Oberheim X-Series: OBX, OBXa, OB8, DMX, DSX PROMMER

OBERHEIM X Synthesizer Series


the Oberheim X System Line Oberheim Synthesizer Line

difference Oberheim
OB-X vs. OB-Xa

OB-X = discrete analogue circuitry, possibly SSM?
OB-xa = Curtis Chipsthe 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)
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

Oberheim OB-X Synthesizer
enlarge oberheim OBX? just click it!
-all obx pics thanks to theo bloderer / bluesynths.com
Oberheim OB-X Synthesizer

Oberheim OB-X Synthesizer
one voice can be controlled from the back.. click pic!

Oberheim OB-X Synthesizer
OBX Envelopes..
Oberheim OBX Synthesizer

Oberheim OB Xa.. the jump synth (uaa I hate to mark it like that).. better mention it was played by Depeche Mode…!!)
Also there was an Expander “xpander” version available .. don’t confuse those with THEEE Oberheim Xpander (see above)

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..

oberheim obxa
OBxa Problemzone: Nach Bestücken und Verlöten der Bauteile auf den Platinen wurden sie in ein chemisches Reiningungsbad gesteckt, gegen dreck.
wirkung: nach einiger Zeit wurden Trimmpoti-Oberflächen angegriffen und die Widerstandswerte schwankten daher. ICs wurden per Sockelsteckverbindung befestigt, wg. besserer Servicefreundlichkeit. auch die Kontakte in den aufgelöteten Steckverbindungen bekamen Kontaktschwierigkeiten.
was tun? Alle Trimmpotis und IC-Sockel raus, neue Potis und die ICs reinlöten.
Informationen von Tom Oberheim / Marcus Ryle.
Oberheim OB-Xa
click image to enlarge..
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”..
OB 8

quite close concept to ob x.. the classic oberheim
see the midi ports?oberheim ob8

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

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



Oberheim OB-8
click image to enlarge..

Oberheim OB-8
click image to enlarge..

Oberheim OB-8
click image to enlarge..
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 sequencer DSX, another part of the oberheim Xa/DX series.. (drum machine dmx,the obx synth and ob-x/xpander – unfortunately there has been another xpander but they sold it as “ob Xpander”.. looks like THE xpander but with the knobs and tech. specs of the X of course..)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) DSX Oberheim Sequencer System
DSX Oberheim Sequencer System
the early digital Sequencer
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 –>

Oberheim digital Sequencer
the DMX belongs to oberheims “x-system”. one of those 12bit drummachines. the category is same as linn drum, drumtracks, drumulator etc..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..)

Oberheim Drummachine Line DMX DX
oberheim dmx
Oberheim OB Prommer

basically some sort of self burning sampler for these drum machine models:
SCI DrumTraks, LinnDrum, Oberheim DMX/DX, Hammond Sakata and Simmons

burning your 8bit samples to an EPROM (electrical programmable read only memory) – typical mid 80ies style..

Oberheim OB Prommer
click Prommer image to enlarge..
thx viewermail studio for pic!

fill other machines with your samples..
mxr drumcomputer


Oberheim Oberheim Synth overview..