[sdiy] SVF resonance overdrive problem

[Harry Bissell Jr]

Not sure if I understood your comment...

The capacitors to ground, driven by a current
source (OTA output) form a classic non-inverting
integrator. Adding a resistor would make it a
"lossy integrator" (ie a low pass filter). The circuit
relies on feedback to remain stable. Resistors to
ground on the outputs are not needed.

Another configuration uses the current source to feed
the inverting input of an opamp, with capacitor
feedback to make an inverting integrator

H^) harry



--- Paul Perry <pfperry at melbpc.org.au> wrote:

> As I said before, i don't believe a 3080 or other
> OTA
> will be happy wiht the output just floating around.
> See, for example, this
>
http://hem.bredband.net/bersyn/VCA/ca3080%20vca%201.htm
> from one of the masters :D Note the 47K to ground.
> Since the OTA is a current amplifier, if you want a
> voltage from it,
> you have to run the output current thru a resistor
> to develop it.
> 
> The buffers & diode inputs aren't the main problem.
> 
> paul perry Melbourne Australia
> 
> ----- Original Message ----- 
> >Unfortunley i do not have a schematic, it's based
> on
> >this circuit
> >http://www.synthdiy.com/show/getfile.asp?get=23
> >I've used LM13700s with the + input grounded,
> leaving
> >buffers and linearization diode inputs unused.
> Could
> >that be a problem?
> 
> Karl
> 
> --- Andrew Simper <andy-list at vellocet.com> skrev:
> 
> > Which circuit are you basing your SVF on? Can you
> > please post a link to the
> > schematic here? Have you checked the SEM SVF
> > schematic
> > (http://www.synthfool.com/schematics/sem.gif)?
> > Forget about the ARP one if
> > you want lower distortion - it actually drives
> more
> > and you loose resonance
> > more quickly, I didn't read you're email properly
> > last night when I was
> > tired. The regular SVF like the SEM keep strong
> > resonance no matter what
> > input level you have.
> >
> > Andrew
> >
> > -----Original Message-----
> > From: Karl Ekdahl [mailto:elektrodwarf at yahoo.se]
> > Sent: 11 December 2006 19:44
> > To: synth-diy at dropmix.xs4all.nl
> > Subject: [sdiy] SVF resonance overdrive problem
> >
> > 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
> >
> >
> >
> >
> >
> >
>
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> >
> 
> 
> 
> 
> 
> 
>
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>