[sdiy] Korg Volca Bass service manual

[synth at schmitzbits.de]

I have one of these, although it currently suffers from non functioning buttons (like many other volcas).
The filter is 12dB. And IMO the Volca Bass distorts too much. Especially if you combine the three VCOs.
Might not be from the filter but the VCA actually.

The VCF is derived from the Korg 700 AFAIK. It's also similar in construction to the MS50 Filter.
Note that there is no trimming, but everything comes from the uC via PWM.
So the VCOs are retuned by that.

Cheers,
 René


________________________________
Von: Synth-diy <synth-diy-bounces at synth-diy.org> im Auftrag von Roman Sowa via Synth-diy <synth-diy at synth-diy.org>
Gesendet: Dienstag, 27. Oktober 2026 09:47
An: Sean Ellis <tensiontype at hotmail.com>; Synth-diy Mailing List <synth-diy at synth-diy.org>
Betreff: Re: [sdiy] Korg Volca Bass service manual

The VCF is taken from early Korgs. This is more or less what's inside
those Keio submodules.
Using logic Schmitt inverter is not such a bad idea and seen in many
simple designs. Although not even specified in datasheet, the trippoint
of modern Schmitt devices is pretty stable.
What's more interesting is the use of the-cheapest-of-all LM324 for
everything except when low Ib is the key factor

Roman


W dniu 2026-10-26 o 22:00, Sean Ellis via Synth-diy pisze:
> https://cdn.hackaday.io/files/1698407266434560/korg_volca_bass_sm.pdf
> <https://cdn.hackaday.io/files/1698407266434560/korg_volca_bass_sm.pdf>
>
> Not sure if this has been shared but here's the manual, as usual some
> interesting circuits from Korg. Schmitt-trigger in the VCO and a very
> low parts count on the VCF, not a trimpot on board! Has anyone heard one
> of these? I'd be interested in how the filter sounds.
>
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