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Oberheim ob-sx
Old 5th February 2009
  #1
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massimo's Avatar
 
🎧 15 years
Oberheim ob-sx

What is the word on these?
should basically be some sort of a poor man's Ob-xa. It's a tweakable preset synth, I see. Smaller footprint is a bonus for me.
Any owners here? Does it make any sense to get one for about one third the price of an Ob-xa? Reliability and spare parts? Last importantly - being a non-keyboardist I need to control it via midi: is there any midi kit for this one, or maybe for the first time I can try to figure out how to make use of the CV to MIDI capabilities of my Xpander?

thanks all
best regards
Massimo
Old 6th February 2009
  #2
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🎧 15 years
respectful bump

Anyone?
Old 8th February 2009 | Show parent
  #3
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🎧 10 years
It doesn't appear that anyone makes a midi kit for it. At least not Kenton or Encore, which is all there really is anymore. And of course, the CV in will only control one voice. So if you have to control it externally (as is your case) there's no way you'll get more than one voice. From that perspective it becomes to you a monophonic synth that is not even fully variable. One more item to note is that it only does 12db filtering, not both the 12db and 24db that the OBXa does.

I don't mean to sound overly negative but that's what it is. If it had been designed such that you could port over OBXa sounds via cassete interface then it would be a bigger hit on the market today (and during its heyday). Nowadays they've become a target for pilfering their CEM chips, although some people do buy them to keep as a functioning instrument...
Old 8th February 2009 | Show parent
  #4
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I used to own an OB-Xa and had it fitted with a MIDI interface (JL Cooper if I remember correctly). It triggered all the eight voices polyphonically, but velocity was monophonic, which felt a bit strange. Don't know if there are mods like this available right now.

You probably don't buy an Oberheim for its versatility, do you? You probably want the classic Oberheim sounds with a bit of tweakability.
I don't know the OB-SX presets, but I'd swear they offer the basics that most players want from an instrument like this.
Buy it and save it from being cannibalized!

Cheers,
Bert
Old 11th February 2009 | Show parent
  #5
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JMJarvinen's Avatar
 
🎧 10 years
The OB-SX

I have OB-SX synth and it is, as the word on the net and on the back of the manual says, based on OB-X technology. A cut-down preset version, budged Obie.. but not less versatile (sounwise).. Althought they tend to go malfunctionin on tuning and filter (mine did :( !!! ) I should get the voiceboards repaired.. Love the synth thought.. bunchy basses, silky strings, cutting-edge synth leads.. excellent sounds, even mine is half-way broken :D The first thing on old Oberheims is that you should give it a warm-up for about 20mins to Β½ hour.. (the OB series do have "Autotune"-button) If you can find Any OB serie Ober-synth with reasonable price in good condition BUY IT !!!!
Old 12th February 2009 | Show parent
  #6
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massimo's Avatar
 
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JM,
based on what I gathered over the net, the guts of the ob-sx are actually those of the OBXa, NOT the OBX as it was originally claimed. Since I am not a keyboardist, being able to drive it via midi or CV would be essential, but I was told in this thread that the CV/Midi conversion provided by my Xpander would not work polyphonically, and no midi kits exist for this machine,
Would be glad to know I am wrong, though...

best regards
Massimo
Old 12th February 2009 | Show parent
  #7
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Heathfinnie's Avatar
 
🎧 10 years
+1. The SX is based off the OB-Xa, not the OB-X.

I wonder why an OBXa midi kit wouldn't work...
Old 12th February 2009 | Show parent
  #8
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JMJarvinen's Avatar
 
🎧 10 years
OB-SX

Well.. if the SX is really based on OBXa, then IΒ΄ve been lied on big time ;D
Even the back cover of the SX manual says : "The OB-SX is a real synthe-
sizer utilizing the same circuitry as the celebrated OB-X"... oh well, my
mistake then (maybe) :D
Old 12th February 2009 | Show parent
  #9
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🎧 10 years
Wasn't there 2 versions of the OB-SX? I seem to remember one had graphics similar to the OB-X and another one looked similar the the OB-Xa graphics. Is it possible that they were actually based off of two models?
Old 12th February 2009 | Show parent
  #10
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clusterchord's Avatar
 
