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I think what seems to be ignored here is all VCAs, OPAs or whatever have their own frequency response which a pot doesn't really have. This will cause a phase shift at some frequency or another and especially with a filter circuit is very likely to move it
into an region of instability. Whether you can pull it back into stability needs to be investigated for each application.<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of brianw <brianw@audiobanshee.com><br>
<b>Sent:</b> 09 February 2024 23:54<br>
<b>To:</b> synth-diy <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] Unique sounding modules that can't have voltage control?</font>
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<div class="PlainText">What about current mirrors? Those are hardly new technology.<br>
<br>
Also, for dual-gang pots, can't you simply put two voltage-controlled circuits in there and control both with the same CV?<br>
<br>
Brian<br>
<br>
<br>
On Feb 9, 2024, at 3:02 PM, Stephen Makdisi <shmakdisi@xvetrd.us> wrote:<br>
> Controlling one current isn’t hard. Controlling two in concert is much harder. And any circuit that needs both sides of a pot (like a Baxandall EQ) will need both sides to match and work together in a consistent, particular way.
<br>
> <br>
> For the one capacitor bass boost/cut Baxandall, where the cap is in parallel with legs 1 and 3 of the pot, it’s worth nothing that the pot value determines not just how much boost/cut, but also the frequency of EQ itself. So the two sides have to rise and
fall in opposite, consistent ways and the equivalent resistance needs to add up to a constant amount.<br>
> <br>
> And for dual gang pots you’re looking at 4 different areas that will need to be controlled at the same time with specific matching curves. As more parts are added tolerances get more important. Temperature stability would be another nightmare I’m sure.<br>
<br>
<br>
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