MATRIXSYNTH: Inside an Oberheim OB-SX

Saturday, June 09, 2007

Inside an Oberheim OB-SX


Click here for more shots via this auction.

The OB-SX is a preset analog polysynth with limited programmability. I always wondered if it was closer to the OB-X or OB-Xa. According to the owner's manual notes below it has the same circuitry as the OB-X.

Update via the comments: "The OB-SX manual says its the same as the "Xa" not "X"! Looking at it right now..." Note: check out the update towards the end of this post as well.

"From the Owner's Manual:
'The Oberhiem OB-SX brings polyphonic synthesis to the discerning keyboardist at an affordable price. It's as simple to use as the popular "string machines" with the versatility of sounds achievable only with a variable synthesizer. The OB-SX is a real synthesizer utilizing the same circuitry as the celebrated OB-X. User programmability is unnecessary since the 'SX' is programmable with 24 sounds including those sounds most used and requested, such as: strings, brass, clavinet, organ, electric piano, bass, flute, and synthesizer solo. Other great sounds, many unique to the 'X' family, are also included. Each program can be modified to ones' own personal taste by adjusting the front panel controls (since they are constantly in edit mode). The programs (sounds) are permanently stored on a plug-in computer memory chip. Should 24 programs not be enough, an additional 24 are available for a nominal charge*. A switch on the back panel is provided to switch from each group. Custom chips can be used by sending an OB-X cassette tape to Oberheim (first 24 programs can be used). The key ingredient to the OB-SX is: although it's as simple to operate as your typical string machine, you can update your sounds by changing program chips.'"

Update:
"Strangely enough, the original sales flyer for the OB-SX (printed around the summer of 1980 I presume) claims it utilizes the same circuitry as the OB-X.

Read for yourselves here (the white text on black background): link

Maybe the SX was originally meant to utilize the same circuitry as the OB-X but that in the end Oberheim chose to base it on Curtis chips seeing as the OB-Xa was soon to replace the OB-X at the start of 1981.

The first OB-SX's (mk I) started to ship in the late summer/fall of 1980 so it did predate the OB-Xa. I'm not sure when the first mk II's shipped though...possibly in the spring/summer of 1981!?

Btw, does anyone here have the 2nd (or 3rd) edition of the service manual for the OB-SX (mk II)? It should be mentioned in there when the mk II first appeared.

Micke"

Update via PeteM in the comments:
"I'm a little late here, but also have a 56 Preset, Blue striped, genuine 5 Voice OB-SX, despite all references stating that the OB-SX only came in 4 or 6 voice configurations.

IMHO it is probably best to think of the OB-SX as a hybrid between the OB-X and OB-Xa, as it shares features with both. I did wonder if the OB-SX was a proof of concept for changing the production techniques from the discreet circuitry of the OB-X, to the more reliable Curtis Chip based voice card circuitry of the OB-Xa. Personally, I consider the OB-Xa as an advanced continuation of the OB-X model, rather than its replacement.

My Owner's Manual First Edition August 1980 states:

"The 0B-SX has been developed using much of the same circuitry as the Oberheim OB-X in order to get true polyphonic synthesizer sounds. This gives you the sound of an 0B-X along with the ease of operation of a pre-set synthesizer."

Owners with later User Manuals can also verify that their manuals refer to the "OB-Xa" instead of the "OB-X", so both camps are correct. This would suggest that the OB-Xa was the next evolutionary step of OB-X project.

As others have already stated, the OB-SX has the Voice Architecture of the OB-X, but using a manufacturing process relying on Curtis chip based voice cards like the OB-Xa. Some of the sounds in the first 24 presets bear testimony to the Cross Mod of the OB-X, yet it generally sounds more like an OB-Xa in 12dB/Oct mode. The sonic similarities between the OB-SX and OB-Xa are largely due to the CEM3340 Oscillators, CEM3320 Filter and CEM3310 Envelope Generators that were common to both machines.

