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Old 03-04-2009, 10:04 AM
nealbeard nealbeard is offline
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Join Date: Feb 2009
Posts: 26
Default Oscillation

Note: This thread was written for the since-discontinued SKM MIDI retrofit for the Casio SK-1. But the issues could apply equally to the UMR.

Hi all.

I recently fitted a SKM to my circuit bent Casio SK1. I'm really stoked with it - it suddenly makes my SK1 so much more versatile and has opened up a whole new realm of musicality.

My only slight problem is an constant unwanted noise background noise that sounds like an oscillation...

As far as I'm aware it only appeared after I installed the MIDI.

It comes out both the original line out from the SK1 and a 1/4 jack line out I ran from the removed speaker.

I've also noticed a battery drain when turned off - I guess this might be connected to the osc noise.

Anyone any ideas of what it could be, or how to troubleshoot it?



(a couple of pics of it here


http://4.bp.blogspot.com/_dPC0urMeEk...h/DSC_0035.JPG )

Last edited by John; 12-15-2011 at 01:22 AM. Reason: Added my note. Moving thread to UMR forum.
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Old 03-06-2009, 07:27 PM
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John John is offline
Join Date: Jan 2009
Posts: 3,007

The way the SKM is connected, together with the way the SKM powers on/off results in the SKM draining a little bit of power at all times.

The solution is to add a toggle switch in the positive power connection between the SKM and the SK-1 circuit board. When you power the SK-1 off, flip the switch also. (not super elegant, sorry )

The audio noise may be caused by the proximity of the SKM ribbon cable connections with the SK's audio amp circuitry (the area of the circuit board near the speaker). By nature the keyboard scan signals are periodic and noisy, so they get picked up by the analog circuitry of the SK. You might get varying amounts of noise by moving the wires around a bit (the ideal solution is to keep them away from the circuit board completely, but this can be difficult without a breakout box). Hope this helps.

The mods look great! I like the colors of the knobs & phone jack.
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Old 03-07-2009, 10:40 AM
nealbeard nealbeard is offline
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Join Date: Feb 2009
Posts: 26

Ahh I see. Many thanks. All my wires run straight across that area... will have a re-jig and see if it helps.

And randomly just fitted toggle switch power off last night before I read this...!

Works a treat and much easier than removing batteries all the time.

Last edited by nealbeard; 03-07-2009 at 11:24 AM.
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