Vintage Synth Repair

I wonder if anyone could help with this one:

On my OBXa, one voice card sound thinner than the others. When 
playing high notes this is less noticable but as going down the 
keyboard it goes and sound thinner, sort of like a high pass filter 
(no low frequencies). I tried to replace the CEMs but it's not in 
there...

Does anyone have any idea what could that be ? I thought it might be 
a calibration problem, would any of that trimpots effect the sound in 
that way has it not been set correctly ?

VCO1 Volts Per Octave
VCO1 High Track
VCO1 Initial Frequency
VCO1 Pulse Width
VCO2 Volts Per Octave
VCO2 High Track
VCO2 Initial Frequency
VCO2 Pulse Width
Filter Envelope Modulation
Filter Resonance
Filter Volts Per Octave (4-Pole)
Filter Volts Per Octave (2-Pole)
Filter Initial Fequency (4-Pole)
Filter Initial Frequency (Both Filters)
VCA Offset

I must say that the tinner sound is general on this card, i.e with 
any preset or setting used, no certain VCO...

Thanks!

>I wonder if anyone could help with this one:
>
>On my OBXa, one voice card sound thinner than the others. When
>playing high notes this is less noticable but as going down the
>keyboard it goes and sound thinner, sort of like a high pass filter
>(no low frequencies). I tried to replace the CEMs but it's not in
>there...


It's difficult or impossible for anyone without intimate knowledge of the 
OBXa to suggest what to look for specifically.  What you need to think about 
is how to most efficiently analyze and approach the problem.  I would 
determine first if any parameters affect this by comparing pulsewidth, 
cutoff, resonance, etc. between the voice cards.  Then maybe I'd compare 
output waveforms or spectra for each voice to see if there's something more 
quantifiable, and find the source of the problem by tracing the signal path. 
  You probably don't even need an oscilloscope if you can use some sort of 
"audio probe" that goes straight into your sound card.

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Thanks, I'll try that...


--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund" 
<gsn10@...> wrote:
>
> >I wonder if anyone could help with this one:
> >
> >On my OBXa, one voice card sound thinner than the others. When
> >playing high notes this is less noticable but as going down the
> >keyboard it goes and sound thinner, sort of like a high pass filter
> >(no low frequencies). I tried to replace the CEMs but it's not in
> >there...
> 
> 
> It's difficult or impossible for anyone without intimate knowledge 
of the 
> OBXa to suggest what to look for specifically.  What you need to 
think about 
> is how to most efficiently analyze and approach the problem.  I 
would 
> determine first if any parameters affect this by comparing 
pulsewidth, 
> cutoff, resonance, etc. between the voice cards.  Then maybe I'd 
compare 
> output waveforms or spectra for each voice to see if there's 
something more 
> quantifiable, and find the source of the problem by tracing the 
signal path. 
>   You probably don't even need an oscilloscope if you can use some 
sort of 
> "audio probe" that goes straight into your sound card.
> 
> _________________________________________________________________
> More photos, more messages, more storage—get 2GB with Windows Live 
Hotmail. 
> http://imagine-windowslive.com/hotmail/?locale=en-
us&ocid=TXT_TAGHM_migration_HM_mini_2G_0507
>