[sdiy] Hex Inverter VCF Idea

[adam at hoodmusic.net]

I did not expect this to get to much of a range, I was thinking it would make a
nice little simple box that would have a nice sound when over driven, mainly I want
something grossly lofi to match my guitar amp. Would there be any advantages in
useing the 4069 instead of the 4049? I have always used the 4049 since I have a
bunch of them.

adam

harry wrote:

> It looks like it could work... but with a limited tuning range and small
> signal handling capability (easily overloaded, probably noisy)
>
> The 'hidden weenie' is the fixed resistors in series. These will set the highest
>
> cutoff frequency... so you want them small. Then you need to suck lots of
> current away from the integrators with the FETs.  I suspect you will need a
> series
> resistor after the FETs as well... sort of a tee attenuator.
>
> In the phaser case... the input impedance of the opamp where the FET shunt is
> connected is very high... in the integrator case... it is very low. The phaser
> does not need a very large tuning range to be effective. Usually you want the
> notches to move
> a couple of octaves at most.
>
> You'd wish you could put the FET in series rather than shunt... but you probably
> can't with the 4049.
>
> I'd say... try it. If it works you'll be a hero... if not you'll be a guru (of
> how/why not to
> do it)
>
> H^) harry
>
> adam at hoodmusic.net wrote:
>
> > I found this in a note book that is about 5 or 6 years old, i am not sure
> > where i got the idea or what it came from,if anything. I just came accross
> > it and found it to be a intresting idea and wanted to see if it was
> > something actualy worth working with. I vaugly remember a phaser that used a
> > 4049 in this manner so i might have gotten that part of it from there, but i
> > really am not sure. All that was in the notebook was what you see at the
> > link, something i drew in school.
> >
> > adam
> >
> > Scott Gravenhorst wrote:
> >
> > > Is this your design?
> > >
> > > adam at hoodmusic.net wrote:
> > > >I found this idea for a 4-pole VCF with VC resonance and a VCA on the
> > > >output in one of my old note books. It uses 2 hex inverters, one for the
> > > >4 stages of the VCF and the VCAs for the resonance loop and output VCA,
> > > >and the other hex inverter is used as six FETs to very the resistance of
> > > >of each stage of the VCF and the VCAs. It is just a rough drawing, and
> > > >is far from a working filter. I wanted to know if it had any chance of
> > > >ever working before I started trying stuff ut in the real world.
> > > >
> > > >http://synth.massiva.com/vcf-4049.jpg
> > > >
> > > >adam
> > > >
> > >
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