Korg Poly800/EX800 Users

Here's the link from another list. It's
Korg poly/ex 800 mod for cutoff/resonance
control, slightly different then usual,
supposedly sounds better. Lots of deatails
and pictures. 

http://synthmod.net/korg/moog_slayer/
 



-- 



marjan


me    : Marjan Urekar
e-mail: urekar.m@...
s-diy : http://surf.to/marjansystems
music : http://go.to/forcemajeure

hi everybody!

anyone tried this yet? scott, you seem to be quite familiar with 
electronics, what exactly does this mod do? why is it connected to the 
power source? and, most important question of em all: how likely is it 
to fry the poly this way? to me the "usual" mod discussed here earlier 
makes perfect sense, since its just replacing the trimpots with ones 
you can turn from the outside - i don´t understand the use od the 
power source here...... well, i think i will be hearing from all of 
you soon.... ;) 

christian
btw marjan: thanks for showing us this different approach!

--- In korgpolyex@y..., ">>>marjan<<<" <urekar.m@e...> wrote:

> 
> Here's the link from another list. It's
> Korg poly/ex 800 mod for cutoff/resonance
> control, slightly different then usual,
> supposedly sounds better. Lots of deatails
> and pictures. 
> 
> http://synthmod.net/korg/moog_slayer/
>  
> 
> 
> 
> -- 
> 
> 
> 
> marjan
> 
> 
> me    : Marjan Urekar
> e-mail: urekar.m@e...
> s-diy : http://surf.to/marjansystems
> music : http://go.to/forcemajeure

>anyone tried this yet? scott, you seem to be quite familiar with
>electronics, what exactly does this mod do? why is it connected to the
>power source? and, most important question of em all: how likely is it
>to fry the poly this way? to me the "usual" mod discussed here earlier
>makes perfect sense, since its just replacing the trimpots with ones
>you can turn from the outside - i don\ufffdt understand the use od the
>power source here...... well, i think i will be hearing from all of
>you soon.... ;)

I'm not that familiar with electronics really.  but I would imagine that the 
trimpots control the CVs controlling the cutoff and resonance, and the way 
it's normally set up it probably adjusts it from whatever amount to ground, 
and the alternative way would adjust it from a positive voltage to ground, 
providing a more pronounced effect.  So instead of only attentuating the 
control voltages it boosts them as well.  I guess it would be possible to 
blow the filter chip but probably not likely.  I don't know the specs of the 
chip so I don't know the maximum voltages but the mod doesn't seem too 
extreme.  As long as it's not exceeding the power supply voltages I wouldn't 
see any reason to worry.

So the end result of it is the knobs have a higher range, and the filter can 
self-oscillate.  BUT the problem with self oscillation on the Poly 800 is 
the way the voice architecture is set up.  Since there's only one filter, it 
goes like DCO > DCA > VCF > VCA.  The DCO and DCA are on the oscillator 
chip, and the VCF and VCA are on the filter chip.  I'm just theorizing here 
really but that's what I think is happening.  The final VCA seems to open 
instantly when you press a key but shuts off abruptly after the release 
cycle of the envelope is finished.  So the end result of this is that if you 
really crank the resonance up, it will self-oscillate but it will continue 
to oscillate at full blast until the final VCA shuts off.

At least that's what was going on with mine, or what I thought was going on. 
  I did the "normal" mod but mine still got to painful self-oscillation.  
One interesting note about it though is that if the oscillators and noise 
were off, it wouldn't do it, the noise had to be cut on 1 or something for 
it to work.

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

> 
> I'm not that familiar with electronics really.  but I would imagine that the
> trimpots control the CVs controlling the cutoff and resonance, and the way
> it's normally set up it probably adjusts it from whatever amount to ground,
> and the alternative way would adjust it from a positive voltage to ground,
> providing a more pronounced effect.  So instead of only attentuating the
> control voltages it boosts them as well. 

Here's some tech overview of what happens in there:
for resonance you have current input to the chip, hence 10k res and 10k
trimpot
fed by CV. Old mod used pot instead pot and all you got is lowering
maximum
resonance to some level (as 10k is left in). 
Atom's mod take different approach, it attenuates incoming res CV and
feeds
old 10k res. So you get the same max resonance as before but now you can
fully
shut resonance, old mod took it to some level but here you can get 0
resoance.
My mod is somewhat different. I installed the switch to choose between
original
line (10k trimpot and 10k res) and new one (100k lin pot, 10k trimpot,
1k res),
that way I got higher resonance (set by trimpot and res, pot to 0), and
it goes
almost to 0 res (pot at the max). Pot is configured as variable
resistor.

Cutoff is bit different. I suspect it's OTA input as it's fed by again
current from +V, lower leg with res and cap is for stabilisation.
Atom's mod substitutes it for voltage divider and feeds current input
with voltage. In theory that would be a problem. Can't say more. I'd
toss in resistor inbetween pot wiper and chip input, 1k or so.
Haven't tried it. Now, if you look at the borad you'll see silkscreened
short link for bypassing trimpot to +V. Hmm, so maybe it really works.
You might even not need 470ohm res he suggested. 



