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</head><body><p>I wasn't able to find a schematic for this but I know they are out there somewhere.</p><p><br></p><p>One technique uses 2 OTAs and 2 half wave rectifiers. You feed the carrier into the + side of one OTA and the - side of the other. You connect the outputs together and buffer them. You feed the modulation into the half wave rectifiers, one being configured for the + side and the other configured for the - side of the modulation. You also invert the - side, convert both to current and drive the OTAs Iabc with those. So the + modulation goes through one OTA and the - modulation goes through the inverted one.</p><p><br></p><p>Even though the AD633 is expensive when you count parts and the cost of board space is the OTA solution going to be cheaper?</p><p><br></p><p>Jay S.</p><p><br></p><blockquote type="cite">On September 13, 2017 at 12:35 PM Tim Ressel <timr@circuitabbey.com> wrote:<br><br><p>Hey y'all,</p><p>I am making a voltage controlled bipolar mixer, so I need a bipolar i.e. 4-quadrant VCA. So 2 channels mixing together with bipolar voltage control. Here is what I am thinking:<br> <strong><a class="ox-318b1645e7-moz-txt-link-freetext" href="http://www.synthdiy.eu/files/BipolarVCA.png">http://www.synthdiy.eu/files/BipolarVCA.png</a></strong><br> A rectifier circuit will drive the 13700 Iabc port and a comparator will drive the switch. <br></p><p>I know I could use AD633s but they are really pricey. Any other clever ways of pulling this off?<br></p><pre class="ox-318b1645e7-moz-signature">--
--Tim Ressel
Circuit Abbey
<a class="ox-318b1645e7-moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></pre></blockquote><p><br> </p><blockquote type="cite">_______________________________________________<br>Synth-diy mailing list<br>Synth-diy@synth-diy.org<br>http://synth-diy.org/mailman/listinfo/synth-diy<br></blockquote></body></html>