🎧 15 years
Quote:
Originally Posted by Arpnutt ➑️
Wasn't there 2 versions of the OB-SX? I seem to remember one had graphics similar to the OB-X and another one looked similar the the OB-Xa graphics. Is it possible that they were actually based off of two models?

yes there are two versions as far as cosmetics, but afaik both have OBXA circuitry, i.e. ****load of CEM chips. im thinking perhaps the writing in OBSX manual that its "based on OBX tehcnology" was meant the same way they said OBXA was "based on OBX technology" when it came out. depends how you define "similar" and "based on".

from manufacturers standpoint they were right - indeed X and XA are built similarly except all discrete circuits were replaced by CEMs. but the topology, design of the voiceboard PCBs, molex connections for power, positions of CPU, MOBO, panel.. everyhting looks pretty much the same. except the sound.
Old 12th February 2009 | Show parent
  #11
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🎧 10 years
OBSX

From VintageSynth.org

The OB-SX was envisioned by designers to be a smaller, lighter, more durable "live performance" version of their (then) flagship OB-X. The OB-SX featured the same VCO/VCF/VCAs of the OB-X and a voice card design similar to the OB-Xa in which polyphony was based on the number of 2-voice PCB cards installed (using CEM/Curtis chips). Sacrifices were made to the OB-X's "knob for each function" programming interface (replaced in the "SX" by a few realtime only filter and envelope controls), the ability to save patches (all sounds were preset in ROM) and the last octave of the keyboard ("chopped" to 48 notes).
Despite the sacrifices, the OB-SX faithfully reproduces the character (and at times the "ill temper" of an all analog design) of the OB-X and OB-Xa. The preset sounds are a bit dated (e.g. early funk & late prog rock), but still usable and the realtime controls allow a good amount of "shaping" to be done. It's important to note that like all Oberheim synths, the OB-SX was a continual work in progress and there were many different revisions made to the OB-SX during its life time. Major revisions included: Early units had 24 presets and mid units had 48 presets and late units had 56 presets (later units had a slide switch on the back to change between banks of presets). The color/case design was changed from the (early units) black & gray of the OB-X to the (later units) black & blue pinstripes of the OB-Xa and OB-8.
Early on Oberheim offered OB-SX purchasers the option of sending in cassette dumps of their OB-X patches and burning them into OB-SX ROMs, so there's the possiblity that the presets in an OB-SX may be unique to that specific unit. Somewhere during production the pre-MIDI "Oberheim System" digital interface was added to the OB-SX, allowing the OB-X to interface with the Oberheim DSX sequencer.
Like all early analog synths the OB-SX is vulnerable to voltage and temperature changes (so make sure you allow the unit to fully warm up and use a voltage regulator/battery backup) and some ICs and replacement parts are now extinct - try before you buy!














HereΒ΄s the most common pics of Obie SX models I could find (used to have
a pic of rare SX with totally black knob panel.. maybe it was only a custom paint-job ) My opinion is that the Stripes Obie SX is the coolest one ;P
Old 3rd June 2009 | Show parent
  #12
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🎧 10 years
Just to add to the debate, I have the original user manual, plus both the Preliminary Service Manual and the Service Manual, and it is based on the OB-X! The voice cards are identical to the OB-X, so you'll see a lot of OB-X buyers getting OB-sXes off eBay to cannibalise the voice cards for their OB-X.

The OB-Xa uses 2 Voices per daughterboard card, whereas the OB-X and OB-sX has 1 Voice per daughterboard card.

Also there are other differences, notably with the filter. The OB-Xa has both 24 dB/Oct and 12dB/Oct a different filter configuration. The OB-X and OB-sX are reportedly 12dB/Oct but they both use a CEM3020 filter chip that is 24dB/Oct as it has Resonance, according to CEM specs. Another Difference is that the OB-X/OB-sX uses Cross Modulation for Oscillator 2 (similar to Prophet V Osc 2 Poly Mod), whereas the OB-Xa uses Filter Envelope instead.

It was possible for an OB-X owner to save their favourite sounds onto cassette, send them to an Oberheim service centre, where they could be blown into the EPROM chips of your OB-sX. It is therefore possible that you might have an OB-sX with custom sounds that are unique to your machine.

