<div dir="ltr">In the early days of opamps, ARP placed a matched FET IC at the inputs of Teledyne and LM301 opamps to increase the input impedance.  That was a Dennis Colin innovation, which he carried to the Aries modular after he left ARP.  There's a lot of circuit design conventions between Aries and ARP products.<div><br></div><div>ARP used this technique in analog synths all the way from the 2500 to the end of the company.  I don't think this was used in the Chroma though, by then FET input opamps were mainstream.</div><div><br></div><div>MC</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Sun, Jun 22, 2025 at 9:05 AM Paul Perry via Synth-diy <<a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr">Electrometer design is one application for matched fets, but there is also a VCA that requires a matched pair:<div><br></div><div><a href="https://www.edn.com/op-amp-linearizes-response-of-fet-vca/#:~:text=FETs%20find%20common%20use%20in,C%20is%20the%20control%20voltage" target="_blank">https://www.edn.com/op-amp-linearizes-response-of-fet-vca/#:~:text=FETs%20find%20common%20use%20in,C%20is%20the%20control%20voltage</a>.</div><div><br></div><div>paul perry Melbourne Australia<br><div><br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Jun 22, 2025 at 6:21 AM Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" target="_blank">mbryant@futurehorizons.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div>




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One place you do see FETs quite a lot is the muting output of mixers - they kill thumps well without distorting the output signal.</div>
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On 2025-06-21 12:53, René Schmitz wrote:</div>
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> FETs have large unit to unit variations, good for one-off hobbyist or<br>
> space mission work, but<br>
> annoying to show-stopper for mass production. So you'll not see them<br>
> that often in the wild.<br>
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