Self-oscillating State Variable Filter

[osterchrisi]

Hey!

I'm building a voltage controlled state variable filter with vactrols and so far everything works out perfect. Nevertheless there's one wish my circuit doesn't fulfill me yet: self-oscillation. It oscillates at high audio frequencies but the lower I take the cutoff frequency the more the oscillation vanishes until a certain point, where it stops completely.

Is there any trick to get a SVF to self-oscillate 'better'?
Thanks a lot for any suggestions!!