Vintage Synth Explorer

Oberheim • OB-Xa

The OB-Xa is a massive analog synthesizer with a very familiar and classic Oberheim sound. Its sound, size and power are very similar to the Prophet 5 from Sequential. However this one has up to 8 voices which can be split, layered and stored!

The OB-Xa was available in four, six or eight voice polyphonic models. They all featured patch memories, also in varying degrees. A minimum of 32 patches were available on early models (4 banks of 8). The maximum amount of patch memory storage found on many OB-Xa's is 120 patch memories. All models of OB-Xa, however, featured the new Curtis chips which offered great stability for an analog synth and they are attributed to its great filters and sounds.

The OB-X was very similar to the OB-Xa except that its voices could not be split or layered and, more significantly, the OB-X had a lowpass-only discrete SEM 12dB/oct state variable filter, which had a great and classic Oberheim sound. The OB-Xa changed that in an attempt to economize manufacturing and increase stability by switching to CEM3320 Curtis chips for its filters. The Xa offered two switchable filter modes: 12 dB/oct (2-pole) or 24 dB/oct (4-pole). This hardware change resulted in a more agressive sound, not quite as creamy as the OBX original, but what still became a "bread and butter" sound of the Oberheim line.

Splitting the keyboard mode separates the OB-Xa into two 4-voice synths with two available patches. The Layer mode plays the two patches simultaneously. There are also some added effect sources, perfect for any analog polysynth, including portamento, unison, sample & hold, chord memory and three LFO's!

However none of the original OB-Xa's have MIDI, unless otherwise having been modified. The OB-Xa is a classic and fat analog machine. It will give you thick analog pads and drones, punchy bass and cyclic analog effects. It's been used in the past by Depeche Mode, Van Halen (Jump!), Gary Numan, Jean Michel Jarre, New Order, Paul Sheafer, Prince, Queen, Jethro Tull, Stevie Nicks, Sneaker Pimps, Rush, Mike Oldfield, Richard Barbieri, the Thompson Twins and Bon Jovi.

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Posting Rules: Please keep your comments relevant! Do not post requests for help, do not use for sales, do not post unless you have something interesting to say about this instrument, or we may delete your post.

 

McFly

Posted 83 days ago

"I think the early designs - the SEM, the OB-1, the OB-X, and the OB-Xa - have somewhat better sound than the OB-8 and the instruments that followed it. I think that's because the sound of the earlier designs is dirtier in subtle ways, and therefore seems to have more guts. The OB-8 is a more perfect design. The autotune routine tunes the oscillaters more perfectly. But the sound is clean...too clean."

(Tom Oberheim on the Oberheim sound)

Tomislav Babi%u0107

Posted 162 days ago

OB-XA is perfectly stable once u replace all capacitors on voiceboards and PSU. i GIG with mine who problems, its warmup time is less than a minute now.

played the OB-8 many times, and indeed XA is rawer/angry sounding. organic. don't mistake a synth in bad shape that drifts all over the place, with OBXA in full force.. 8 is slightly more polite and uniform. like a missing link btwn XA and XPander.

OBXA is the the only machine ever to feature a LP circuit based on SEM 12dB, yet built round CEM3320. once they got to OB-8 the circuit has changed from SVF - resonance doesnt "sing" or sting that way anymore. XA's 24dB filter is a separate circuit and not as good as 8's.

i use it for hi-reso, lo-cutoff voxy pads drones.. easy to get the VCAs to saturate/break... phenomenal sound. also i use it for vibrato brite strings w trademark "Curtis" sizzle

as w OBX, its not a bad idea to replace vco tune trimmers with multi-turns.

cheers
clusterchord

ron

Posted 226 days ago

poppaneedsanap... You can find the service manual online, in it you will see where the trimmers are located. I believe it's one of the last pages? trimmers are labeled. I should warn you, it takes a little time to get all of the voices the same again, but fortunately the procedure is in the service manual and does not require special equipment. Having said that, once you get familiar with the voice cards it's no big deal, and not scary. Like I said, I had to figure out how to tune it, and did so before I had a manual, just from twiddling. But now the machine is more personal, if that counts for anything.

allan

Posted 271 days ago

contrary to belief it was a obx through a marshall stack that was used
on van halens jump , not a obxa as in the video, definately superior to
any oberheim released after

Matruxman

Posted 273 days ago

It lacks proper MIDI (even with retrofit), so I couldn't use computer patch editor that works fine with OB8.
Compared to OB8, oscilators drift alot and that make illusion that synth is rawer, but that 'gift' is not something I very much appreciated by OBXa.
Replacing it by OB8 resolved several key issues incl. important one reliability.
OBXa also lacks some important functions of OB8, so if choice is there opting for OB8 seems as clear choice.

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