SV: Re: SV: Re: SV: [sdiy] QVCO schemo up

[karl dalen]

--- Don Tillman <don at till.com> skrev:

> JH, Ian, SDIYers,
> 
>    > From: "JH." <jhaible at debitel.net>
>    > Date: Sat, 12 Nov 2005 16:04:55 +0100
>    > 
>    > > infact this cirquit is nothing more then a variation of the
>    > > SVF!
>    > 
>    > Sure - what else should it be?
> 
> Maybe it should be an actual Hopf Bifurcation device?
> 
> Ian, would you say that your approximation of the original equations
> has changed the circuit from being an actual Hopf Bifurcation device
> to a State Variable Filter oscillator?  
> 
> Why do a Hofp Bifurcation device at all?  Maybe it would be musically
> useful to disturb it from its oscillating state.  Any thoughts?

>    > It's a 2nd order differential equation in the most direct
>    > realisation.  If it's dampded, it's a filter. If it's not, it's
>    > an oscillator. The art lies in keeping it _just_ so undamped,
>    > that it oscillates without increasing amplitude.
> 
> Right.  There's a large class of circuits made from filters and
> feedback that will oscillate when you crank up the resonance.  That
> includes the Moog Ladder filter and State Variable Filters.

So a filter that oscillates is a oscillator
and a oscillator that dont oscillate is a filter?

What is then the moog source function generator when multipple triggered?
A oscillator, a function generator or a first order filter!?

All 3 are awfully close to be the same! No?

> It also includes the Wein Bridge oscillator in the famous original
> Hewlett-Packard audio oscillator, which used the heating of a light
> bulb filament to adjust the feedback and stabilize the amplitude.  And
> the phase-shift oscillator used in so many guitar amp tremelo
> circuits.  And twin-tee based oscillators.  And many more.

> So, the State Variable Filter oscillator is well known.  The question
> is, does Ian's variation of the stabilizer with the zeners provide
> better (or otherwise more musical) performance?  I dunno.
> 
> And...
> 
> One of the problems with filter-feedback oscillators is that they take
> a while to stabilize.  So, for instance, I would be interested in
> seing how Ian's circuit reacts to a large sudden step change in
>frecuency.

Im FM it now with a square, it jumps just as quickly as
a typical saw core would do to the same type of modulation.

KD