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/5240It'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.jpgI 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.