<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="">No, it’s not the size. If that were the case, the message would not have come through. It is probably some weirdness in the formatting itself. I’ve asked David a copy of the original message to check.<div class=""><br class=""></div><div class="">Ben</div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 21 Apr 2020, at 23:29, Pete Hartman <<a href="mailto:pete.hartman@gmail.com" class="">pete.hartman@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">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 class=""><br class="">Pete</div><br class=""><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" class="">jamoore84@gmail.com</a>> wrote:<br class=""></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" class=""><div class="">Not sure if the issue is on my end, but the picture attachments aren't rendering. Anyone else?<br class=""></div></div><br class=""><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" class="">dixon@mail.ubc.ca</a>> wrote:<br class=""></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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<div class=""><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class="">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 class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><u class=""></u> <u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><img width="545" height="452" id="gmail-m_-6116696493604605017gmail-m_-530258260745333728gmail-m_-4674945564304717009_x0000_i1026" class=""><u class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><u class=""></u> <u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class="">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 class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><u class=""></u> <u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><img width="619" height="494" id="gmail-m_-6116696493604605017gmail-m_-530258260745333728gmail-m_-4674945564304717009_x0000_i1027" class=""><u class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><u class=""></u> <u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class="">In what way does the output of the diff
pair not look like a sine wave?<u class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="2" color="navy" face="Arial" class=""><span style="font-size:10pt;font-family:Arial;color:navy" class=""><u class=""></u> <u class=""></u></span></font></p>
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</span></font></div><p class="MsoNormal"><b class=""><font size="2" face="Tahoma" class=""><span style="font-size:10pt;font-family:Tahoma;font-weight:bold" class="">From:</span></font></b><font size="2" face="Tahoma" class=""><span style="font-size:10pt;font-family:Tahoma" class=""> Synth-diy
[mailto:<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank" class="">synth-diy-bounces@synth-diy.org</a>] <b class=""><span style="font-weight:bold" class="">On
Behalf Of </span></b>Donald Tillman<br class="">
<b class=""><span style="font-weight:bold" class="">Sent:</span></b> Tuesday, April 21, 2020
12:45 PM<br class="">
<b class=""><span style="font-weight:bold" class="">To:</span></b> René Schmitz<br class="">
<b class=""><span style="font-weight:bold" class="">Cc:</span></b> <a href="mailto:synth-diy@synth-diy.org" target="_blank" class="">synth-diy@synth-diy.org</a><br class="">
<b class=""><span style="font-weight:bold" class="">Subject:</span></b> Re: [sdiy] An Improved
Sine Shaper Circuit</span></font><u class=""></u><u class=""></u></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">On Apr 17, 2020, at 8:53 AM, Donald Tillman <<a href="mailto:don@till.com" target="_blank" class="">don@till.com</a>> wrote:<u class=""></u><u class=""></u></span></font></p>
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<u class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">On Apr 17, 2020, at 1:56 AM, René Schmitz <<a href="mailto:synth@schmitzbits.de" target="_blank" class="">synth@schmitzbits.de</a>> wrote:<br class="">
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Interesting circuit, and a great article.<br class="">
I'm pretty sure I have seen a similar technique before, because I have used it.
(cusp canceling)<u class=""></u><u class=""></u></span></font></p><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class=""><br class="">
I am very familiar with cusp cancellation. I've used it also. And
it's mentioned in the article.<br class="">
This is not cusp cancellation.<u class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">I'd like to expand on this for a moment...<u class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">I think the phrase "cusp cancellation" has, accidentally,
been misused a lot. And that's caused confusion.<u class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class=""><u class=""></u> <u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">"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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class=""><u class=""></u> <u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">So I guess Dennis Colin (ARP, Aries) got to the circuit first.<u class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class="">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 class=""></u><u class=""></u></span></font></p>
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<div class=""><p class="MsoNormal"><font size="3" face="Times New Roman" class=""><span style="font-size:12pt" class=""> -- Don<u class=""></u><u class=""></u></span></font></p>
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<div style="font-variant-caps:normal;text-align:start;word-spacing:0px" class=""><p class="MsoNormal"><font size="1" face="Menlo" class=""><span style="font-size: 9pt; font-family: Menlo;" class="">--<br class="">
Donald Tillman, <u class=""></u><u class=""></u>Palo Alto<u class=""></u>, <u class=""></u>California<u class=""></u><u class=""></u><br class="">
<a href="http://www.till.com/" target="_blank" class="">http://www.till.com</a><u class=""></u><u class=""></u></span></font></p>
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