[sdiy] which zener and current limiting resistor?

[keith sterling]

I have a synth with a +-15V supply and need 16 pots to wipe from 10V to 
GND and 2 pots to wipe from 5V to GND for cv generation.  So I think I 
need 2 zener diodes to generate the 10V and the 5V.  How do I calculate 
the size of the current limiting resistor and current rating of the 
diodes?  My supply doesn't have a lot of headroom so less current drawn 
is better.

I tried using a 2 resistor voltage divider but then every control 
affected all the other controls!  Pretty hard to dial in a sound that 
way!

cheers,
keith sterling