The main differences in voice architecture between the OB-SX and OB-Xa are that the OB-SX uses Oscillator Cross Modulation like the OB-X, whereas the OB-Xa uses Filter Envelope to modulate the Oscillators instead. The OB-SX voice card only has a single CEM3320 Filter chip in 12dB/Oct mode, whereas the OB-Xa has both a 12dB/Oct and 24dB/Oct filter chip on each voice card.

Kenton can partially MIDI retrofit an OB-SX to recieve only Note On/Off data using an OB-X MIDI kit rather than an OB-Xa kit, which probably creates further debate about which OB family member the OB-SX takes after."

17 comments:

  1. i used to have one of these, and it s EXACTLY the same sound as the obx
    there were 2 models, dark grey like the obx and with blue stripes like the obxa

    ReplyDelete
  2. I've got an OB-SX now, and used to own an OB-Xa until very recently, and I can also say that with the exception of less voices there are some identical patches. Still, there's a molecule or two less warmth & character in the SX. I'm not very techy, but are the chips any different in the Xa?

    ReplyDelete
  3. I heard they are different and that OB-X was closer to the SEM in design, but according to Synthtech the OB-SX and OB-Xa used the same chips: link. More confusion...

    If the OB-SX came out before the OB-Xa maybe it was the first iteration. I do know you cannot swap the voice boards between the OB-SX and OB-Xa.

    ReplyDelete
  4. Wow this comes up again??

    For the last time the OB-SX is nothing like the OB-X (discreet except for CEM3310 for EGs). The voice boards are very similar to the OB-Xa (all CEM chips for VCO/VCF/EGs) but are smaller in size and only have 1 CEM3320 per voice instead of 2.

    ReplyDelete
  5. Thanks. I think what's interesting her is how the manual claims the circuitry is the same. Yes this is common practice, but interesting nonetheless.

    ReplyDelete
  6. The OB-SX manual says its the same as the "Xa" not "X"! Looking at it right now...

    ReplyDelete
  7. Nice. I'll update the post. Thanks!

    ReplyDelete
  8. Strangely enough, the original sales flyer for the OB-SX (printed around the summer of 1980 I presume) claims it utilizes the same circuitry as the OB-X.

    Read for yourselves here (the white text on black background):

    http://www.bernhard-doering.de/Synthi-Museum/Museums-Guide/Oberheim/OB-SX/ob-sx.html

    Maybe the SX was originally meant to utilize the same circuitry as the OB-X but that in the end Oberheim chose to base it on Curtis chips seeing as the OB-Xa was soon to replace the OB-X at the start of 1981.

    The first OB-SX's (mk I) started to ship in the late summer/fall of 1980 so it did predate the OB-Xa. I'm not sure when the first mk II's shipped though...possibly in the spring/summer of 1981!?

    Btw, does anyone here have the 2nd (or 3rd) edition of the service manual for the OB-SX (mk II)? It should be mentioned in there when the mk II first appeared.

    Micke

    ReplyDelete
  9. Thanks Micke, updated the post with that as well. I was just reading the OB-Xa manual today and I found the following snip interesting:

    "Several improvements have been made to the OB-Xa since its introduction in December 1980. These improvements are listed below along with the page in this manual that discusses them.

    120 PROGRAM STORAGE
    IMPROVED AUTO TUNE CIRCUIT
    8 SPLIT AND 8 DOUBLE COMBINATIONS
    SQUARE WAVE ON THE MODULATION PANELL"

    All of these are standard with the OB-Xa and with your dates I can only assume they are referring to the OB-X in comparison. This actually makes sense if you think of the OB-Xa as a the next version of the OB-X. What's interesting is this again assumes Oberheim tried to market the OB-Xa as an OB-X just like the Access Virus b and c for example, however the c can completely cover the b as it is the same software. The OB-Xa can't cover the OB-X as they are completely different. Fascinating stuff...

    ReplyDelete
  10. Huh? You don't make sense Matrix. Those additional features were added to the Xa later it didn't initially ship with them (just as the manual says)...

    ReplyDelete
  11. Micke, I've got the OB-SX service manual 2nd Edition. The change started with SN 794801. The voice boards are the same. Mostly the mkII changes were just cosmetic (pin-stripe look to match Xa)...
    BTW, tell those loser childish VSE moderators to get bent...

