I used to have an OB-SX. If you have the 56 patch version, the switch
has no effect. You select the patches using a combination of the bank
buttons: A, B, C, AB, AC, BC, ABC, plus the patch number button. You
end up with a total of 56 patches using all of the combinations. I am
guessing it is something similar with the other versions.

--- In oberheim@yahoogroups.com , "Paul White" <pjwhite@...> wrote:
>
> --- In oberheim@yahoogroups.com , "synthy55" <synthy55@> wrote:
> >
> >
> > recently picked up an ob-sx, it has a switch on the back to flip
> > between banks of preset patches, but nothing happens when you flip
> the
> > switch, maybe you have to press a button as well , i don't have a
> > manual, anyone know how to do it
> >
>
> I'm not completely sure, but I think the bank select switch is there
> for an _optional_ EPROM containing more patches. If you look inside
> the OB-SX, you'll probably see an empty EPROM socket somewhere on the
> main circuit board.
>