Upgrades on the way.. ;)
A bit of a late post this as I’ve had my Odyssey operational for some months now, but at least there is a lesson to be learned here. To recap the situation a bit, the power supply failure with my Arp Odyssey caused something on the VCF circuit on board C to fail. This board also hosts the AD/ADSR generators and the output amplifier, but they weren’t affected by the PSU problems.
Repairing the VCF section turned out a trip far more winding than expected. I made a false diagnosis in the process and thus ended up “downgrading” back to the original 4023 VCF module AND even (unnecessarily) removing the potting material in order to be able to measure the entire VCF circuit in detail! I won’t go into details about de-potting, but if you want to read about the process, check out this excellent page @ ArpTech.
Anyway, as I was getting nowhere poking around the 40235 dual VCF module, the idea with the VCF downgrade was to restore the synth to factory spec. Less complex design, calibration procedures corresponding to the original service spec and a factory etched board should help removing possible DIY errors from the problem solving equation.. And besides, the 40235 is bit of a bitch to measure thanks to its compact part layout :)
The negative power supply rail dropout that I experienced whilst repairing board B of my Arp Odyssey back in 2008 decided to become a permanent annoyance some months ago. When finally having the time for repairs, I decided to do the upgrade I had been pondering on during the 2008 repairs. So, 7×15 series regulators it is then!
Moving on with the Odyssey mods..
I wanted to add CV/Gate I/O to the Odyssey without drilling the enclosure (reversible modding FTW). No choice but to make the mods external, maybe route some other signals as well.. As you probably guessed already, here’s where my Breakout Box comes into play!
Looking around the net I found some old posts where Gene Stopp had provided his solution, so I took that as a starting point. For the interconnect between the box and Odyssey, I cut up a old 25-pin DSUB extension cable. No need to solder connectors and the cable fit neatly through one of the jack holes on the rear. Who needs a sustain pedal anyway ;).. Here’s the schematic for the Breakout Box:
For the casing I picked this old plastic project box I had lying around. It somewhat matched the main colors of a whiteface Odyssey so in that sense it was a rather obvious choice.
As mentioned before, this seemed like a must-have mod. During the years Odyssey was manufactured, the filter module evolved from a 12dB/oct version to a 24dB/oct version and the design was changed from a bi-quad OTA version to a Moog-style transistor ladder version. Having both of these version incorporated in the same synth would give a larger “palette” to work with, especially if/when external signal/control inputs are added.
So yeah.. Nothing too overly difficult with this board (and once I had all the parts) besides the few spots yours truly forgot to solder and then wasted time on measuring and scoping the obvious.