OB-8 Calibration

[jhaible]

Hi Tim,

I discoverd the ENV time adjustment problem when I tried to calibrate
my own OB-8. You're right, setting the voltages to 0.00V must be
an error in the service docs. I wouldn't even get the 0V in my OB-8,
but that was the best that could have happened ! Otherwise there would
have been just one more sluggish sounding OB-8 in the world ...
Aparently the right voltage is slightly negative, I think -250mV is about
right.
(But check the archives, see below.)
And there must be many OB-8's around that have the ENVs calibrated
to 0V, or as close to 0V as possible,with the result that the envelopes
are way too slow. At first I wouldn't believe it, but meanwhile I got so
much feedback about it that I'm quite sure that most of the OB-8's
reputation of being somewhat inferior to a OB-Xa is simply because
of this misprint or error in the service docs. Imagine every decent
OB-8 going into service (to make it 100% perfect again) would leave
the repair shop with slowed down envelopes, if the tech follows
the service manual ...

There is a text I've written about that in the Oberheim section of 
Music Machines at hyperreal. I don't recall every detail, so just
get that text and calibrate your Obie acording to this instruction.
(The exact voltage is printed there, too.)

Hope this helps, and sorry I'm not of much help for the VCF
calibration. I'd say program a sound with a distinct filter sweep
at medium resonance, play along and adjust all voices to sound
similar by ear. Each voice being perfectly identical to the other
is boring anyway ...

JH.

----------
> Von: Tim Curtis <sexsymbol at execpc.com>
> An: synth-diy at mailhost.bpa.nl
> Betreff: OB-8 Calibration
> Datum: Samstag, 27. Februar 1999 10:33
> 
> Here's one that some of you will probably find pretty basic...
> 
> My OB-8 (rev. A8) had lost all it's patches (battery died) and I just
> reloaded a cassette that I had into it for the time being.
> 
> It neede calibrating, so I followed the procedure in the manual.
> However, there are a couple things I'm wondering about.  Perhaps someone
> knows the answers offhand.
> 
> First, there are release, decay, and attack adjustments for the VCA and
> Filter that the manual says should be adjusted for 0.00V.  There is no
> way that my OB-8 can be adjusted to that degree - it manages to get to
> about -182mV.  Is this a misprint?  From the range I have I'm guessing
> around -250mV?
> 
> Also, when calibrating the filters, the manual lists a procedure that
> consists of turning up the resonance, volume envelope sustain, and
> program vol/bal, while turning everything else down, turning off all
> switches but the tracking switch, and adjusting the volts per octave
> trimmer (t106) to calibrate the filter to the octave.  When I get this I
> get a VERY slow portamento between notes, and it's pretty much
> impossible to hear the octaves with that taking place.  Is that normal,
> or is it also a misprint?  Is there another method I should try?  The
> filters are DEFINITELY in need of calibration.
> 
> Thanks for any help,
> 
> 
> Tim
> 
>