    ReplyDelete
  12. does anyone have a list of the "program" names? (or link to such)

    I have a 56 program version and would love to know which is supposed to be the Flute, clavinet, and Strings, etc.

    ReplyDelete
  13. Thanks, Dougt

    You mean the change (to the mk II version) started with SN 804801 (ie Dec 1980), right?

    This would make sense since the OB-Xa was introduced around that time.

    Incidentally, the 1st edition of the OB-SX service manual (November 1980) mentions that it uses discrete VCA's (3080 op amps with TL081 buffers) rather than CEM 3060s as used in most OB-SXs.

    Micke

    ReplyDelete
  14. Doh, I think anonymous is right in regards to my comment. I read the manual wrong. So... if square wave on the modulation panel was added, what was there before? There are three buttons, sine, square and S/H which you can see here. Where there only two buttons in the first revs?

    ReplyDelete
  15. Afaik all of the X's and Xa's had sine-, square- and sample & hold buttons on the main front panel.

    The 'modulation panel' is the area on the left of the keyboard with the two modulation levers/LFO controls.

    According to the owners manual (page 16 -- LFO Controls):
    "a square wave can be obtained by pushing and holding the bend lever towards the rear (away from you), while at the same time pulling up on the RATE knob".

    It appears the first units of the OB-Xa lacked this feature.

    Micke

    ReplyDelete
  16. I'm a little late here, but also have a 56 Preset, Blue striped, genuine 5 Voice OB-SX, despite all references stating that the OB-SX only came in 4 or 6 voice configurations.

    IMHO it is probably best to think of the OB-SX as a hybrid between the OB-X and OB-Xa, as it shares features with both. I did wonder if the OB-SX was a proof of concept for changing the production techniques from the discreet circuitry of the OB-X, to the more reliable Curtis Chip based voice card circuitry of the OB-Xa. Personally, I consider the OB-Xa as an advanced continuation of the OB-X model, rather than its replacement.

    My Owner's Manual First Edition August 1980 states:

    "The 0B-SX has been developed using much of the same circuitry as the Oberheim OB-X in order to get true polyphonic synthesizer sounds. This gives you the sound of an 0B-X along with the ease of operation of a pre-set synthesizer."

    Owners with later User Manuals can also verify that their manuals refer to the "OB-Xa" instead of the "OB-X", so both camps are correct. This would suggest that the OB-Xa was the next evolutionary step of OB-X project.

    As others have already stated, the OB-SX has the Voice Architecture of the OB-X, but using a manufacturing process relying on Curtis chip based voice cards like the OB-Xa. Some of the sounds in the first 24 presets bear testimony to the Cross Mod of the OB-X, yet it generally sounds more like an OB-Xa in 12dB/Oct mode. The sonic similarities between the OB-SX and OB-Xa are largely due to the CEM3340 Oscillators, CEM3320 Filter and CEM3310 Envelope Generators that were common to both machines.

    The main differences in voice architecture between the OB-SX and OB-Xa are that the OB-SX uses Oscillator Cross Modulation like the OB-X, whereas the OB-Xa uses Filter Envelope to modulate the Oscillators instead. The OB-SX voice card only has a single CEM3320 Filter chip in 12dB/Oct mode, whereas the OB-Xa has both a 12dB/Oct and 24dB/Oct filter chip on each voice card.

    Kenton can partially MIDI retrofit an OB-SX to recieve only Note On/Off data using an OB-X MIDI kit rather than an OB-Xa kit, which probably creates further debate about which OB family member the OB-SX takes after.

    ReplyDelete
  17. WWW.MIDISOFT.DE rm@midisoft.de build+bid by ebay worldwide a OBSX CC MIDIPLUCK WITH FULL 32 PARAMETER WE OBX AND BCR2000 MIDIMAPPING FOR OBSX PROGRAMMER 430 € and OBX OBCa OB8 CC MIDI for 430 € by www.midisoft.de
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    ReplyDelete

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