AW: making LP filters into HP

[Haible_Juergen#Tel2743]

>             I guess what I'm really wondering is do state-variable
>   models have to be designed from the ground up as state variable or can
>   you "enhance" any LP filter to get a high pass response <<with>>
>   adjustable Q?

You can also get a HP response by switching each stage from
LP to HP: For HP, use the capacitor of each stage as input.
A 4p2t switch should work for the whole filter.
Resonance is possible in this configuration, but not as smooth as
in the LP case.
By tapping a common 4pole LP after the 1st, 2nd or 3rd stage
you get 6dB/12dB/18dB LP filter.
Especially the 6dB is nice, as it has resonance(!). I built this into
my OB-8.

JH.