Minimoog VCF

[Rene Schmitz]

Hi Sean,

At 12:07 11.03.99 -0800, you wrote:
>Oh, gee, thanks.  I guess NOTHING I do is good enough, huh? Is that what
>you are trying to say?  Awww, ol' Sean just went and RUINED CHRISTMAS!!
>
>OK, total joke.  I didn't know that the version on my site didn't work
>reliably (I couldn't get it to work, but I suck at analog stuff). Mind
>if I put a link to your schematic on my page, in addition to the old
>links?

;) Sorry, I did not want to imply that there is something wrong with that
schemo. I couldn't get it to work either. But there must be a trick with
that four transistors of the output amp, there are drawn numbers at each of
them, 1 to 4, I could imagine they were thermally coupled or matched or
something, but that image leaves this open.
Of course feel free to put a link on that image! I uploaded a new version
with a minor error corrected. 

>
>This is definitely a part of the Minimoog sound, at least according to a
>very informative post by Michael Caloroso a few years back.  As the
>resonance amplitude decreases with lower frequencies, the amount of bass
>frequencies cut out below the resonance decreases also.  For lower
>cutoff frequencies, not only is the cutoff lower, but the energy below
>the cutoff point increases.  This is probably why the Minimoog is such a
>great bass synth: for resonant filter sweeps, there will be more
>"bottom" with a given amount of resonance than with a filter with
>constant resonance amplitude.  There will be lots of resonance for the
>attack and decay of the sound (the "zap" or "dmmp" part of the sound, if
>you will), but the sustain will have less resonance, and more bass.  The
>Moog Taurus' filter had a similar mechanism going on, while the Taurus
>II had a constant amplitude resonance filter; the original Taurus is
>supposed to be much "fatter," perhaps due to the filter quirks.

The tb-303 has also an AC-decoupled filter (funny, the time-constant is
aproximately the same!) What you say makes perfect sense and it describes
the sound, that I got. 

Bye 
 Rene 




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