Korg Poly-800 mods tips & tricks

Next week I’m going to help a guy who has bought some sort of mod package from Curcuit Benders (http://www.circuitbenders.co.uk/synthmod/POLYEX.html) containing components and instructions for modding a Korg Poly-800. He didn’t want to do the soldering himself, since he had never done that before, so I said I would give him a hand.

Even though I’m quite good at soldering, I have never actually opened up an old synth in order to mod it, so I’m going to do things veeeery slow, documenting everything along the way. This specific mod doesn’t seem that hard (famous last words), but are there any general advices you can give me for these kind of things? Should I be careful grounding myself, will thouching that specific component trigger the self-destruct mechanism, and so on?

Thanks in advance.

I never really bother with earth straps on modern and new stuff but for vintage kit you should wear one since you can’t easily replace some of the chips.

I opened a Poly 800 I had to fix some crackles and it wasn’t hard to open and was fairly simple inside. Google for inside pictures before you open up to see how you feel about it.

Be prepared to vacuum out a ton of dust :slight_smile:

Ok, thanks! I’ll have the vacuum cleaner ready :slight_smile: I’ve seen some pics of what it looks like inside, and it looks fine. That in combination with the fact that there aren’t that many things I need to solder (and desolder and resolder) made me accept doing this; otherwise I would have declined, since it is not my synth.

Hrrm, I probably need to drill a bit in the enclosure in order to fit a few additional pots, etc. I think it is made of some sort of plastic material. No pitfalls there? The whole enclosure doesn’t just crack when starting to drill in it?

Start with a small hole and go up to the desired diameter. One good advice when it comes to vintage gear desoldering action: be extra careful, as some manufacturers PCBs are nothing better than pressed paper and you can easily lift a pad. So don’t pull out desoldered caps etc. with great force, as this can end up with a serious amount of work to fix this again.

I fitted a quite complex mod to my old EX-800 (module version of Poly-800), and it wasn’t too challenging, in the end. It’s not too hard to work with. Your friend may want to consider the Hawk-800 and AtomaHawk mods, though. Those were what I fitted. They essentially replace the CPU of the synth, and add the other common hardware mods, and hugely extended MIDI spec, extra LFOs, more patch memories, and a load of other stuff.


Thanks, nightworxx andtoneburst. I’ll look into those other mods too.

Hrrm, this mod was an interesting experience… I’m concerned about one thing: When the filter is opened fully through the original control panel, I can’t seem to close the filter completely by turning the pot. Yeah, the sound gets considerably more “bassy”, but the lowest frequencies doesn’t go away. Is this an indication of some error on my side, or has this got to do with the pot value, i.e. if using another pot with a larger max resistance, I would be able to close the filter more?

Check the patch you’re playing on. If I set my cutoff high in the patch itself, then the cutoff pot won’t be able to close the filter fully. And vice versa. If you set it in the middle then you’ll have proper full control

@mfc83: Thanks! There is no internal battery, so all patches were deleted when I started working on the synth :slight_smile: So I manually go to some default setting, where the filter is fully opened. When it is about halfway, I can kill the signal almost completely with the added pot, so I guess it is working then…

I thought I would just sum up my experiences, having completed the mod in May. Perhaps some DIY n00b like myself will find this thread useful:

  • The soldering was not that hard, but I guess one should be aware of the fact that it is quite different than soldering parts on a brand new PCB. You have to think more about where you place the parts, where your wires should go, etc. Removing components from the PCB and then adding wires to the old holes required a certain amount of… gentle violence, but it went well in the end.

  • The part where I had to drill in the case was the most difficult, mostly due to lack of experience. Placing the holes was one thing - at first I drilled two holes too close to each other, which I noticed when trying to place the two pots underneath and they just bumped into each other. D’oh. It all went well in the end, but I feel it could have been much better, cosmetically. Well, that is something I will be extra careful with next time.

In the end the guy who owned the synth was very pleased: “It sounds like a new instrument!”, he said. And he got it for free, since I felt I could not demand any money due to my n00bishness.