Path: csiph.com!1.us.feeder.erje.net!3.us.feeder.erje.net!feeder.erje.net!news.linkpendium.com!news.linkpendium.com!panix!not-for-mail From: Hul Tytus Newsgroups: sci.electronics.design Subject: Re: OpAmp Feedback Resistance vs. Stability Date: Thu, 30 Mar 2017 06:09:17 +0000 (UTC) Organization: PANIX Public Access Internet and UNIX, NYC Lines: 26 Message-ID: References: <772ddd19-f896-480a-804c-b1fbd98d9c3e@googlegroups.com> <7e508400-8e68-4351-a5b3-6a7052c351db@googlegroups.com> NNTP-Posting-Host: panix2.panix.com X-Trace: reader1.panix.com 1490854157 3201 166.84.1.2 (30 Mar 2017 06:09:17 GMT) X-Complaints-To: abuse@panix.com NNTP-Posting-Date: Thu, 30 Mar 2017 06:09:17 +0000 (UTC) Xref: csiph.com sci.electronics.design:454205 Familiar numbers. Nice to see the correct ones. Hul tabbypurr@gmail.com wrote: > On Thursday, 30 March 2017 04:18:18 UTC+1, Tim Wescott wrote: > > On Wed, 29 Mar 2017 22:54:13 +0000, Hul Tytus wrote: > > > > > Tim - the early opamps (lm707??) required "compensation" so that the > > > loop gain was less than unity at the frequency where the phase shift was > > > 180 degrees. The first opamp that completely compensated itself, ie > > > could be used at unity gain with no weird behavior, was, I think, the > > > single version of the lm747. > > > Those versions that required compensation had special pins for > > > capacitors. But the circuitry between the output and the negative input > > > could also be used for compensation, that is to reduce the loop gain > > > with a low frequency rc filter. That is probably what you were doing > > > with the rail to rail opamp. A 1K resister and 20 pf creates a 3 db > > > point around 8 mhz or so. > > > > I got out of college just as those weren't being used much any more. > The 709 was the popular uncompensated one, and the 741 the number 1 unity stable opamp for a long time. There were others of course before & after, eg the 702. And even valve opamps. > NT