[sdiy] Ms20 filter clone PBC?

[JH.]

>I remember coming up with similar conclusions, that the HP is actually
>more of a one pole.

No, it's still a 2-pole HPF, even though it's 6dB/Oct in HPF mode.
Must be a zero exactly compensating one of the (real) poles (as long as no 
feedback is applied).
But with feedback applied, the poles become complex, and you get resonance.

(You can actually measure a higher slope - like 8dB/Oct - near the resonance 
point in that case,
but that's an effect that happens in all resonant circuits, and isn't used 
to characterize the "slope", so
Ian is perfectly right with 6dB/oct.)

JH.