Korg Poly800/EX800 Users

Hi Atom,

I am working on the new aTomaHawk board mod kit and have a question
for you.

Is the only reason you replaced VR2 with a pot so that you could
control VCF cutoff via a knob instead of via the VCF cutoff parameter?

Because it appears to me that providing cut off control via the
existing circuitry will work just fine. The goal is to provide a knob
to control control cut off.

Then, you replaced VR5 so that you could really push the resonance
into self oscillation. That will definitely need a digital
potentiometer put in its place. However, I am wondering why you use a
log pot. I would have thought that the resonance response on the
filter chip would have been linear. And you ground one side which is
completely different to the way the trimmer is set up. Why?

Thanks for your help,

Mike.

Thanks for that Dave,

The problem I'm having right now is choosing the right digital
potentiometer for the job. The versions that I got as samples from
Maxim are only 5Volt operation. No good for the Poly because the audio
is 10V (-5<->+5).

Analog devices does one that is 10-30V but then the logic control is
difficult because it would "see" logic zero only at -5 volts which
doesn't match up the Poly either.

I have the same problem with the FM mod too because you want to be
able vary the amount of DCO that is injected into the VCF. Once again,
the range is -5<->+5.

So I am kinda scratching my head right now.

Mike.


--- In korgpolyex@yahoogroups.com, "David Mochen" <davidmochen@...> wrote:
>
> Hi
> 
> Just a small note... Atom's great design has been tweaked a bit by
this guy Olaf, who replaced the 50k cutoff pot with a 100k pot for a
broader response. I am using 100k on my Poly and the sweeping range is
very very sweet. You might want to try 50k and 100k for your aTomaHawk
board :)
> 
> Of course Mike, you might as well want to add a switch for toggling
on/off MoogSlayer. Olaf did this also via a hardware switch...

> 
> thanks galore
> 
> Dave
> 
> ps: glad that the aTomaHawk moniker caught on! :D
> 
>   ----- Original Message ----- 
>   From: korgpolyex800 
>   To: korgpolyex@yahoogroups.com 
>   Sent: Monday, March 17, 2008 2:21 PM
>   Subject: [korgpolyex] Moog Slayer mod - question
> 
> 
>   Hi Atom,
> 
>   I am working on the new aTomaHawk board mod kit and have a question
>   for you.
> 
>   Is the only reason you replaced VR2 with a pot so that you could
>   control VCF cutoff via a knob instead of via the VCF cutoff parameter?
> 
>   Because it appears to me that providing cut off control via the
>   existing circuitry will work just fine. The goal is to provide a knob
>   to control control cut off.
> 
>   Then, you replaced VR5 so that you could really push the resonance
>   into self oscillation. That will definitely need a digital
>   potentiometer put in its place. However, I am wondering why you use a
>   log pot. I would have thought that the resonance response on the
>   filter chip would have been linear. And you ground one side which is
>   completely different to the way the trimmer is set up. Why?
> 
>   Thanks for your help,
> 
>   Mike.
>

The Maxim DS1660 is bipolar +/- 5 volt. Will this work? I read the 
Max5160 datasheet could it be used with an op amp for feedback 
control?

--- In korgpolyex@yahoogroups.com, "korgpolyex800" 
<korgpolyex800@...> wrote:
>
> Thanks for that Dave,
> 
> The problem I'm having right now is choosing the right digital
> potentiometer for the job. The versions that I got as samples from
> Maxim are only 5Volt operation. No good for the Poly because the 
audio
> is 10V (-5<->+5).
> 
> Analog devices does one that is 10-30V but then the logic control is
> difficult because it would "see" logic zero only at -5 volts which
> doesn't match up the Poly either.
> 
> I have the same problem with the FM mod too because you want to be
> able vary the amount of DCO that is injected into the VCF. Once 
again,
> the range is -5<->+5.
> 
> So I am kinda scratching my head right now.
> 
> Mike.
> 
> 
> --- In korgpolyex@yahoogroups.com, "David Mochen" <davidmochen@> 
wrote:
> >
> > Hi
> > 
> > Just a small note... Atom's great design has been tweaked a bit by
> this guy Olaf, who replaced the 50k cutoff pot with a 100k pot for a
> broader response. I am using 100k on my Poly and the sweeping range 
is
> very very sweet. You might want to try 50k and 100k for your 
aTomaHawk
> board :)
> > 
> > Of course Mike, you might as well want to add a switch for 
toggling
> on/off MoogSlayer. Olaf did this also via a hardware switch...
> > 
> > thanks galore
> > 
> > Dave
> > 
> > ps: glad that the aTomaHawk moniker caught on! :D
> > 
> >   ----- Original Message ----- 
> >   From: korgpolyex800 
> >   To: korgpolyex@yahoogroups.com 
> >   Sent: Monday, March 17, 2008 2:21 PM
> >   Subject: [korgpolyex] Moog Slayer mod - question
> > 
> > 
> >   Hi Atom,
> > 
> >   I am working on the new aTomaHawk board mod kit and have a 
question
> >   for you.
> > 
> >   Is the only reason you replaced VR2 with a pot so that you could
> >   control VCF cutoff via a knob instead of via the VCF cutoff 
parameter?
> > 
> >   Because it appears to me that providing cut off control via the
> >   existing circuitry will work just fine. The goal is to provide 
a knob
> >   to control control cut off.
> > 
> >   Then, you replaced VR5 so that you could really push the 
resonance
> >   into self oscillation. That will definitely need a digital
> >   potentiometer put in its place. However, I am wondering why you 
use a
> >   log pot. I would have thought that the resonance response on the
> >   filter chip would have been linear. And you ground one side 
which is

