[sdiy] OB-SX auto tune problem

Matti Kari maza at maza.fi
Fri Sep 24 17:32:45 CEST 2010


I recently acquired an Oberheim OB-SX for a good price. It is the last 
model built with 56 presets and in perfect condition externally & 
internally, except that the autotune sometimes (say: usually) fails on 
some voices, except that voices #1 and #2 never fail and the voice #6 is 
the most unreliable.

I have already verified that the problem is not on the voice cards 
themselves by swapping them around - no change. Also I've changed the 
4051 and TL082 chips that generate the (I assume) tuning voltages for 
the oscs - no change.

What is interesting and may have something to do with the problem is 
that now that I calibrated all the voice cards (auto tune switched off, 
of course), the auto tune tunes them almost exactly a whole step higher 
(i.e. playing a C key plays D), and I need to compensate this using the 
master tune pot.

Any ideas? I've already calibrated the synth according to the service 
manual and all the voltages are what they should.

Thanks in advance,


Matti Kari
maza at maza.fi
040 838 6607

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