[sdiy] which zener and current limiting resistor?

[Tim Parkhurst]

On 8/10/06, keith sterling <keithsterling at sbcglobal.net> wrote:
> 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
>

Hey Keith,

Have you tried a resistor on the wiper? I've seen several CV summers
done this way (one end of the pot tied to +V, other end of pot to GND,
wiper to R and the R to the CV input). For example, a "Coarse" tune
pot will have a 100K  in its connection to the summer, while the
"Fine" tune pot will have a 3Meg (or something in that neighborhood).
Seems to work well, just experiment with the R to get the right value.
BTW, I'm assuming you're limiting the CV just to limit the range (as
opposed to limiting the CV to avoid killing circuitry powered by +5V).


Tim (killed quite a bit of circuitry in my time) Servo
-- 
"Imagination is more important than knowledge." - Albert Einstein