[sdiy] OBX-a Poly mod

[doug at synthark.com]

Yes, the DW-8000 uses the same filter as the DSS-1, but only the DSS-1 
implements the 2/4-pole filter mode.  The Poly-800 uses the same filter 
too, which is why a switch for the filter mode is a common mod (since it 
only uses one filter for all voices).  I'm curious what your colleague 
comes up with for the DW-8000 mods!

---
Doug Huseby
http://synthark.com
http://synthark.org


On 2025-10-03 01:04, Mattias Rickardsson wrote:
> 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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