There were 3 models
MK I - original made approx 1979 (approx 2 years before OB-Xa debuted) 24 sounds, OB-X paint work.
MK II - as MKI but with 48 sounds (2 lots of 24 sounds) and has a switch on the rear panel to select between the 2 banks of 24 sounds.
MK III - 56 Sounds using combinations of A, B, C buttons, in OB-Xa paint job. Manufactured around 1982. Mine was Feb 1982 model.

They typically come in either 4 or 6 Voice configurations, but I've got a rare 5 Voice model (stamped on the serial number plate).

As for MIDI, the Oberheim was the easiest and cheapest to retrofit. I believe that it is possible to retrofit an OB-sX using an OB-X retrofit kit. There is the option of using a MIDI to CV converter with the Gate In and CV In jacks, but this will only play Voice 1.

Sonically it is a bit grainier than an OB-Xa, but still that classic OBie sound. Tom Oberheim allegedly designed the filters for good brass sounds, which might go some way to explaining the "Big Sound" that people associate with Oberheim. Like most analogues, they need to warm up. They are easy to manually tune, and I personally found it worth the hassle just to get the Obie Sound.

JMJarvinen your OBie is not a custom paint job as I also have a MK III OB-SX that comes in the OB-Xa style paint job, and is identical to your markings, even on the pitch bender panel.

Pete
Old 3rd June 2009 | Show parent
  #13
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🎧 10 years
More on the OB-sX...

The filter on the OB-X and OB-sX is 12dB/Octave, as I probably gave the impression that the CEM3020 was only a 24dB/Oct filter, but it can be configured for 2 pole or 12dB/Oct use.

The fact that the OB-Xa uses both 24dB/Oct and 12dB/Oct ought to convince some people that the OB-sX is a preset OB-X, not a preset OB-Xa. Don't let the Ob-Xa style paint job of an OB-sX MK III fool you. Still not sure?

I'll quote form the OB-SX Polyphonic Synthesizer Owner's Manual, First Edition August 1980, (my emphasis is in bold font):

"The OB-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 OB-X along with the ease of operation of a pre-set synthesizer."

"FILTER FREQ
This control determines the initial cut-off frequency of the Filter on each voice. The Filter is a two-pole, low-pass type."

"The Oberheim 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 'XS' is pre-programmed 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 one's 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 sounds are available for a nominal charge. A switch on the back panel is provided to switch from each group. Custom chips can be made by sending an OB-X cassette tape to Oberheim (first 24 programs only 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."

The date of the Owner's Manual pre-dates the OB-Xa. The OB-Xa was not released until 1981, depending upon which part of the planet you are on.

I beleive the OB-Xa style paint job of the OB-sX MK III is responsible for most of the confusion.

Last edited by PeteMOBie; 3rd June 2009 at 12:02 PM.. Reason: error - "changingprogram"
Old 3rd June 2009 | Show parent
  #14
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🎧 10 years
Quote:
Originally Posted by JMJarvinen ➑️
From VintageSynth.org

"The OB-SX featured the same VCO/VCF/VCAs of the OB-X and a voice card design similar to the OB-Xa in which polyphony was based on the number of 2-voice PCB cards installed (using CEM/Curtis chips)."
Contradicting itself there, it was either the same (discrete) VCO/VCF/VCAs of the OB-X or OB-Xa 2 voice cards (using CEM/Curtis chips). Couldn't be both.

I wouldn't know, but I wouldn't use VSE as a definitive sourse either. Most of the write ups are out of date, and a fair amount of wrong information too.
Old 3rd June 2009 | Show parent
  #15
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🎧 10 years
Quote:
Originally Posted by steveman ➑️
Contradicting itself there, it was either the same (discrete) VCO/VCF/VCAs of the OB-X or OB-Xa 2 voice cards (using CEM/Curtis chips). Couldn't be both.

I wouldn't know, but I wouldn't use VSE as a definitive sourse either. Most of the write ups are out of date, and a fair amount of wrong information too.
Agree with you Steve. Most people haven't seen an OB-SX and an OB-Xa opened up. I have. The OB-X and OB-sX have 1 Voice per board, whereas the OB-Xa has 2 Voices per card. The voice card architecture and circuitry layout is different between the OB-X/OB-sX and the OB-Xa. You cannot plug an OB-Xa board into an OB-sX/OB-X, and vice versa. But you can plug an OB-sX board into an OB-X and vice versa.

