Oberheim ob-sx

[LWG]

Originally Posted by PeteMOBie

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."

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.

Hello,

Three things pertaining to the early gray units:

1.) They only use a partial CEM chip set. The vca is more discreet than
the full CEM model.

2.) Note: The oscillators also have cross-modulation, something that can
be confirmed from the voice card diagram in the first edition (11/80)
service manual. This was an OB-X feature,
as the OB-Xa dropped X-mod in favor of envelope generator control
(voice modulation).

3.) According to Oberheim, the gray SX models accepted patch data
dumps from the OB-X series.

These three pieces of information (along with the first edition owner's manual statement you quoted) strongly suggest that although the first (gray)
OB-SX models adopted a Curtis vco, vcf, and envelope generator chips,
they were seemingly using a modified design to model the sound of the OB-X, even to the point of making patch data compatable between the two. Xa isn't in the picture yet.
I also noticed from the YouTube clip of the Mk 1, has a slightly grainier sound than the full CEM units.

Regarding the later blue pinstriped versions, the second edition owner's manual (10/81) states:

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

This is true of the blue pinstriped version, in that it uses a complete CEM chip set for vco, vcf, vca, & egs however, you pointed out that there seems to be cross-modulation used in presets even on the later units.
The second edition owner's manual describes several presets as using cross-mod: BC6 (X-mod delay), ABC2 (X-mod Bells).
Remember, the Xa no longer had cross mod. I would have to look at a later edition service manual (which I don't have) to further verify whether they left the cross-mod function unchanged on the later SX models.
If true, it would seem that the pinstriped SX units have a full CEM chip set, and is soundwise modeled on the OB-Xa, but retained the
cross-modulation feature from the first OB-X.
If the cross-modulation function is retained on the later striped units, one wonders how they could have used an OB-Xa to provide patch data for these units.
You could probably get some insight into how the presets were done (and exactly what machines they used) by asking one of the original patch programmers with Oberheim from around that time: Todd McKinney and
Marcus Ryle were among them.

Tom Oberheim (Welcome back!) would probably have many answers, but more than likely has his hands full with his new company.

Regards,


Lawrence

[PeteMOBie]

Hi Lawrence
Thanks for the extra info from the second edition. From what you have provided, it is little wonder that there has been so much confusion as to whether the OB-SX is OB-X or OB-Xa based, especially when Oberheim make both statements in different editions of the OB-SX User's Manual.

As a general observation, it might be that some OB-SX owners could find that they have purchased/inherrited additional Voice cards that are different, with respect to the VCA circuitry, to what came in their machine.

My model is the later MK III (assuming MKI 24 sounds, MKII 48 sounds, MK III 56 Sounds) Feb 1982, 5 Voice, and I was tempted to get extra voice cards from eBay last year, so could have got cards with the earlier VCA circuit. I'm still tempted to get a few cards to max out my little OBie to 6 voices plus some spare cards. I wouldn't mind using a spare OB-SX voice card to build my own SEM type project around it. First though, I have to attend to the capacitors on the current boards.

Lawrence, are you able to provide a list of the Patches and their corresponding names from your later edition User's Manual please?

I note that a few sounds are clearly Cross Modulation based, as I have about 2 esoteric metallic sounds and a Honner Pianet bell type sound. If an OB-Xa owner sent in a tape of a sound using Filter Env, I guess this would be translated into a Cross Modulation setting. Also, what happens when the OB-Xa user had a patch with the 4 Pole filter activated? Would that just get translated into 2 Pole to be compatible with the OB-SX?

I suspect that when an OB-X (or OB-Xa) user sent in their tape of 24 sounds, Oberheim engineers might have had to tweak the settings to allow for the difference between discreet circuits of the OB-X and the CEM based circuits of the OB-SX.

