifting the resonant frequency center in steps to a point where it sounds very "Stratty". The Decade circuit appears to be an integral part of the low-impedance circuitry, and probably relies on the inductance of the pickups as part of its filter network.

So it all depends on where the Decade Control is located in the circuit; it's very sensitive to the interaction it has with other components. If it's placed before the input of the OD and PB circuits while in low-impedance mode, it functions as it was designed to. However, in high-impedance mode at that location (right after the transformer), it functions as a treble-cut circuit, but the capacitor values are too high-- even the smallest capacitor value causes a severe treble cut. If the Decade control is located at the output of the OD and PB circuits, it acts as a treble-cut circuit in both low and high-impedance modes, but with a much more usable treble cut range. Oh yeah... if you place the Decade circuit before the transformer in high-impedance mode, you don't get the severe treble cut, but you don't get a very noticible effect from the circuit. To remind you, that's how the stock circuit works and my reason for bothering to mess with this stuff...

An true electronics gearhead could probably figure this stuff out easily and come up with the optimal component values. I'm not, so I used what was already there and experimented...(In fact, I don't identify some of my "fixit" capacitors because I don't know their values-- they came from a bag of yanked parts and the identification markings are worn or too difficult to read now.) The Decade Switch's capacitor values were selected by really smart guys for low-impedance use. One way to make it usable in both high and low impedance modes (if you don't mind the behavioral change in high-impedance mode) is through switching. A 3-pole double-throw transformer slide switch places the Decade circuit before or after the active circuits, depending on whether low or high impedance modes is selected. (I had to put a bypass capacitor at the input of the PB circuit in high-impedance mode to stop an oscillation problem.)

I figured that I would need to replace the Treble-cut pot anyway since I didn't think that the original 1K pot would really work in this circuit. Instead of a capacitor, I tried an inductor I'd saved from an old dead Schaller wah-wah pedal. Wow: A bass-cut circuit. In high-impedance mode, together with the Decade switch, this formed a band pass filter, where the Q would sharpen as the bass was cut. This gave a slight wah-wah-like tonal coloration. Playing around with this using distortion, I could "sculpt" feedback; playing through an external wah-wah, I could tailor the signal so it was just right for the full sweep range of the wah-- not too shrill, and not too bassy. (It also does unusual things through a Octaver.) This eliminated the need for the original circuit's bass control and left an extra control pot-- This became a separate presettable treble cut control for the OD circuit (which I think sounds better when it's less fizzy); its capacitance adds to whatever is selected on the Decade control.

The Third Tone/Mode Position: Although I'd originally configured this position of the Tone Select Switch for passive/dead battery mode, it occurred to me that there really wasn't a need for the passive modes. A battery change is quick and easy, and the passive modes don't really bring much new to the sound except reduced volume. In fact, that can be a major liability if the tone/mode selector switch is thrown quickly and carelessly while playing.

I toyed with several options, including installing a switchable "cascade" (PB connected to OD)/passive mode in the third position, but this really wasn't do-able with an additional 3PDT switch (you need 4 poles). The simplest option would have been to wire the selector redundantly: 0D-PB-0D. Instead, I did a variation on this: At the output of the first OD position, I installed an inline capacitor. Very simple, but with a big effect.

Installed like this, instead of shunting high frequencies to ground (like a treble-cut circuit), the high frequencies are passed and the low frequencies are blocked. This makes the sound different from the other OD position and can produce a super-fizzy OD sound. Yeeeech, right? Well, yeah... very '60s-ish. However, the interaction with the fully in-circuit bass-cut inductor and the Decade Switch capacitors creates a much sharper resonance. Twirling the bass-cut knob produces a very distinct "wah", and the Decade Switch selects different frequency spectrum centers. Practically speaking, wah-wah circuits really are easier to operate on the floor inside a pedal, but it's interesting to have the tonality of a half-cocked wah available at the guitar at the flip of a switch. (And to think that I made fun of Gibson's bizarre circuitry...)

Battery Control: The replacement pots for the new bass and treble cut circuits were a little tricky. I wanted to install a battery-off switch since it's easier than unplugging the guitar, and having this function in a pot would make life much simpler for me. For some reason, pots with rotary switches seem to have fallen out of favor, while the push-pull switch pots seem to be all the rage. The problem is, push-pull pots are tall and take up a lot of vertical space. That was relevant since I was fitting two circuit boards in the cavity, one on top of another. Besides, for this application, having the switch function at the end of a pot's travel seems like a good idea since you're less likely to accidently switch power off while playing (which is not a happy thing). They also look less dorky (which is extremely important). In addition, the pots needed to have knurled shafts which were long enough to poke up through the guitar's face. I wasn't going to be too picky about the value or taper, since I had only a vague idea which values I could get by with. Fortunately, my tool shed came to the rescue, with its supply of scavenged parts. I found two 10K pots with SPDT switches, very small with long knurled shafts. Although most of the effect occurs at the end of the pots' travel (audio taper), this works okay since this makes the pots less likely to be switched off. (Anyway, I wasn't in a position to be real picky.) The battery's ground lead goes to the OD's treble-cut pot switch and then to the stereo/switch jack (for redundancy). This kills power to active circuits. The other switch on the bass-cut pot takes the bass-cut inductor out of circuit-- this is mainly noticible when using the 3rd Tone Select (high resonance OD) position and restores most of the bass.

