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Old 1st May 2012, 07:07 PM   #4931
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Quote:
Originally Posted by nigel pearson View Post
I think people often refer to this . Daugherty and Greiner 'Some Design Objectives for Audio Power Amplifiers' March 1966, IEEE Transactions on Audio and Electroacoustics '.
Where the mis-conception started, here's yet another level headed critique. This is actually very good and clearly written.
Slew Rate etc.
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Last edited by scott wurcer; 1st May 2012 at 07:10 PM.
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Old 1st May 2012, 07:17 PM   #4932
bcarso is offline bcarso  United States
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Default An older reference

Langford-Smith ed., Radiotron Designer's Handbook 4th ed. 1952, supplement as it appears in April 1965 printing.

Although little detail is provided, it's clear that people were both aware of and concerned about high rate-of-change signals overloading feedback amplifiers.
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Old 1st May 2012, 07:35 PM   #4933
bcarso is offline bcarso  United States
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Originally Posted by john curl View Post
Sure it is, it was our linear design BIBLE at the time.
Although I treasure my copy, there is only so much room in a single book, regardless of how lengthy, particularly one that has a unified treatment of both tubes and transistors.

A quote from the chapter Large-Signal Amplifiers: "If careful choice of device and operating conditions and the use of local feedback do not reduce the static nonlinearity [note the implication that there is a dynamic nonlinearity ] to an acceptable value, over-all feedback must be used in addition. With so many design variables involved, there is little wonder that the designers of very-low-distortion audio amplifiers achieve fame and often have standardized amplifiers named after them!" (Cherry and Hooper, Amplifying Devices and Low-Pass Amplifier Design, Wiley, 1968, pg. 879).
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Old 1st May 2012, 09:02 PM   #4934
dvv is offline dvv  Serbia
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If memory serves, Otala never claimed to have discovered hot water, much less slew rate, he was concerned with transient phenomena and did say something to the effect of a larger slewing rate being an advantage.

What made him SO different from many others was that he identified the problem as he saw it and proceeded to solve it in a clear cut example of his amp. As some will remember, Per Oscarson of Norway obtained the rights to manufacture it, and thus Electrocompaniet was born.

In that example, Otala did insist on several points:

1. Pure class A operation down to -17 dB of nominal power (or was that 14 dB, not sure),

2. Open loop bandwidth as wide as possible, and he demonstarted 100 kHz with off-the-shelf inexpensive transistors, but 20 kHz as the very least, and

3. No more than about 20 dB global NFB.

Whether you believe that or not is your personal business. I tried it enough times in my life that I do believe he was right, perhaps not in each and every detail, but overall definitely.

No science anyone can throw at me can change the fact that I hear what I hear, and that is taht most amps made along those design lines tend to sound better than those using lots of global feedback. If my ears tell me one thing, and all the scince of this world says another, then the science is wrong, period.

Ultimately, science had proved that the world was flat, that Earth was the center of the universe and that politicians actually had a brain installed, even if disfunctional.
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Old 1st May 2012, 09:07 PM   #4935
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1000 pages and NO reference to slew rate?
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Old 1st May 2012, 09:18 PM   #4936
dvv is offline dvv  Serbia
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Originally Posted by john curl View Post
I am not here to praise Otala, but to defend him.
Matti, like me, while acquiring some experience in amplifier design, LISTENED FOR HIMSELF, rather than going with the accepted trends of the day.
Many here like to claim that there was lots of info about slew rate limiting in the mid 1960's, on, but there was NOT! I know, because Cherry and Hooper wrote a book in the late '60's on amplifier design and there is NOTHING about slew rate limiting or anything nearly related to it in the entire 1000 page (approximately) book. I personally looked into what I had available back in 1970 or so, and it was very little, indeed. OF COURSE, we knew what slew rate was, all the IC op amps were limited by it, often fatally for anything but servos. But how to improve it, except for increasing gain-bandwidth of the design, itself, was not self-evident at the time.
Of course, an additional class by R.G. Meyer solved that dilemma, as did Solomon's excellent paper in the early 70's, then it was obvious.
John, we're both old enough to know that for every new notion, there will always be a slew of detractors. Remember that Columbus almost got burnt alive for believing that the Earth was round. Somehow, there are always many more naysayers than people with fresh new ideas.

