<p><span class="h-card" translate="no"><a href="https://chaos.social/@gsuberland" class="u-url mention">@<span>gsuberland</span></a></span> yeah i figured that you&#39;re using the FET as a modulator but it wasn&#39;t completely clear for what purpose</p>

<p>I&#39;m not even sure how to properly describe this. &quot;nonlinear modulating low-pass filter&quot;, I guess?</p><p>the core of it is that the MOSFET is a big power FET with a ton of Cgs. combined with the 220k resistor, you get a low-pass filter. the channel A voltage is adjusted by the opamps to keep the MOSFET sub-threshold.</p><p>except the really evil part of this is that the MOSFET&#39;s gate capacitance is dependent on Vds. so channel B modulates Vds, adjusting the filter&#39;s cutoff frequency.</p>

<p>we have a winner!</p><p><a href="https://aus.social/@nickzoic/113921516097962178" target="_blank" rel="nofollow noopener noreferrer" translate="no"><span class="invisible">https://</span><span class="ellipsis">aus.social/@nickzoic/113921516</span><span class="invisible">097962178</span></a></p>

<p>alright, let&#39;s go with one final hint that&#39;s REALLY going to bake your noodle.</p><p>the MOSFET never turns on. at all.</p>

<p>ok, a few of you have gotten very close so I&#39;m going to provide a bit more help</p>

<p><span class="h-card" translate="no"><a href="https://mastodon.social/@gamingonlinux" class="u-url mention">@<span>gamingonlinux</span></a></span> good</p>

<p><span class="h-card" translate="no"><a href="https://mastodon.social/@shriramk" class="u-url mention">@<span>shriramk</span></a></span> That warms my heart. I’ve always took sneering at this book as a sign of a joyless person.</p>

<p>anyone who asks an LLM is instantly disqualified and also loses my respect.</p>

<p>one hundred internet points if you can successfully guess what this circuit does, and how.</p><p>three hints:</p><p>1: it&#39;s pretty weird.</p><p>2. the inputs and outputs are no more than a couple tens of kilohertz (and are not a fixed frequency - the values shown in the sim below are arbitrary)</p><p>3: it only works in a real circuit and if you simulate this you will not see it doing the weird thing.</p><p>UPDATE: we have a winner. solution is here: <a href="https://chaos.social/@gsuberland/113921571918206983" target="_blank" rel="nofollow noopener noreferrer" translate="no"><span class="invisible">https://</span><span class="ellipsis">chaos.social/@gsuberland/11392</span><span class="invisible">1571918206983</span></a></p>