Re:Re:Low Noise Op Amps

<CENTER> <DIV class=msgTitle><SPAN class=listTitle><STRONG>QRP-L</STRONG></SPAN> </DIV> <DIV class=metaIdxNav><NOBR>[<A href="http://www.kkn.net/archives/html/QRP-L/">Top</A>]</NOBR> <NOBR>[<A href="http://www.kkn.net/archives/html">All Lists</A>]</NOBR> </DIV></CENTER> <CENTER> <DIV class=topLinks> <TABLE class=mainNav width="100%"> <TBODY> <TR> <TD align=left width="33%"><SPAN class=topDateNav><NOBR><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00210.html"><prev</A> <STRONG>[<A href="http://www.kkn.net/archives/html/QRP-L/2001-06/index.html#00211">Date</A>]</STRONG> <A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00212.html">next></A></NOBR></SPAN></TD> <TD align=middle width="34%"> <xFORM action=/archives/cgi-bin/namazu.cgi method=get><NOBR><INPUT name=query><INPUT type=submit value=Search name=submit></NOBR><INPUT type=hidden value=QRP-L name=idxname> <SMALL><NOBR>[<A href="http://www.kkn.net/archives/cgi-bin/namazu.cgi?idxname=QRP-L">Advanced</A>]</NOBR></SMALL></xFORM></TD> <TD align=right width="33%"><SPAN class=topThreadNav><NOBR><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00183.html"><prev</A> <STRONG>[<A href="http://www.kkn.net/archives/html/QRP-L/2001-06/threads.html#00211">Thread</A>]</STRONG> <A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00276.html">next></A></NOBR></SPAN></TD></TR></TBODY></TABLE></DIV></CENTER> <DIV class=msgSubject> <H2>RE: [99348] Re: Op Amps. Interchangeable?</H2> <DIV class=msgLinks> <TABLE width="100%"> <TBODY> <TR vAlign=baseline> <TD align=left><SPAN class=authorLink>from [<A href="http://www.kkn.net/archives/cgi-bin/namazu.cgi?query=%2Bfrom%3ADan.Tayloe%40motorola.com&idxname=QRP-L&sort=date%3Alate"><EM>Tayloe Dan-P26412</EM></A>]</SPAN></TD> <TD align=right><SPAN class=bookmarkLink>[<A href="http://www.kkn.net/archives/cgi-bin/mesg.cgi?a=QRP-L&i=87568F78ABDCD211A0AC0008C707718B058C2C80%40az10exm03.sat.mot.com">Permanent Link</A>]</SPAN><SPAN class=orgLink>[<A href="http://www.kkn.net/archives/cgi-bin/extract-mesg.cgi?a=QRP-L&m=2001-06&i=87568F78ABDCD211A0AC0008C707718B058C2C80%40az10exm03.sat.mot.com">Original</A>]</SPAN></TD></TR></TBODY></TABLE></DIV></DIV> <DIV class=msgHead> <TABLE> <TBODY> <TR vAlign=baseline> <TH align=right><STRONG>To</STRONG>: </TH> <TD align=left>"'Dennis Payton'" <<A href="mailto:dpayton%40fwi.com">dpayton@fwi.com</A>>, "QRPL (E-mail)" <<A href="mailto:qrp-l%40lehigh.edu">qrp-l@lehigh.edu</A>></TD></TR> <TR vAlign=baseline> <TH align=right><STRONG>Subject</STRONG>: </TH> <TD align=left>RE: [99348] Re: Op Amps. Interchangeable?</TD></TR> <TR vAlign=baseline> <TH align=right><STRONG>From</STRONG>: </TH> <TD align=left>Tayloe Dan-P26412 <<A href="mailto:Dan.Tayloe%40motorola.com">Dan.Tayloe@motorola.com</A>></TD></TR> <TR vAlign=baseline> <TH align=right><STRONG>Date</STRONG>: </TH> <TD align=left>Tue, 5 Jun 2001 07:36:47 -0700 </TD></TR></TBODY></TABLE></DIV> <DIV class=msgBody> <TABLE cellSpacing=1 width="100%"> <TBODY> <TR> <TD><PRE>The pin out on almost all single, dual, and quad op-amps the same, so there is no problem from that view point. Quad parts are sometimes favored over duals because they take up less space and sometimes cost less per op-amp. A LM837 is a nice part (4.5 nV/SqrtHz) and is indeed the quad version of the LM833. It is true that after the first preamp, noise is less of a factor. I eval‎uate this by taking the noise of the first stage (4 nV/SqrtHz) and multiplying by the voltage gain of that op-amp stage. I don't know what the gain is in your receiver, but you can calculate it from the ratio of the feedback resistor to the input resistor. Suppose you have a gain of 100 (input 50 ohms, feedback 5K ohms), the output noise is 4*100 or 400 nV/SqrtHz. Noise adds with the sum of the squares, so if you use 18 nV/SqrtHz in the 3 stages of phase shifting, the resulting noise is: Sqrt(18*18 + 18*18 + 18*18 + 400*400) = 400.4 nV/SqrtHz Notice that each of the phase shifters have unity gain, and each contribute 18 nV/SqrtHz of noise. However, in this case the 400 nV/SqrtHz term dominates and the more noisy TL072/TL074s contribute a neglectable amount of noise. Recompute this and check with the actual gain the preamp uses. In the above example, I would rather use TL074s than the LM837s because of power consumption. Low noise parts consume more power. LT1115s (0.9 nV/SqrtHz) take about 8 ma per op-amp, LM833/837 and NE5532 (4 nV/SqrtHz) take about 