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Originally Posted by PeteMOBie  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.
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)
<- 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.
