Korg Poly800/EX800 Users

After thinking about it for a long time, I finally did it. Or "them," to be more accurate. Within the last couple of weeks, I've done mods to two of my Poly-800s: the Moog Slayer, 12/24 dB, FM-800, and battery backup on one machine, and just the Moog Slayer on the other.

Obviously, these mods really open up the sound-making capabilities of these machines. At first, I didn't understand what the FM-800 was capable of until I did some reading. Then, once I figured it out, I was blown away with what it can do, and really glad I did it.

The only other thing I'm thinking about doing is putting a knob on the front panel to control the noise level (parameter 33). Has anyone done it?

Aaron

Hi Don,

I found a blog post in which a guy added a noise knob to his EX800. He doesn't say how well it works or anything. But he apparently just replaced VR3 with a full-sized pot. Not sure what value he used, though. Click here to see pictures of the mod.

Aaron

--- In korgpolyex@yahoogroups.com, "backshall1" <backshall1@...> wrote:
>
> The filter FM needs a lot of harmonics to work with, so playing an interval
> like a fifth really works well. You can do that with the chord memory, or in
> double mode you can set the DC0 2 interval (parm 31). I don't think the
> internal sequencer works when you are using chord memory so if you need the
> sequencer you will have to use a double mode patch to get the interval. Set
> the cutoff way down low, the resonance way up, and add a touch of FM.
>
>
>
> I have also been thinking of adding a noise level knob, mostly because if
> interactions with the external input I added. There seem to be three choices
> when it comes to where to inject the external input signal into the VCA/VCF
> (DCO1, DCO2, Noise). I currently have it connected to the DCO1 input but was
> thinking of moving it to the noise input. In that case, I believe parm 33
> would need to be up high to let the external sound through but then I would
> get noise too, so a separate knob for noise level would be essential. I
> would be very interested in hearing from people who added an external input
> to see how they did it. There are definitely tradeoffs among the choices.
>
>
>
> As for adding the noise knob, it might be as simple as replacing VR3 with a
> full size potentiometer. It would take some testing to determine the exact
> value to use, and R34, R35 might need to be changed so you can get the
> minimum noise level down closer to zero. The current value of VR3 (1 Meg)
> will take the noise level well above the factory spec of 0.3V p-p, so you
> have to be careful there. It might be easier to put the pot from IC2 pin2 to
> ground. Like I said, this needs some testing unless someone else has already
> done it.
>
>
>
> Don Backshall
>
>
>
> _____
>
> From: korgpolyex@yahoogroups.com [mailto:korgpolyex@yahoogroups.com] On
> Behalf Of AARON
> Sent: Friday, November 23, 2012 1:48 AM
> To: korgpolyex@yahoogroups.com
> Subject: [korgpolyex] Mods complete (for now, anyway)
>
>
>
>
>
> After thinking about it for a long time, I finally did it. Or "them," to be
> more accurate. Within the last couple of weeks, I've done mods to two of my
> Poly-800s: the Moog Slayer, 12/24 dB, FM-800, and battery backup on one
> machine, and just the Moog Slayer on the other.
>
> Obviously, these mods really open up the sound-making capabilities of these
> machines. At first, I didn't understand what the FM-800 was capable of until
> I did some reading. Then, once I figured it out, I was blown away with what
> it can do, and really glad I did it.
>
> The only other thing I'm thinking about doing is putting a knob on the front
> panel to control the noise level (parameter 33). Has anyone done it?
>
> Aaron
>

I just recently posted a vid on how I ran a external input to the filter on here.

http://launch.groups.yahoo.com/group/korgpolyex/message/5240

It's a crappy quality vid, but it gets the point across and demo's several different audio signals ran thru the filter along with ext. audio and the DCO's turned on too.



Here's a good pic of the Korg's NJM2069 filter for reference below-

http://img.photobucket.com/albums/v207/abcSweep/KorgNJM2069.jpg



I ended up using Pin 19 on the NJM2069 filter to inject an external audio signal. Pin 1 is where I hooked up my ext. audio's ground.

What I discovered was this:

Noise goes into the filter at Pin 7. Pin 8&9 are VCA control lines for the Noise signal. Pin 10 is hard lined to Pin 19.

When I tried to inject the audio signal at Pin 7, I had to turn VR3 up to get the ext. audio signal thru. You'd think I wouldnt have to do this, but that's exactly the reaction I got.. it was as if VR3 was controlling the VCA inside the filter.
I had the Noise parameter 33 set to max, thinking I could turn the Noise down with VR3 and Parameter 33 would control the VCA inside the filter chip. But this isnt how it worked out.
What ended up happening was I had to turn VR3 back up in order to hear my ext. audio. It was the only way I could hear my ext. audio signal when injecting it at Pin7.

So I decided to go to the next Pin in the Noise signal path to try and get my ext. signal into the filter. I chose Pin 19. When I did that, I ended up having to turn my ext. audio signal way down... but I was able to keep my Noise signal off and clearly hear my ext. audio.

I was able to keep DCO1/2 off completely using their Volume Parameters. I could also turn DCO1/2 on with their Volume Parameters.. thus making it possible to have all four signals running thru the filter at one time- DCO1, DCO2, Noise and Ext. Audio.

When I get back in there to do a permanent ext. audio jack, I'll most likely put some kind of volume attenuator either outside the case via a VR or a fixed value resistor inside the case.. I'm thinking fixed value or an internal VR will be the way to go.. to avoid an over-driven signal from getting thru (an ext. VR might get turned up too high accidentally).
The korg was very sensitive to the ext. audio volume. I barely had my JX1 volume up.. I was using the Left/Mono output from the JX1, NOT the headphone output.
I dont know if an over-driven external signal going into the filter would damage it or not.. I was lucky it didnt happen to me. But I will be very careful next time I go mucking around in there.
So my caution to anyone injecting a signal at Pin 19 is, start with a very low volume signal and barely bring it up.


I need to get back in there and re-check if I can turn Noise up/down independently of my ext. audio signal. I cant think why on earth I couldnt. But just for the sake of verification I'll do it using both the Parameter 33 Noise Volume control and the VR3 adjustment.

-Blaine

--- In korgpolyex@yahoogroups.com, "backshall1" <backshall1@...> wrote:
>

> I have also been thinking of adding a noise level knob, mostly because if
> interactions with the external input I added. There seem to be three choices
> when it comes to where to inject the external input signal into the VCA/VCF
> (DCO1, DCO2, Noise). I currently have it connected to the DCO1 input but was
> thinking of moving it to the noise input. In that case, I believe parm 33
> would need to be up high to let the external sound through but then I would
> get noise too, so a separate knob for noise level would be essential. I
> would be very interested in hearing from people who added an external input
> to see how they did it. There are definitely tradeoffs among the choices.
>
>
>
> As for adding the noise knob, it might be as simple as replacing VR3 with a
> full size potentiometer.