I have an Octave Cat SRM with the SSM2040 filter chip, and a MOTM 440 filter. I can vouch for the fact that the 440 filter in the 'normal' mode sounds (timbral response) just like the SSM2040 LPF in the Cat. As I use it, the 440 has a quieter background, although I don't know if that is purely due to the filters themselves, or possibly the VCA and other signal paths in the Cat. You wouldn't really notice too much... until you listen to them side by side. I also notice when the Cat breaks into resonance at high Q, the oscillation is louder (but the same tone), and is a bit less controllable at the breakpoint than with the 440. The control aspect could be the age of the synth and the use of an old slider for resonance on the Cat vs. the better quality pot on the 440...I don't know. I haven't really explored if the two react the same to overdrive.
The 440 has also has a Bass switch you can flip to 'Enhance'. This makes the low end stay beefed up at higher cutoff and Q (compared to some loss of bass on the 'normal' 2040). Nice improvement, and you can always switch back to the true original response if you want. It's sort of like the loudness button on a stereo receiver.
John Blacet did a module back in the '70's called the 'Phase Filter'. I believe it configured the SSM2040 chip into different filter modes. I wonder if the MOTM 440 could be modified to do the same?
-Karl.
In a message dated 6/22/2007 1:08:33 A.M. Eastern Daylight Time, djhohum@... writes:
> This is hands down, my favorite filter. I wonder if the MOTM 440
> really sounds like the real thing?
I don't know, it would be interesting to hear from people who have
tried either the MOTM design and or JHs design next to the real thing.
It's certainly a filter worth building and if the discrete designs are
good, or perhaps even, perfect to human ears, then that makes sourcing
a real 2040 less important for diy efforts.