<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr">This is all very helpful. Thank you all!</div><div dir="ltr"><br><blockquote type="cite">On Feb 9, 2020, at 12:10 PM, Jacob Watters <jacobwatters@gmail.com> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><div dir="auto">You could always try switched resistors instead. Then you use pwm to control the duration each resistor is in place. The clock frequency should be well above the audio range.</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun., Feb. 9, 2020, 12:53 p.m. Tom Wiltshire, <<a href="mailto:tom@electricdruid.net">tom@electricdruid.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space"><div>Yes, I agree! So we’ve found two examples for you, Didier! Phasers and OTA filters both use the OTA like a variable resistance.</div><div><br></div><div>Tom<br><div><br><div>
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<div><br><blockquote type="cite"><div>On 9 Feb 2020, at 12:16, Richie Burnett <<a href="mailto:rburnett@richieburnett.co.uk" target="_blank" rel="noreferrer">rburnett@richieburnett.co.uk</a>> wrote:</div><br><div><div>The OTA acts as a variable resistor here:<br><br><a href="https://electricdruid.net/wp-content/uploads/2017/04/CEM3320LowpassFilterStage.png" target="_blank" rel="noreferrer">https://electricdruid.net/wp-content/uploads/2017/04/CEM3320LowpassFilterStage.png</a><br><br>-Richie,<br><br><br><br>-----Original Message----- From: Tom Wiltshire<br>Sent: Sunday, February 09, 2020 11:40 AM<br>To: Didier Leplae<br>Cc: Synth DIY<br>Subject: Re: [sdiy] LM13700 as VC resistor<br><br>OTA-based phaser designs are about the only application I can think of where the OTA functions like a resistor rather than a VCA. Even then it’s perhaps arguable.<br><br>Have a look at schematics for the EH Small Stone and the many subsequent derivatives.There’s also a good explanation on R.G.Keens page about phasers:<br><br><a href="http://www.geofex.com/article_folders/phasers/phase.html" target="_blank" rel="noreferrer">http://www.geofex.com/article_folders/phasers/phase.html</a><br><br>HTH,<br>Tom<br><br><br>==================<br> Electric Druid<br>Synth & Stompbox DIY<br>==================<br><br><br>On 8 Feb 2020, at 09:58, Didier Leplae via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" target="_blank" rel="noreferrer">synth-diy@synth-diy.org</a>> wrote:<br><br><br>I am curious to know anyone’s opinions on using the LM13700 as a voltage controlled resistor.<br><br>The LM13700 datasheet has a couple schematics which I have tried building, with mixed results. I’m having a hard time knowing what sort of resistance I am getting as the multimeter gives strange and inconsistent readings.<br><br>The information on the datasheet is somewhat incomplete in my opinion and it is not easy to find much info online either.<br><br>It doesn’t seem like it is common practice to use these as VC resistors. Is that because it doesn’t work very well? Or use too many parts?<br><br>Any insight on this would be appreciated.<br>I’m interested mostly in the single ended schematic at the moment.<br><br>Thank you,<br><br>Didier<br><br><br><br>_______________________________________________<br>Synth-diy mailing list<br><a href="mailto:Synth-diy@synth-diy.org" target="_blank" rel="noreferrer">Synth-diy@synth-diy.org</a><br><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank" rel="noreferrer">http://synth-diy.org/mailman/listinfo/synth-diy</a><br><br><br><br>Virus-free. <a href="http://www.avg.com" target="_blank" rel="noreferrer">www.avg.com</a><br><br><br><br><br><br>_______________________________________________<br>Synth-diy mailing list<br><a href="mailto:Synth-diy@synth-diy.org" target="_blank" rel="noreferrer">Synth-diy@synth-diy.org</a><br><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank" rel="noreferrer">http://synth-diy.org/mailman/listinfo/synth-diy</a> <br></div></div></blockquote></div><br></div></div></div>_______________________________________________<br>
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