After sewing the patient up, it was time for an extended test drive that would determine whether I'd be forever tortured by Tinkerer's Remorse...

Nawwww... I think it sounds great, gives lots of flexibility, and despite all the knobs, is actually easy to use. The Tone Selector switch is more accurately a mode switch with presettable active modes to switch between (similar to switching pickups). The active modes each give a range from clean to dirty through their pots' settings, so it's possible to "park" and operate within a single mode, blending in and out of overdrive and using the global tone modifier controls, Pickup Selector, and Phase Switch for tonal variety.

The Pickup Booster gives a sparkly clean and hi-fi sound, with full-range bass and treble-- it's indistinguishable from the unmodified passive sound, except louder (it starts at +6dB gain). Operationally, the master volume shouldn't be glued at 11 since the Decade and Bass Cut circuits reduce the output level, which may need to be made up. Running the volume full-up isn't a great idea anyway, since the Pickup Booster's high output will overdrive most inputs (It was envisioned as a "clean" mode). Running the 25K master volume half-cracked doesn't seem to affect the frequency response at all.

The Overdrive circuit has a different tonality, even when clean (less hi-fi)-- that variety is a good thing for the purpose of mode-switching (otherwise, what would be the point?). However, I usually prefer the maxed OD sound with less treble fizz. Presetting the OD treble-cut pot, PB Subvolume, and OD Gain controls makes mode switching pretty painless. The high-resonance OD mode can provide a radically different sound but can also be set to sound just slightly different from the normal OD mode. Its output is usually lower because more bass is shaved off, but adjusted for resonance, it can produce some really peaky (and annoying) sounds.

Although I originally considered the low-impedance mode to be secondary, it does have some unique and interesting sounds which are now more usable due to the active circuitry. The output boost from these circuits can adequately drive a high-impedance amp, although it doesn't have the steroidal kick of its effect in high-impedance mode. Even with the Drive cranked up, the OD output doesn't ever get really dirty. (I suppose if I replaced the Tone Selector with a 4-pole 5-position switch and added a PB-OD cascade mode, that would take care of that!)

I have to admit that I feel a little bit guilty for having bastardized the guitar's ingenious circuitry and clobbered its potential future collector's value. It's kind of a paradox-- these low-impedance Les Pauls aren't very popular because of their low-powered, low-impedance circuitry. This has resulted in these guitars being grossly undervalued despite their sound, their playability, the quality of their crafting, their rarity, their uniqueness, and their place in Gibson's history. "Frankenpauling" the guitar in this way is kind of brutish, certainly doesn't bolster its value to others, and will undeniably hurt it if these guitars someday do become popular and I want to sell it to finance the construction of my pyramid. What can I say? I didn't buy this guitar to sell it: I liked it before my modifications, but I like it even more now-- plus I had a blast working on it and learned a lot. Once you stop seeing your guitar as an investment, you can approach it as something to be played and be played with.

Okay, it's not pretty, but works well and reliably-- Hey, it's genuine homemade prototype quality! I made sure that stuff was gonna stay put, soldering the inductors' copper housings to the switch and pot. With the cover plate on, the circuitboards are mashed into position and hemmed in by the battery box and switch/transformer, so they really don't have anywhere to go. The cavity later got lined with copper foil, and I added a few more wires. The circuits are acceptably quiet, even in my electrically noisy work area. All it needs now is a whammy bar (jez kidding). -11/08/03

In theory the idea seemed promising, however in practice, it didn't turn out to be such a great idea. Connecting the two circuits in parallel didn't produce a terribly different sound: The circuit's tonalities are very similar, so the effect wasn't like a layering of distinct tones. It mainly gave the OD a little more bass. Ho-hum.

In series, the effect was pretty drastic. The overdrive range was extended way beyond fuzz and I had to insert a resistor between the circuits to lower the maximum output of the PB circuit. This might have been a usable mode if it had resided better within the switch. Unfortunately, switching between it and an adjacent mode produced a horrendous pop and gain jump, so it really wasn't practical.

The 4-pole switch wasn't a total waste though. The additional positions and wiring options let me add tone control wiring options to additional PB and OD modes, so that it was possible to switch between modes that had different preset tone control mixes-- for example, PB set with simple treble cut and OD set with Decade switch and bass cut, and vice versa. It's every bit as bizarre as Gibson's original Tone Select switch, but has a lot more range in the tones you can switch between.