This just got traced by Aion and he was kind enough to share the schematic along with a cool tracing journal on his blog. As to what the SS-3 is, it's like a beefed up Cornish G-2, which is his take on the Distortion+. The original uses 2, single op amps, but for the sake of space and simplicity I've used a single dual op amp. It'll be tight, but it should fit in a 1590B. Like all Cornish pedals, it's designed with buffered bypass so the FSw labels on the layout refer to a DPDT footswitch. If wiring for true bypass, ignore those labels (and the 51k and 91Ω resistors at the bottom right corner of the board). But if you want to build it like the original, wire the in/out jacks to the in/out pads, one side of a DPDT footswitch to the FSw pads, and the other side for the on/off LED indicator.
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