A significant number of articles on the web are from people who never used or loked inside the machine. They might have come across the MK III OB-sX in it's "OB-Xa style" paint job and just assumed it was Ob-Xa based.
Old 4th June 2009 | Show parent
  #16
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Your post is very informative and appreciated, particularily in establishing that the OBSX is largely based on the OBX rather than the OBXa. However there are a couple of points that I would take issue with. The OBXa quite definitely has one voice per board, in the same manner as the OBX and OBSX. Also, when Oberheim says "same circuitry as the celebrated OBX" I think they mean to say they have the same general type of signal path. They are certainly not the same component-wise, as it's well known that the OBX uses discrete osscilators and filters whereas the OBSX uses Curtis chips. I also have big trouble believing that you can plug an OBSX voice card into an OBX (and vice-versa). They are not even the same dimensionally, as the OBSX cards are more narrow and appear to have pins in different places from the OBX card....
Old 4th June 2009 | Show parent
  #17
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🎧 15 years
Quote:
Originally Posted by PeteMOBie ➑️
Agree with you Steve. Most people haven't seen an OB-SX and an OB-Xa opened up. I have. The OB-X and OB-sX have 1 Voice per board, whereas the OB-Xa has 2 Voices per card. The voice card architecture and circuitry layout is different between the OB-X/OB-sX and the OB-Xa. You cannot plug an OB-Xa board into an OB-sX/OB-X, and vice versa. But you can plug an OB-sX board into an OB-X and vice versa.

A significant number of articles on the web are from people who never used or loked inside the machine. They might have come across the MK III OB-sX in it's "OB-Xa style" paint job and just assumed it was Ob-Xa based.

then, my friend it is you who haven't looked properly into the machines opened. heh

i have here both OB-X and OB-Xa, and some spare OB-SX voiceboards too. i'm afraid most things you stated are absolutely incorrect.


first, OB-Xa uses one voicecard per voice. there are, just like it the OB-X, two racks of four voiceboards one atop another. and CEM3320 is capable of both, 12dB or 24dB, depending on how its implemented in the circuit. OBXa uses two CEM3320s, bcs it actually has two separate filters for two respective slopes.

second, OB-X is a fully discrete machine in audio path. It does not use CEM for filter. Its filter, vco and vca are variant on S.E.M. design. only the envelopes are CEM3310. (a pair of bigger chips on the left of the pic)

Oberheim ob-sx-myobx-voice.jpg <- obx

and third, as i've said before, the OB-SX, both cosmetic versions (grey and bluestripped) are using CEM chips for everything, like OB-Xa does, and voicecard looks almost identical to OB-Xa voicecard. it is not exact drop-in replacement bcs the size is little smaller, and theres only one 3320 slot (only 12dB/Oct on SX), but it can and is often bastardized for CEMs to fix OB-Xa or OB-8. i have four of such OB-SX voiceboards right here. on the right side you can spot a pair of CEM3340 vcos on both cards.

<-obsx
<-obxa

a friend of mine also has a working OB-SX, blue-stripped. and it very well sounds like my OBXa. and yes it was opened many times. and finally here's a video showing the early version OB-SX, where u can clearly recognize the formation of CEM chips from the voicecard pic i posted.




Old 4th June 2009 | Show parent
  #18
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
regarding midi:
really anything is possible. if you can't find a kit you can make one (or have one made).

if you like the sound of the beast and you want to keep it i suggest starting a thread on the geekslutz pages to that end.
you could also email kenton. they've always been very helpful to me.

i'm sure you can get midi on the thing and at not too high a price. when you're done you'll have a very rare, valuable and sort after synth! you won't lose money on the midi fit! you'll gain.
Old 4th June 2009 | Show parent
  #19
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🎧 10 years
Quote:
Originally Posted by steveman ➑️
I wouldn't know, but I wouldn't use VSE as a definitive sourse either. Most of the write ups are out of date, and a fair amount of wrong information too.
tons of wrong info on vse
they state all kinds of crap that just isn't true or is completely false.
sad thing is people take it as gospel and you get lots of misinformation that propagates as the truth because of vse.

for instance off the top of my head on some things i keep seeing over and over that bug me...
vse is waaayyy off on arp 2600 versions and filters that came with each of the revisions as well as oscs used
vse says the yamaha tg-33 is an sy-22 in a rack with 12 bit pcm samples, when in reality it's a cut down sy-35 (missing only the sequencer) in a rack with 16 bit samples per the tg-33 manual itself. how people still think it's an sy-22 when they clearly sound different on the strings and brass and such presets and the manual itself states 16 bit samples is beyond me.
Old 5th June 2009 | Show parent
  #20
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🎧 10 years
Clusterchord, thanks for your update. I stand corrected. Thanks for expanding my knowledge on these machines. I checked with my brother and it was not an OB-Xa that we saw in the workshop but an OB8, as he reminded me that it had MIDI and the exposed pan pots for the voices on the side panel. I have no doubt that you are correct, and your photos have helped resolve this mystery.

