John Curl's Blowtorch preamplifier part II - Page 3592 - diyAudio
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Old 26th February 2013, 05:17 PM   #35911
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Gpagag, OF COURSE, we worry about costs for a 'cost effective' high quality phono stage like the JC-3. We WOULD have used the AD797, if we had not found a similar, lower priced IC to replace it. I don't like to pay extra either, if I can get the same performance with something less expensive.
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Old 26th February 2013, 05:23 PM   #35912
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Jack Bybee is an old man. At 84 years old, he is NOT into 'mass production' of whatever he makes. He just does the best that he can, at a few different price points. He certainly works harder than I do, but he seems to need the activity. I can sit around arguing with people here, '-), but Jack needs to get out of the house, itself. This is a great excuse to do so, AND he has a bunch of hi end customers who invite him to their house (or country) to listen with them.
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Old 26th February 2013, 05:24 PM   #35913
SY is offline SY  United States
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I have not seen as much practical design info in later articles in the AES, compared to past decades.
Perhaps because this aspect of audio (getting an electrical signal from point A to point B and making it bigger or smaller) is a solved problem and there's little or no truly new research to do in that area?
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Old 26th February 2013, 05:25 PM   #35914
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Once again, this is the distortion spectrum of the JC-1. It is WORSE than the JC-2 by more than 10 times. Please note.
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Old 26th February 2013, 05:26 PM   #35915
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Maybe, SY.
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Old 26th February 2013, 06:13 PM   #35916
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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.
John, I think you should give Matti (and yourself) some credit for opening the minds of audio designers 35 yrs ago to these TIM and slew rate issues. Since then, most savvy designers (and lots of them here) know how to avoid them; it's not that you tell them anything new.
Granted, there are still designers or amateurs that think feedback causes slew rate limiting or TIM, but hey you can't educate everyone.

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Old 26th February 2013, 06:22 PM   #35917
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Feedback IS a necessary factor to give normal slew rate limiting. The op amp is a perfect example of worst case slew rate limiting, in principle.
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Old 26th February 2013, 06:37 PM   #35918
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I have not seen as much practical design info in later articles in the AES, compared to past decades. That is why I have put some 'old' stuff up, for those of you who might have been children when it was first introduced.
A lot of it is now issued by committees as advisory papers. Of course it is on topics of current interest such as digital transport of audio signals.

Too often tutorials seem to be confused with being new information.

I had a recent conversation about advances in audio. My point was not the difficulty in keeping up with what is new, rather it is getting a better understanding of what is basic.

You know stuff like why double blind testing is not very useful.
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Old 26th February 2013, 06:45 PM   #35919
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As if I knew
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Granted, there are still designers or amateurs that think feedback causes slew rate limiting or TIM, but hey you can't educate everyone.
jan
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Feedback IS a necessary factor to give normal slew rate limiting. The op amp is a perfect example of worst case slew rate limiting, in principle.
Teaching is a hard job.
But being a student, is a mind bogging situation.
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Old 26th February 2013, 06:49 PM   #35920
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Feedback IS a necessary factor to give normal slew rate limiting. The op amp is a perfect example of worst case slew rate limiting, in principle.
You must be kidding! Slew rate limiting is caused by insufficient charging current for a capacitor in the amp (often the compensation cap).
It can occur also in open loop amps, if you feed them high-level, fast signals faster than the designed-in slewrate.

It is true that is you have a marginal design, adding feedback can worsen the occurence of slew rate limiting because it increases the error signal at the input, but it doesn't cause SRL.
Fear for slew rate limiting is no reason to shy away from feedeback - you just have to get yourself a competent design.

jan
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