Hmm...nope. I don't believe that anyone who really could hear a difference wouldn't also hear the noise floor (it was fairly obvious). Which leads me to conclude that you deliberately got one wrong so that you could then make the claim you just have.

Sneaky, but not sneaky enough.

I agree. The filter of OB-X is one of the most exciting, maybe even THE most exciting sounding one of all polyphonic analogues (imho). It really has a noble shine and sweetness, and it doesn't thin out at all at high resonance settings. It also sounds less transistory (due to the discrete design) than the CEM3320 based ones in OB-Xa and OB-8.

I think the OB-X is a good go if you want to have the basic sound of the SEM based Eight Voice but with full programmability and easier handling. The voice cards use CEM3310s for the EGs instead of the discrete ones in the SEM (I guess mainly to save space) and it (unfortunately) lacks the state variable multimode feature (cut down to 12db lowpass here), but on the other hand it has more modulation features and cross modulation for non-harmonic sounds. If you don't calibrate the voices to sound exactly the same you even also have some of the voice variation magic of the Eight Voice.

Regarding lacking multimode, I once read that the filters of OB-X can be given back the multimode functionality with a mod. I decided against it since I didn't want to destroy the beautiful interface drilling holes etc.

The main problems of OB-X are a) that there aren't too many devices around since it only was built for about one year before it was replaced with OB-Xa and b) it can be unreliable because of all the tons of plug contacts, some of the ICs can be susceptible to heat, and the old tantalum condensers tend to die after 32 years (there are many...). So never do a blind purchase unlike you are ready to invest a lot of additional time and money afterwards.

Regarding voice wiring, you can see the similarities of the SEM and a voice card of OB-X here:

SEM (click to enlarge):


Top right: Oscillators (Temco regulated), top left: filter, bottom left and right: discrete EGs

OB-X voicecard (featuring replaced trimpots, click to enlarge):


Left side: Discrete oscillators (Temco regulated), top right: discrete filter (the small chips are just opamps), bottom right: the two CEM3310 envelope genarator chips (which replace the discrete ones of the SEM)

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Here's a useful article btw regarding OB-X vs. OB-Xa and SEM:
http://www.sonicstate.com/synth/oberheim_ob-x/

I agree. The filter of OB-X is one of the most exciting, maybe even THE most exciting sounding one of all polyphonic analogues (imho). It really has a noble shine and sweetness, and it doesn't thin out at all at high resonance settings. It also sounds less transistory (due to the discrete design) than the CEM3320 based ones in OB-Xa and OB-8.

I think the OB-X is a good go if you want to have the basic sound of the SEM based Eight Voice but with full programmability and easier handling. The voice cards use CEM3310s for the EGs instead of the discrete ones in the SEM (I guess mainly to save space)

and it (unfortunately) lacks the state variable multimode feature (cut down to 12db lowpass here)

Regarding lacking multimode, I once read that the filters of OB-X can be given back the multimode functionality with a mod. I decided against it since I didn't want to destroy the beautiful interface drilling holes etc.

OB-X voicecard (featuring replaced trimpots, click to enlarge):

From that article: "At the prices both these OB's are going for, you could afford to have both for less than a JP8000!"

Clearly the description was written quite a few years ago, eh? Damn, I hate being reminded of how I missed the boat by not snatching up some of these pieces before the prices shot up, LOL. Honestly, though, I was so into digital stuff like Kurzweils and Wavestations and then VSTi's for a long time that I wasn't even paying attention to the prices of vintage analog, so I didn't realize they were so much on the rise until the prices had already gotten high. Then I looked around eBay and was like, "WTF happened? Last I knew, Jupiter 8's were only going for $2,000."

Now, it's kind of too late on a lot of this stuff, at least in terms of what I'd be willing to pay. $4K for an OB-X is getting too close to the price of an SE CODE, which I'd personally find more desirable to own.

Yeah, but that's really only for OB-Xa and OB-8, not OB-X. E.g. this OB-X went for $6'499.00 on ebay:
http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=30059 6914897+

As said by Vectorman, probably too late...

Unfortunately these are only one-offs...