Doepfer

> understood that the a108 can be overdriven to make dirty sounds.  

Any filter can be overdiven. Just exceed the headroom of the circuit 
and with your signal and: viola! distortion.  Of course, the subtle 
characteristics of the distortion are dependant on many factors. 

You can also use the Doepfer A119 to increase a signal to coax 
distortion from your filters.

Good luck,

Matthew