[sdiy] SVF High Pass Mode not Cutting Off

[Magnus Danielson]

On 10/29/2011 02:51 PM, rob at emulatorarchive.com wrote:
> 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.

Sounds like the upper frequency limit is set too low, such that you 
saturate too early. Shift the filter capacitors to move the filtere up 
in frequency should require less current for the same frequency and 
hence the saturation current would give a high cut-off to "close" the 
filter.

So, try swapping in smaller integrator capacitors to achieve this.

Cheers,
Magnus