[sdiy] Designing 4-pole filters with identical 2-pole stages - why not?

[Neil Johnson]

Hi Matthias,

> If designing 4-pole Butterworth filters using 2-pole Sallen-Key
> sections is to "specify what you want" and you then use tables or
> other design methods to end up with the answer Q=0.541 and Q=1.307,
> and you do this several times, wouldn't it be appropriate to call it
> "the usual way"? :-)

I take the view that folks far cleverer than me have done all the hard
thinking about this, so just read out the capacitor values from the tables,
scale for frequency and impedance, and job done.

There is the added benefit of knowing that if you have something on paper
that is not in the book then you're going to get something other than what
you wanted.

In simple terms: more time for smoothies :)

Neil
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