[sdiy] Formant 24dB filter

[Grant Richter]

Try AC coupling the resonance feedback loop. Add a series capacitor to block
DC feedback.

> 
>> Has anyone who has built the Formant 24dB filter had a problem when the
>> filter tries to go into oscillation?  My filter seems to work perfectly well
>> most of the time, but if the 'Q' control is set to maximum and the Frequency
>> knob turned up, the filter just latched up rather than oscillates.
>> Admittedly, the construction manual states that a resistor in the feedback
>> circuit should be chosen so as to avoid oscillation.  However it doesn't say
>> bad things will happen if oscillation starts?
>