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Old 22nd January 2013, 10:28 PM   #33371
bcarso is offline bcarso  United States
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Quote:
Originally Posted by Telstar View Post
Chris, I think I have the Boyk-Sussman paper, I'll check tomorrow from PC and attach if I do. I have read something from Sussman and he definitely was on the right track.
Here's a link: http://www.its.caltech.edu/~musiclab...er-acrobat.pdf
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Old 22nd January 2013, 10:40 PM   #33372
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Originally Posted by Telstar View Post
It would be nice if we could rely on simpler measurements, but they led astray many audio designers in the 70s and still do today.
I always thought that measurements, and specially THD were proposed to help designers to improve their designs, and optimize values, not more. It is the marketing guys witch had used-it for commercial argues. Look, Telstar, even here, nobody can agree their value :-)
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Old 22nd January 2013, 11:08 PM   #33373
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Originally Posted by Max Headroom View Post
None of the good opamps (OPA627, AD797, OPA134 ...) has any residual 7th above -120dB. They do not sound same, but the 7th is not the reason.
Hello again Pavel, I respect your measurements data, that said it reads that you are making subjective comment here. Could you please elaborate on your subjective findings of these opamps, or at least your subjective findings of differences between this collection of opamps.
If I may add my $0.02 of experience. Some OPA characteristics are only poorly understood and receive little attention among the Golden Pinnae. Here are 3
  • RFI immunity. Pavel has said a lot about this. It is particularly important with the unbalanced leads used by the Golden Pinnae. IMHO, in microphones, it is one factor that distinguishes the Great Mikes from the toys.
  • Requirement for good decoupling & layout. Naive decoupling as in JC2 Mk1 is practically guaranteed to ensure OPA627 AD797 & the new uber OPAs will not meet their low distortion potential and exhibit insidious stability even if they do not burst into oscillation.
  • Many of the new uber OPAs exhibit the 'latching and phase reversal on overload' you get with TL07x family.
To investigate, none of these need more than a scope, some way of generating RFI (eg mobile phone), some rudimentary way of measuring distortion and your ears.

I'll pontificate on why OPA134 family seems to come recommended even though, these days, its spec is quite mediocre as measured in simple circuits, ie test rig. It does VERY well on the above 3 points compared to practically all other supa OPAs and the new uber OPAs.

There was a long thread (can't find it so must be on another forum) where someone was trying to 'improve' an old mixer by swapping OPAs.

Lengthy advice by many gurus and some pseudo gurus (ie yours truly) led him to revamp the earthing and decoupling system. (It's really quite difficult to do earthing & decoupling properly on a large & complex system like a broadcast mixer. Which is why an old Calrec will have a MUCH better spec than cheaper stuff though they appear to use the same ingredients) This improved THD by 20dB overall and even more in specific circuits.

Now it was much easier to see the difference between OPAs, including THD and little bursts of oscillation which he laboriously dealt with. OPA134 gave the best overall THD c/f with several supa stuff that have been mentioned on this thread.

IMHO, this is cos, even with much improved decoupling & earthing, the other supa & uber OPAs needed still better attention to approach their potential performance. The less fussy OPA134 was closer to its potential performance.

Looking at the datasheet spec and making 'calculations' doesn't absolve you from measuring the complete device to see if your 'calculations' are correct.

One of the new uber OPAs tried was LM4562 which I believe is LME49710 family with a different cheaper process. This has latching and phase reversal issues. It is inappropriate for simple single supply circuits and also certain filter & EQ circuits.

While the above is obviously slanted towards pro-mixer design, it will have audible consequences in simpler Golden Pinnae design too ... eg where using 'stuff hand carved by virgins from solid Unobtainium' takes priority over basic layout & decoupling considerations. The AD797 datasheet covers important points on decoupling which EVERY user should follow.

Layout is a more 'black art' issue where, from the circuits presented on this thread, even (pseudo?) gurus may need further study.

