Casiotone CT-640


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I'm looking at one of these for a customer. It's progressively out of tune, from low to high on the keyboard. Starts out OK, but by the uppermost octave, it's 3 cents or more out of tune. Anyone seen this before? Any known fix? Looking, I couldn't find a factory reset routine (yeah, it is old). Contacted Casio, got a service manual, and neither one of us saw a reset in it. So yeah, it may be too old to have one. They lost their "old guy" about ten years ago, so no one knows any unpublished info there. I'm hoping someone here does. Let me know. Thanks!
 
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happyrat1

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Your problem is probably not in the software but rather a pitch bend wheel that's gone bad.

I doubt you'd find a new replacement part for that antique in this day and age but you may want to try opening it up, spraying the pot with pot cleaner and try your hand at recalibrating the spring so that it stays neutral during play.

Or, quick and dirty fix, if possible see if you can disable the pitch bend outright either in the menus or physically by detaching it and inserting a fixed resistor network at neutral pitch.

Gary ;)
 

happyrat1

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Your problem is probably not in the software but rather a pitch bend wheel that's gone bad.

I doubt you'd find a new replacement part for that antique in this day and age but you may want to try opening it up, spraying the pot with pot cleaner and try your hand at recalibrating the spring so that it stays neutral during play.

Or, quick and dirty fix, if possible see if you can disable the pitch bend outright either in the menus or physically by detaching it and inserting a fixed resistor network at neutral pitch.

Gary ;)

Hi Gary, thanks for the reply! Unfortunately, I don't think pitch bend was a gleam in a designer's eye back in '88. At least not for this model. :(
 
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BTW, if you're looking for tech info you should google and try and contact people who are into "Casio Circuit Bending."

eg.

https://spectrum.ieee.org/geek-life/hands-on/how-to-bend-a-vintage-casio-keyboard

https://www.circuitbenders.co.uk/synthmod/SK1.html

https://www.google.ca/search?q=circuit+bending+casios

These guys have hacked old and cheap Casios for years and years and done some pretty amazing stuff with those things.

Gary ;)

Thanks - I've seen a bit about it, but just thought it was strictly for modding. I'll look into it.
 
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SeaGtGruff

I meant to play that note!
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I wonder if it might be an unavoidable consequence of the way the keyboard generates sound waves for the various note frequencies? In other words, maybe that's actually "normal" behavior for that keyboard?

Recently, on another keyboard forum, there was an interesting discussion about how well different synths maintain accurate tuning if you send them a full range of MIDI Note values (0-127). I think the discussion was about analog synths, but the general issue might apply to digital synths as well-- namely, how accurately they can generate waves with specific frequencies via their electronics. I'm not sure what method the CT-640 uses, but 3 cents doesn't seem like much of a drift-- unless you meant 30 cents?

This actually reminds me of something that freaked me out the first time I heard about it, which is the practice of deliberately tuning a piano so the lowest keys are a bit flat and the highest keys are a bit sharp, or something like that. I'd think that this would sound bad, but apparently some people think it sounds better that way?
 

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