Old Crow's Oberheim OB-X Clone Project

via oldcrow on Muff's

First post with initial diagram above: "Ever since playing MC's OB-X at AHMW, I got it into my head to try and make one--gotta be cheaper than ebay! This meant making my own voice cards, first in the original form factor to test first on a "host board" to power and provide pots and switches for the voice board under test, then later in an actual OB-X. Since the vintage cards used CEM3310s and discrete everything else, I made the EGs in non-custom form using JH's VC_HADSR as a design reference (it was inspired by the 3310). It works on a breadboard, so they're in the CAD schematic and the "hard" part of the layout is done: the VCOs. I squashed the circuits a bit in order to open up some room on the board as my EGs were going to be a tad larger than a single 16-pin chip; they each use 4 chips, 4 transistors and a handful of passives. Throughhole parts as my eyes have gotten too bad to hand solder SMT very well (but I have a full SMT factory line for that if I ever make more than 8 of these ;)

The CA3080s are replaced by 13700s, which are dual 3080s. I do not bother with the darlington buffers. The CA3086 transistor array is replaced by two LS318s, and those mount over SMT TC resistors (see A3A, A3B in image). I do use some SMT bypass caps as the original board features no bypass caps whatsoever, save for the DC filter caps on the local voltage regulators."

Follow-up with the pics below: "Slowly the master vision takes shape: here is a nearly-finished host board with a fully-populated carrier board mounted to it, and the carrier board loaded with a slot adapter and attached crowbx voice board."

For those not familiar with Old Crow, you can find his site here. He has been most often referred to here on MATRIXSYNTH for his KORG Polysix battery fix.