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Circuitbenders Forum => Circuitbending discussion => Synths & Samplers => Topic started by: hellomynameis on September 17, 2008, 05:14:23 PM

Title: Korg Poly 800
Post by: hellomynameis on September 17, 2008, 05:14:23 PM
Hey guys,

I recently did the cut off and rez filters and also added the fm synthesis which is found on the moog slayer page. But however I cannot help but notice that there are way more mods.

I was just curious about the switch for the FM and the input from an external source, as well as the 12dB / 24dB switch.

Is there any info I can have about wiring these?

Thanks
Title: Re: Korg Poly 800
Post by: nochtanseenspecht on September 17, 2008, 07:59:42 PM
hmm, i can't help you, but there must be more mods possible.. filter in would be nice.
i sold my poly 800 long time ago, but i remember that after i installed the FM mod, the filter seemed
weaker, it screamed less... did you notice that to ? o , i remember there was a back up battery mod
on the web as well that i can reccomment, at least if you have an early revision. and there are some trimpots
that you could exchange with a normal pot, like white noise, if i remember well..
nice synth, the poly800. still miss it sometimes... but i exchanged it for a casio vz1, wich i don't regret
Title: Re: Korg Poly 800
Post by: hellomynameis on September 17, 2008, 10:10:44 PM
Yeah I added the battery because it was an early revision and didn't have one. That was the first mod I did and then I installed the FM synthesis mod and then finally sorted out my Cut Off and Rez today because it didn't work.

I just noticed the mods on the website and was curious about them really, it's quite a nice synth really but I havn't been able to use it because still waiting on a power supply  :P

Also was thinking about this mod: http://patrioticduo.tripod.com/hawk800/index.html

but I'm not sure if I am really up to ripping IC's out yet lol
Title: Re: Korg Poly 800
Post by: nochtanseenspecht on September 17, 2008, 11:22:19 PM
Quote from: hellomynameis on September 17, 2008, 10:10:44 PM

Also was thinking about this mod: http://patrioticduo.tripod.com/hawk800/index.html

but I'm not sure if I am really up to ripping IC's out yet lol

interesting mod, but for the price you could buy a second poly800 also... anyway it would be worth if you could
tweak parameters with cc's, if that is possible.. it would live more... programming was a bit slow with the buttons, but ok.
maybe piggyback ic's ?  anyway, mod the thing as much as you can ! for it has a good sound and it is word to put some
energy to get out more.. and who cares about a few extra holes in the case, it is an ugly plastic box anyway ;)

hey but be carefull with the reso.. you'll easily hurt something ;D  the value you program with the buttons, will be the
upper limmit ... so if you set it to 13 or so, your always save.  i still blame the moog slayer mod (partly) for destruckting
my ears ;)
Title: Re: Korg Poly 800
Post by: hellomynameis on September 17, 2008, 11:35:49 PM
haha fair enough, I havn't had a chance to really mess around with the reso and cut off just yet but however I have found some even more useful info on some of the mods done on this website based around the NJM2069 VCF chip which has so much potential! From reading this I believe that you only have to short out two pins on the IC in order to get the 12/24dB filtering, but who knows!

Also says there are 3 sources for external input on the chip and you can control the VCF externally using CV's... mmm very interesting but I think I would simply like to put in the 12/24dB mod then add more control over the FM synthesis as well as an audio in. The 12/24dB mod shouldnt be too hard as well as the audio in. I imagine the FM synth expandability will be more difficult... :)

here is the link before I forget!

http://sounddoctorin.com/synthtec/korg/njm2069.htm
Title: Re: Korg Poly 800
Post by: Circuitbenders on September 18, 2008, 07:12:57 AM
The 12/24db mod is easy but to be honest it doesn't make that much difference. If i recall correctly all you have to do is cut the track coming from pin 6 of the NJM2069 and wire a switch to select output from pin 5 or 6.

Off the top of my head, the  external audio can be wired into either pin 19,20 or 21.
Title: Re: Korg Poly 800
Post by: hellomynameis on September 18, 2008, 12:59:46 PM
Yeah I figured the 12/24db switch won't be much use, but then again my FM 800 pot is too close to rez and cut off so I figured I could put a switch in there.

I found the yahoo group detailing lots of info with the switches for the 12/24db switch. All you have to do is cut one leg of a cap and solder to a middle lug of a switch and then either pin 5 or 6 on the njm chip.

The audio input also involves soldering to a cap as well, however I assume you can just put a pot in here? Or would it be wise not to? I'll crack it open tonight and have a look, also going to install the switch and move the fm 800 elsewhere on the board
Title: Re: Korg Poly 800
Post by: hellomynameis on September 19, 2008, 12:55:24 AM
Ah did the switch today and also installed the audio filter in, havn't been able to test yet sadly due the requirement of a power supply!

Ended up removing the FM mod for now, I'm thinking of installing the selector switch sometime soon, although I could find no info on any hook up points. Also got to do level pot at some point but i'm currently lacking in pots! Pics to follow...