[sdiy] Polymoog resonator question
Donald Tillman
don at till.com
Sun Oct 7 04:51:57 CEST 2018
> On Oct 6, 2018, at 5:56 PM, rsdio at audiobanshee.com wrote:
>
> I tried this is Grapher, but need some hints. Is C in farads or nanofarads? What about s? Also, there aren’t enough parentheses for me to tell whether sC is in the numerator or denominator.
No, I totally goofed. Let's try that again:
This is for the pots tuning the integrators on the Polymoog filters:
Open up a new graph plot, lin-log.
Use this equation:
y = Rmin / (Rpot(1-x) + Rmin)
Or for this case, a 2.4K resistor in series with a 10K pot:
y = 2400 / (10000(1-x) + 2400)
X is the pot turning (0 to 1).
Y is the log of the attenuation.
Set it to only show the x values from 0 to 1 (View -> Frame Limits).
This is the loss the pot adds, going from full CCW to full CW.
It's not a straight line, but it's plenty close.
And you can compare it to a regular passive attenuator with the same values. Add a second equation, use the condition operator:
y = (1/(Rpot + Rmin)){(2x-1)Rpotright + Rpotleft + Rmin for 0.5 <= x
(2x)Rpotleft + Rmin for x < 0.5
For a 10K audio taper pot split 17%/83% (pot left, pot right), and a resistor Rmin to ground:
y = (1/(10000 + 2400) {(2x-1)8300 + 1700 + 2400 for 0.5 <= x
(2x)1700 + 2400 for x < 0.5
Compare the two, and the first looks much better.
(They should begin and end at the same points.)
-- Don
--
Donald Tillman, Palo Alto, California
http://www.till.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20181006/2ed5214c/attachment.html>
More information about the Synth-diy
mailing list