POLY 800 knobs mods

[Frank Lemieux]

At 09:28 AM 10/13/98 CST, Adrian Corston wrote:
>>>> i am new to this list and was just womndering if any1 has sone the
cuttoff
>>>> fequency and resonance knobs additions to a poly-800 b4.  i have heard it
>>>> is simple but i dont want to delve without some good advise.

>When you have the case open, try adjusting the VR2 and VR5 trimmers
>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

I almost blew my tweeters first time I was testing the mod.  Painful
self-oscillation. feedback chaos! 

>>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'm setting up a DPDT switch near the knobs to select between the trimmers
and the pots, so I can either have the original sounds or twisty-knob fun
depending on my mood.

>Next project: buy another Poly-800 and rack mount it :-)

Korg has done it already for you, in the form of the EX-800 :)

>Hmmm... I should trace some tracks; it may be possible to use an
>op-amp and some discrete bits and do a CV cutoff/res inputs mod...

VR2 and VR5 are wired as rheostats, with two leads shorted.  Simple as ya
get short of them providing cv jacks for ya. :)

There are a couple of mods I'd like to do eventually, once I have more
confidence in my skills.  A rotary encoder replacement for those bothersome
up/down buttons.  Sliders replacing the r-blocks so that I'll have more
control over the waveshape than just saw/square.  Audio in for the filter.
Enough blinky LEDS to put a christmas tree to shame.  :)

I'm looking for a pair of strap pegs.  My poly-800 was sold to me as
"broken", and the previous owner had lost the pegs sometime in the past,
poking about fruitlessly inside it.  I suppose I'll eventually DIY
something, but I'd rather pay a little cash than have it fall apart and
shatter at some inconvenient time...  Anyone with a spare pair of pegs,
contact me...

	--F--