<div dir="ltr">Same here Jimmy, I contacted Dave off list about it. I suspect that perhaps they exceed the size limits that Ben described earlier this week.<br><br>Pete</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Apr 21, 2020 at 3:58 PM Jimmy Moore <<a href="mailto:jamoore84@gmail.com" target="_blank">jamoore84@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Not sure if the issue is on my end, but the picture attachments aren't rendering. Anyone else?<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Apr 21, 2020 at 2:29 PM David G Dixon <<a href="mailto:dixon@mail.ubc.ca" target="_blank">dixon@mail.ubc.ca</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy">I just simulated the Thomas Henry
transistor-pair sine shaper, and compared the output to a 90-degree phase
shifted pure sine wave of equal amplitude. It is virtually impossible to
tell the two apart – THD = 0.57% -- light blue is the pure one, orange is the
shaped one.<u></u><u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy"><img width="545" height="452" id="gmail-m_-6116696493604605017gmail-m_-530258260745333728gmail-m_-4674945564304717009_x0000_i1026"><u></u><u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy">Here’s the sine shaper circuit I’m
simulating – this is exactly the circuit I build into all my VCOs (transistors
are 2N3904, opamp is TL07X – the 11k resistors get me closer to 10Vpp than 10k):<u></u><u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy"><u></u> <u></u></span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy"><img width="619" height="494" id="gmail-m_-6116696493604605017gmail-m_-530258260745333728gmail-m_-4674945564304717009_x0000_i1027"><u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy">In what way does the output of the diff
pair not look like a sine wave?<u></u><u></u></span></font></p>
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<p class="MsoNormal"><b><font size="2" face="Tahoma"><span style="font-size:10pt;font-family:Tahoma;font-weight:bold">From:</span></font></b><font size="2" face="Tahoma"><span style="font-size:10pt;font-family:Tahoma"> Synth-diy
[mailto:<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank">synth-diy-bounces@synth-diy.org</a>] <b><span style="font-weight:bold">On
Behalf Of </span></b>Donald Tillman<br>
<b><span style="font-weight:bold">Sent:</span></b> Tuesday, April 21, 2020
12:45 PM<br>
<b><span style="font-weight:bold">To:</span></b> René Schmitz<br>
<b><span style="font-weight:bold">Cc:</span></b> <a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a><br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [sdiy] An Improved
Sine Shaper Circuit</span></font><u></u><u></u></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">On Apr 17, 2020, at 8:53 AM, Donald Tillman <<a href="mailto:don@till.com" target="_blank">don@till.com</a>> wrote:<u></u><u></u></span></font></p>
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<u></u><u></u></span></font></p>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">On Apr 17, 2020, at 1:56 AM, René Schmitz <<a href="mailto:synth@schmitzbits.de" target="_blank">synth@schmitzbits.de</a>> wrote:<br>
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Interesting circuit, and a great article.<br>
I'm pretty sure I have seen a similar technique before, because I have used it.
(cusp canceling)<u></u><u></u></span></font></p>
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I am very familiar with cusp cancellation. I've used it also. And
it's mentioned in the article.<br>
This is not cusp cancellation.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">I'd like to expand on this for a moment...<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">I think the phrase "cusp cancellation" has, accidentally,
been misused a lot. And that's caused confusion.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">"Cusp cancellation" should mean that we've already got a
pretty good approximation going, but the cusps of the triangle are still coming
through a little bit. And we can cancel those by subtracting a small
amount of the original triangle wave. Sweet!<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">This would be because the transfer curve of the diff amp pair isn't
completely flat at the top and bottom. The tanh() curve is asymptotic,
so there will always be a little slope on the peaks.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">The most common next step is to apply negative feedback around the diff
amp pair. This could be in the form of a feedback resistor, or by adding
small emitter resistors. The negative feedback plumps up the curve and
flattens the slope at the peaks for a better overall fit. Nice!<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">But here, with the Colin/Henry/Guest/Tillman (Have I got everybody?
In order?) approach, the output of the diff amp pair isn't remotely close
to a sine wave. Not even trying. And none of us are using negative
feedback to plump out the curve. We're not in the cusp cancelling
business, we're doing something else.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">I got here by applying actual cusp cancellation to an actual diff amp
pair with negative feedback and a pretty good sine approximation. Then I
refined it with thousands of simulations, which lead me away from cusp
cancelling, and toward considering a compound curve of tanh(x) - βx, expressly
for the bumps and the sine shape in between. And the rest as I described.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">So I guess Dennis Colin (ARP, Aries) got to the circuit first.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">So, I'll claim that if a small amount of the original triangle wave is
subtracted from a wave that's roughly sinusoidal, then it's actual cusp
cancellation.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">But if the diff amp pair contribution doesn't look like a sine wave,
and there's no negative feedback, and the transfer function can be put into the
form tanh(x) - βx, then it's this other approach that Dennis Colin pioneered.<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt"> -- Don<u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="1" color="black" face="Menlo"><span style="font-size:9pt;font-family:Menlo;color:black">--<br>
Donald Tillman, <u></u><u></u>Palo Alto<u></u>, <u></u>California<u></u><u></u><br>
<a href="http://www.till.com" target="_blank">http://www.till.com</a><u></u><u></u></span></font></p>
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