TB303 filter

[Dan Gendreau]

-----Original Message-----
From: Jeroen Proveniers

>Hello,
>recently I've made the TB303 filter just to try it out, but I have a
problem.
>When I turn up the resonance I also get a 'basscut' effect, the sound gets
quite thin. I
>only used feedback to the filter, e.g only a single potentiometer, not a
dual type, and I
>only use the filter out (the upper side of the resonance pot). I used the
Oakley TB3030
>schematic. (I will build my own TB3030 very soon).
>The TB303 uses some form of Q compensation. Without, will I get the result
I have?
>So probably I must include a summing amplifier to sum filter out and
resonance?
>Anyway, I'm going to throw away this experimental board, and I'm planning
to build the
>Oakley VCF with a MIDI interface, but I just wanna know if I'm right...
>JJ


The filter in the TB3030 is based on the original Roland TB303. My 303
sounds the same when you turn up the resonnance. The Q compensation you
mention keeps the sound at the same relative volume level as you change the
Resonance. Rather than making the knee of the filter louder(as Q usually
does), it keeps the knee at the same loudness and reduces the low-pass
level. This is one part of the character of the TB303.

-Dan G.