Hi Matt,
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Well, if the filters on two voices are opening up too much that would point to replacing the?filter over the vco chips. (A VCF with a different frequency response?would change your filter FM sounds also)
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All the IC's are in sockets, so It's easy to change out the VCF chip. Also you could
trade VCF chips from another voice.
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If changing out VCF chips does not work, You could try the VCO's next.
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Next, ?I would look at the coupling capacitors in the voices that are causing problems.
The FM signal feeds to the VCF through a?2.2uF 50 Vcap?. Also?the voice output signal has one. During a tuning sequence these could be causing?"not correct" calibration constants
to be stored in memory, thereby causing your filter chips to be off.
After doing any of these changes, You should run all the tuning routines.?Then try it out.??
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Statically the capacitors in the voice signal have been the most common?fail.?They tend to fail over time, and?are probably at least?15 YO.? They are very inexpensive, it's just takes time.
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These are the most likely capacitors to change:
The capacitor value is 2.2 uF 50 V The voltage rating must be 50V or it will limit the signal?
that goes through it.? I would not want to use a larger voltage rating either, as it may damage components downstream from it.?
note:? x = voice number
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Cx02??? FM in
Cx49??? VCA out? - Main Voice out to final mix.? -? Most likely Bet IMO
Cx48?? VCF out
Cx47?? VCA in??
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As far as the Matched sets go. I have always been curious as to what parameters they are matched for??In theory the tuning routines in the Xpander/M12 should take care of any differences between any set of chips.
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Good Luck
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Karl Schmeer
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