TB303 filter

Don Tillman don at till.com
Tue Aug 1 07:57:55 CEST 2000

   Date: Mon, 31 Jul 2000 12:07:31 -0700
   From: Jim Patchell <patchell at silcom.com>

   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.

   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 resonance.

   I like to build in both options.  

The ARP 1047 "Multimode Filter/Resonator" module from the old ARP 2500
had both resonance modes switch selectable.

(It also had a number of cool features; voltage controlled Q, a second
switchable Q value under keyboard gating control, and variable notch
frequency relative to the tuning frequency.  Really impressive module.)

  -- Don

Don Tillman
Palo Alto, California, USA
don at till.com

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