I have not seen the insides of an OB-X. The only ones I have seen used were by Richard Barbieri of Japan and Brian May of Queen on the Flash Gordon sound track. I have not heard of anyone having to tweak OB-SX voice cards to make them fit an OB-X, but was going off what my service engineer said, although he now deals mainly with digital stuff.

I've re-read the OB-SX manual with your corrections in mind and note that in one section Oberheim say that it "... uses much of the same circuitry as the OB-X", then on the back cover says "... utilizing the same circuitry as the celebrated OB-X". This seems to be a contradiction, but both statements could in fact be true. It all depends on what we read into "much of the same circuitry" and "same circuitry". This was a user's manual afterall, so is not going to go into great detail about the small circuitry differences between the OB-X and OB-SX. Maybe Oberheim were trying to say that most of the circuit board concepts were derived from the OB-X, but leaving room for "improvements" or "updates" by switching to CEM based sound cards, yet still in essence giving an OB-X sound.

One point made earlier is that the OB series is an ever evolving project. Therefore, it could be that the OB-SX is in fact a hybrid or transition model between the OB-X and OB-Xa. Maybe the basic circuitry connecting the VCO's, VCF, VCA's and Envs is the same as per OB-X, but they substituted CEM chips for the discreet functions of the OB-X.

As I originally stated, a CEM3020 can be modified to operate in 12dB/Oct mode, even though it is mainly used in 24dB/Oct mode, so it might be that Oberheim customised the circuitry surrounding the CEM3020 chip to get as close as possible to the discreet circuitry of the OB-X and hence "the OB-X" sound and 2 pole (12dB/Oct) filter they refer to.

The Voice architecture is, TTBOMK, as the OB-X, but using the CEM chips instead of discreet circuits, as a forerunner to the OB-Xa. There are some sounds I get on my OB-SX that clearly have cross modulation between Osc 1 and Osc 2, to get Honner Pianet type piano sound, or metalic sounds. From what I remember using the OB-Xa, it replaced Cross Modulation with a Filter Envelope, so you could use the Filter Env to modulate the pitch for those falling pitch Prophet V-ish type of sounds.

Your comment that the OB-SX sounds closer to an OB-Xa is as valid as mine that I have heard OB-X sounds in mine, as I've recognised ABC8 as close to a sound Brian May used with his OB-X on Queen's soundtrack to the Flash Gordon movie. Then again some sounds are as you say OB-Xa identical.

The more I think about it the more I'm convinced that the OB-SX is a Hybrid beast forming the stepping stone from the OB-X with it's discreet S.E.M style circuitry, to the CEM based OB-Xa. Oberheim might have used the OB-SX as a proof of concept in the CEM based production techniques as a forerunner to the OB-Xa.

I can only envy you for having an OB-Xa and an OB-SX side by side.

I've enjoyed learning more about the X family from you all, so thanks for taking the time to add your comments and pics.
Pete
Old 5th June 2009 | Show parent
  #21
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🎧 10 years
The OBSX would become a hot keyboard if Encore Electronics (Tony Karavidas) would make a MIDI interface for it. Here's why. Generally with his stuff you can port in patches through system exclusive into the new memory which is on the kit (which replaces the old memory circuits). This means that you could port in sounds from the OBX, which in turn means that the OBSX becomes a fully variable synthesizer....albeit the variability has to come from a "mother keyboard" (the OBX). It would be the same idea as a with the Yamaha DX7 and TX7, where one is fully variable and the other is fully variable in the sense that it takes patch data from the mother keyboard. Of course you don't physically need to have the mother keyboard, you just aquire OBX patch data from some third party and load it in...
Old 5th June 2009 | Show parent
  #22
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🎧 10 years
Question for Clusterchord.
Your friend has opened his OB-SX many times, as have I. It wouldn't be to tweak the manual tuning trim pots on the oscillators by any chance would it? Or am I the only one needing to retune every now and then?

