on Friday ran out at lunchtime to buy a new SD-1, on my way home brought the components for the mods to OD-1 specs.
few hours ago I tried the stock SD-1.. i still quite like the SD-1 in standard spec, even if its a bit meh.
so just finished modded it to the later dual opamp OD-1 specs. sounds really really good. colours the sound hugely - very bright. changing the EQs on my 2204 to suit, the most amazing 80s metal tone comes out. cleans up well too.
found some circuit tweaks on the net to make it closer to the original quad op-amp version, which I'll now try. will report back