I got a couple of samples from AD, did some measurements and, as I see it, it's an OPA627 with benefits. One notable exception: +PSRR @ 100KHz sux. Opa627 is 20dB better.
I am reminded of the 3 stages of anything: re PIM
First, it doesn't exist.
Second, it exists, but it is not important. (where we are now with Scott and Bob)
Third, we invented it!
Tune in, in future,for the resolution of this question.
Never said it didn't exist, and I stand by my opinion that it will not prove to be very important. You have not presented any compelling evidence to the contrary.
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BUT, is it xover distortion, or noise? Scott, please address the question.
You should be able to answer this question by yourself, straight from the datasheet information.
Hint: You have the noise density (fig. 3), you have the THD+N vs. output level (fig. 16, corrected), you know the noise gain, you have the THD+N bandwidth (same fig. 16), you can calculate an approximate of THD (without noise) @1KHz and draw your own conclusion.
Still confused? Look here: http://www.analog.com/static/imported-files/tutorials/MT-049.pdf
You are welcomed.
Good question John. I don't understand either why THD+N is measured at all, even by professionals.
Luckily, I can measure (and see!) the residual without that ****** N, by averaging the signal, even a million times if necessary.
I am reminded of the 3 stages of anything: re PIM
First, it doesn't exist.
Second, it exists, but it is not important. (where we are now with Scott and Bob)
Third, we invented it!
Tune in, in future,
John,
First, I never said PIM did not exist.
I did suggest that it was measurably very small in amplifiers that had very small distortions of other kinds.
But most importantly, I showed that PIM is not exacerbated in any way by low open loop bandwidth.
Otala was not wrong in exposing PIM. He was wrong in asserting that it was due to low open loop bandwidth.
I realize that it is knee-jerk intuition to think that PIM gets worse with low open-loop bandwidth, but the math and the measurements do not support it.
He was also wrong in not putting the magnitude of feedback-generated PIM into context with PIM that exists even in amplifiers without negative feedback.
John, once again, I ask how you distinguish PIM from TIM when you are using the DIM test.
One more question: how do you ever know that it is PIM that you are hearing in listening tests?
Cheers,
Bob
Bob, interesting reply.
You can tell PIM from TIM WHEN that mathematical relationships of some of the 'IM' products do NOT match an integer algebraic sum or difference of the test tones. Please note that several 'blips' or whatever they are called, do NOT match anything, in Fig. 3 of the 1976 paper, presented at AES-NY. This is because they are PIM, not TIM. Yet, they are the same height as many other 'blips' on the screen, that we are testing for, and expect. Is this to be ignored?
Show Barrie Gilbert, where he went wrong, as well. You can't just handwave that away.
You can tell PIM from TIM WHEN that mathematical relationships of some of the 'IM' products do NOT match an integer algebraic sum or difference of the test tones. Please note that several 'blips' or whatever they are called, do NOT match anything, in Fig. 3 of the 1976 paper, presented at AES-NY. This is because they are PIM, not TIM. Yet, they are the same height as many other 'blips' on the screen, that we are testing for, and expect. Is this to be ignored?
Show Barrie Gilbert, where he went wrong, as well. You can't just handwave that away.
Scott, Dick Sequerra says to tell you that I am right about this. Maybe, sometime, you should ask him how he used your AD797 in his preamp. You might be surprised, if you don't know already. Go on, it won't effect your friendship with him. He might even be more at ease with you, discussing these things in future. I learn new things from him, all the time.
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Everyone else, the reason PIM might be even more important than TIM, is that it is more dissident from the musical scale, for one major reason. This could put in on par, with aliasing, as far as sensitivity is concerned, just because of that. How would you like to listen to aliasing frequencies throughout the audio frequency band? PIM gives the same potential for this sort of thing. How much is just detectable? .1% .001% Who knows?
If you mean the THD graph, yes, I found that yesterday. Don't know much about this part, but it probably will not be available in TO-99 cans.
BTW - Hopefully people can play with samples and make up their own minds, as I don't promote here.
Im not much of a 8 leg type but have used AD817 and AD829 in the past but this chip , ADA4898, although not referenced for audio should do very well in future, certainly deserves TO-99 can if it would make it even better.
The guys at National are going to have a rude awakening when they listen to this one.
I once heard a dead bug bouncing on a cone of a stage monitor, through microphone and PA! Can you imagine how quiet was that rattle? But it was heard, and it was very annoying. Why? Because it did not hide behind harmonics of the musical signal. That's why when people say that they don't like the sound of very accurate according to THD measurements amp because it sounds "too sterile" I know it is not "sterile", it is dirty, but the dirt is not aligned with harmonics.
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