<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=""><div class=""><div><blockquote type="cite" class=""><div class="">On Nov 22, 2022, at 2:01 AM, Lanterman, Aaron D via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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Does anyone recognize the topology Don is using here in the bandpass sections?
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<div class="">The low and high bands are 3-pole Sallen-Keys, but I’m not sure what’s going on in the middle filters.</div></div></div></blockquote><br class=""></div></div><div><br class=""></div><div><div class="">Hey Aaron,</div><div class=""><br class=""></div>It's a twin-tee filter, but connected in an unusual way. </div><div><br class=""></div><div>The input is directed into the twin-tee's "ground", and the twin-tee's normal notch filtering action is the opamp's feedback loop.</div><div><br class=""></div><div> -- Don</div><div><div class=""><div class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div>--<br class="">Donald Tillman, Palo Alto, California<br class=""><a href="https://www.till.com" class="">https://www.till.com</a></div></div></div></div></div></body></html>