[sdiy] 2164 Korgasmatron VCF

[Stewart Pye]

Hi David,

Does your 2164 VCF sound like the LM13600 based Korg circuit?

Regards,
Stewart.


David G. Dixon wrote:
> I think I've figured out the panel for my 2164 Korgasmatron VCF.  It's
> amazing how laying out a panel sets strict limits on the functionality of a
> module.
>
> I've laid out the PCB for a three-input mixer, AC/DC input coupling switch,
> independent coarse and fine cutoff controls, 1V/oct + 2 CVs (one standard,
> one +/-), resonance controls and sine amplitude controls for both HP and LP
> stages.  However, to keep the panel from getting completely out of control,
> I've eliminated fine cutoff and standard CV controls (retaining the 1V/oct
> and +/- CV controls).  I've also given separate HP and LP outputs.  This
> gives 12 knobs, 10 jacks and 1 switch (!).  The panel is 3U wide in
> pseudo-MOTM format.
>
> I've been looking around at some other MS20 filter clones.  The "Analogue
> Solutions" one looks similar to mine in concept (albeit without the sine
> amplitude control, no mixer, and with an onboard VCA).  On the other end of
> the spectrum is the MOTM 420, which only emulates half of the MS20 filter,
> with a switch for selecting HP, LP, and N modes.  The website says that the
> HP and LP are 12dB and the N is 6dB.  However, in the original, the HP is
> actually 6dB at zero resonance, and increasing the resonance gives adds a
> 12dB BP response to the HP in a way which actually renders it difficult to
> classify in those terms.  In any case, to emulate a complete MS20 filter
> requires two MOTM 420s (which, at $339 each, makes for a pretty expensive
> filter indeed -- mine will cost about $90 to build).
>
> I'd like to hear some opinions on how useful the HP/LP/N switch is on the
> 420.  The sound samples are indeed impressive.  In the actual filter, one
> can get an HP by turning the LP cutoff all the way up, and LP by turning the
> HP cutoff all the way down.  N and BP responses are obtained by setting the
> HP and LP cutoffs low/high or high/low, respectively.  N/BP widths can be
> modulated by keeping one constant and modulating the other.  This gives an
> incredible range of timbre control.  I'm just wondering whether it would be
> worth it to make each stage multimode, or to leave them as is, as per the
> original.
>
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