<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">too many replies, sorry! <div class=""><br class=""></div><div class="">I goofed, the spread is more like 300mV. if you barely tweak the bottom resistor, you can narrow it to ~120mV. If you tweak your expectations, you can use whatever lol <br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Dec 3, 2020, at 6:45 PM, David G Dixon <<a href="mailto:dixon@mail.ubc.ca" class="">dixon@mail.ubc.ca</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div dir="ltr" align="left" class=""><font color="#0000ff" size="2" face="Arial" class=""><span class="869543400-04122020">Here's my schematics (attached as PNG files). The
trapezoid generator (picture 2) looks remarkably similar to Chris
McDowell's. These schematics were generated in
Multisim.</span></font></div>
<div dir="ltr" align="left" class=""><font color="#0000ff" size="2" face="Arial" class=""><span class="869543400-04122020"></span></font> </div>
<div dir="ltr" align="left" class=""><font color="#0000ff" size="2" face="Arial" class=""><span class="869543400-04122020">On the Control schematic (picture 1), the pot on the
left is the Width control, and the pot in the centre is the Fader. Both
are subject to voltage control (as indicated by the little function generator
graphics). The 1.87k resistor on the Width pot is to limit the
upper voltage to about 10V, and the weird buffer circuit on the bottom of the
Fader pot is to set the bottom fader voltage to -12mV.
Originally I had this grounded, but the voices wouldn't shut off completely
when the fader was all the way down if the Width control voltage was low.
Putting this tiny buffered voltage there fixed it, and I had a spare opamp
on the board, so no worries.</span></font></div>
<div dir="ltr" align="left" class=""><font color="#0000ff" size="2" face="Arial" class=""><span class="869543400-04122020"></span></font> </div>
<div dir="ltr" align="left" class=""><font color="#0000ff" size="2" face="Arial" class=""><span class="869543400-04122020">The opamp with the 9.09k resistors is there
to apply a linear transformation to the Width voltage. This
linear equation is V_2 = (V_1 + 2)*5/11. This voltage becomes the
upper voltage on the Fader pot, and that is what guarantees that the
trapezoids fit nicely into the Fader window at all Width settings.
This voltage also drives a linear VCA which scales the incoming Fader control
voltage so that this CV has the same effect on channel scanning regardless
of the Width setting. </span></font></div><br class="">
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<font size="2" face="Tahoma" class=""><b class="">From:</b> Dakota Melin [<a href="mailto:dksynth@gmail.com" class="">mailto:dksynth@gmail.com</a>]
<br class=""><b class="">Sent:</b> Thursday, December 03, 2020 10:38 AM<br class=""><b class="">To:</b> David G
Dixon<br class=""><b class="">Subject:</b> Re: [sdiy] CEM3340 question -- interpolating scanners
(again)<br class=""></font><br class=""></div>
<div class=""></div><span style="background-color: rgb(255, 236, 179); font-size: 12px;" class=""><span style="background-color: rgb(255, 236, 179); font-size: 12px;" class=""><span style="padding: 3px; line-height: 1.6; background-color: rgb(255, 236, 179); font-style: normal; font-size: 12px; font-weight: normal;" class="">[<strong class="">CAUTION:</strong>
Non-UBC Email]</span></span></span>
<div dir="auto" class="">Would love to see these new scanner schematics! </div>
<div dir="auto" class=""><br class=""></div>
<div dir="auto" class="">-dk</div>
<div class=""><br class="">
<div class="gmail_quote"> </div></div></div>
<span id="cid:2F929279-59DF-4F8B-83DD-471201021BFE@lan"><New Scanner Schematic 3.png></span><span id="cid:ED27DE9A-9D1C-4FAA-8CD2-A5998836EE12@lan"><New Scanner Schematic 1.png></span><span id="cid:1AECC4D3-6C7A-4C3F-9213-D84D4A062FD1@lan"><New Scanner Schematic 2.png></span>_______________________________________________<br class="">Synth-diy mailing list<br class=""><a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a><br class="">http://synth-diy.org/mailman/listinfo/synth-diy<br class="">Selling or trading? Use marketplace@synth-diy.org<br class=""></div></blockquote></div><br class=""></div></body></html>