I don't have the E-MU HPF schemo here, but I do have the LPF schemo.
It's a somewhat typical transistor ladder design. However, their
philosophy was very much a high fidelity approach, instead of
allowing filter overdrive. My E-MU filter sounded full but clean. It
doesn't surprise me that they would leave res off of the HPF to avoid
distortion.
Their UAF filter (state variable) had somewhat more individual
character, with that cool kbd percussion/final Q arrangement.
Moe
>>>>
revtor@a... schrieb:
> Hey, I was reading the great EMU modular guide pdf doc,
> and noticed that their HPF didn't have res control
> because it introduced distortion. How's our friend the
> 420 do in this respect in HP mode? Don't have one (yet)
> to fiddle with but I was just wondering..
I don't have the EMU docs in front of me (and yes,
that's some excellent reading !). But in general,
the main reason for reluctance to give a 4pole
HPF resonance or even self oscillation, is
that unlike a 4pole HPF, the oscillation is not
pure, or there would be oscillations at higher
frequencies rather than the desired cutoff frequency.
This is a general problem of "polygon" type HP
filters, as Bernie Hutchins showed in an old
electronotes article. (Sorry, don't know the number.)
<<<<