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.

Jim

March 26, 2011 @ 11:38 pm

A bunch of these comments are dead on regarding the OBxa tuning stability. If you replace ALL 7 electrolytic caps per soundboard, you are in business. When the caps are replaced and the cards re-tuned, the OBxa will stay in tune cold, warm, and hot WITHOUT having to hit autotune. If you are hitting the auto tune every 10 minutes and have voice boards occasionally fail, grab some 15uf or 22uf caps, a solder [beep] er, grab your iron and go to work. Promise you that in 3 hours your OBxa will run like new! Might as well replace the filter caps and the rest of the tantalum and electrolytic caps too!

AlexD

March 17, 2011 @ 2:39 am

Fantastic machine ! With incredible sound ! Long time dreamed and now comes reality ;-)
I have the pleasure to have an OB8 and from last week an OB-Xa.
Now I'm searching for a original presets file for my Alzheimer OB-Xa 120 preset to compare my self the difference between this 2 models.

James

February 13, 2011 @ 6:37 am

Playing one of these is a smile a minute! Although the OB-xa can also do harsh and aggressive, it has its soft side too which is often overlooked. The Pratt & Reed keyboard has nice action and is easy to rebuild, level and drop in new bushings. The factory presets showcases much of what the synth can do especially the 128 program models. Split and stacked presets are limited to 8 memory. The key to the sound is in its tuning instability. It is near impossible to perfectly tune each card; the 'Autotune' calibration only adds to the 'character'. Be prepared to get under the hood if you buy one.

John

November 18, 2010 @ 3:06 pm

I have all the large Obies, despite the 4 and 8 voice :-( and they are all fantastic.
OB-X, OB-Xa, OB-8, M12, especially the OB-Xa and OB-8
are still very cheap nowadays in my opinion.
Personally i prefer them all over a Jupiter 8, i'll never sell them......so don't bother ;-)

RetroSound

November 12, 2010 @ 3:34 pm

The OB-Xa is a fantastic analog synth. The sound is very different to discrete OB-X, harder and more angry. The OB-X is more lush and warm I like both.
OB-Xa demo: http://www.youtube.com/watch?v=byxQ6aQRGis

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