[sdiy] SVF High Pass Mode not Cutting Off

[rob at emulatorarchive.com]

Hello list,
I have recently built a couple of 2-pole State Variable Filters (OTA 
designs either using BA6110 IC or transistor current mirror OTA)  and 
both have the same problem that in Low Pass mode the frequency cutoff is 
perfect and does its job, but in High Pass mode the filter will not 
cutoff and go into silence. Freq pot does modify the cutoff in HP, but 
not to full cutoff. Any ideas on whats wrong would be most gratefully 
received.

Many Thanks
Rob