<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>A lot of the early Moog modules used 100k input impedance.</p>
<p>I am *still* using a big batch of 100k 1/4 watt resistors I
bought almost 30 years ago!<br>
</p>
<div class="moz-cite-prefix">On 11/13/20 4:06 PM, tpuefke via
Synth-diy wrote:<br>
</div>
<blockquote type="cite"
cite="mid:Tef8jBybFwymb_DcDsZxezYH-UIhDGiiujo_3vH2aXJB7sSWFnTo2D5VA5gcDzIF8mme-Lchf2EwQ2Ak9DevOfSgsrHcRksptGHQo1wPrYk=@protonmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div><span style="color:rgb(0, 0, 0)"><span
style="font-family:"Helvetica Neue", Helvetica,
Arial, sans-serif"><span style="font-size:14px">>100k
shows up a lot in eurorack circuits since it's the defacto
input impedance.</span></span></span><br>
</div>
<div><br>
</div>
<div>Could it be that a lot of (more recent) Eurorack circuits are
heavily inspired by Ray Wilson? ;-)<br>
</div>
<div><br>
</div>
<div>As to the context and design intention behind my question, in
this case it's less specific, general curiosity. I'm just trying
to weigh the options, for example for small circuits, or like
Mattias mentioned in low-noise signal paths. <br>
</div>
<div><br>
</div>
<div>I was suspecting that input impedance plays into this, but
for op-amp stages other than inputs there would be no obvious
reason to use values as high as 100k unless to conserve power.<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>thanks,<br>
</div>
<div>Tom<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐<br>
</div>
<div> On Friday, 13. November 2020 22:48, ben gebhardt via
Synth-diy <a class="moz-txt-link-rfc2396E" href="mailto:synth-diy@synth-diy.org"><synth-diy@synth-diy.org></a> wrote:<br>
</div>
<div> <br>
</div>
<blockquote class="protonmail_quote" type="cite">
<div style="font-family:Helvetica Neue, Helvetica, Arial,
sans-serif;font-size:13px;">
<div><br>
</div>
<div dir="ltr" data-setdir="false">(first time poster!)<br>
</div>
<div dir="ltr" data-setdir="false"><br>
</div>
<div dir="ltr" data-setdir="false">Hi Ian,<br>
</div>
<div dir="ltr" data-setdir="false"><br>
</div>
<div dir="ltr" data-setdir="false">Usually in my experience
one would scale down resistors around an opamp to generally
lower the johnson noise contribution. Additionally there is
something to be said for high impedance nodes and coupling
in radiated noise from external sources but usually that's
only problematic over 1M. <br>
</div>
<div dir="ltr" data-setdir="false"><br>
</div>
<div dir="ltr" data-setdir="false"><span><span
style="color:rgb(0, 0, 0)"><span
style="font-family:Helvetica Neue, Helvetica, Arial,
sans-serif">As to why it's commonplace, I'm not sure
which schematics you are referring to, but as
mentioned, 100k shows up a lot in eurorack circuits
since it's the defacto input impedance.</span></span></span><br>
</div>
<div dir="ltr" data-setdir="false"><br>
</div>
<div dir="ltr" data-setdir="false">There are a ton of other
factors in the decision of this resistor, it's hard to
generalize rationale w/o the context of the circuit and
design intentions. Happy to comment on something more
specific.<br>
</div>
<div dir="ltr" data-setdir="false"><br>
</div>
<div dir="ltr" data-setdir="false">Ben.<br>
</div>
<div><br>
</div>
</div>
<div class="yahoo_quoted">
<div style="font-family:'Helvetica Neue', Helvetica, Arial,
sans-serif;font-size:13px;color:#26282a;">
<div>On Friday, November 13, 2020, 04:16:17 PM EST, Mattias
Rickardsson <a class="moz-txt-link-rfc2396E" href="mailto:mr@analogue.org"><mr@analogue.org></a> wrote:<br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div>
<div>
<div>
<div>
<div>
<div dir="ltr">Mattias Rickardsson <<a
rel="nofollow" shape="rect" target="_blank"
href="mailto:mr@analogue.org"
moz-do-not-send="true">mr@analogue.org</a>>
skrev:<br>
</div>
<blockquote style="margin:0 0 0
.8ex;border-left:1px #ccc
solid;padding-left:1ex;">
<div>
<div>
<div><br>
</div>
<div>And perhaps 10k-22k for TL06x.<br>
</div>
</div>
</div>
</blockquote>
</div>
</div>
<div><br>
</div>
<div>I should have written 22k-47k.<br>
</div>
<div>
<div><br>
</div>
<div>/mr<br>
</div>
<div><br>
</div>
<div>
<div>
<blockquote style="margin:0 0 0
.8ex;border-left:1px #ccc
solid;padding-left:1ex;">
<div>
<div><br>
</div>
</div>
</blockquote>
</div>
</div>
</div>
</div>
</div>
</div>
<div>
<div>_______________________________________________<br>
</div>
<div>Synth-diy mailing list<br>
</div>
<div><a shape="rect"
href="mailto:Synth-diy@synth-diy.org"
moz-do-not-send="true">Synth-diy@synth-diy.org</a><br>
</div>
<div><a shape="rect"
href="http://synth-diy.org/mailman/listinfo/synth-diy"
target="_blank" moz-do-not-send="true">http://synth-diy.org/mailman/listinfo/synth-diy</a><br>
</div>
<div>Selling or trading? Use <a shape="rect"
href="mailto:marketplace@synth-diy.org"
moz-do-not-send="true">marketplace@synth-diy.org</a><br>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
Synth-diy mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Synth-diy@synth-diy.org">Synth-diy@synth-diy.org</a>
<a class="moz-txt-link-freetext" href="http://synth-diy.org/mailman/listinfo/synth-diy">http://synth-diy.org/mailman/listinfo/synth-diy</a>
Selling or trading? Use <a class="moz-txt-link-abbreviated" href="mailto:marketplace@synth-diy.org">marketplace@synth-diy.org</a>
</pre>
</blockquote>
</body>
</html>