BTW, humble 5532/4 benefits from the recommendations in the AD797 datasheet. When properly implemented in real applications, it often rivals the new uber OPAs. It's evil unique Class B output stage is particularly clever with vanishingly small 7th harmonic.

Last edited by kgrlee; 22nd January 2013 at 11:13 PM.
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Old 23rd January 2013, 02:37 AM   #33374
fas42 is online now fas42  Australia
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Quote:
Originally Posted by kgrlee View Post
IMHO, this is cos, even with much improved decoupling & earthing, the other supa & uber OPAs needed still better attention to approach their potential performance. The less fussy OPA134 was closer to its potential performance.
Richard, this seems a point overlooked again and again in the audio world, to its continuing detriment. The better the part or component the better it has be designed in, or integrated. Sloppiness will always be penalised by injecting higher levels of objectionable, audible artifacts.

The only measurements that count, are those of a complete system, under stress - meaning amplifiers working hard into nasty loads, lots of mains and RF interference in the mix. Ivory tower spec'ng and verifying doesn't cut it as far as the ear/brain is concerned ...

Frank
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Old 23rd January 2013, 03:12 AM   #33375
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Pavel

Congratulations on your payment of tuition at the John Curl school of audio design. Your work and measurements that John likes will be used in his designs

So now it is your opamps and my resistors.

Brad

You previously asked how some of the issues relate to the BT thread.
The stuff I have been trying to show are almost all incorporated in the BT. However JC has noted a few new twists.
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Old 23rd January 2013, 03:29 AM   #33376
1audio is offline 1audio  United States
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Originally Posted by kgrlee View Post
One of the new uber OPAs tried was LM4562 which I believe is LME49710 family with a different cheaper process. This has latching and phase reversal issues. It is inappropriate for simple single supply circuits and also certain filter & EQ circuits.
The LM4562 and LME49720 are the exact same die. The part numbers were rolled to add the part to the rest of the new audio focused NS lineup. Nothing more or less. You can get them in metal cans, which are reputed to sound better. Improved EMI resistance?

Swapping opamps casually is like swapping dual triodes with no effort to adjust the circuit. Its frustrating but necessary to look at the details of the circuit before swapping or anything may happen. Most non-audiophile products are built to minimum specifications for performance and when the specs are met development stop and they are tested for emi compliance, safety etc.which will catch many of the problems that audiophile products are often susceptible to. Casually swapping parts can upset a very carefully balanced applecart.
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Old 23rd January 2013, 03:56 AM   #33377
Bonsai is offline Bonsai  Taiwan
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Originally Posted by Esperado View Post
I always thought that measurements, and specially THD were proposed to help designers to improve their designs, and optimize values, not more. It is the marketing guys witch had used-it for commercial argues. Look, Telstar, even here, nobody can agree their value :-)
Of course. Measure it. If the distortion is too low, it must have too much feedback, so tell the engineers to make it higher and then claim no feedback or low feedback.

Its what the people want. So give to them.

My interpretation. Not necessarily my view . . .

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Old 23rd January 2013, 04:02 AM   #33378
Bonsai is offline Bonsai  Taiwan
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"Improved EMI resistance?""

Nothing to improve that will add real value if your system design and layout are well done. They are using these things in soundcards sitting on MTBDs with wideband hash
(digital and PSU) in a metal box and still deliver better than -120dB - with some even 10 dB better than this.
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Old 23rd January 2013, 04:24 AM   #33379
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Originally Posted by 1audio View Post
The LM4562 and LME49720 are the exact same die. The part numbers were rolled to add the part to the rest of the new audio focused NS lineup. Nothing more or less.
Bob Pease told me the number was changed because in another language LM4562 sounded like a word you would not use in polite company.
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Old 23rd January 2013, 04:30 AM   #33380
bcarso is offline bcarso  United States
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Originally Posted by simon7000 View Post
Bob Pease told me the number was changed because in another language LM4562 sounded like a word you would not use in polite company.
That reminds me of at least a few stories along similar lines. One was that Enco (anyone remember that gasoline brand?) meant "stalled car" in Japanese.
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