Korg Poly800/EX800 Users

FM-800 Filter Mod for Korg EX-800 and Poly-800
http://synthmod.net/korg/fm800/

who wants to be the first to send samples, pictures and reviews?


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Wow, what nasty sounds!  Thank you atom smasher!

With the filter in self-oscillation you get real "FM" sounds.  Without
being able to precisely scale the filter keyboard tracking it's not
really playable, but it is great for sfx.

With resonance down there is the potential for more musical, playable
tones I would describe as grungy, especially with filter cutoff down as
well.  With cutoff halfway up I could get some tones reminiscent of a
cello or a human voice.


I recorded sounds and took pictures last night, I'll try to get them up
tonight.


One thing I noticed is that the effects seemed to come and go on every 3rd
or 4th key?  I'm not sure if this is just a product of the frequencies
involved?

Trying to understand the schematics on the web is a pain, so I'm wondering
what's the difference between r74-pin 7 of IC4 that we're using and
r76-pin 7 of IC5 that we're not?


Once again, thanks atom!

Tim

On Mon, 10 Apr 2006, Atom Smasher wrote:

> FM-800 Filter Mod for Korg EX-800 and Poly-800
> http://synthmod.net/korg/fm800/
>
> who wants to be the first to send samples, pictures and reviews?
>
>
> --
>          ...atom

On Tue, 11 Apr 2006, Tim Bieniosek wrote:

> Wow, what nasty sounds!  Thank you atom smasher!
=============

you're welcome.


> With the filter in self-oscillation you get real "FM" sounds.  Without 
> being able to precisely scale the filter keyboard tracking it's not 
> really playable, but it is great for sfx.
>
> With resonance down there is the potential for more musical, playable 
> tones I would describe as grungy, especially with filter cutoff down as 
> well.  With cutoff halfway up I could get some tones reminiscent of a 
> cello or a human voice.
>
> I recorded sounds and took pictures last night, I'll try to get them up 
> tonight.
>
> One thing I noticed is that the effects seemed to come and go on every 
> 3rd or 4th key?  I'm not sure if this is just a product of the 
> frequencies involved?
==================

that's odd.... does it seem to do that on different patches with different 
filter settings?


> Trying to understand the schematics on the web is a pain, so I'm 
> wondering what's the difference between r74-pin 7 of IC4 that we're 
> using and r76-pin 7 of IC5 that we're not?
===================

from memory... IC5 operates on DCO2, which isn't always available. IC4 
operates on DCO1 which is always available.

note that you can use this mod even if DCO1 level is 0.


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 	 and small enough to win."
 		-- Johnathan Kozol

Since there is voltage control available for pitch it is probably even
possible to do some kind of real FM. But since there's only one osc,
it will be self-modulation. And the osc isn't designed for this either
so it will probably result in some kind of wierd sounds. Especially,
since we don't have smooth waveforms like sine waves.

If you take a closer look at the schematics, the pitch-bend output of
the IC8 multiplexer feeds into the oscillator clock control circuit.
This is also where vibrato gets inserted into synthesis.

Maybe it's possible to route bend to filter cutoff via a switch,
allowing joystick control of the filter.

On Tue, 11 Apr 2006, austeritygirlone wrote:

> Since there is voltage control available for pitch it is probably even 
> possible to do some kind of real FM. But since there's only one osc, it 
> will be self-modulation. And the osc isn't designed for this either so 
> it will probably result in some kind of wierd sounds. Especially, since 
> we don't have smooth waveforms like sine waves.
=============

it seems that the DCOs exist virtually in IC3. if that's the case, they 
wouldn't respond well to any modulation in the audio range.

my *guess* is that it would be unusable noise.


> If you take a closer look at the schematics, the pitch-bend output of 
> the IC8 multiplexer feeds into the oscillator clock control circuit. 
> This is also where vibrato gets inserted into synthesis.
============

DCO implemented in old hardware: pitch bend and vibrato are slow enough 
for the DCOs to track... i have my doubts about FM in the audio range.


> Maybe it's possible to route bend to filter cutoff via a switch, 
> allowing joystick control of the filter.
==============

or just use the moog slayer mod... you can use a joystick instead of 2 
knobs, if you prefer ;)

seriously, you can find 2 axis joysticks in electronic surplus catalogs, 
although you'll probably want to change the pots from linear to log taper.


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         ...atom

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 		-- Buddha

oh... if anyone can take pictures of the INSIDE of their synth before, 
during or after the mod, that would be great... especially close-ups of 
the wiring.

and we're *all* still waiting for samples!

thanks!


