TB303 filter

Jim Patchell patchell at silcom.com
Mon Jul 31 21:07:31 CEST 2000

Hairy Harry wrote:

> The State Variable filter does the reverse... as Q is increased the peak
> gets louder and the passband stays at the same level.
> Some hear the first as being "sounds the same" (not me) some call it
> "bass is reduced as Q increases" (that's what I hear) but this is
> subjective.
> The State Variable, because of the increased peak amplitude, IS likely to
> clip first. You need to reduce the input level as Q increases. The Ladder
> will not have this effect.

    Actually, you can do the same trick with a State Variable filter.  If you
look on page 19 of http://www.silcom.com/~patchell/smb1/smb.pdf, which is the
state variable filter on the synth I am building right now, if you use R334 for
the input, this is your standard state varible input where the passband gain
stays the same and the peak increases with higher resonance (Q).

    If you use U74/U72A (U72A also controls Q) path for the input, the gain of
the peak stays the same and the passband gain will decrease as increase

    I like to build in both options.  I prefer having the passband gain decrease
with Q, but that is my preference.  I like to have the option of changing my
mind (I would make a great polititian).

    -Jim (never could make up his mind).

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