[sdiy] [OT] Analog synths with 2 pole filters

Andrew Simper andy at cytomic.com
Fri Feb 22 15:20:10 CET 2013

On 22 February 2013 22:00, <rburnett at richieburnett.co.uk> wrote:
> Op-amps operated as finite-gain blocks will exhibit more phase-lag at high frequencies, so I would expect state-variable filters
> to be more inclined to self-oscillate at the high end of their cutoff frequency range than the low end.  Given that they are theoretically
> critically stable when there's no damping feedback, this effect should be quite noticeable.  Can anyone who's built one confirm or dispute this?

I can confirm that this is the case with my friend's Oberheim SEM,
which is I think one of the synths that prompted him to think that
"most" 2 pole filters didn't self oscillate. I'm not sure if this is
an original SEM or the recent re-make version.


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