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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’ve struggled with this mightily and come
to no solution in the analog realm. The problem is that there seems to be
no way to implement the magic of a potentiometer fed on both ends with VCAs.
I’ve been through the math, and it seems impossible. The original
circuit (two diodes and a potentiometer in the loop of a tri-square oscillator)
is so simple and elegant, and yet so elusive for voltage control, other than
physically rotating the damn pot with a servo.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>It’s easy to get saw-to-tri-to-ramp with
VCAs, but the trick is to maintain the same frequency when you do so. That’s
the impossible part.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>It is probably easily done digitally, but where’s
the fun in that?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Unless I’m dumb.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>ackolonges fds<br>
<b><span style='font-weight:bold'>Sent:</span></b> Monday, February 17, 2020
6:02 AM<br>
<b><span style='font-weight:bold'>To:</span></b> SDIY List<br>
<b><span style='font-weight:bold'>Subject:</span></b> [sdiy] LFO VC Skew?</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'>Hi All,<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'>I'm a big fan of the 'skew'
(sweep from sawtooth, through triangle, over to ramp wave) function of some
analogue LFOs and find it indispensable. I would love to be able to CV the skew
function though it generally doesn't seem to be an option. Some circuits seem
to control skew by having a pot control the balance between current flowing
each direction via two diodes with opposite polarity (eg. the MFOS VCLFO
circuit, or the Nicolas Woolaston LFO circuit), which seems like a particularly
tricky thing to be able to voltage-control.<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'>I was wondering if
anyone here knows of any existing circuits which provide that functionality, or
have any ideas as to how one may go about making it happen?<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face=Calibri><span
style='font-size:12.0pt;font-family:Calibri;color:black'>Thanks a lot for any
input </span></font><font color=black face=Calibri><span style='font-family:
Calibri;color:black'><span id="🙂">🙂</span></span></font><font color=black
face=Calibri><span style='font-family:Calibri;color:black'><o:p></o:p></span></font></p>
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