[sdiy] OBX-a Poly mod

[Mattias Rickardsson]

On the topic of adding poly-mod to old polysynths:
A colleague of mine is reverse-engineering the Korg DW-8000 (hardware and
firmware) and just found both an unused 12dB/oct filtermode and a couple of
unused CVs on the board. One of these CVs could select filtermode and the
other control poly-mod amount to filters, globally. I hope to sketch him a
solution adding 2 x SSI2164 VCAs and analog switches on a small
daughterboard, and he could include these parameters in a new firmware.

But perhaps all synths don't have these hidden possibilities :-)

/mr

Den fre 3 okt. 2025 04:18brianw <brianw at audiobanshee.com> skrev:

> Agreed.
>
> If there is a schematic for any poly-mod, each OBX-a voice would require a
> VCA for mod depth, and a couple of analog switches to choose between filter
> envelope and OSC2 sources, plus some more analog switches to choose the
> destinations. Not only would the VCA need a dedicated CV in the patch, but
> those switches would need a few bits of storage to select the modulation
> path in each voice.
>
> Brian
>
>
> On Oct 2, 2025, at 6:36 PM, Michael E Caloroso wrote:
> > I have never heard of an OB-Xa mod that adds P5-style polymod.  Frankly
> it would be useless unless a new programmable CV for mod depth can be
> implemented.
> >
> > MC
> >
> > On Thu, Oct 2, 2025 at 3:14 PM ulfur hansson wrote:
> >> i came across this matrix-synth post that features images of an obx-a
> fitted with a mysterious JL-Cooper mod, allowing for prophet-5 style
> poly-mod.
> >>
> >> does anyone happen to have any information on the kits design?
> >>
> >> ...or if i should end up feeling brave and design a board to achieve
> something similar - any thoughts?
> >>
> >> thanks y'all!
> >> sincerely,
> >> -úlfur
>
>
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