Quote:
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