Someone recommended replacing the finger trim pots for the Oscillator tuning with higher quality pots, as the originals were cheapo units. Has anyone done this? If so did it improve tuning stability?

The Auto tune on mine has gone as it is now set to some wierd Arabian sounding scale. Has anyone else had a similar problem with Auto Tunes?

I've had to replace the Voice DIP switch twice in 6 years, now, plus the usual cleaning.

Otherwise for a machine that is over 27 years old, I still get a lot of pleasure from playing mine, as it is very usable.

I understand that Kenton no longer provide MIDI retro-fits for Oberheims. I did wonder if anyone had a MIDI converter that took advantage of the Computer socket on the rear panel, much in the same way that Kenton made kits for the Roland Jupiter 8 and Juno 60, as these Rolands had a connector for an interface bus that allowed the Juptier 8 to talk to an MC4/8 (can't remember which, might have been both) or a JSQ sequencer.

I also see that Philip Rees MIDI2CV units are no longer available, so I guess that leaves Kenton and the CV In and Gate In jacks for Voice 1 as the only definite option.
Old 5th June 2009 | Show parent
  #23
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🎧 10 years
Quote:
Originally Posted by PeteMOBie ➑️
I understand that Kenton no longer provide MIDI retro-fits for Oberheims.
Well, you obviously didn't bother to look at either the Kenton or Encore sites...
Old 5th June 2009 | Show parent
  #24
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🎧 10 years
Thanks for the sites Rangoon

Actually I did contact Kenton over a year ago, but was advised that they didn't do any kits for the OB-SX at the time, nor did they do any MIDI kits that used the Computer socket on the OB-SX.

Kenton used to make one way MIDI retro fits (MIDI In only) for some keyboards, as I considered it for my old Moog Opus 3.

I've never heard of Encore, so there website is quite a revelation, so thanks again for that.

Still begs the question, would a retro fit kit for an OB-X or OB-Xa be compatible with an OB-SX?
Old 6th June 2009 | Show parent
  #25
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🎧 10 years
Quote:
Originally Posted by PeteMOBie ➑️
Still begs the question, would a retro fit kit for an OB-X or OB-Xa be compatible with an OB-SX?
If any of them were close to being compatible it would be the OBX, because Oberheim implies that the OBSX is parameter-wise compatible with the OBX (pointed out in your post). The problem is that it would likely be a custom job where you would have to send the keyboard to California, which is not feasible given your geography....

Are you aware of synthrepairs.com in Sidney? Maybe he could get some very basic interface going on, either through that computer port in the back or actual MIDI...
Old 6th June 2009 | Show parent
  #26
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🎧 10 years
Wow, there's someone in Australia that might be able to do a retro fit?

You guys know more about what goes on down under than I do.

As far as I know, I'm the only one in Western Australia with an OB-SX. Not sure about the rest of the country. My service engineer said mine was the first OB-SX he'd fixed, and he's in his 60's now, having started with analogue in the early 70's. There's very little information about them on the web, apart from a few dedicated folk like yourselves. I've learned so much more about my own little OBie just spending a few days on this forum than I have in the last 6 years.

Thanks again for all the info, corrections and advice.
Old 8th June 2009 | Show parent
  #27
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🎧 10 years
As this thread has been such a great source of info for me, I'd like to give back to this forum in some way as a thank you for all your time advising, corrections and recommendations.

If anyone needs a copy of the OB-SX Service Manual to help them add MIDI or for curiosity, please let me know, and I will scan my copy and make it available for whoever needs it. Same goes for the User's Manual, although there's not much in it. I can even post hard copies if you prefer.

