Hi Alan,

I went ahead and made a video of the Korg's unstable filter artifacts. Maybe in hearing it, you can diagnose what it sounds like the problem might be.

http://www.youtube.com/watch v=SttZhs7sKHE

Thanks for your help!

-Kaleb

--- In korg_mono-poly@yahoogroups.com , Alan Dicker <alanmdicker@...> wrote:
>
> velocity sensitive this would make me suspect a dry solder joint or badly sat IC.  ~A recording might help a video would be even better if you say its effected by the pressure you hit the key with. Is it also effected by after touch or how much pressure is applied while the key is held   does the problem go away when you have the hold function on and you not physical touching any keys   is the problem present when the filter EG knob is sat at 0.  Is it only the cut off frequency that is effected or are the fluctuations in amp level or pitch also and does have trigger set to single or multiple effect the problem   allot of question I know but if its not simply dirty pots we need to figure out what else it may be.
>
> Alan
>
>
>
> ________________________________
> From: Kaleb <turboswami@...>
> To: korg_mono-poly@yahoogroups.com
> Sent: Friday, 23 September 2011, 7:59
> Subject: [korg_mono-poly] Re: Warbling Filter "Drop Out" Artifacts
>
>
>  
> Yea, the cutoff knob, itself, turns perfectly smoothly without any scratching or artifacts. It seems it is only when hitting a key does the warbling change in pitch occur in self-oscillation, or the dramatic drop off in regular VCO playing.
>
> Strangely, the filter artifacts seem to be velocity sensitive -- that is, the harder I play the keys, the more dramatic and noticeable the noise is.
>
> Granted, I'm sure it would not hurt to clean out the pots, the filter section knobs, themselves, are still functioning perfectly. This seems to be something related to the keyboard or EG
>
> I should record a bit to get your guys' perspective on it.
>
> -K
>
> --- In korg_mono-poly@yahoogroups.com , Alan Dicker <alanmdicker@> wrote:
> >
> > My first port of call for this type of problem would be to clean the pots associated tot he filters cut of frequency.  that's cut off, EG intensity and KBD track.  these wobbly artifacts are not the type you get from improver calibration those are more akin to high frequency side band distortion or aliasing effects in the digital realm.  This is good news for as you prober re-calibration of the filter section should be performed with an oscilloscope 'a very expensive bit of kit.  All you should have to do is pop to your local electronics store Maplin, Radioshak and pick up some switch cleaner.  You will then want to switch off and unplug your MP4 from the mains and open up it up  by removing the 3 screws from the underside where the top cover meets and the 4 screws from the top cover need to be removed also.  The cover which holds all pots and switches then will hinge open revealing the back side of the pots.  squirt a little
> cleaner in to the
> > pots you should be able to find a little indent where the spray can get in.  once you have squirted then turn and tune and turn the pots and then turn them again as this motion is cleaning them.  You can paform this action with the MP$ plugged in and running in hold so you can here the effect of the signal cleaning up but as you admit your self to not being an electronics expert I would close the lid and run it  with the crews not yet in place so you can here if the signal is cleaning up and then switch off and clean some more and so on.  just a good idea not to expose your self to high voltages around the PSU boards or have the possibility of a zipper or your can of spray falling in and bridging a contact and shorting something out.
> > That as I say would be my first port of call.  if that has no effect on the problem then it may be that your filter chip is on the way out and you need a new one.  You can still pick up SSM2044 for around £20 UK try ebay or Vintage Planet.nl or any other number of websites which may be local to you.  If your luck your current chip will be in a socket rather than soldered directly in to the circuit board.  if its socketed you will only need to pull the old one out and push the new one in taking note of the correct orientation tot he marked pin 1.  if it soldered you will need to unsolder or cut the old chip out and solder in a socket to house the new chip.  The main challenge here is that once a new chip is in place you should really re-calibrate the filter section so it might be a job for a service tech with the right tools anyway.  Using a scope he should be able to check if the random voltage effecting the cut off originates
> from the filter
> > chip its self or from else where.
> > So yeah my advice buy some switch cleaner and give the pots a clean and if that doesn't work take it to a service tech.
> >
> > Alan
> >
> >
> >
> >
> > ________________________________
> > From: Kaleb <turboswami@>
> > To: korg_mono-poly@yahoogroups.com
> > Sent: Wednesday, 21 September 2011, 10:20
> > Subject: [korg_mono-poly] Warbling Filter "Drop Out" Artifacts
> >
> >
> >  
> > Hello,
> >
> > My beloved Mono/Poly recently started to develop a warbling seemingly-random filter "drop out" sound. These artifacts are noticeable when playing the VCO's, but are most noticeable when bringing the LPF into self-oscillation -- at which point dramatic shifts in pitch occur.
> >
> > I must admit, the random warbling sounds pretty awesome, in its own right, but it is driving me crazy that I cannot shut it off. The pure tone of my oscillators can no longer be achieved or held for any period of time.
> >
> > How does one recalibrate the filter section Is it a particularly difficult or involved procedure Do you have the documentation on doing this in a PDF form
> >
> > I am, by no means, an electronics expert. I have done some simple things to my Korg over the 15 years of my owning it, like cleaning contacts, wire repair, etc, but have not needed to replace any components yet. Hopefully this filter recalibration will do the trick though!
> >
> > Thanks for your guidance,
> >
> > -Kaleb
> >
> > PS
> >
> > Additionally, there are some screws missing (from the front knob surface, which keeps it down, and also from the bottom, for securing the keyboard/pitch wheel components. Any idea of where I can purchase these specific screws Or other components, like scratchy pot replacement
> >
>