> I guess it would be possible to
> blow the filter chip but probably not likely.  I don't know the specs of the
> chip so I don't know the maximum voltages but the mod doesn't seem too
> extreme.  As long as it's not exceeding the power supply voltages I wouldn't
> see any reason to worry.
> 

you can blow it even in normal voltages

> So the end result of it is the knobs have a higher range, and the filter can
> self-oscillate.  BUT the problem with self oscillation on the Poly 800 is
> the way the voice architecture is set up.  Since there's only one filter, it
> goes like DCO > DCA > VCF > VCA.  

rather  DCO1 > DCA > 
	DCO2 > DCA > VCMIXER > VCF > VCA
                  NOISE> VCA > 

Chip's onboard VCA is used to control noise level. VC mixer sets
individual
levels of each DCO. DCA is performed in oscillator chip (BTW these are
real
DCOs, while those in Junos and JX's are DCOs with analog
core-integrator)
After the chip is only chorus circuit and left/right mixing opamps.

> The DCO and DCA are on the oscillator
> chip, and the VCF and VCA are on the filter chip.  I'm just theorizing here
> really but that's what I think is happening.  The final VCA seems to open
> instantly when you press a key but shuts off abruptly after the release
> cycle of the envelope is finished.  So the end result of this is that if you
> really crank the resonance up, it will self-oscillate but it will continue
> to oscillate at full blast until the final VCA shuts off.
> 

What really happens is that you don't have VCA after VCF, that's why you
get that effect.


> At least that's what was going on with mine, or what I thought was going on.
>   I did the "normal" mod but mine still got to painful self-oscillation.
> One interesting note about it though is that if the oscillators and noise
> were off, it wouldn't do it, the noise had to be cut on 1 or something for
> it to work.
> 

Strange, mine oscillates witout any input, no problem. And it's quite
nice
chip, I like selfocs resonance. Sounds much better than CEM VCF chip
IMO.

-- 



marjan


me    : Marjan Urekar
e-mail: urekar.m@...
s-diy : http://surf.to/marjansystems
music : http://go.to/forcemajeure

Well it always nice to reply your own mail:

> Cutoff is bit different. I suspect it's OTA input as it's fed by again
> current from +V, lower leg with res and cap is for stabilisation.
> Atom's mod substitutes it for voltage divider and feeds current input
> with voltage. In theory that would be a problem. Can't say more. I'd
> toss in resistor inbetween pot wiper and chip input, 1k or so.
> Haven't tried it. Now, if you look at the borad you'll see silkscreened
> short link for bypassing trimpot to +V. Hmm, so maybe it really works.
> You might even not need 470ohm res he suggested.


I got it right except that additional resistor is already there
(22k) so Atom's mod is quite right. It'll work no problemo.
That 470-510 ohm res is there to put cutoff in useable range.

So this looks just OK...

Have fun...


-- 



marjan


me    : Marjan Urekar
e-mail: urekar.m@...
s-diy : http://surf.to/marjansystems
music : http://go.to/forcemajeure

> I got it right except that additional resistor is already there
> (22k) so Atom's mod is quite right. It'll work no problemo.
> That 470-510 ohm res is there to put cutoff in useable range.

i´m no wizard at electronics, does 470-510 ohm mean that i can use any 
resistor between 470 and 510 ohm or does it mean something different?

christian

btw: please someone answer my question regarding the backup-battery as 
the doc in the files-folder does describe how to install the batttery 
when no "soldering island" is present but skips a comment on how to 
install it when the islands actually are there... where does + go?

>Here's some tech overview of what happens in there: for resonance you >have 
>current input to the chip, hence 10k res and 10k trimpot fed by >CV. Old 
>mod used pot instead pot and all you got is lowering maximum
>resonance to some level (as 10k is left in). Atom's mod take different 
> >approach, it attenuates incoming res CV and feeds old 10k res. So you 
> >get the same max resonance as before but now you can fully shut 
> >resonance, old mod took it to some level but here you can get 0 
> >resoance. My mod is somewhat different. I installed the switch to >choose 
>between original line (10k trimpot and 10k res) and new one >(100k lin pot, 
>10k trimpot, 1k res), that way I got higher resonance >(set by trimpot and 
>res, pot to 0), and it goes almost to 0 res (pot at >the max). Pot is 
>configured as variable resistor.

that's a really good idea....much better than the way the normal mod works.

>Cutoff is bit different. I suspect it's OTA input as it's fed by again
>current from +V, lower leg with res and cap is for stabilisation.
>Atom's mod substitutes it for voltage divider and feeds current input
>with voltage. In theory that would be a problem. Can't say more. I'd
>toss in resistor inbetween pot wiper and chip input, 1k or so.
>Haven't tried it. Now, if you look at the borad you'll see silkscreened
>short link for bypassing trimpot to +V. Hmm, so maybe it really works.
>You might even not need 470ohm res he suggested.

makes me really wish there was actually a datasheet available.

you should try giving the filter a 2-pole switch as well.

>Strange, mine oscillates witout any input, no problem. And it's quite
>nice chip, I like selfocs resonance. Sounds much better than CEM VCF >chip 
>IMO.

I agree.  Best filters I've ever heard, particularly right on the edge of 
self-oscillation.  The same filters are also used in the DW-8000 and I think 
they sound a bit better there....too bad the DW-8000's waveforms have no top 
end.  Interesting that yours would oscillate with no input....

and sorry about the technical errors...never saw the schematics so it's 
really just guessing.

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp