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The KORG Poly800 Synth

Tweaking the little hybrid digital/analogue beastie

The Poly800 comes from the early 80s, an era of transition between analogue and digital.  As such, it features the stable pitch of digitally controlled oscillators with the warmth and fatness of analogue filtering, envelopes and processing


Oscillators:  8 DCO (Digitally Controlled Oscillators), either 1 per voice (8 note polyphony) or "layered" with 2 DCOs per voice (4 note polyphony, but "fatter" sound)

Filter:  1 VCF (Voltage Controlled Filter). The single analogue filter can sometimes be limiting, but it is also one of the coolest features - in "single trigger" mode, if you overlap your key presses (ie. start the next note before you release the last one), the filter is not retriggered; the result being a filter envelope sweep.

Keyboard:  4 Octave, non velocity sensitive.

LFO:  Pitch and/or filter

Joystick:  X-Axis: Pitchbend. +Y-Axis: DCO Mod. -Y-Axis: VCF Mod

Effects:  Chorus on/off (though I have no idea why anyone would have the chorus off - sounds pretty weak and dead without it)

Construction: Fairly heavy-duty plastic. Light. Strap pegs.


The most common modification of the Poly800 series is control knobs for filter cutoff and resonance.  With so many people wanting to manually tweak filters, it's amusing to see just how simple it is to rewire this inexpensive little synth to do what everyone else is primarily buying ultra-expensive virtual-analogue or "classic" analogue synths for.

Adding these knobs is as easy as removing two trimpots on the main board and replacing them with panel-mounted variable resistors.   The physical removal of these trimpots can prove a little tricky as you have to unsolder three legs at the same time - best to destroy the pot and remove it in 3 pieces, the rest of the job is pretty straightforward.

The trimpots in question were intended as fine-tuning pots for initial setup, basically to tune the filters of each synth to roughly the same settings to counter any discrepancies in other components, etc.  But users discovered that they also gave a reasonable sweep range for manual tweaking - hence the bypassing with panel-mounted pots.  The trimpots in question are VR2 (Filter Cutoff, 100K log) and VR5 (Filter Resonance, 10K log).

I have set my patches up so that their default sound is correct when the Cutoff knob is set halfway, and the Resonance knob is fully down.   This allows a filter cutoff sweep range below and above the preset cutoff, and an increasing resonance range (NB: Test your patches with the resonance knob all the way up - too much resonance in your patch can lead to very painful self-oscillation when you sweep the resonance knob up!  I usually push the patch settings so that it is just below (or just above) the point of self-oscillation at maximum knob tweak).  This way, your patches will sound right by default, and you can then use the knobs to tweak around your default settings.

Another mod that seems to be gaining popularity is that of changing the Poly's appearance.  The most common way of doing this is with a can or two of spraypaint.

(Note for Brian:  You didn't leave your email address so I couldn't respond.  Can't remember the exact brand of spray paint I used, it was an automotive touch-up spray, something like "PowerTouch".  Any automotive spray should work.  You may or may not want to use a plastic primer spray first;  but I don't believe I used one this time, and it's working fine.)

Personally, I painted only the "top shell" of the keyboard, but you could do both top and bottom, or even the keys if you were so inclined (and know of a paint that won't wear off with use!).

The main factor you need to consider (apart from the obvious "what colour am I going to make it?!") is that of which text/graphics you want to keep from the original look, and how you are going to go about keeping them.  For instance, I decided that the scales for sequencer speed and volume were not required, as I just adjust these by ear, but I wanted to keep the actual labels so I knew which knob or slider was which.  I wanted to keep all of the text in the keypad area, so I decides it was just easier to mask off a rectangle around that area, rather than try to mask each individual bit of text.

I decided I'd keep the entire "patch parameter sheet", so I simply masked it off entirely, but I have seen others that completely painted this area (See Aaron Jasinski's yellow poly)

I also decided that the back panel (ie. the KORG logo and the jack / switch labelling) was too complicated to get a decent result if masked off, so I decided to completely paint it, with the intention of making a custom KORG logo, and perhaps putting some sort of markers on the bottom half of the shell to tell me which switches / jacks were which.  But as I get more used to the layout of the switches etc., this labelling may not be necessary.

Once you decide what you want to keep, carefully mask it off.  Remember, the better the job of masking, the more professional the result will be.  This was the second time I had done a poly, and though this one's not perfect as such, it's a lot better than my original one because of the planning and attention to detail

I highly recommend disassembling the keyboard before doing any spraying.  Not only does it reduce the risk of stuffing up, but it also makes the process much easier.  Be sure you know where every wire and screw goes - most of the cables and sockets are clearly labelled, but it never hurts to take extra precautions.  The only real thing that isn't designed for disconnecting is the ground wire from the motherboard(?) to the metal plate behind the "patch sheet".  With this cut (make sure you know how you are going to re-attach it later!), and everything else disconnected or unscrewed, the top shell should be completely free and stand-alone, ready for its makeover.

The rest is pretty-much self-explanatory.  Double-check your masking, recheck you've got everything, go over the re-assembly in your head just to make sure, then get spraying!  Don't rush it, do a whole heap of light coats at intervals, don't try to get full coverage in the one hit, all the usual tips that go with doing a good spray job.

Once it's all finished and fully dry, re-assemble and enjoy your "NEW!" Poly!

My red Poly800, with filter cutoff and resonance knobs, silver 
buttons / sliders / volume, and chrome joystick


spacer Document last modified:
12 September 2005
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