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Old 30th November 2011, 07:42 PM   #18541
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I know that Studer used something like this with an external PP output stage in their first solid state A-80's. Worked OK, compared to the next generation A80 that used another approach. I showed Willi Studer the measurement comparisons, myself. (however, little was done about the situation)
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Old 30th November 2011, 07:58 PM   #18542
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Scott, I really don't know what you are referring to, when you denote fet input op amps, with regard to my opinion.
As you know, I prefer fet input over bipolar input in many applications. However, I use the AD797's in the input stage of my ST1700B analyzer, because they are so quiet, with great success. In fact, I helped Dick Sequerra do the same thing a few months ago.
I find that there is a difference when using IC's for measuring equipment (where they work well) and for audio, (where they sometimes fail to sound right). I learned this by relying on you, Scott, and your jfet input op amp, the AD712, and unfortunately, having to remove it from the input of my first Parasound power amp effort, when reviewers heard a problem. I got the criticism of my boss, for putting it in, in the first place, and trusting that it would sound OK. And I had to make an alternative version that we still use today for Parasound power amps. Once bit, twice shy, they say! '-)
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Old 30th November 2011, 09:04 PM   #18543
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When it comes to IC's, I can't get more than a 'B' rating using IC op amps exclusively. I have certainly tried hard enough. Good: connectors, board layout, passive parts like caps and resistors, thick aluminum shielding, super power supply regulation, etc., etc. Ticked my boss off. He wants 'A's' from me, not 'B's' from my efforts, but it was not to be, no matter how hard we tried. After all, the JC-1, and the JC-2 were 'A's', why not the JC-3? Well, guess what, every input IC that I tried sounded different. I settled for a device sounding as good as any other and cost effective as well. I use no ADI parts in the JC-3. However I did design an AD825 into a power amp fairly recently, with great success. Can anyone figure out why?
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Old 30th November 2011, 09:16 PM   #18544
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Quote:
every input IC that I tried sounded different.
I have had the same experience for ten years of experiments, even with fast opamps. Anyway, as a rule, FET input, low noise, low distortion and SR >= 50V/us were the best sounding, with several exceptions like AD844.
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Old 30th November 2011, 09:25 PM   #18545
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Quote:
Originally Posted by john curl View Post
However I did design an AD825 into a power amp fairly recently, with great success. Can anyone figure out why?
Why it was successful or why you designed it into a power amp?

Maybe this -

"High output drive capability
Drives unlimited capacitance load
50 mA min output current"

Or this -

"High Speed
41 MHz, -3 dB bandwidth
125 V/s slew rate
80 ns settling time"
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Old 30th November 2011, 09:26 PM   #18546
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High open loop bandwidth.
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Old 30th November 2011, 09:44 PM   #18547
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Originally Posted by Joshua_G View Post
Indeed, there is no stereo set in the world, at any price, that can faithfully emulate a live concert of un-amplified acoustic instruments.

As for recent recordings of classical music, indeed there are some exceptions that stand out, above the average majority.
Please name a couple.
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Old 30th November 2011, 09:49 PM   #18548
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Originally Posted by john curl View Post
When it comes to IC's, I can't get more than a 'B' rating using IC op amps exclusively.
Same here John.
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Old 30th November 2011, 11:08 PM   #18549
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Originally Posted by john curl View Post
High open loop bandwidth.
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Old 30th November 2011, 11:47 PM   #18550
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It seems to be related to differential phase.
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