[sdiy] SVF resonance overdrive problem

[Dave Manley]

Harry Bissell Jr wrote:
> This circuit is really two independant VCFs...
> one is a state variable (Odyssey) and the other
> is a (oops... Moog) ladder LPF (ARP2600)
I have seen this schematic for the "40235" before but never really 
looked at it. 
The ladder circuit is different from the 4012 used in the 2600.  Reading
the notes I see it is actually the ladder filter from the Odyssey.

What purpose do the diode wired transistors u4a and u5a serve?

What does u6a do?

-Dave