[sdiy] State Variable Filter Practical Maximum Q

[Scott Gravenhorst]

James Patchell <patchell at cox.net> wrote:
>Scott Gravenhorst wrote:
>> Hello all,
>>
>> Is there a practical maximum Q for an analog state variable filter?  I.e.,
>> a maximum Q value at which the filter is stable and won't self-oscillate.
>>
>The maximum Q of a State Variable Filter is very dependent on  the 
>quality of the active components in the circuit.  What you will notice 
>is that as the resonant frequency is increased, the Q  will increase 
>(refered to as Q enhancement).  The maximum Q will be dictated by the 
>open loop gain of the amplifiers.  So the two most important parameters 
>would be unity gain crossover and the open loop gain...(i.e..a 741 will 
>just not work as good as a TL071 which will not work as good as a ..... ).

Thanks Jim, that's sorta what I figured, noise generated by active components would be
something that would supply the energy to kick it into oscillation given enough gain at
high Q settings.  I assume this also applies to voltage controlled state variable filters.

-- ScottG
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