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Old 10th March 2013, 05:48 PM   #2821
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by myhrrhleine View Post
Keep in mind that an FFT is being used.
Therefore, the band width is 1Hz or less per bin.
I guess a better approach is --> pls send me recommendations for the very best opamp IC (or discrete) that would have the lowest noise and the lowest thd at 10 v p to p up to 100KHz into 10K. The very best out there.... known... not guesses. I can do my own guessing.

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Old 10th March 2013, 07:37 PM   #2822
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Originally Posted by RNMarsh View Post
I guess a better approach is --> pls send me recommendations for the very best opamp IC (or discrete) that would have the lowest noise and the lowest thd at 10 v p to p up to 100KHz into 10K. The very best out there.... known... not guesses. I can do my own guessing.

Thx-RNMarsh
Dick,

I did a project where I compared the LM4562, the AD797, a NOS Signetics NE5534 and a Burr Brown (forget which.) A few months later got in more samples of the LM4562, AD797 and the Burr Brown. I also used a newer JRC 5534 (I think that was it.)

Well the first time the LM4562 measurements were RFI contaminated, The AD797 measured not very good, the Burr Brown decent and the NE5534 decent. Repeating the test The LM4562 with input chokes, but also different date code was way better, The AD797 newer sample was quite good, The Burr Brown had a lot more 1/F noise and the 5534 copy had serious RFI issues.

So my approach since then has been to install a good gold socket and test each individual chip in my stock. (Also eliminates the issue of working impedances.)

So even though I have done measurements, I don't have any useful answers.

P.S. I think the first AD devices were actually returns to the authorized distributor where I got them as some were DOA.
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Old 10th March 2013, 10:30 PM   #2823
RNMarsh is offline RNMarsh  United States
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Well that is what I have been going thru as well... put in a socket and start plugging in everything I can find... was hoping others knew of an opamp I havent tried yet. Thank you for responding. Any others out there --- even to eliminate some others.

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Old 11th March 2013, 12:22 AM   #2824
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Originally Posted by RNMarsh View Post
Well that is what I have been going thru as well... put in a socket and start plugging in everything I can find... was hoping others knew of an opamp I havent tried yet.
I'll repeat that layout, earthing & decoupling are AT LEAST as important as the OPA. You need to do at least what's recommended in AD797 datasheet for ALL the OPAs you mention if you're after 1ppzillion THD.

The RFI is an indication that you need to work on these. Chokes, especially SMD ones or anything with ferrite will also introduce THD.

Another good tutorial is Cyril Bateman's series on capacitors where he describes a 1ppzillion oscillator for his tests. Note the OPAs he recommends.

Also, I can tell you from experience is that a DIP8 socket WILL degrade performance at these levels cos layout bla bla.

BTW, LM4562 and its more expensive cousins suffer from latching which is bad enough to have serious problems on power up in single supply applications.

Quote:
Pls... explain What causes the latching IF the input is limited to such an extent that you cant overdrive the amp into clipping or latching? What condition causes latching? I was day dreaming during that part of the talk.
The problem is placing these diodes so they don't introduce additional distortion while protecting against latching, overload etc.

Last edited by kgrlee; 11th March 2013 at 12:33 AM.
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Old 11th March 2013, 12:29 AM   #2825
fas42 is online now fas42  Australia
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Quote:
Originally Posted by kgrlee View Post
Also, I can tell you from experience is that a DIP8 socket WILL degrade performance at these levels cos layout bla bla.
I would run a million miles from ever using an IC in a socket ...

Frank
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Old 11th March 2013, 12:33 AM   #2826
PHEONIX is offline PHEONIX  Australia
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Originally Posted by fas42 View Post
I would run a million miles from ever using an IC in a socket ...

Frank
Hi Frank,

Does this go for the Intel/AMD chip and socket in your PC.
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Old 11th March 2013, 12:59 AM   #2827
fas42 is online now fas42  Australia
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Originally Posted by PHEONIX View Post
Hi Frank,

Does this go for the Intel/AMD chip and socket in your PC.
If working in a pure digital environment one can generally get away with it over the long term. However, as someone who used a typical cheap PC in a beachside environment and had it rendered it unusable in less than a year by salt induced green sludge seeming to magically develop everywhere there were "gold" connectors I'm still not so keen on the idea ...

Audio is an area where you have to be fussy, really fussy, if you want the best sound - every potential weakness should always be eliminated.

Frank

Last edited by fas42; 11th March 2013 at 01:01 AM.
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Old 11th March 2013, 02:06 AM   #2828
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Originally Posted by RNMarsh View Post
. . . pls send me recommendations for the very best opamp IC (or discrete) that would have the lowest noise and the lowest thd at 10 v p to p up to 100KHz into 10K. . . .
The most extensive (400 pages!) set of measurements I'm aware of is Samuel Groner's "Operational Amplifier Distortion" report, linked from < http://www.sg-acoustics.ch/analogue_...mps/index.html >.

The fact that he presents measured results as a series of graphs rather than a few isolated measurements (or a single "measure of goodness") underscores the oft-repeated comment that you really need to consider circuit details outside the opamp itself before claiming the superiority of one over another. His report includes both integrated and discrete amps but doesn't have data for many of the most recent high-performance designs. If somebody has test gear that can replicate his measurements for a few of his examples, they can work at extending the data base to include other devices.

Dale
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Old 11th March 2013, 10:20 AM   #2829
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by kgrlee View Post
I'll repeat that layout, earthing & decoupling are AT LEAST as important as the OPA. You need to do at least what's recommended in AD797 datasheet for ALL the OPAs you mention if you're after 1ppzillion THD.

The RFI is an indication that you need to work on these. Chokes, especially SMD ones or anything with ferrite will also introduce THD.

Another good tutorial is Cyril Bateman's series on capacitors where he describes a 1ppzillion oscillator for his tests. Note the OPAs he recommends.

Also, I can tell you from experience is that a DIP8 socket WILL degrade performance at these levels cos layout bla bla.

BTW, LM4562 and its more expensive cousins suffer from latching which is bad enough to have serious problems on power up in single supply applications.

The problem is placing these diodes so they don't introduce additional distortion while protecting against latching, overload etc.
Thank you for the info. BTW -- I am using the commercially available oscillators to try the opamp upgrades in.... Like a K-H or HP and the like.... the grounding, shielding, bypassing et al is done for me.
Thx-RNMarsh
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Old 11th March 2013, 10:28 AM   #2830
RNMarsh is offline RNMarsh  United States
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Originally Posted by dchisholm View Post
The most extensive (400 pages!) set of measurements I'm aware of is Samuel Groner's "Operational Amplifier Distortion" report, linked from < SG-Acoustics Samuel Groner IC OpAmps >.

The fact that he presents measured results as a series of graphs rather than a few isolated measurements (or a single "measure of goodness") underscores the oft-repeated comment that you really need to consider circuit details outside the opamp itself before claiming the superiority of one over another. His report includes both integrated and discrete amps but doesn't have data for many of the most recent high-performance designs. If somebody has test gear that can replicate his measurements for a few of his examples, they can work at extending the data base to include other devices.

Dale
Good stuff in there. I went and read it all. I had read it in its first incarnation years ago. The expanded testing is really helpful. I'll order some more opamps to try out. So far the LT1468 has given me excellent results and it tests by SG very well also.

I have SW's recommendation on order for awhile now. Trying to sqeeze some more dB's out of this stuff used in testing.

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