The first schematic posted isn't of the Boss OC-2, but a modded "chopped version"Forewords:
Before diving into OC-2 modding it is important to know, that three different versions exist: The old Japanese, the old Taiwanese and the "new" Taiwanese.
The old Jap. and Tai are identical, while the newer Tai has some different ICs, a different PCB and a different power-section.
-The different IC's should not make a difference. (There is some hype about Jap's sounding better, tracking better and being full of magic. I don't buy it.)
-The different PCB made production cheaper and accords for the changed ICs.
-The different power-section allows the newer Tai to operate on a 9v regulated supply, whereas the old ones required a, I think it was, 9.6v non regulated.
The easiest way to spot the difference is to locate the psu jack. If its PCB mounted, it's the new, if not, its the old.
Schematics only exist (to my knowledge) of the old one. http://www.hobby-hour.com/electronics/s/oc2-octave.php
Both schematic and PCB of the old is listed here.On Improving tracking on bass:Technique
First of all it is very important to notice, that technique and string age plays a big role in OC-2 tracking.
With my old strings and good technique, I get good tracking down to G. And can get it to hold the low E for just a moment.
Play with your right hand (left for lefties) fingers close to the neck.
Play up the neck, avoid open strings and frets close to the nut.
Mute ALL other strings, than the one you are playing. Especially when playing close to the 12'th fret, make sure to mute the strings properly. If more than one string rings out, the OC-2 will have a very hard time, guessing what you are playing. Remember it's monophonic.Dead spots
Around ~5-9 fret on the G string the OC-2 will always (on most basses) sound like crap. This is due to the deadspot. Deal with it, and play those notes on another string."Not tracking" or "sounding like shit"
Many people confuse "not traking" and "sounding like shit". When I said I get good tracking down to G, that was true. BUT it sounds like shit, when playing down there. "not tracking" sounds like either noise or an appegiator on acid (or simply an unoctaved note), "sounding like skit" sounds like a broken car, or something flapping.
Octaving a note at 55Hz(low A) will produce a note of 22.5 Hz - that's very close to what is inaudible. Don't overdirve it
The OC-2 doesn't have a lot of headroom, I can easily overdrive it with my active bass. If it distorts (especially on the E sting), turn down the volume of your bass.Improving tracking electronically
If after perfecting your technique, you still find the tracking of the OC-2 lacing, well it is meant for guitar. Tuning some of the filters might produce a better result.
Double C21, C5 and C4. This limits treble to the tracker.
Double or tripple C22 and C23. These are the most important c
aps to fiddle with. I personally haven't changed the ones in mine, but have simulated it and it seemed to work.
All information is obtained through own experimentation, and is by no means a complete answer, but a poke in the right direction.