POLY 800 knobs mods

[Johan Persson]

> When you have the case open, try adjusting the VR2 and VR5 trimmers
> (I did it with a sequence running) on the main board attached to the
> bottom of the case to see what sort of effect you will get. The
> trimmers are basically a fine adjust - you still get to set the
> basic cutoff and amount of res in the patch, but then you can
> adjust it over a usable range on the trimmers. The res goes spastic
> all the way up and I don't know how good for the synth it is at
> extremes. My personal rule of thumb is, if it is distorting, wind it
> back (after you sample it ;-)
>
> I had to unsolder a resistor on the far left hand side which grounded
> a metal strip on the bottom of a piece of cardboard which sits under
> the PCB. Your mileage may vary here, I expect. There are seven screws
> holding the board down you'll need to remove. The board is double-
> sided, so be careful removing the trimmers that you don't lift the top
> track.
>
> >From there, I ran some ribbon cable to the front panel in the blank
> space above the joystick, where I drilled two holes and mounted two
> 25mm 100K linear pots. Well actually I couldn't find a 100K pot so I
> used a 1M one, which didn't work very well - the useful values were
> at each end of the turn of the pot and there was little effect in the
> middle. I'll be replacing it with a 100K tonight and I'm sure it'll
> work much better.

I used a 1M pot for the cut-off and it works great. Actually I used 100k at first,
but 1M gives a wider cut-off range. For the resonance I think I used 15k, but a
bigger value is recommended... just haven't got around to replace it.
Otherwise the description above is exactly as I did. Not complicated at all and
well worth it.

Someone said something about a knob to change the parameter values (instead of
those #¤%!! up/down buttons). Some time ago I tried this with a "pulse-knob" (a
knob with four outputs: two for each direction) I just soldered to the buttons.
This was not very successful, though. The Poly800 can't read the pulses that quick
and it disturbed me so much I had to remove it.

/ Johan