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

[cheater cheater]

Other than cutting off the caps off the feedback or using *just* the
caps, has anyone tried other nonlinearities? Softer ones perhaps, such
as soft clipping (arctan) or soft expanding (tan)?

Regarding cutoff-dependent resonance, wouldn't an LR or "solid state
LR" filter in the feedback loop be able to provide the right kind of
compensation?

Cheers,
D.

On Sat, Feb 23, 2013 at 12:57 AM, David G Dixon <dixon at mail.ubc.ca> wrote:
>> > This is absolutely what I found with the SSM2164 SVF. It
>> squeals like hell at the top, but getting a reliable
>> oscillation down to the lowest frequencies requires a lot more gain.
>> >
>> > Dave Dixon and Olivier Gillet and I all shared notes on
>> this filter, so perhaps they have something to add on this
>> point? -Guys?
>
> I can corroborate this observation.  Use high quality, low-leakage caps
> (polystyrene, high quality polypropylene) for a start.  I prefer
> double-ranging my oscillating filters, using 100x larger caps for LFO-range
> oscillation.
>
> Also, concerning using zeners in the BP feedback, I was originally concerned
> because this also limits the amplitude of the filter even when it isn't
> oscillating.  However, given the propensity for the 2164 SVF to give very
> high amplitudes at high (but sub-oscillatory) resonance, I found the zeners
> to be generally desirable.  We've certainly had no complaints with our
> eurorack SVF filter in this regard.
>