[sdiy] SVF resonance overdrive problem

[Harry Bissell Jr]

This circuit is really two independant VCFs...
one is a state variable (Odyssey) and the other
is a (oops... Moog) ladder LPF (ARP2600)

The SVF will have resonance above passband gain
(as mentioned earlier)

That said... I like the sound of an SVF... it gets
louder with higher resonance. And it will distort
if you push too far.

I wonder if in the original question... if the circuit
is using an OTA without the traditional attenuator
on the input. This would distort badly by the time you
reach 20mV ???

H^) harry


--- Andrew Simper <andy-list at vellocet.com> wrote:

> A slightly different configuration that the regular
> SVF is the ARP
> structure, which drives the input signal more than a
> regular SVF, but you
> only get a low pass output, and if my analysis is
> right a high/band pass
> output depending on resonance (output of first OTA).
> Here is a schematic:
> http://www.till.com/arptech/40235/40235.pdf
> 
> Andrew
> 
> -----Original Message-----
> From: Harry Bissell Jr
> [mailto:harrybissell at prodigy.net] 
> Sent: 11 December 2006 20:10
> To: Karl Ekdahl; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] SVF resonance overdrive problem
> 
> The most common SVF configuration has a resonant
> peak that exceeds the
> passband amplitude (the peak has MUCH higher gain).
> This is normal.
> 
> There is a way of injecting the input through the
> resonance path, which
> limits the peak amplitude to the same value. The
> passband amplitude goes
> down. This is how the Moog ladder filter behaves.
> 
> Another way is to introduce a "Q limiter" into the
> resonance feedback path.
> I use back to back zeners to increase the resonance
> feedback (lower Q) when
> the signal amplitude gets too high. (I use 5.1V
> zeners).
> 
> Typically, low frequency harmonics are stronger and
> tend to overload the
> filter. As the filter sweeps down, the zeners
> conduct and reduce the filter
> resonance.
> 
> This does NOT sound transparent... but it does stop
> the overload. I used the
> technique in my Hex Guitar processor (Muffy III)
> because I cannot fidget
> with signal levels while playing live. The "Q limit"
> saves the day at high
> resonance levels.
> 
> H^) harry
> 
> 
> 
> --- Karl Ekdahl <elektrodwarf at yahoo.se> wrote:
> 
> > Hi list,
> > 
> > i've built a OTA-based SVF whose resonance
> distorts heavily if i have 
> > to high input-volume. The problem is that "to
> high" is something like 
> > >20mVpp so that won't do. Can anyone give me a
> hint on what's wrong, 
> > is this a common problem with SVFs?
> > 
> > Karl
> > 
> > 
> > 	
> > 	
> > 		
> >
>
_________________________________________________________
> > Flyger tiden iväg? Fånga dagen med Yahoo! Mails
> inbyggda kalender. 
> > Dessutom 250 MB gratis, virusscanning och
> antispam. Få den på: 
> > http://se.mail.yahoo.com
> > 
> 
> 
> 
> 
> 
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.409 / Virus Database: 268.15.15/581 -
> Release Date: 09/12/2006
> 
> 
> 
> 
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.1.409 / Virus Database: 268.15.15/581 -
> Release Date: 09/12/2006
> 
> 
> 
>