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Old 26th February 2013, 01:39 PM   #35891
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Sorry that my references are beneath you, SY. I thought I was really helping would be designers with knowledge developed over 35 years ago. It doesn't have to be 're-invented' here.
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Old 26th February 2013, 01:49 PM   #35892
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Quote:
Originally Posted by john curl View Post
In all fairness, most midfi equipment is made with a modified 741 type topology, even today, so while slightly improved, the new devices suffer from much the same distortion generating mechanisms as earlier devices.
In all fairness, I am not much interested in uA741 or its slightly improved versions.

What is quite interesting is the fact, that the AD797, with no extraordinary slew rate 20V/us, performs in a 19 + 20 kHz test much better than many (or most of) devices with slew rate > 50V/us. It also performs better in a 30kHz THD test. So, it is not only about slew rate. Of course, it will not handle well 5MHz full scale signal. But, as you are saying, we should argue reasonably. 5V/us is definitely not enough and 1000V/us is definitely not necessary.
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Old 26th February 2013, 01:51 PM   #35893
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A teacher who keeps telling his class that they are thick and lazy, while refusing to explain the subject matter to them but offering anecdotes instead of derivations, should not be surprised if the naughty but bright kids at the back of the class start drooling and making paper aeroplanes.
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Old 26th February 2013, 01:56 PM   #35894
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Quote:
Originally Posted by PMA View Post
What is quite interesting is the fact, that the AD797, with no extraordinary slew rate 20V/us, performs in a 19 + 20 kHz test much better than many (or most of) devices with slew rate > 50V/us. It also performs better in a 30kHz THD test.
But you're ignoring the invisible 7th harmonic that we've been assured is what separates mid-fi junk like the 797 from fine high-end designs.
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Old 26th February 2013, 02:03 PM   #35895
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Quote:
Originally Posted by PMA View Post
In all fairness, I am not much interested in uA741 or its slightly improved versions.

What is quite interesting is the fact, that the AD797, with no extraordinary slew rate 20V/us, performs in a 19 + 20 kHz test much better than many (or most of) devices with slew rate > 50V/us.
VERY low open-loop BW and LOTS of feedback.
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Old 26th February 2013, 02:04 PM   #35896
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This reminds me of the incident in the movie: 'Legally Blonde', where the student comes to a law class at Harvard University and is asked to leave, BECAUSE she did not read the assignment in advance. And I just ask that many here read the material offered, before asking me questions about the subject. Is it too much to ask? '-)
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Old 26th February 2013, 02:08 PM   #35897
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Originally Posted by SY View Post
But you're ignoring the invisible 7th harmonic that we've been assured is what separates mid-fi junk like the 797 from fine high-end designs.
Oh I am sorry. You mean designs like this one:

Click the image to open in full size.

Parasound Halo JC 2 line preamplifier Measurements | Stereophile.com

If you look at the image, what is the line at 16kHz? Isn't it the 7th?
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Old 26th February 2013, 02:33 PM   #35898
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To be fair, those are really pretty excellent measurements. No better than one can do with a cheap IC op-amp, but far better than many high end designs.
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Old 26th February 2013, 02:35 PM   #35899
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Wow, PMA. Thanks for showing me something that I did not previously see or know about. When you can get 7th harmonic from an all Class A, all FET, balanced complementary differential design, you have a mystery. I will have to look into it.
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Old 26th February 2013, 02:45 PM   #35900
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Quote:
Originally Posted by john curl View Post
When you can get 7th harmonic from an all Class A, all FET, balanced complementary differential design, you have a mystery.
No mystery at all (most of the things you cite go to even order harmonics). Why not take credit for doing it right and avoiding the issue?
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