<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr">Bingo! That’s mostly how I use it. There are lots of great phasey modulations possible. </div><div dir="ltr"><br></div><div dir="ltr">Ian</div><div dir="ltr"><br><blockquote type="cite">On Feb 19, 2020, at 10:39 AM, Ben Riggs <benalog1977@gmail.com> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><meta http-equiv="content-type" content="text/html; charset=utf-8">I have always liked the idea of a VC controllable ramp-tri-saw morph and have been playing with it for years.. but for a VCO. The thought for me was not the usefulness of the wave-morph itself but how it affected a pulse shaper, in that it would not only give VC pulse width but VC phase shift modulation.<div><br></div><div>No idea if it actually sounds useful though.</div><div><br></div><div>I had been trying to modify Sams idea to use AD633 instead of RC4200.. but there is always more pressing things going on in my life and I’ve got other unfinished projects before starting new ideas.</div><div><br></div><div>Ben.</div><div><div><br><div dir="ltr">Sent from my iPhone</div><div dir="ltr"><br><blockquote type="cite">On 18 Feb 2020, at 1:40 pm, ackolonges fds <ackolonges@hotmail.com> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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Thanks so much everyone for your input. <br>
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Those that mentioned digital options - yes indeed it's quite straightforward to implement such a thing via digital means, but I would like to try for the analogue route.
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Thanks a lot for that link to the SNICster Ian, that's a heck-of-a waveshaper!</div>
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It would indeed be great to find out how the Electrik Multiwaves implements this function, maybe if Vinicius see this he might be willing to let us know his approach.</div>
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Also a big thanks to Ben for alerting us to the Wave Morph website. They mention that the VCS3 uses such a circuit, but I was unable to find info on that because the link was broken. He has a hand-written sketch by Don Tillman, that I can't fully parse (does
anyone know if anyone ever built that one?), and mentions that Sam Houshu had a design of such a function but that link is also broken. His Wave Morph looks to do just what I'm after, but uses the RC4200, a long out-of-production chip. I'd much rather use
the LM13700 OTAs that I have plenty of, or a modern drop in replacement for the RC4200 if anyone knows if such a thing exists. He mentions an OTA version, but alas, another wrong link.
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So, I'm waiting with baited breath to see the magic that David has in mind!<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> David G Dixon <dixon@mail.ubc.ca><br>
<b>Sent:</b> Tuesday, February 18, 2020 6:53 PM<br>
<b>To:</b> 'ackolonges fds' <ackolonges@hotmail.com>; 'SDIY List' <synth-diy@synth-diy.org><br>
<b>Subject:</b> RE: [sdiy] LFO VC Skew?</font>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy">Nevermind. I think I might have figured it out. And the beauty of it is that I think I can do it by adding one very simple component to a linearized 2164
VCA circuit.</span></font></p>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy">The trick is that if the log of X is log X, then the log of 1/X is –log X. Look at Mike Irwin’s article and see what I saw, and how it can easily be done.</span></font></p>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy">Now I feel even more stupid for not seeing that three years ago, when I was struggling with this. Now I should have a design ready by tomorrow. Stay tuned.</span></font></p>
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<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>David G Dixon<br>
<b><span style="font-weight:bold">Sent:</span></b> Monday, February 17, 2020 6:37 PM<br>
<b><span style="font-weight:bold">To:</span></b> 'ackolonges fds'; 'SDIY List'<br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [sdiy] LFO VC Skew?</span></font></p>
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<font size="2" face="Arial" color="navy"><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.</span></font></p>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy"> </span></font></p>
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<font size="2" face="Arial" color="navy"><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.</span></font></p>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy">It is probably easily done digitally, but where’s the fun in that?</span></font></p>
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<font size="2" face="Arial" color="navy"><span style="font-size:10.0pt; font-family:Arial; color:navy">Unless I’m dumb.</span></font></p>
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<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></p>
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<font size="3" face="Calibri" color="black"><span style="font-size:12.0pt; font-family:Calibri; color:black">Hi All,</span></font></p>
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<font size="3" face="Calibri" color="black"><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.</span></font></p>
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<font size="3" face="Calibri" color="black"><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?</span></font></p>
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<font size="3" face="Calibri" color="black"><span style="font-size:12.0pt; font-family:Calibri; color:black">Thanks a lot for any input
</span></font><font face="Calibri" color="black"><span style="font-family:Calibri; color:black"><span id="x_🙂">🙂</span></span></font><font face="Calibri" color="black"><span style="font-family:Calibri; color:black"></span></font></p>
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