The OBX has an upper and lower voice tray, each of
which has space for 4 voice cards. This is also true
of the OBXa.
The two layers are interconnected by either a ribbon
or long darning needle type rods, I forgot which.
I've owned both of these instruments, but it's a
while since I looked inside.
The voices only sound if the switches allocating them
are in the correct position, and the auto-tune can
bring them into locally correct pitch.
The information on the insides of these oldies has
been posted before, but some of the scans are almost
unusable.

The voice cards are NOT interchangeable between these
two models, even if you could find them.
The OBX had no voice card voltage regulation, and the
tuning is therefore so liable to step changes due to
poor contacts that it was a chore to play except in
unison, where the tuning wierdos fattened the voices
nicely, but somewhat randomly.
The OBXa voice cards have an on-board voltage
regulator, which keeps the cards more stable, but not
really that closely matched with temperature
variation, so once again, the tuning isn't digitally
perfect and the voice thickening is a feature here
too. I generally put some mod on the pitch of osc2
anyway, so fatter chorus.

I also owned the OB8 which definitely has ribbons, and
a totally redesigned interior. Only the case is
similar.The OB8 has none of this, and sounds more like
the original Matrix 6.
Even though they put in a voice tuning scatter
parameter in page2 when that arrived, they still
didn't sound the same, bathwater gone, where's the
baby. For a time I had 2 OB8's but still didn't get a
sound like the OBX or OBXa.
The bigger box means there's room for Triggers and
gates, pedals in and pan pots on the outside of the
cse. They also upgraded the modulation section to
include externally clocked arpeggiation, at least from
the DMX or similar. The patches are storable via MIDI,
but the instrument had nowhere to store any names you
might have wanted, even though my patch librarian did.

Regarding the OBX repair, it's not easy, many parts
are long obsolete.
My remaining OBXa has been out of action for some
years now, so have been layering M6,M1000 and when I
can face the complexity of the beast, the Xpander.

Those who can't find the real thing may be interested
to know that there are to my ears, some very close
approximations of the Oberheim factory patches in the
Kurzweil K2500 factory patches, even without FX added.





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