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<DIV dir=ltr align=left><SPAN class=951560623-13112020><FONT color=#0000ff
size=2 face=Arial>I concur with Ian. However, I have had circuits where
opamps with 100k feedback resistors screamed like banshees, while with 10k they
didn't oscillate at all. Hence, if stability is an issue, I often default
to the lower value. I also end up using 30k quite often. This is
often just a matter of convenience. If I'm using a 2164 in my circuit,
there will be 30k resistors, so I often just apply them to the opamp circuits as
well. They always work just fine.</FONT></SPAN></DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
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<FONT size=2 face=Tahoma><B>From:</B> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <B>On Behalf Of </B>Ian
Fritz<BR><B>Sent:</B> Friday, November 13, 2020 11:13 AM<BR><B>To:</B>
tpuefke<BR><B>Cc:</B> Synth-Diy mailing list<BR><B>Subject:</B> Re: [sdiy]
Voltage Feedback Resistors and Circuit Stability<BR></FONT><BR></DIV>
<DIV></DIV><SPAN
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Non-UBC Email]</SPAN></SPAN></SPAN>
<DIV dir=ltr>R values around 100k or so give a good compromise between noise and
power consumption.</DIV>
<DIV dir=ltr><BR></DIV>
<DIV dir=ltr>Ian</DIV>
<DIV dir=ltr><BR>
<BLOCKQUOTE type="cite">On Nov 13, 2020, at 9:59 AM, tpuefke via Synth-diy
<synth-diy@synth-diy.org> wrote:<BR><BR></BLOCKQUOTE></DIV>
<BLOCKQUOTE type="cite">
<DIV dir=ltr>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">I
was hoping someone more experienced could help shine some light on this issue.
This is still quite puzzling to me as a non-engineer.<BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px"><BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">Looking
through my collection of schematics from various places like MFOS (bless his
soul), I see a lot of the standard 100k resistor in negative feedback op-amp
configuration, for inverters, mixers, attenuators... For a long time i have
been adapting these as my go-to values without giving it much thought and
usually it works pretty well. The odd schematic here and there uses lower
values.<BR></DIV>
<DIV
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<DIV
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<DIV style="WORD-WRAP: break-word">Considering that high feedback resistance
implies a higher gain potential, shouldn't lower values (e.g. 10k, 1k even)
usually be a better choice in terms of circuit stability? <BR></DIV>
<DIV style="WORD-WRAP: break-word">Or is this a non-issue for fractional gain
setups? <BR></DIV>
<DIV><BR></DIV></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">I've
been wondering about this for a while now and recently stumbled across this
post discussing Rf values and op-amp input capacitance:<BR></DIV>
<DIV
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<DIV style="WORD-WRAP: break-word">
<DIV style="WORD-WRAP: break-word"><BR></DIV>
<DIV style="WORD-WRAP: break-word"><A style="COLOR: rgb(45,113,184)"
href="https://www.analog.com/en/analog-dialogue/raqs/raq-issue-122.html">https://www.analog.com/en/analog-dialogue/raqs/raq-issue-122.html</A><BR></DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>What are the pros and cons in your experience for using high resistances
like these, in attenuator / unity inverter setups
especially? <BR></DIV></DIV></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px"><BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">Higher
resistances simply to reduce current consumption in bigger circuits? What
about resistor noise?<BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px"><BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">Just
trying to wrap my head around this to be able to make more informed decisions.
<BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">Any
feedback is HIGHly appreciated. :)<BR></DIV>
<DIV
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<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px"><BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">thanks,<BR></DIV>
<DIV
style="TEXT-TRANSFORM: none; TEXT-INDENT: 0px; FONT: 15px monospace; WORD-WRAP: break-word; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(60,60,60); WORD-SPACING: 0px; -webkit-text-stroke-width: 0px">Tom<BR></DIV>
<DIV
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