Sometimes, I think our progress depends more not on new and fresh ideas, but on our capability to deal with mediocrity, as chains of mind are the hardest chains known to man. In every social system, there will always be those who had carved their own little comfy niche they stand to lose with further evolution, and they will defend them with their lives.

Far too manmy scientists today have no inkling of backing off with grace. There is no shame in not knowing something, the shame is not wanting to understand another man's point of view. Refusing to understand just because someone else thought of it first.

And that is a terminal illness, no cure.
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Old 1st May 2012, 09:20 PM   #4937
SY is offline SY  United States
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Originally Posted by dvv View Post
Remember that Columbus almost got burnt alive for believing that the Earth was round.
I see that you and John took history from the same professor.
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Old 1st May 2012, 09:34 PM   #4938
FrankWW is offline FrankWW  Canada
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Remember that Columbus almost got burnt alive for believing that the Earth was round.
no. he didn't.

he had chinese maps from venice, i believe.

lots of folk knew what was 'over there'
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Old 1st May 2012, 09:46 PM   #4939
SY is offline SY  United States
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Originally Posted by FrankWW View Post
no. he didn't.

he had chinese maps from venice, i believe.

lots of folk knew what was 'over there'
Interestingly, he DID have beliefs that clashed with contemporary wisdom. For example, he thought that Asia was much closer going Westward, that the Earth diameter was smaller than had been believed for about 2000 years, that there was no continent between Europe and Asia, and that Japan was very far east of China.

Of course he was wrong about all that, but it's not as good a story if you tell the truth.
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Old 1st May 2012, 09:52 PM   #4940
dvv is offline dvv  Serbia
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Originally Posted by SY View Post
I see that you and John took history from the same professor.
Very possibly, SY.

I'm 59 years old, and in my schooling, went through, in proper sequence, Yugoslav, Turkish, Pakistani, Yugoslav, British and Yugoslav educational systems. I have lived (lived = 1 year or longer), beside naturally my own country, then Yugoslavia, now Serbia, in Turkey, Britain and Egypt.

All that has taught me to be tolerant of other people's views, habits, cultures and customs. But also to stand up and be counted for my own.

I honestly believe Otala, and by extension John, are right. I do not expect other people to believe it, if they so choose, and will never think less of them because we don't agree. Wahab, for example, who is known by his choosing not to agree with Otala's theories, is no less respectable for me just because we disagree on this one point. Chances are we might agree on many other points, who knows. Inch'Allah, as the Arabs would say.

I disagreed with you, and most likely will again, but again, if we dig a little deeper than one or two theories, we would very likely find many a common point. I believe that is quite natural.

In the end, it comes down to why are we here. Are we here to learn more from the very differences of opinion, to show off our alleged knowledge, to get some help from alike souls, or whatever.

Your, or anybody else's disbelief in one of my beliefs merely serves to make me check and recheck my own beliefes, and if I find them valid nonetheless, to hone them further. Or, if your arguments seem valid to me, to modify and even change my beliefs. Or, if you should tell me, for example, that I shy away from FETs because I don't know how to work with them, all I can do is confirm my ignorance with them because that is the truth - but I am willing to learn, to change my views if I see reson for it.

It's all about how one perceives the differences between us. Unfortunately, mankind has always seen them as reasons for believeing in their own particular superiority and righteousness; I choose to see them as our common wealth, our joint pool of thought, as the difference neccessary for progress. If you didn't disagree with me, what would push me harder to move on, work harder?
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