From what I can see there is no content difference between the Preliminary Service Manual and the Service Manual, apart from the title page. But if you want both, just ask!
Old 8th June 2009 | Show parent
  #28
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🎧 15 years
Quote:
Originally Posted by PeteMOBie ➑️
Question for Clusterchord.
Your friend has opened his OB-SX many times, as have I. It wouldn't be to tweak the manual tuning trim pots on the oscillators by any chance would it? Or am I the only one needing to retune every now and then?

hi Pete. two things you can/need to do.

in case you havent changed the capacitors on your board, like ever since the synth was made, you should asap. electrolytics typically have life expectancy of 18 - 20 years. after that they dry out, either completely or become unstable, changing values.

this makes the synth absolutely impossible to tune or retain the tune for a longer period of time. new caps on them voiceboards and PSU, besides remedying this, also lower the noise, restore the transients, and make the warm-up period extremely shorter. my re-capped OBXa needs less than a minute now. when i bought it it took 5 to 10.

don't use cheap ones, but rather a brand name like nichicon or panasonic audio.

second: in order to make the trimmers easier to position (old trimmers get dirty and lose the continous, smooth range i.e. jumping over areas..) , and make the synth more stable overall (esp if u move it arround) u should replace them with multiturn trimmers. not all, but VCO1 and VCO2 tune, and perhaps the HI RANGE trimmers too. i want to replace the VCF cutoff trimmers too bcs im having trouble calibrating all 8 filters to exact same position.


parts are not expensive, but there's some time and solder required to do this. ive done the capacitors few yrs ago, and am getting ready to do the trimmers just now.


cheers


Quote:
Originally Posted by Rangoon ➑️
The OBSX would become a hot keyboard if Encore Electronics (Tony Karavidas) would make a MIDI interface for it. Generally with his stuff you can port in patches through system exclusive into the new memory which is on the kit (which replaces the old memory circuits). This means that you could port in sounds from the OBX, which in turn means that the OBSX becomes a fully variable synthesizer....albeit the variability has to come from a "mother keyboard" (the OBX).
phuuuk id love that. id get a SX right away for my gigs, and leave the big oberheim at home. however, knowing Tony, and how slow he develops things bcs of his day job (he promised a new eeprom version of the JP8 retrofit some 3 or 4 yrs ago, i stopped holding my breath), i doubt it. he did tell me while he was developing the new OBXA retrofit that it will have ability to receive and TRANSMIT !! all midi controllers from his front panel pots in the next update. that would be just awesome.. we can only wait..
Old 8th June 2009 | Show parent
  #29
LWG
Gear Nut
 
🎧 10 years
Re: Thread Topic

Hello,

The earlier gray and black versions of the OB-SX and the later black with blue stripes are not identical.
The gray SX has a CEM osc, filter, & egs, but the vca is not, as its a CA3080 with op amp buffering (tl0-81).
You can verify this in the first edition sevice manual (November 1980).
Older units such as these are a sort of transition between the older Oberheim deisigns and the fully CEM-based ones.
The later editions with blue pinstriping have a CEM3060 vca, i.e, a full
CEM chip set. They are actually closest to the OB-Xa.
In order to fully service the later models, you'll need a second edition service manual.


Regards,


Lawrence
Old 9th June 2009 | Show parent
  #30
Here for the gear
 
🎧 10 years
Hi ClusterChord
Thanks for the advice on capacitors and trimmers.

My ESQ-1 has gone wierd all of a sudden, and apparently the main cause is capacitors going on the power supply board. So that's another job for me. Sorry to say I couldn' afford the Matrix 6 at the time, so went with the Ensoniq.

I've compared your OBXa voice board against the OB-SX from your pics, and note that the OB-Xa has better quality Osc Frequency trimmer pots. My service guy has replaced a few components and sorted a few dry solder joints, so it is better now. I have to remind myself that my model is over 27 years old, so am impressed that it has lasted this long.


Hi Lawrence
Thanks for your Service Manual update. I wasn't aware there were other manuals out after 1980. It makes sense that there will be some changes as on my Feb 1982 OB-SX 56 Preset model, the groups are selected by multiple combinations of the A, B, C Group buttons in the same manner as the OB-Xa, so I guess there will be some differences in the circuitry to reflect this change. I also have to remind myself that the OB-SX ran in parallel with the OB-X and OB-Xa.

Does anyone have a later edition User Manual? I'd be curious to know if it lists all 56 sounds, as the 1980 edition I have only lists the first 24 presets.

I was actually planning on selling my OB-SX, but I'm not so sure now, having got it back from being repaired/serviced, and reading all the encouraging entries and keen interest in them on this forum.

To make matters worse I've seen the Tom Obeheim New SEM pages on the web and want one more than a Moog Little Fatty.
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