-- 
         ...atom

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Here we go:

http://bieniosek.com/fm-800.html

Sound samples and some before + after pics.

After building an x0xb0x I was feeling bold enough to solder directly to 
the original resistors.

Comments please!



Atom Smasher wrote:

> oh... if anyone can take pictures of the INSIDE of their synth before, 
> during or after the mod, that would be great... especially close-ups of 
> the wiring.
> 
> and we're *all* still waiting for samples!
> 
> thanks!
> 
>

On Tue, 11 Apr 2006, Tim Bieniosek wrote:

> http://bieniosek.com/fm-800.html
>
> Sound samples and some before + after pics.
>
> After building an x0xb0x I was feeling bold enough to solder directly to 
> the original resistors.
===============

good work!

the "Noisy SFX", "Hi-Q Filter" and "Scale" samples don't sound anything at 
all like what i'd expect to hear from a poly-800... to my ears it's more 
like a cross between a DX-100 and an ARP 2600.

"It Might Be Music" is also good, but less extreme. it sounds more like a 
poly-800... but with something different...

and you're in philly? so under the Picture, Sample, Lunch-Ware License you 
can take me to lunch at kingdom of the vegetarian (11th, near arch st) 
next time i'm in town? it's right around the corner from 8th street music, 
we can look for lost treasure!

hhmmm... in the picture, you soldered to the end of R22 that's physically 
closer to R23... the other end (that's electrically connected to R23) is 
supposed to get the connection. it seems to work for you, but i suspect 
you might be losing a little bit of the low end from the range of your 
filter cutoff.

maybe i should make that more clear in the diagram...?


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On Tue, 11 Apr 2006, Atom Smasher wrote:

> maybe i should make that more clear in the diagram...?
====================

updated diagram - http://synthmod.net/korg/fm800/fm-800.png

http://synthmod.net/korg/fm800/


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         ...atom

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 	 any individual wire was guesswork. It was even conceivable
 	 that they watched everybody all the time. But at any rate,
 	 they could plug in your wire whenever they wanted to."
 		-- George Orwell, "1984"

Great, that should make it impossible to mix up if you're as careless as
me. :)

I'll fix mine tonight and take a new photo.

And let me know next time you're in Philly!

Tim

On Wed, 12 Apr 2006, Atom Smasher wrote:

> On Tue, 11 Apr 2006, Atom Smasher wrote:
>
> > maybe i should make that more clear in the diagram...?
> ====================
>
> updated diagram - http://synthmod.net/korg/fm800/fm-800.png
>
> http://synthmod.net/korg/fm800/
>
>
> --
>          ...atom

So!  The interesting results from last night's experimenting is... I like
my "mistake" better :)

It sounds like you get less of the filter cutoff range if you do it the
"right" way.  I couldn't get the filter to do the whole subsonic -
infrasonic sweep that I showed off in my demos, or the vowel sounds.

So as soon as I was done testing the intended mod, I put mine back to the
wrong way :)  The sounds are just cooler.  I'd invite others to try it
out and see what they like.  (There is also a photo up of the "right way"
now.)


I think I've nailed down the other issue with some notes not being
affected.  As I suspected, in 8-voice mode you don't get the FM effect if
the CPU decides to use DCO 2.  For instance, playing a run you get 4 notes
with FM follwed by 4 notes, no FM.  In 4 voice mode you don't have this
problem.  I also tested it by bridging r74 to r76 (summing the outputs
of the DCOs) and that fixed the note skipping.

There must be a place further down the line where we can take the full
audio signal and use that as the modulation source?

Tim

On Tue, 11 Apr 2006, Atom Smasher wrote:

> On Tue, 11 Apr 2006, Tim Bieniosek wrote:
>
> > With the filter in self-oscillation you get real "FM" sounds.  Without
> > being able to precisely scale the filter keyboard tracking it's not
> > really playable, but it is great for sfx.
> >
> > With resonance down there is the potential for more musical, playable
> > tones I would describe as grungy, especially with filter cutoff down as
> > well.  With cutoff halfway up I could get some tones reminiscent of a
> > cello or a human voice.
> >
> > I recorded sounds and took pictures last night, I'll try to get them up
> > tonight.
> >
> > One thing I noticed is that the effects seemed to come and go on every
> > 3rd or 4th key?  I'm not sure if this is just a product of the
> > frequencies involved?
> ==================
>
> that's odd.... does it seem to do that on different patches with different
> filter settings?
>
>
> > Trying to understand the schematics on the web is a pain, so I'm
> > wondering what's the difference between r74-pin 7 of IC4 that we're
> > using and r76-pin 7 of IC5 that we're not?
> ===================
>
> from memory... IC5 operates on DCO2, which isn't always available. IC4
> operates on DCO1 which is always available.
>
> note that you can use this mod even if DCO1 level is 0.

