UAF (was: Re: [sdiy] Another filter option...)

[jhaible]

> Another option I have for doing a VCF would be to base it on the
> old E-Mu Modular Universal Active Filter design. I'd need permission to
> release the design though, since Rossum put the guts of most of his most
> innovative stuff into potted modules.
>
> Any opinions on the UAF?

I played around with this one recently. The older version, with only one
opamp
in the signal path, and the integrators discreete. I ran into a problem with
the
LM318 opamps. These are very fast (for the time) opamps with internal
compensation for unity gain stability. But on my veroboard circuit, I ran
into stability problems. (Yes, I did care about bypassing caps etc.) Sure, I
got it stable, but not with the original component values. But all efforts
to
stabilize it will compromise speed, so I did not get the fabulous constant
Q over frequency range of the original. (I never had an original to compare,
but I think this, and the low noise, is what made it a standout SVF back
then.)

JH.