the OB X wasn't part of the x-system all x-synthesizers
are compatible optically and dimensions

the ob-x has Crossmod which never came back on the later machines ob-x and ob-8

the xa added a split/double mode and was expandable from 4 to 8 voices with 2-voice cards.. and it also had 2 and 4pole filters, the obx had no 4pole mode..
the OBX has Crossmod. the OBxa hasn't, but the OBx has no self oscillating filters (12dB/oct is often limited to non max reso/self oscillating)

OBSX:
a preset version of the OBX

find a nice pic/brochure and largest pic on the web of the OB-X here::
Bernhard Dörings Synth site

btw: thanks to axel fischer for help.. (the ob Xa was "in may way" at his house))

this machine is part of the X-System
(DMX drums,
DSX sequencer
OB-Xa synthesizer)

1980, 2 VCOs
1 LFO (20hz max)
and 2 ENVs
all quite standard
no FM / ringmod.

the obx was it's predecessor in 1979 and is the rarer one of both. - it is now famous for the "jump" sound of van halen - but it is not just "jump", some brasses and pads.. it's like the oberheims are: fat and warm. very "broad and wide" sound! thats they key .. and maybe explains the success in the 80ies! it's still big in sound..

LPF 12dB/oct oder 24dB/oct.
self reso.
resolution 64steps = 6bit
osc sync
no xmod(ringmod or FM
has chord memory, 32 RAM , up to 120 memories.
LFO with s/h
unison mode, split and double also.
no midi, that was the new thing in the ob8 "obie eight"..

OB8 quite same features as OBXa.. but a bit more and midi..

structure:
switchable 2 or 4 pole LPF (low pass filter), 8 voices (instead of modular voices expandable like the obxa) with 2 VCOs (saw,pulse,tri), syncable, arpeggiator and lfo. splitable, 120 patch memories. (de)tune each voice and let them sound unison! standard version has NO midi, later version have like the model shown here. It was made from 1983 to 1985, maybe the DX7 was a big opponent (remember: the ppl wanted "realistic" e pianos , haha) but this is the "jump" synth.. or better: the ob xa is the jump synth, this one is,too ;) but it CAN sound gooood!! this one got famous for it's pads, "brasses" etc.. oberheim did one of the best sounding and warm curtis based synth. like the xpander it has a very warm sound and very easy to use,
thanks for photos by P.M.Mahr from

http:// www.twicethemovie.com

OB8

want nice filter modulation by VCO? check j.haibles mod

2 VCOs and ARP'er and detunable voices (faaaat!)
midi .. the coolest kit had 9 channels (retrofittable)

timeline 1974 - 1986:
SEM/2,4,8voice -> OB I -> obx -> obxa -> ob8
-> matrix and xpander line

the OB-8 added some features on "page 2" (double "click" the chord memory button) like LFO key sync for phase control / retrigger modes, LFO quantize and more - the OB8 has at leasst 3 LFOs, 2 because you have 1 LFO per layer and another one "non programmable" on the mod / wheel section (called lever @ oberheim).

the ob8 is the most powerful one in the OB series (obx,oba,ob8) but also has not xmod like the obx.

the X System connectors are a 2 "Blocks" of Connectors (2 white very unusual sockets with lots of pins, one for trigger one for CV)

on the left: the analog step sequencer that came with some of the X-Voice models,

below: filtermodule (external)

see more on this design in the SEM section..

click to enlarge -->

there were 2 versions, the "stretch DX " (mid / above) and the (right / below) DMX

click to enlarge -->

triggering DMX :
if you have a trigger out (like eg. one of the three trigger outs of a tr808) you could trigger: directly and DIY yourself some of those trigger interface pins.. or easier: use the clock in to trigger the machine , set eg the cowbell of the 808 every step = on and you have a perfectly in sync DMX.. the clock in should be the leftmost jack seen from the back..

most oberheim drummachines do not have midi since they had their DX system (or DMX system..)