[sdiy] Rick Jansen's Moog ladder filter design question... answers found.

[Jean-Pierre Desrochers]

> I'm about to build the modified Moog ladder filter you posted here:
> 
> http://dropmix.xs4all.nl/rick/Emusic/Moog/moogvcf_schematic.gif
> 
> I would like to change the resistor R15 2k37 1% for a 1k 1%
> 3300ppm tempco but this will change the overall A3 opamp gain
> and screw up the 1v/oct ratio on input called "KOV" and all
> the other CV inputs. Since I don't know the exact mv/oct
> value this schematic needs at Q1 base for a good oscillation
> tracking, can you help ? I think I'll just have to also
> change both P3 & R17 values right ? But to what values ?

I finaly found a schematic with what I needed.
http://www.bernacomp.com/elec/og2/og3_moogladder2.gif

The CV expo converter here uses 1k 3300ppm tempco
in its opamp feedback loop to drive a Moog ladder VCF
which has about the same parts as Rick Jansen's design..
Even the parts designators are the same.
http://www.bernacomp.com/elec/og2/og3_moogladder1.gif

This design has 1v/oct CV inputs (+CV1, +CV2) and that's what I needed.
I think I'll use Rick's VCF design (with bonus thermal CA3046 compen.)
but change the expo converter for Scott Bernardi's.

Best of both worlds...
Thanks for all helpers who replied.
JP