> There must be a place further down the line where we can take the full
> audio signal and use that as the modulation source?

How about taking the already filtered output? Some kind of wierd
feedback filtering. 

Mixing noise into filter cutoff will result in something nice, too. I
have this on another synth.

And what about feeding both of those into resonance cv?

But when doing that much wirings, one might have to amplify the
signals with opamps to prevent the CVs from feeding forward into the
audio path or into each other.

But where to intall all those pots?

On Thu, 13 Apr 2006, Tim Bieniosek wrote:

> So!  The interesting results from last night's experimenting is... I 
> like my "mistake" better :)
>
> It sounds like you get less of the filter cutoff range if you do it the 
> "right" way.  I couldn't get the filter to do the whole subsonic - 
> infrasonic sweep that I showed off in my demos, or the vowel sounds.
>
> So as soon as I was done testing the intended mod, I put mine back to 
> the wrong way :)  The sounds are just cooler.  I'd invite others to try 
> it out and see what they like.  (There is also a photo up of the "right 
> way" now.)
=======================

i *think* what's happening is that as you turn the FM knob, it's also 
affecting the cutoff. you could (according to this theory) achieve the 
same thing by wiring it the "right" way and turning the FM and cutoff knob 
together.

you could also turn the knobs in opposite directions, or independently, or 
at different rates... in other words, you can do the same thing, and more. 
the "mistake" would sound more dynamic because it's doing more than one 
thing at a time; adjusting the FM and the cutoff.

if it sounds good, do it. but if you get a chance to test out my theory, 
let us know how it goes.


> I think I've nailed down the other issue with some notes not being 
> affected.  As I suspected, in 8-voice mode you don't get the FM effect 
> if the CPU decides to use DCO 2.  For instance, playing a run you get 4 
> notes with FM follwed by 4 notes, no FM.  In 4 voice mode you don't have 
> this problem.  I also tested it by bridging r74 to r76 (summing the 
> outputs of the DCOs) and that fixed the note skipping.
=============

that makes sense...


> There must be a place further down the line where we can take the full 
> audio signal and use that as the modulation source?
==============

yes, but not without extra circuitry or potential to really screw things 
up. one good place to tap into that signal would be IC1 pins 10/19, but it 
would need to be amplified before you could wire it into other 
destinations. before that point, you've got two separate paths; after that 
point, you've got filtered (mutilated, moog-slayed and fm'ed) signal. it 
might be a good source for some modulation routings, but i have no plans 
to look into it.

prior to that, DCO1 and DCO2 have independent paths, arriving at IC1 pins 
20/21.


-- 
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On Thu, 13 Apr 2006, Tim Bieniosek wrote:

> So as soon as I was done testing the intended mod, I put mine back to 
> the wrong way :)  The sounds are just cooler.  I'd invite others to try 
> it out and see what they like.  (There is also a photo up of the "right 
> way" now.)
====================

you have the moog-slayer mod, too? and the FM mod is currently wired the 
"wrong" way?

turn the filter cutoff knob all the way down, and see if anything happens 
when you adjust the FM knob.

lemme know what happens...

i suspect nothing will happen. with it wired the "right" way, you get the 
filter adjusted by the FM knob.


-- 
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 		the United Catholic Church

On Tue, 11 Apr 2006, Tim Bieniosek wrote:

> With the filter in self-oscillation you get real "FM" sounds.  Without 
> being able to precisely scale the filter keyboard tracking it's not 
> really playable, but it is great for sfx.
====================

are you noticing a problem with the FM tracking the keyboard? that may be 
a side effect of the "wrong" wiring... check it out if you run more 
tests...


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no, the filter tracks well enough only like 2 octaves at best. and
afaik there's no way to calibrate this.

On 4/13/06, Atom Smasher <atom@...> wrote:
>
>  On Tue, 11 Apr 2006, Tim Bieniosek wrote:
>
>  > With the filter in self-oscillation you get real "FM" sounds.  Without
>  > being able to precisely scale the filter keyboard tracking it's not
>  > really playable, but it is great for sfx.
>  ====================
>
>  are you noticing a problem with the FM tracking the keyboard? that may be
>  a side effect of the "wrong" wiring... check it out if you run more
>  tests...
>
>
>
>  --
>           ...atom
>
>    ________________________
>    http://atom.smasher.org/
>    762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
>    -------------------------------------------------
>
>        "I am somehow less interested in the weight and
>        convolutions of Einstein's brain than in the near
>        certainty that people of equal talent have lived and
>        died in cotton fields and sweatshops."
>              -- Stephen Jay Gould
>
>
>
>
>
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The strange truth -- turning the FM knob raises filter cutoff slightly 
at it nears the midpoint, then lowers it again as the knob goes all the 
way up.

