AW: Korg MS 20 Filter Differences

[JH.]

From: "Tim Stinchcombe" <>
>Only in as much that until the end of 2000, when Korg divulged the =
>circuitry
>inside the Korg35 'chip', the only way to find out was in there was to =
>have
>reverse-engineered one, by very carefully chipping the epoxy away (Paul
>Schreiber did this whilst developing the MOTM-420), whereas I suspect =
>the
>later OTA-based schematics have been around for many years before that.

Hmm ... it was me who developed the MOTM-420 circuit, and it's based on the later OTA filter version MS-20.
I happen to have a clone of the older Korg-35 filter in my JH-720 - maybe that's where the "epoxy" stuff comes from :)
I think the two filters sound remarkably similar, and the distortion is mostly created with diodes in *both* versions, so the
difference between the OTAs and the BJT transistors inside the Korg-35 may not make that much of a difference in sound. The Korg-35
has the benefit of being an increadibly ingenious and unique way to build a filter from garden variety transistors (it's just
ordinary SMT components inside), while the OTA version has less CV feedthru.
Also, Korg used different VCAs, so a slight difference in sound my not only be due to the filters.

There's a paper somewhere on th ewab which makes an in-depth analysis of the minor differences between these filters, but I don't
have the  link at hand right now.

JH.

[Frank Vanaman]

Hi all--

I think JH did the MOTM-420 design?

Maybe this could be a case of "fractured history" that includes a
recollection of Old Crow (Scott Rider) deconstructing the Yamaha SY-2 and/or
GX-1 filters by using some sort of nasty solvent.

http://www.oldcrows.net/~oldcrow/synth/yamaha/cs80/ne_proj.html

Frank

-----Original Message-----
From: "Tim Stinchcombe"
>the only way to find out was in there was to =
>have
>reverse-engineered one, by very carefully chipping the epoxy away (Paul
>Schreiber did this whilst developing the MOTM-420

[john mahoney]

At 09:01 AM 11/5/2009, JH. wrote:
>... The Korg-35 ... [is] just ordinary SMT components inside...

What?! No, it can't be! Say it ain't so!

LOL.

John

[Tim Stinchcombe]

> >Only in as much that until the end of 2000, when Korg divulged the =
> >circuitry inside the Korg35 'chip', the only way to find out was in
> >there was to = have
> >reverse-engineered one, by very carefully chipping the epoxy
> away (Paul
> >Schreiber did this whilst developing the MOTM-420), whereas
> I suspect =
> >the
> >later OTA-based schematics have been around for many years
> before that.
>
> Hmm ... it was me who developed the MOTM-420 circuit, and
> it's based on the later OTA filter version MS-20. I happen to
> have a clone of the older Korg-35 filter in my JH-720 - maybe
> that's where the "epoxy" stuff comes from :)

Many apologies to Juergen for not properly crediting him with the design
effort, but I was basing my statement on this post to AH from way back in
March 1999:

http://search.retrosynth.com/ah/search/lookit.cgi?-v9903.1480

From that you will see that there is no acknowledgement of anyone else being
involved, and I simple assumed Paul was using MOTM in a collective sense,
hence the 'we'. There it clearly implies that the epoxy was removed (by
whatever means) to reveal the SMT device arrangement inside! (This was
'before my time' - I didn't get into synths until 2001 - so have no
first-hand knowledge from that time, and I have tried pretty hard to get my
facts straight by a fair degree of scouring the web, but it looks like on
this occasion I was a little askew!)

> There's a paper somewhere on th ewab which makes an in-depth
> analysis of the minor differences between these filters, but I don't
> have the  link at hand right now.

That'd be me I expect :-)

http://www.timstinchcombe.co.uk/synth/MS20_study.pdf

Tim
__________________________________________________________
Tim Stinchcombe

Cheltenham, Glos, UK
email: tim102@...
www.timstinchcombe.co.uk

[JH.]

>> Hmm ... it was me who developed the MOTM-420 circuit, and
>> it's based on the later OTA filter version MS-20. I happen to
>> have a clone of the older Korg-35 filter in my JH-720 - maybe
>> that's where the "epoxy" stuff comes from :)

>Many apologies to Juergen for not properly crediting him with the design
>effort, but I was basing my statement on this post to AH from way back in
>March 1999:
>
>http://search.retrosynth.com/ah/search/lookit.cgi?-v9903.1480

No problem. :)
I love both versions of the filter, BTW.

>> There's a paper somewhere on th ewab which makes an in-depth
>> analysis of the minor differences between these filters, but I don't
>> have the  link at hand right now.
>
>That'd be me I expect :-)
>
>http://www.timstinchcombe.co.uk/synth/MS20_study.pdf

Right!!  That's it! :)

JH.