As I said before, I've learned so much more about the history of my OB-SX from this site in the last few days. About 6 years ago I added a review of the OB-SX on some web site (might be Harmony Central) and referred to it as a preset OB-Xa, with similar voice cards to an OB-Xa. I must therefore be getting old or suffereing a memory lapse to have forgotten that, so thanks to everyone here for correcting my faulty memory. I wonder if Kenton or Encore do memory updates for grey matter? lol

In view of what everyone has said, would it be a fair to regard the late model OB-SX as a variable/preset 2 Poled filter, Cross Mod version of the OB-Xa?

Cheers
Pete

[LWG]

Originally Posted by PeteMOBie

Lawrence, are you able to provide a list of the Patches and their corresponding names from your later edition User's Manual please?

Yes, but atm I don't have a working scanner. Will see what I can do
as time permits.

Originally Posted by PeteMOBie

I note that a few sounds are clearly Cross Modulation based, as I have about 2 esoteric metallic sounds and a Honner Pianet bell type sound. If an OB-Xa owner sent in a tape of a sound using Filter Env, I guess this would be translated into a Cross Modulation setting. Also, what happens when the OB-Xa user had a patch with the 4 Pole filter activated? Would that just get translated into 2 Pole to be compatible with the OB-SX?

I doubt that all the parameters directly translated. I'm also am inclined to think they would have had to offload patch data from the X/Xa,tweak them slightly on an external device, then burn them to PROM.
But again, I believe Oberheim's programmers from around that time would probably be able to clarify that.

Originally Posted by PeteMOBie

In view of what everyone has said, would it be a fair to regard the late model OB-SX as a variable/preset 2 Poled filter, Cross Mod version of the OB-Xa?

I believe thats accurate, or more simply its an OB-X/Xa hybrid; it has the same voice architecture (2-osc/2-pole/cross mod) as the first OB-X, but the chip set/sound of the OB-Xa.

The gray units could also be termed an OB-X/Xa hybrid, but with a sound and and ckt design thats just a bit more transitional, compared to the pin-striped units.
It would seem, that gray models were a proving ground for modeling the old SEM OB sound with an IC-based design.


Regards,


Lawrence

[carlheinz]

I really like all the oberheim stuff slightly off the technical end of the topic....The single most important feature of the XA over the SX that rocks my world is layering or stacking 2 presets on one note.You cannot layer on the X or the SX..I don't think

[BiAge]

Hello,
this is my first post here and after reading this many posts about some OBs I have to comment:

OB-X voice-structure:
VCO: discrete
ENV: CEM3310
VCF: discrete (OTAs and OPs)
VCA: discrete (some OTAs and OPs)
VCA for Voice summery : discrete (OTas OPs), this VCA is for volume and
not on the voice-boards

OB-SX (all versions):
VCO: CEM3340
ENV: CEM3310
VCF: CEM3320 (2-pole)
VCA: discrete (CA 3080 OTA)
VCA for voice summery: discrete (OTA OPs)

OB-Xa (all versions):
VCO: CEM3340
ENV: CEM3310
VCF: CEM3320 (2x, one 2-pole, one 4-pole)
VCA: discrete (CA3080 OTA)
Summery-VCA: CEM3360

Additional information:
All versions of the OB-SX have the same voice-cards. There are only
differences in frontpanel, housing and presets. First units like OB-X, later like Xa and up to 56 presets.
The VCF-layout (OB-SX and OB-Xa 2-pole) is exactly the same.
In all OBs are some technical changes over the time. I have seen diff. colours and versions of PCBs with minor changes and there are some firmware-versions on the Xa.
So much confusion ? No !
The technical layout of the voice-cards in SX and Xa are very very near. The main difference is the second 4-pole-VCF of the Xa. The OB-X is much more different !

I hope this information is usefull for you. I collected the details after repairing (and using !!) many Oberheim-synths in good old germany.

BTW:
Some of the pictures here are made by myself and showing parts of my personal gear. It is no problem to take it from my website but it would be nice to mark them with the original source.

Thank you.