(this is still wired the "wrong" way)

Atom Smasher wrote:

> 
> you have the moog-slayer mod, too? and the FM mod is currently wired the 
> "wrong" way?
> 
> turn the filter cutoff knob all the way down, and see if anything happens 
> when you adjust the FM knob.
> 
> lemme know what happens...
> 
> i suspect nothing will happen. with it wired the "right" way, you get the 
> filter adjusted by the FM knob.
> 
>

Just got my Poly-800 today for a whopping HANDSHAKE! Being a bench
tech I am sure to do the MODs and will be delighted to post pics of
before/during/after! I just hope this thing works as it is. It was
left at a local music gear shop here where my bassist sells/rents
studio and PA gear. The guy said to do what they wanted with it and it
didn't quite fit in next to the OASYS, Tritons or the Kharmas so they
called me to come rescue it before it went to the dumpster. If it's
dead I may have some parts for someone! Wish me luck, unless you need the
parts!


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

>
> oh... if anyone can take pictures of the INSIDE of their synth before, 
> during or after the mod, that would be great... especially close-ups of 
> the wiring.
> 
> and we're *all* still waiting for samples!
> 
> thanks!
> 
> 
> -- 
>          ...atom
> 
>   ________________________
>   http://atom.smasher.org/
>   762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
>   -------------------------------------------------
> 
>  	"When the President does it, that means that it's not illegal."
>  		-- Richard M. Nixon, 19 May 1977
>

> Just got my Poly-800 today for a whopping HANDSHAKE! Being a bench tech 
> I am sure to do the MODs and will be delighted to post pics of 
> before/during/after! I just hope this thing works as it is. It was left 
> at a local music gear shop here where my bassist sells/rents studio and 
> PA gear. The guy said to do what they wanted with it and it didn't quite 
> fit in next to the OASYS, Tritons or the Kharmas so they called me to 
> come rescue it before it went to the dumpster. If it's dead I may have 
> some parts for someone! Wish me luck, unless you need the parts!
==================

sweet!

what i'm needing is pictures of the inside, especially if you replace one 
or both resistors with 0.25W vertically oriented resistors. that part 
seems to be confusing people. i'd take pictures of the inside of my 
ex800... but... i don't want to confuse anyone ;)

i'd be surprised if it's dead. they're tough little synths. if it looks 
good, it should either work or be an easy fix.

keep us updated....


-- 
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 	 real American talk like that."
 		-- Frank Hague, Mayor, Jersey City, NJ
 		Addressing the Jersey City
 		Chamber of Commerce, 12 Jan 1938

Yeeeeeeeeeah!!! :DDDD

Pics and mp3s will follow soon :DD


Thanks a lot Atom Smasher!

Manu

On Mon, 1 May 2006, Manu wrote:

> Yeeeeeeeeeah!!! :DDDD
==================

so... um... how do you like it?


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 	Valerie Plame in the close confines of the White House:
 	"I don't know if we're going to find out the senior
 	 administration official. I don't have any idea."
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> so... um... how do you like it?

With milk and pizza :D

I have some pics, but no homepage to show it. I can email it to you if 
you want to include some pics in your page for extra clarity (and maybe 
correct me if I've made something in the wrong way). I've recorded a 
small mp3 to illustrate the results, too, and I'll record some more 
later. But now, I need my milk and my pizza :D

Manu

On Mon, 1 May 2006, Manu wrote:

>> so... um... how do you like it?
>
> With milk and pizza :D
>
> I have some pics, but no homepage to show it. I can email it to you if 
> you want to include some pics in your page for extra clarity (and maybe 
> correct me if I've made something in the wrong way). I've recorded a 
> small mp3 to illustrate the results, too, and I'll record some more 
> later. But now, I need my milk and my pizza :D
===============

yeah, send pictures and sample off-list, if you have them. i'm pretty sure 
the list doesn't allow attachments.

and check out <http://notmilk.com/>.


-- 
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pics and sample posted - http://synthmod.net/korg/fm800/notes/

thanks manu... send more samples if you can...


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more samples - http://synthmod.net/korg/fm800/notes/

thanks again manu!


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