<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Oct 6, 2018, at 5:56 PM, <a href="mailto:rsdio@audiobanshee.com" class="">rsdio@audiobanshee.com</a> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">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.<br class=""></div></div></blockquote><br class=""></div><div>No, I totally goofed. Let's try that again:</div><div><br class=""></div><div>This is for the pots tuning the integrators on the Polymoog filters:</div><div><br class=""></div><div>Open up a new graph plot, lin-log.</div><div><br class=""></div><div>Use this equation:</div><div><br class=""></div><div> y = Rmin / (Rpot(1-x) + Rmin)</div><div><br class=""></div><div>Or for this case, a 2.4K resistor in series with a 10K pot:</div><div><br class=""></div><div> y = 2400 / (10000(1-x) + 2400)</div><div><br class=""></div><div>X is the pot turning (0 to 1).</div><div>Y is the log of the attenuation.</div><div><br class=""></div><div>Set it to only show the x values from 0 to 1 (View -> Frame Limits).</div><div><br class=""></div><div>This is the loss the pot adds, going from full CCW to full CW.</div><div><br class=""></div><div>It's not a straight line, but it's plenty close.</div><div><br class=""></div><div>And you can compare it to a regular passive attenuator with the same values. Add a second equation, use the condition operator:</div><div> </div><div>y = (1/(Rpot + Rmin)){(2x-1)Rpotright + Rpotleft + Rmin for 0.5 <= x</div><div> (2x)Rpotleft + Rmin for x < 0.5</div><div><br class=""></div><div>For a 10K audio taper pot split 17%/83% (pot left, pot right), and a resistor Rmin to ground:</div><div><br class=""></div><div>y = (1/(10000 + 2400) {(2x-1)8300 + 1700 + 2400 for 0.5 <= x</div><div> (2x)1700 + 2400 for x < 0.5 </div><div><br class=""></div><div class=""><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;">Compare the two, and the first looks much better.</div><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;"><br class=""></div><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;">(They should begin and end at the same points.)</div><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;"><br class=""></div><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;"> -- Don<br class="">--<br class="">Donald Tillman, Palo Alto, California<br class=""><a href="http://www.till.com" class="">http://www.till.com</a></div>
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