[PeteMOBie]

Thanks for the update BiAge.
I've had a look at my voice cards and confirm that I have non-CEM chips for my VCA, but everything else is CEM based. As I seem to have 2 VCA chips per voice card, I'm guessing that it's one VCA per Oscillator.

I've scanned my 1980 user manual as a PDF if anyone is interested.

Here's my late model. I need to replace the Osc Finger Trim Pots, to stabilise the tunning, and the springs on 2 keys, as the keys do not bounce back up straight away when released. Everything else is great, apart from the Autotune that I never use anyway.

[JMJarvinen]

PeteMOBie

Wow, if I ever got hold on second OBSx that would be like yours; blue lining
and extra presets badge on it

The little-bro Obie has more common with the OBXa (technically, vcos,
vcfs use same chip) than with the OBX; very punchy sound (I don´t
mean that the OBX would be any worse..soundwise or technically)

Hmm.. what would be the price on bluestripe OBSx with more patches;
definitely would love to have second one

[PeteMOBie]

JMJarvinen

Thanks for the comments. nice to know there are people that appreciate these 'little' Obies. I've certainly had fun with mine. I like to think that mine came from Oberheim's golden era towards the end of the analogue age. I'm not sure how many of the late models sold as that's around the time when the Roland Juno 6 and Korg Poly 6 hit the scene. Mine's a 5 Voice, rather than the usual 4 or 6 voice configuration, so I guess they wre aiming at hard up keyboard players who couldn't afford an Oberheim OBXa or Prophet 5.

I'll actually be selling mine, as I have to downsize. In the process of ordering the Finger Trim Pots for the Oscillator freq.

[PeteMOBie]

Hi fredpilki

As I've received a request for a copy of the Service Manual, I'll scan my OB-SX Service Manual tonight. I cannot see any difference between the Preliminary Service Manual and the Service Manual, both dated 1980, so will copy the Service Manual. I'll break it down into sections to make emailing easier.

Meanwhile, here's the list of 24 sounds from my 1980 User Manual.



Cheers
Pete

[massimo]

So, in conclusion, is there anybody out there who has a MIDI kit actually working on his Ob-Sx?
Encore Electronics did not answer my e-mails, unfortunately, while Kenton replied they seem to recall from several years ago that an Ob-X kit would at least trigger notes on the Ob-Sx.

Best regards
Massmo

[frico]

If it's any help, here's my email conversation with the guy from Encore electronics on the subject:

Hi there, i have an oberheim ob-sx and was wondering if your obx-a kit might work with it. Any thoughts?
Thanks,
Conor

Hi Conor,

No, they are not compatible.

Regards,

Tony

thanks tony. Do you think a tech might be able to modify it to get note on/off data into the ob-sx?

No.

[massimo]

who knows about the OBX interface instead....

[massimo]

Received replies from Kenton and Encore:

Kenton: (they POSITIVELY recall the OBX kit worked at least for note on/off).

Here's the last mail
Massimo
-so you positively recall an OBX kit actually worked for at least receiving note on/off on the obsx, right?

John
-Yes

Massimo
What you are saying (re. previous mail) is that an Obie tech (there is one here in Rome) wouldn't practically know where/how to install one such kit on an ObSx, or what?

John
-A good technician should be able to get the notes working without too much trouble. I doubt that they would get the pitchbend / modulation etc. going. We wouldn't be able to provide any assistance as we don't have any first-hand information on the OB-SX (we don't have one here). Regards John

Encore:

Massimo
-Someone mentioned to me that an OBX (NOT Ob-Xa) Midi kit should work with an Oberheim Ob-Sx for receiving at least note on/off.
Do you have any experience/comment on this?

Tony
-I've never tried it! There is different code in those instruments, so I wouldn't be too hopeful.

Massimo
-no hope to see any such box implemented in the future...?

Tony
-It's very unlikely unless I discover it's extremely easy. There isn't much demand for the obsx. I would also need to get one here for a while.

So, anyone volunteering to send them a unit so they can give it try?
(I do not yet own one)

best regards
Massimo