Thanks Karl, great advice! I definitely need to try swapping chips first-it seems to be a day to day thing where one day the filters really sound out of wack, and then other days (like today) they are pretty much all in tune.
But it's also good to know about those caps...
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--- In xpantastic@..., Karl Schmeer <shire03@...> wrote:
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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--- On Fri, 11/13/09, mattvrazo <vrazomatt@...> wrote:
From: mattvrazo <vrazomatt@...>
Subject: [xpantastic] Total Filter Replacement: good idea?
To: xpantastic@...
Date: Friday, November 13, 2009, 4:09 PM
??
I have posted in the past about my filter FM not being consistent across all voices-2 voices in particular are always different. Even with FM off, there are still fairly noticeable differences in the filter of those two voices compared to everything else.
So I am assuming that either the filter chips for those two voices are going south OR the VCO chips are. I have spares for both, but before I start pulling things out, I am wondering which chip is the more likely one to be an issue?
Filter FM is linked to osc 1, so if there are issues with that VCO chip, it will sound off (even if the VCOs themselves are perfectly in tune). But given that the filter sounds more bright or "different" on those same voices, even with FM off, I am thinking it is more likely a filter chip issue... The FM doesn't bother me so much, but having slightly different filter "openness" on 2 voices does.
What should my plan of attack be (i.e. start swapping chips, or throw in replacements) ?
Also, will I notice much difference compared to the remaining voices if I replace one or 2 filter chips? i.e. is it better to replace all 6 for a consistent sound, or does it make any difference? 3372s are fairly cheap now, so I wonder if it is better to buy a "matched" set?
