<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="">Or stick 470pF caps on it and turn up the cutoff frequency CV.<div class=""><br class=""></div><div class="">Honestly, why not? More juice through the OTAs should help with the very-low-current effects Roman mentioned, and bigger caps would mean that a few pF of stray capacitance isn’t such a big deal. Although I agree that 470pF isn’t a huge jump up.</div><div class=""><br class=""></div><div class="">Tom</div><div class=""><br class=""><div class="">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 8 Jan 2021, at 16:36, Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">I’ve just looked at the 3320 circuit diagram and it shows 300pF capacitors. With through hole I wonder if you can keep the stray capacitances low enough to be worrying that much about matching capacitors ? You may be better off trying to add small parallel capacitors on each 300pF in turn in situ to see where you can improve the Q.<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><b class=""><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif;" class="">From:</span></b><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif;" class=""><span class="Apple-converted-space"> </span>ColinMuirDorward [<a href="mailto:colindorward@gmail.com" class="">mailto:colindorward@gmail.com</a>]<span class="Apple-converted-space"> </span><br class=""><b class="">Sent:</b><span class="Apple-converted-space"> </span>08 January 2021 17:28<br class=""><b class="">To:</b><span class="Apple-converted-space"> </span>Roman Sowa<br class=""><b class="">Cc:</b><span class="Apple-converted-space"> </span>Mike Bryant; <a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a><br class=""><b class="">Subject:</b><span class="Apple-converted-space"> </span>Re: [sdiy] VCF caps in modern synths<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><o:p class=""> </o:p></div><div class=""><div style="margin-left: 30pt;" class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class="">> Close matching of capacitors gives close matching of the real pole frequencies, and this requires less feedback gain to reach self-oscillation.<o:p class=""></o:p></div></div><div class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class="">To reach self-oscillation, is it to be expected that more feedback gain is required at lower frequencies? I'm trying to imagine how less-well-matched capacitors would contribute to the frequency-dependancy factor.<o:p class=""></o:p></div></div></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><o:p class=""> </o:p></div><div class=""><div class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class="">On Fri, Jan 8, 2021 at 8:20 AM Roman Sowa <<a href="mailto:modular@go2.pl" style="color: purple; text-decoration: underline;" class="">modular@go2.pl</a>> wrote:<o:p class=""></o:p></div></div><blockquote style="border-style: none none none solid; border-left-width: 1pt; border-left-color: rgb(204, 204, 204); padding: 0cm 0cm 0cm 6pt; margin-left: 4.8pt; margin-right: 0cm;" class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class="">><span class="Apple-converted-space"> </span><br class="">>> do not show microphonic effect<br class="">> This was fixed in X7Rs over 20 years ago. I keep seeing this coming up as a reason and ask for people to show me a modern quality X7R (from Samsung, Yageo, etc) that has microphony. I'm sure there are some cheap and nasty ones that still do it but the quality brands fixed this for smartphone use ages ago.<br class=""><br class="">Maybe I'm biased, and you are probably correct. Not so much nowadays as<span class="Apple-converted-space"> </span><br class="">it used to be. But still I was able to see microphonic effect on new<span class="Apple-converted-space"> </span><br class="">1210 10uF cap. It was just 1mV bump but still. So I withdraw my claim<span class="Apple-converted-space"> </span><br class="">about "piezoelectric transducers"<br class=""><br class="">><span class="Apple-converted-space"> </span><br class="">>> dielectric absorption<br class="">> Again barely an effect with modern units.<br class=""><br class="">my very recent experience proved it's still a problem. By mistake I put<span class="Apple-converted-space"> </span><br class="">X7R diped multilayer THT cap instead of C0G in oscillator timing. They<span class="Apple-converted-space"> </span><br class="">look the same, little yellow thingies, only differ with one letter I<span class="Apple-converted-space"> </span><br class="">can't see without glasses. And it caused huge spike that could be<span class="Apple-converted-space"> </span><br class="">explained only by dielectric absorption. By "huge" I mean nearly 10% of<span class="Apple-converted-space"> </span><br class="">full voltage span. Replacing with C0G made the spike disappear.<br class="">And it was in only tiny 1n cap. Might get worse in bigger capacitances.<br class=""><br class="">><span class="Apple-converted-space"> </span><br class="">>> and all those things end up as distortion in audio path.<br class="">> < 0.001% on an AP in my latest mic amp/ADC combo. Do you need any better ?<br class=""><br class="">no, I don't, you win.<br class=""><br class="">Roman<br class="">_______________________________________________<br class="">Synth-diy mailing list<br class=""><a href="mailto:Synth-diy@synth-diy.org" target="_blank" style="color: purple; text-decoration: underline;" class="">Synth-diy@synth-diy.org</a><br class=""><a href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank" style="color: purple; text-decoration: underline;" class="">http://synth-diy.org/mailman/listinfo/synth-diy</a><br class="">Selling or trading? Use<span class="Apple-converted-space"> </span><a href="mailto:marketplace@synth-diy.org" target="_blank" style="color: purple; text-decoration: underline;" class="">marketplace@synth-diy.org</a><o:p class=""></o:p></div></blockquote></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><br clear="all" class=""><br class="">--<span class="Apple-converted-space"> </span><o:p class=""></o:p></div><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><a href="https://www.instagram.com/colinmuirdorward/" target="_blank" style="color: purple; text-decoration: underline;" class="">https://www.instagram.com/colinmuirdorward/</a><o:p class=""></o:p></div></div><div class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman", serif;" class=""><a href="https://www.instagram.com/colinmuirdorward/" target="_blank" style="color: purple; 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