<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=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">Am 04.08.2024 um 19:13 schrieb Benjamin Tremblay via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>>:</div><br class="Apple-interchange-newline"><div class=""><meta charset="UTF-8" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; 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; float: none; display: inline !important;" class="">I can imagine making a state variable filter using a dual DAC as the ‘gain' stages. </span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; 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;" class=""></div></blockquote></div><br class=""><div class="">Looong time ago (past millennium) I built a state variable filter like this, using the DAC8408. The circuit is in the data sheet, see page 13:</div><div class=""><a href="https://www.analog.com/media/en/technical-documentation/data-sheets/DAC8408.pdf" class="">https://www.analog.com/media/en/technical-documentation/data-sheets/DAC8408.pdf</a></div><div class=""><br class=""></div><div class="">One caveat, if you build the integrators as shown in the circuit (R from DAC8408, discrete C): The absolute value of R is quite inaccurate, see „Input resistance" on page 2: 6 to 14 kOhms! It was necessary to build a rig to measure the resistance of each DAC chip and calculate the proper C values.</div><div class="">If you use the internal „feedback resistor“, the problem goes away, since the feedback resistor is well matched to the other resistors that form the DAC. But for a programmable integrator you need an additional Opamp then.</div><div class=""><br class=""></div><div class="">@Chris: that circuit works well with bipolar signals.</div><div class=""><br class=""></div><div class="">Ingo</div></body></html>