Minimoog VCF

[Fraser, Colin J]

> -----Original Message-----
> From: Sean Costello [mailto:costello at seanet.com]
> Sent: 12 March 1999 12:28
> To: tomg
> Cc: synth-diy at mailhost.bpa.nl; Rene Schmitz
> Subject: Re: Minimoog VCF
> 
> Just had an idea: To use the tomg filter design, but get that "phat"
> Minimoog bass sound, just change the coupling of the ladder 
> to the 3080
> diff amp. Instead of using direct coupling, couple the ladder to the
> diff amp with .22 uF caps, with 47k resistors going to ground between
> the caps and the 3080.  Heck, you could have this as a switchable
> option, for a constant resonance/Minimoog response option.  
> Seems easier
> to build than the Minimoog filter. (If this is a bad idea, hey, it's
> late at night, I've spent the last 18 hours modifying and 
> compiling a 60
> second composition that takes 15-20 minutes to compile, and I suck at
> analog circuits.) 

If you just want the filter resonance to reduce at low cutoff frequencies,
you could add voltage control of resonance, and modulate the resonance cv
with the filter cutoff cv. Then you would have variable control over the
amount of resonance loss at low frequencies, or even an inverse response -
more res at low fc.
I'll need to patch this up on my modular and see if it gives added 'phat'.


Colin f