[sdiy]Do you need to add more functions to your favorite LP4P VCF ?

[Dave Manley]

m.bareille at free.fr wrote:
> http://m.bareille.free.fr/modular1/vcf_multimode/extrapole.htm
>   
I was curious about the performance of this circuit and ran spice on a 
few of the configurations.  AC analysis shows the response is very 
sensitive to component tolerance, and using 1% resistors can cause 
variation up to 30 dB at low frequencies in the 4P BP configuration (I 
set the RC value in the cells to 1K and 0.5u, and stepped the ABCD 
resistors, for example 100K simulated from 99K to 101K in steps of 
500).  If I get a chance I'll spice all the configurations.

I'd be interested in seeing the measured response of the real world 
circuit in various configurations.  I would think that the variation 
seen must cause an audible difference.  I guess it depends on what you 
want, but does this circuit need even tighter tolerance parts, or trimpots?

-Dave