> >   completely different to the way the trimmer is set up. Why?
> > 
> >   Thanks for your help,
> > 
> >   Mike.
> >
>

On Mon, 17 Mar 2008, korgpolyex800 wrote:

> Is the only reason you replaced VR2 with a pot so that you could control 
> VCF cutoff via a knob instead of via the VCF cutoff parameter?
===============

that seems to be a fair assessment.


> Because it appears to me that providing cut off control via the existing 
> circuitry will work just fine. The goal is to provide a knob to control 
> control cut off.
================

yeah, that should work, although it would have limited resolution. at 
higher resonance settings it become a zipper effect.


> Then, you replaced VR5 so that you could really push the resonance into 
> self oscillation. That will definitely need a digital potentiometer put 
> in its place. However, I am wondering why you use a log pot. I would 
> have thought that the resonance response on the filter chip would have 
> been linear.
===================

i used log because it produces a better response than linear. try it both 
ways, and see which one sounds/feels better.

that one, and the linear taper pot for the FM-800 mod, surprised me.


> And you ground one side which is completely different to the way the 
> trimmer is set up. Why?
===================

i can't say, without having the schematics in front of me, but it works!


-- 
         ...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'm glad there are other sane people on this list that can help me get
through life.

Those are the samples I have. LOL - I will get to work on it straight
away.

Mike.

--- In korgpolyex@yahoogroups.com, "narfman96" <narfman96@...> wrote:

>
> The Maxim DS1660 is bipolar +/- 5 volt. Will this work? I read the 
> Max5160 datasheet could it be used with an op amp for feedback 
> control?
> 
> --- In korgpolyex@yahoogroups.com, "korgpolyex800" 
> <korgpolyex800@> wrote:
> >
> > Thanks for that Dave,
> > 
> > The problem I'm having right now is choosing the right digital
> > potentiometer for the job. The versions that I got as samples from
> > Maxim are only 5Volt operation. No good for the Poly because the 
> audio
> > is 10V (-5<->+5).
> > 
> > Analog devices does one that is 10-30V but then the logic control is
> > difficult because it would "see" logic zero only at -5 volts which
> > doesn't match up the Poly either.
> > 
> > I have the same problem with the FM mod too because you want to be
> > able vary the amount of DCO that is injected into the VCF. Once 
> again,
> > the range is -5<->+5.
> > 
> > So I am kinda scratching my head right now.
> > 
> > Mike.
> > 
> > 
> > --- In korgpolyex@yahoogroups.com, "David Mochen" <davidmochen@> 
> wrote:
> > >
> > > Hi
> > > 
> > > Just a small note... Atom's great design has been tweaked a bit by
> > this guy Olaf, who replaced the 50k cutoff pot with a 100k pot for a
> > broader response. I am using 100k on my Poly and the sweeping range 
> is
> > very very sweet. You might want to try 50k and 100k for your 
> aTomaHawk
> > board :)
> > > 
> > > Of course Mike, you might as well want to add a switch for 
> toggling
> > on/off MoogSlayer. Olaf did this also via a hardware switch...
> > > 
> > > thanks galore
> > > 
> > > Dave
> > > 
> > > ps: glad that the aTomaHawk moniker caught on! :D
> > > 
> > >   ----- Original Message ----- 
> > >   From: korgpolyex800 
> > >   To: korgpolyex@yahoogroups.com 
> > >   Sent: Monday, March 17, 2008 2:21 PM
> > >   Subject: [korgpolyex] Moog Slayer mod - question
> > > 
> > > 
> > >   Hi Atom,
> > > 
> > >   I am working on the new aTomaHawk board mod kit and have a 
> question
> > >   for you.
> > > 
> > >   Is the only reason you replaced VR2 with a pot so that you could
> > >   control VCF cutoff via a knob instead of via the VCF cutoff 
> parameter?
> > > 
> > >   Because it appears to me that providing cut off control via the
> > >   existing circuitry will work just fine. The goal is to provide 
> a knob
> > >   to control control cut off.
> > > 
> > >   Then, you replaced VR5 so that you could really push the 
> resonance
> > >   into self oscillation. That will definitely need a digital
> > >   potentiometer put in its place. However, I am wondering why you 
> use a
> > >   log pot. I would have thought that the resonance response on the
> > >   filter chip would have been linear. And you ground one side 
> which is
> > >   completely different to the way the trimmer is set up. Why?
> > > 
> > >   Thanks for your help,
> > > 
> > >   Mike.
> > >
> >
>