OK , I have been recently in possession of two OB-6s, one a replacement for the other. One was a SEQUENTIAL serial #03638 and the other was a DSI serial number #03632. How close is that?
Here's a photo of both of them.
Just out of curiosity, does the later serial number OB-6 with Sequential printing on the rear have the same printing on the front edge below the keys as the earlier Dave Smith labeled unit ? Or did they just change the Dave Smith logo on the rear to Sequential ?
Everything is the same except the rear logo change. The beautiful "Tom Oberheim" signature is still there front right. No added 'sequential' on the front left or anything either.
I'm a big fan of the sequential name and logo, moreso than the DSI logo, on the newer Rev 2s (my ex rev 2 was one of the first) and the Prophet 6 it really suits it.
However, as an owner of an OB-6 in the 03Xxx (3000's) range with the DSI logo on the back, I honestly believe on the OB-6, this synth of all, works BETTER having both Tom's and Dave's signature logos on. Probably the only time you'll hear me say that (as the sequential logo is just better in general on all his other synths).
OB-6 was a joint one-off product wonder synth between 2 legends so it makes sense both of their signatures are on there, not just because of having two real names but because it (to me) looks better with the Tom's signature thing, in keeping, while the sequential logo looks a bit stuck on and out of context with the emphasis on Tom's signature front and back.
At the end of the day though it really doesn't matter one bit, and anyone worried about their OB-6 having the older logo shouldn't, it's the "original and classic" look with the 2 legendary sigs, anyone with the newer logo also.. don't worry.. nobody cares once you start playing that bad-boy and the gorgeous sonics hit you (and as players we don't really see the rear that much anyway).
I wouldn't go assuming there were any hardware changes between DSI/Sequential badges units either, it would put weird rumors out there. Yes EARLY <1000 serial? or so OB-6s did have slightly different hardware (glitchy sometimes as confirmed above) but any 3000 series or higher, regardless of a painted logo on the back, is going to be pretty much the exact same synth with exact same quality. One bad unit of either badging doesn't mean anything about the rest of them!