Korg Poly800/EX800 Users

Hopefully AtomSmasher is out there,

The Moog Slayer mod seems to be picking up pin 7 of the op amp (IC4)
that is being driven by DCO1 output. This I believe to be the square
wave output of DCO1.

Did you ever try to use pin 1 (DCO1 triangle wave)?

You are feeding that DCO1 wave into VCF LIN (pin 13). I suspect this
is a linear control line for the VCF cutoff.

How did you arrive at the 5K POT and 1K fixed resistor values? Was it
trial and error or what method did you use to arrive at those values?

The reason I ask is because the digital pot I am considering using is
a 10K and so I may need to rework the bias resistors. Any light you
can shed on this would be much appreciated.

The good news is that with digital controls, we'll be able to set up
single and double modes to work consistently with the VCF cutoff. And
the other good thing is that we may be able to send the noise
generator into the VCF LIN signal too. So I am going to start circuit
bending this weekend and see what I can come up with.

12/24db filter is also definitely going to be included.

Mike.

On Fri, 22 Feb 2008, korgpolyex800 wrote:

> The Moog Slayer mod seems to be picking up pin 7 of the op amp (IC4)
> that is being driven by DCO1 output. This I believe to be the square
> wave output of DCO1.

=============

the FM-800 mod...

> Did you ever try to use pin 1 (DCO1 triangle wave)?

==============

IIRC, i tried that but the results were better (more harsh and extreme)
taking a signal from pin 7. with this type of effect the goal is to use a
modulating signal with the most harmonics; square wave vs triangle, square
wave wins ;)

> You are feeding that DCO1 wave into VCF LIN (pin 13). I suspect this is
> a linear control line for the VCF cutoff.

===============

i believe that's correct.

> How did you arrive at the 5K POT and 1K fixed resistor values? Was it
> trial and error or what method did you use to arrive at those values?

===============

theory: the 5K pot is acting as a voltage divider so in theory anything
5-100k should work fine. the 1k resistor provides isolation from the knob
"grounding out" pin 13 of IC1, and shouldn't be too critical.

practice: the combination of 5k linear pot and 1k resister is the "sweet
spot" where the range adjusts very smoothly from no effect to full effect
(full effect being about what you'd get if you shorted IC4 pin 7 to IC1
pin 13). also it has little/no influence on the filter settings when the
knob is turned all the way down.

IIRC, i went through a lot more experimenting than i'd expected before i
got that combination, and everything else had severe nonlinearities when
adjusting the pot through its range, didn't cover the full range and/or
adversely affected the range of the filter when the knob was fully CCW. it
also surprised me that a linear pot gave the best response.

> The reason I ask is because the digital pot I am considering using is a
> 10K and so I may need to rework the bias resistors. Any light you can
> shed on this would be much appreciated.

==============

that's a tough one... would bias resisters affect the "curve" of the pot?
maybe two 10k linear digital pots in parallel??

you may be able to experiment and find a replacement for the 1k resistor
that works with a 10k pot... since the resistive/reactive impedance of IC1
pin 13 is unknown, i would speculate that experimentation would be far
more productive than calculating.

another option would be this... have an op-amp with the gain controlled
either digitally or via your digital pot; the input of the op-amp comes
from IC4 pin 7; the output of the op-amp pass through a 1k resistor on
it's way to IC1 pin 13. you should be able to find a sweet-spot where this
gives the same effect as the original mod... and... with an amplifier in
the circuit you could even go beyond the range of the original mod ;)

ascii art (may not survive yahoo):

gain
control
|
___ | _______
IC4| |\| |IC1
pin7|---| >--\/\/\/--|pin13
| |/ 1k |


--
...atom

________________________
http://atom.smasher.org/
762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
-------------------------------------------------

"It's just a goddamned piece of paper!"
-- George "dubya" Bush,
referring to the United States Constitution, 2005

I am thinking about trying the FM mod with the white noise generator.

Has anyone tried that?

Mike.

It would be great if you could get it to Sample and Hold... Or am I showing my ignorance here?

Alan,

I think you might be talking about the random waveform that is now
available in the second LFO pushing into the VCF cutoff.

The level of the VCF cutoff randomly changes each time the LFO2 cycles.

I was referring to sending the noise direct into the VCF linear
cutoff. Sort of quasi noise FM modulation.

Mike.

--- In korgpolyex@yahoogroups.com, Alan Currall <alan@...> wrote:
>
> It would be great if you could get it to Sample and Hold... Or am I
> showing my ignorance here?
> ac
> On 25 Feb 2008, at 6:08PM, korgpolyex800 wrote:
>
> > I am thinking about trying the FM mod with the white noise generator.
> >
> > Has anyone tried that?
> >
> > Mike.
> >
> >
> >
>

I'm with you now Mike. My understanding of synthesis is ropey at the best of times, but I can see what you mean now.

On Mon, 25 Feb 2008, korgpolyex800 wrote:

> I am thinking about trying the FM mod with the white noise generator.
>
> Has anyone tried that?

=================

worth a shot... and if it works (ie: sounds good) you can easily add a
switch between DCO/noise for the mod source.


--
...atom

________________________
http://atom.smasher.org/
762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
-------------------------------------------------

"Do not wait; the time will never be 'just right.'
Start where you stand, and work with whatever
tools you may have at your command, and better
tools will be found as you go along."
-- Napoleon Hill

--- In korgpolyex@yahoogroups.com, Atom Smasher <atom@...> wrote:

>
> On Mon, 25 Feb 2008, korgpolyex800 wrote:
>
> > I am thinking about trying the FM mod with the white noise generator.
> >
> > Has anyone tried that?
> =================
>
> worth a shot... and if it works (ie: sounds good) you can easily add a
> switch between DCO/noise for the mod source.
>
> I think that's what I did to mine the other day. I did yhe 12/24 filter mod, but ended up

with an extra wire, from C103's negative lead... so I put that on a pot with a wire from vr3,
the bottom right pad just above c25. when I turn that knob, the noise modulates the 2nd
dco, but only if parameters 71-76 are engaged. What happens is like a stepped pitch
sweep or dive, depending on the attack or sloe settings. Doesn't work with res turned up,
and I'm having trouble with getting the original noise signal back. I had it earlier today but
it split again. Maybe if someone who knows the biz could do the noise modulation mod
and share the results. I like it, but did I mess up the white noise? Thanks for the mods
Atom! Please check out my H ex 800 in photos.

> --
> ...atom
>
> ________________________
> http://atom.smasher.org/
> 762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
> -------------------------------------------------
>
> "Do not wait; the time will never be 'just right.'
> Start where you stand, and work with whatever
> tools you may have at your command, and better
> tools will be found as you go along."
> -- Napoleon Hill
>