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Circuitbenders Forum => Drum machines => Circuitbending discussion => Korg => Topic started by: davethedoobie on September 18, 2010, 06:40:05 PM

Title: Korg kpr-77 High pitched whine on output - HELP!
Post by: davethedoobie on September 18, 2010, 06:40:05 PM

Hi, I have been restoring a dilapidated Korg KPR-77 back to life after the previous owner left the batteries in and they leaked twenty years ago.  I have managed to get all but the toms working again (their is a faint sound - so that's another problem to solve).  It took much sourcing of the parts I can tell you.  However, I have an issue that the is annoying and I seek your help.  The problem is a high pitched whine that only disappears when I brigde the R76 resistor on the board.

I would be grateful for any help or advice as I hope to modify this once I have it fully working again.

I know it is probably an easy fix but at the moment I can not see the wood for the trees.

Title: Re: Korg kpr-77 High pitched whine on output - HELP!
Post by: Gordonjcp on September 18, 2010, 06:51:17 PM

What's the value of R76?  Has it gone high in value?

Title: Re: Korg kpr-77 High pitched whine on output - HELP!
Post by: Matt the Modulator on September 18, 2010, 06:56:23 PM

i had the same problem with the toms i replaced the volume slider and that sorted it

Title: Re: Korg kpr-77 High pitched whine on output - HELP!
Post by: davethedoobie on September 18, 2010, 09:12:06 PM

Thanks Gordon and Matt appreciate the response.

The resistor value is 220kohms +/- 5%. 

I gave the pot a good clean inside and managed to get the Hi tom sounding but I have noticed that the volume fades after a few minutes then, when I switch it off and turn it back on the hi tom sounds again.