OBERHEIM SYNTH

Before you said if you changed the voice board you still had the same 
problem.  If that is the case, the problem is not on your voice card 
so don't try changing parts on the voice card. 

You say the problem it is only with OSC1.  So if you ONLY have OSC1 
on you hear distortion, but if you ONLY have OSC2 on there is no 
distortion (make sure OSC2 is at full level), correct?  If the 
problem really is with just OSC 1, see the next paragraph.  If the 
problem only happens when both OSCs are on, the output level is 
likely too high.  Each voice passes through a passive (i.e. resistor 
divider with a pan) before the final output stage.  The pan was the 
most likely cause, but you already tried that.  Try panning the voice 
hard left and hard right.  Do you have the distortion in both 
positions? 

Does the problem happen on both the Saw and the Pulse shapes?  Does 
the Pulse Width change as you spin the PW knob? If the problem is 
only with the Pulse Wave I have some ideas. 

Let me know what happens.  


--- In oberheim@...m, "jringmrath" <jringmrath@...> wrote:
>
> I tried panning the distorting voice card and cleaning the pots- it 
didn't help.  I do only 
> hear it when I have OSC 1 engaged - with just OSC 2 I don't hear 
the distortion.  The weird 
> thing is that I tried replacing the Curtis 3340 for OSC 1 and I get 
the same distortion, so I 
> don't think it is the chip.  Any other thoughts?
> 
> Jonathan
> 
> --- In oberheim@yahoogroups.com, "nelsonj_sce" <nelsonj_sce@> wrote:
> >
> > As for the distortion, try panning your bad voice and see if that 
> > helps the problem.  Also clean the pan pot with some component 
> > cleaner.   
> > 
> > As for the "ghost" note...I have to think more about that. 
> > 
> > --- In oberheim@yahoogroups.com, "jringmrath" <jringmrath@> wrote:
> > >
> > > I have an 8-voice OBXa and have a couple of nagging issues I 
> > haven't been able to resolve.  
> > > 
> > > First, I seem to get some slight distortion from voice board 
#8.  
> > If I move the board to 
> > > another location, it sounds fine.  If I move a known good voice 
> > board to the #8 position I 
> > > get the same distortion.  It is most obvious on the organ-type 
> > sounds.  I have been using 
> > > it as a 7-voice until I can track down the problem.
> > > 
> > > Second, if I play the chord "G,C and Eb" in the middle octave 
of 
> > the keyboard, it also 
> > > sounds the "E" below the G.  Needless to say, this can be 
> > annoying!  Must be something 
> > > having to do with the keyboard scanning, but I don't know what 
> > exactly.  The double mode 
> > > also doesn't seem to work 100%.  Maybe a related issue?
> > > 
> > > Any thoughts on what might be causing these and how to fix 
them?  I 
> > have the schematics, 
> > > but I don't really know what I'm looking at since I'm not a 
tech.
> > > 
> > > Thanks for any help or advice!
> > > 
> > > Jonathan
> > >
> >
>