[sdiy] MS-20 Filter Clone Queries

[Tim Stinchcombe]

> > Also, this schem says it runs on +/-12V, while I'd been planing on a
> > +/-15V standard for my system. In general, is current consumption
> > the main issue for running at 12V? What needs to be changed if I
> > want to run the filter at 15V?
> 
> 
> Only thing I think you'd really need to change is R6. U1b is keeping  
> the top of R6 at virtual ground, so the -12 and ground through the  
> 470K resistor create a reference current. If you change to a 
> -15, I'd  
> change the 470K to something else that maintains more or less 
> the same  
> current. <<snip>>

I was going to say as much myself last night, but Aaron beat me to it.
However on checking a little more, I note that Rene's original specified
that value for R6, and it already ran off +/-15V, and indeed so did the
original Korg circuit. With those values in the circuit, assuming pot T1 has
been set to give 1V/octave, a 2V control input should give a cut-off of
around 8.5kHz; with a CV in of -7V the cut-off is around 16Hz. This may
account for the funny arrangement of T2/T3/P3 - for my money I'd have a
separate preset across the rails to offset this, to give a more tractable 0
to 10V CV in range, say.

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk
www.timstinchcombe.co.uk