Three Pedals for the Shredder-kings under the sky,
Seven for the Metal-lords in their halls of stone,
Nine for Power Groups doomed to die...
Excerpt from Lord of the Pedal Board...
In 1977 Boss entered the world of compact guitar effects pedals with the release of three pedals - the OD-1 Overdrive, the PH-1 Phaser, and the SP-1 Spectrum. In honor of the 40th anniversary of their release, Boss produced a limited run anniversary set of 1500 units with reproductions of all three of these pedals. They had to make a few changes to the circuit and some component substitutions, of course, but the final circuit adjustments were all still performed by hand on the new production units just as they were with the originals. The SP-1 was essentially a parametric equalizer pedal that could really create some unique sounds if fed into a boost pedal. With original copies costing anywhere from $500-$800 - and the limited reissues at nearly the same price point, this would seem to be an ideal candidate for DIY clones.
For this build I'm using the AionFX Chroma PCB (above). This is not one of Aion's new Boss clones, it's been around a while, and I've actually owned the PCB for a bit and am just now getting around to getting it built. For anyone who has been watching my other Boss pedal builds, there's one thing that will be immediately obvious. The PCB looks very simple compared to pretty much any other Boss pedal. AionFX even lists this as an "easy" build (though not a "beginner" build), and by and large it is - except for one little detail.
AionFX's documentation implies that the Chroma is the first DIY clone of this particular pedal, and a quick Google search failed to turn up any other DIY versions. The reason for this is the SP-1 Balance potentiometer is a bit odd. It is a dual gang A10K/C10K pot. The top wafer is 10K log, but the bottom wafer is 10K anti-log. You can't actually go out and buy one of these, so you have to make it - and this is the only part of the build that is fairly tricky.
Fortunately there are some great instructions in the build documentation on how to build your own 10KA/C dual gang. First you have to carefully open an A10K dual gang and an A10K single pot. Because of the geometry of a dual gang pot, you can use a normal A pot upside down to create a C pot.
Separating the A10K wafer from the single potentiometer is tricky. You have to break away the plastic from the shaft without damaging the carbon surface. You'll also need to bend back the legs of the potentiometer or you won't be able to fit it onto the dual gang body.
Once you've bent the legs back, it's a simple matter of carefully placing the single A10K wafer onto the bottom of the dual A10K pot, and now you have an A10K/C10K pot! As you can see from the photo above, there's one small problem - the legs from the regular A10K pot are much too long - so I trimmed them back and shaped them with a file to match the original bottom wafer (below).
With my custom potentiometer built, I tested it on my multi-meter to make sure it was still working properly. I'd bought a couple of extra A10K dual gang pots just in case my first attempt was less than satisfactory! Fortunately based on the static resistance and the sweep profile (by eye, I didn't plot it or anything) - both the A and C sides of the pot appeared to be functioning normally.
In addition to the A10K/C10K potentiometer, the build also uses a B100K dual potentiometer as well. I think this is my first pedal that actually uses two dual-gang pots, and it looks fairly cool in the enclosure! Fortunately the fit of my cobbled together dual potentiometer was at least as good, if not better, than the stock dual B100K so getting everything soldered in was easy.
As with my other recent Boss builds, this one pays homage to the original enclosure. Sound-wise the pedal appears to be functioning perfectly as well. It is a bit of a niche pedal, and some people don't see a lot utility for it, but I kind of like it. With the added level knob, it can act as a boost on its own. It also seems to pair very well with the neck position on my Stratocasters, so I want to experiment more with it and see if it finds a semi-permanent home on the board!
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