LME49990 Audio Op-Amp - better than AD797? - diyAudio
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Old 28th January 2010, 06:01 PM   #1
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Default LME49990 Audio Op-Amp - better than AD797?

National Semiconductor released a top class audio operational amplifier again:
http://www.national.com/pf/LM/LME49990.html#Overview
http://www.national.com/ds/LM/LME49990.pdf

Who have heard them already?

Thank you for your comments.

Last edited by tiefbassuebertr; 28th January 2010 at 06:05 PM.
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Old 28th January 2010, 06:15 PM   #2
mlloyd1 is online now mlloyd1  United States
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looks interesting spec-wise, but also looks like these parts are not quite "generally available" yet ...

mlloyd1
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Old 28th January 2010, 07:35 PM   #3
DuncanV is offline DuncanV  Netherlands
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Nice specs indeed.

What do we think about the suggested output compensation network as showed on page 9 from its datasheet?
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Old 31st March 2010, 09:37 AM   #4
VLSI is offline VLSI  Australia
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I swapped the LME49720 for the JFET LME49990 in my phono preamp today (basic single chip active feedback design) and it is so much quieter with the new LME49990, Can someone please explain to me why this would be so? I have not played enough vinyl yet to tell if it sounds sonically much different nor have I compared it to my 2 stage passive EQ phono preamp I built with the LME49710HA. Is anyone else experimenting with the LME49990 for phono pre amp's?
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Old 31st March 2010, 10:22 AM   #5
Bonsai is offline Bonsai  Taiwan
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Is your phono cartridge MM or MC?
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Old 31st March 2010, 11:31 AM   #6
VLSI is offline VLSI  Australia
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My brain has been in neutral most of the day today, It was the LME49880 JFET chip I tried today (not the LME49990). I will try the LME49990 tomorrow.
The cartridge is a Ortofon MC-30 with an Ortofon T-30 transformer, so the preamp is seeing a 47K input. It is the basic circuit as shown on some of the older NS data sheets.
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Old 31st March 2010, 01:15 PM   #7
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Quote:
Can someone please explain to me why this would be so?
LME49720 has very high current noise which makes it a poor choice for the rather high source Z of a phono catridge. A JFET input stage has very low current noise.

Samuel
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Old 31st March 2010, 11:24 PM   #8
VLSI is offline VLSI  Australia
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Thanks Samuel
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Old 1st April 2010, 12:20 AM   #9
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Just downloaded the LME49880 datasheet - what a hatchet job! The many and various distortion plots show around 0.02% THD at 20kHz - methinks someone didn't factor in the 101 factor of their distortion magnifier... Either that or the headline distortion figures are marketing fluff.

As for the output compensation network - they don't explain why its necessary, apart from improving settling time. Bizarre. What's getting into National these days? this datasheet really isn't up to their usual professional standards, doesn't build confidence for their parts.
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Old 1st April 2010, 02:47 AM   #10
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Originally Posted by abraxalito View Post
What's getting into National these days? this datasheet really isn't up to their usual professional standards, doesn't build confidence for their parts.
This is what happens when you lay off the "institutional memory" of a large corporation.

In my real biz we are seeing this with all sorts of huge companies -- they lay off a foreman or plant manager who had been there for 30+ years and then have all sorts of manufacturing issues -- I've been a close-observer of economic and business cycles for almost 40 years and there's something particularly nasty and ugly about this one with how its gutting middle management, where rubber meets the road. Different from 1971, 1982, 1991 etc. The guys at the top (accountants, washed-up Fortune 500 or McKinsey guys) have been parachuted in and have no sense of the organization. All you have to do is look at where the exec resides vis a vis where the company does business -- GM is exempla par gratia.

Who in their right mind would lay off Bob Pease?
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