3.5 ma per op-amp, as opposed to more noisy types such as TL074s and others in the 0.5 to 1.5 ma range. However, other considerations come into play later on in the audio chain. A TL074 is good for unity gain stages, but work poorly in high gain audio stage because of its low gain-bandwidth of 4 MHz. 4 MHz sounds high compared to audio, but when configured for a gain of 100x, the bandwidth reduces to 40 KHz (4 MHz/100), leaving little spare excess gain at the high end audio frequencies. Excess gain is used as feedback and reduces distortion in the audio pass band. For higher gain audio, higher gain bandwith parts are better, such as the LM833 (15 MHz gain-bandwidth) or the LM5532 (10 MHz). The LT1115 make a superb first stage preamp not only because of its ultra low noise, but also because it has a gain-bandwidth product of 40 MHz, 10x that of a TL074. It is obvious that it was intended as a professional high end audio part. In addition to the above, I like to use the low noise parts on the speaker side of the volume control because these will minimize the amount of background "hiss" that will be heard when the volume is turn way down. - Dan, N7VE -----Original Message----- From: Dennis Payton [<A href="mailto:dpayton@fwi.com">mailto:dpayton@fwi.com</A>] Sent: Monday, June 04, 2001 7:06 PM To: Tayloe Dan-P26412 Subject: Re: [99348] Re: Op Amps. Interchangeable? Hi Dan, Thanks a million for taking the time to share the info. Could I bother you with another short question? One that will show my ignorance? My biggest problem is selecting a quad op amp for the mini-R2, since I can't find NE5514's. I've been told that after the NE5532 preamps, noise figure is much less important and TL074's will work fine. Also I've wondered about using 5532's all the way through. (Showing my ignorance, is there some reason that a quad op amp would be favored over two duals?) Then I found Digi-Key sells LM837 quad op amps, which someone told me are 833's. Would you advise me as to the best direction to go? Thanks again! Denny N9JXY </PRE></TD></TR></TBODY></TABLE></DIV> <DIV class=msgLinks> <TABLE width="100%"> <TBODY> <TR vAlign=baseline> <TD align=middle><SPAN class=subjectLink>[<A href="http://www.kkn.net/archives/cgi-bin/namazu.cgi?query=%2Bsubject:%2F%5E%28%3F:%5E%5Cs%2A%28re%7Csv%7Cfwd%7Cfw%29%5B%5C%5B%5C%5D%5Cd%5D%2A%5B:%3E-%5D%2B%5Cs%2A%29%2A%5C%5B99348%5C%5D%5Cs%2BRe%5C:%5Cs%2BOp%5Cs%2BAmps%5C.%5Cs%2BInterchangeable%5C%3F%5Cs%2A%24%2F&idxname=QRP-L&sort=date%3Alate">More with this subject...</A>]</SPAN></TD></TR></TBODY></TABLE></DIV> <DIV class=tSlice> <TABLE cellSpacing=1 cellPadding=4 width="100%"> <TBODY> <TR vAlign=baseline> <TD align=left><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00183.html"><STRONG><Prev in Thread</STRONG></A>]</TD> <TH align=middle width="100%"><STRONG>Current Thread</STRONG></TH> <TD align=right>[<A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00276.html"><STRONG>Next in Thread></STRONG></A> </TD></TR> <TR class=tSliceList> <TD colSpan=3> <UL> <LI><B><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00177.html" name=00177>[99348] Re: Op Amps. Interchangeable?</A></B>, <I>Tayloe Dan-P26412</I> <UL> <LI><B><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00183.html" name=00183>Re: [99348] Re: Op Amps. Interchangeable?</A></B>, <I>Paul Christensen</I> </LI></UL> <UL> <LI><SPAN class=sliceCur><STRONG>RE: [99348] Re: Op Amps. Interchangeable?</STRONG>, <EM>Tayloe Dan-P26412</EM> <B></SPAN><=</B> <LI><B><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00276.html" name=00276>RE: [99348] Re: Op Amps. Interchangeable?</A></B>, <I>Tayloe Dan-P26412</I> </LI></UL> <DIV></DIV></LI></UL></TD></TR></TBODY></TABLE></DIV> <DIV class=botLinks> <TABLE width="100%"> <TBODY> <TR vAlign=baseline> <TH align=right>Previous by Date: </TH> <TD width="100%"><STRONG><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00210.html">FS: Ten Tec Century 21 and 670 keyer</A></STRONG>, <EM>Gene Sailsbury</EM></TD></TR> <TR vAlign=baseline> <TH align=right>Next by Date: </TH> <TD width="100%"><STRONG><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00212.html">Wide posts, how come?</A></STRONG>, <EM>Bob Tellefsen</EM></TD></TR> <TR vAlign=baseline> <TH align=right>Previous by Thread: </TH> <TD width="100%"><STRONG><A href="http://www.kkn.net/archives/html/QRP-L/2001-06/msg00183.html">Re: [99348] Re: Op Amps. 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