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<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=917571417-04042017>The "sine wave" being generated by that 3RC circuit is
not very good, with 4 or 5% THD at best. A sine wave from a good
sine VCO would be less than 1%, and a self-oscillating filter sine can be
0.1%.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=917571417-04042017></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=917571417-04042017>Plus, this circuit only works at one frequency.
It would have to be redesigned for other frequencies.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=917571417-04042017></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=917571417-04042017>I just designed a circuit that works OK. You
simply take the square wave through a linear VCA (like a linearized 2164) and
into a Miller integrator. The integrator must be slightly "leaky" to
keep the resulting triangle wave centred about 0V -- maybe a 1nF cap and a 1M to
3.3M resistor across the feedback -- the bigger the resistor, the
straighter the sides of the triangle wave, but the slower the response.
Then, the gain of the linear VCA must be proportional to the frequency of the
square wave. This can be achieved with something like an LM331, or a
simple charge pump circuit will do (a couple caps, a diode, a transistor, a
resistor). The problem is that the "homemade" F2V converter might not have
a very good response time, so the triangle wave's amplitude will be all over the
map if the frequency changes suddenly.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2
face=Arial></FONT> </DIV>
<DIV dir=ltr align=left><SPAN class=917571417-04042017><FONT color=#0000ff
size=2 face=Arial>I'm still working out some quirks, but I'll report back when I
have something worth building.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2
face=Arial></FONT> </DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <B>On Behalf Of </B>Elaine
Klopke<BR><B>Sent:</B> Tuesday, April 04, 2017 3:33 AM<BR><B>To:</B>
synth-diy@synth-diy.org<BR><B>Subject:</B> [sdiy] Square to
Sine<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV>Does this actually work? </DIV>
<DIV id=AppleMailSignature><A
href="http://www.learningaboutelectronics.com/Articles/Square-to-sine-wave-converter-circuit.php">http://www.learningaboutelectronics.com/Articles/Square-to-sine-wave-converter-circuit.php</A></DIV>
<DIV id=AppleMailSignature><BR></DIV>
<DIV id=AppleMailSignature>I would assume that being 3 RC networks in series
means quite the drop in volume.</DIV>
<DIV id=AppleMailSignature><BR></DIV>
<DIV id=AppleMailSignature>Also, in a related article they show two networks
in series converting the square wave to a triangle. </DIV>
<DIV id=AppleMailSignature><BR></DIV>
<DIV id=AppleMailSignature>All of the converters being dependent on the
frequency of the input wave being roughly the same as what the RC networks are
tuned to. </DIV>
<DIV id=AppleMailSignature><BR></DIV>
<DIV id=AppleMailSignature>Thanks guys!<BR><BR>Sent from my
iPhone</DIV></BLOCKQUOTE></BODY></HTML>