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Old 12th September 2012, 09:31 AM   #1081
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Esperado View Post
OPEN LOOP Bandwith and Slewrate are correlated, that's what i wrote. Please, read correctly and/or learn.
Open loop bandwidth is an envelop curve, witch shows the max gain an amp is able to provide for each frequency.
To understand how bandwidth depend both of the open loop bandwitch and gain factor of an amp, please, read:
Gain?bandwidth product - Wikipedia, the free encyclopedia
To understand what is slewrate, please read: Slew rate - Wikipedia, the free encyclopedia
TIM, (also called slewrate distortion :-) is produced when the amp is not fast enough to follow the correction signal, please, learn or try to understand.
Please read some books and try not to confuse DIYers here with YOUR wrong assertions.
And, by the way, please, learn in the same time how to post in a non aggressive and disagreeable way, and not be ridiculous.
Sorry if you are offended, but what you write is just not correct. I suggest Bob Corddel book, not wikipedia.
Bandwith and Slewrate are NOT correlated.
TIM is not result of Negative Feed Back, but in most cases is result of not enough high Slawrate, by the way,for 100W amp 50V/usec is more then enough. What means the amp is not fast enough, low Slewrate??
Don't bee angry, but you are wrong.
dado
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Old 12th September 2012, 09:44 AM   #1082
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Quote:
Originally Posted by Joachim Gerhard View Post
Many think for example that Rise Time and Slew Rate are the same.
Well, let says that they are two different ways of looking at the same thing. :-)
Please, somebody can explain Dadod the difference between Open Loop bandwidth and bandwidth ?
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Old 12th September 2012, 09:48 AM   #1083
sonnya is offline sonnya  Denmark
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Stop stop....

TI has through newnes published a book called "OP AMPS for EVERYONE" by CARTER and MANCINI. ISBN 978-1-85617-505-0-90000

Read chapter 1 - 13.!! Please!!!!
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Old 12th September 2012, 09:56 AM   #1084
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Here is a slew rate nomograph that shows how much slew rate is required.
I think Dadod knows what the difference between open loop bandwidth and bandwidth is.
I have participated in threads where we also discussed if it is more beneficial to raise the open loop bandwidth or go for massive gain in the bass. Unfortunately we did not find an agreement so i gave up.
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File Type: png Slew Rate Nomograph.png (108.5 KB, 242 views)
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Old 12th September 2012, 10:34 AM   #1085
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Joachim, i don't realy understand your monograph with *fixed values*. For several reasons.
One is TIM and IM continuously *reduce* as much you are reducing the slewrate of an amp.
On the amp i was comparing Voltage feedback with so called "cureent feedback", same schematic, i simulated (and measured) the followings, with the same closed loop gain:
Square waves (gives an idea of the slewrate): http://www.esperado.fr/images/storie...do/square2.gif
Harmonic distortion: http://www.esperado.fr/images/storie...ion-curves.gif
IM: http://www.esperado.fr/images/storie...ion-curves.gif
Bandwith: http://www.esperado.fr/images/storie.../response2.gif
(Simulation is interesting while it lies only on calculations, so: theoretical.)

On my point of view (i hope it was the same you tried to defend) there is no doubt slew rate is the goal, as i said, not massive increase of the gain of an amp. My religion since decades. The reason to live of the SSA.
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Old 12th September 2012, 10:53 AM   #1086
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This was probably true for 1930s when source material was slow and low definition.But 8V/us for 100W amp is really a joke.
It may be good for Public Address amps...

Last edited by BenY; 12th September 2012 at 10:57 AM.
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Old 12th September 2012, 11:24 AM   #1087
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Quote:
Originally Posted by dadod View Post
Bandwith and Slewrate are NOT correlated.
I wrote OPEN LOOP Bandwith, you argue about Bandwith. Am-i not clear ?
Slew rate is just a method to evaluate the open loop bandwith of a closed loop amp. Done for that. To measure the slewrate, you need to over saturate the amp, for there is no influence of the gain factor. *Just the switching time*.
Quote:
Originally Posted by dadod View Post
TIM is not result of Negative Feed Back, but in most cases is result of not enough high Slawrate, by the way, for 100W amp 50V/usec is more then enough. What means the amp is not fast enough, low Slewrate??
dado
That's exactly what i said from the beginning: "Result of not fast enough Slewrate ... in a closed loop amp." (Consequence of delays, distortions and phase turn of the feedback signal due to slow response ).
In a ideal perfect amp with no feed back, and a limited slewrate and bandwidth, just high frequencies will be not reproduced. No IM generated.
To give an image, it is like in a car accident. Damage is caused with the speed in correlation with the slow response of the driver. More the speed is high (hf ), more you need fast (slewrate) reflexes ( feedback).

No, 50V/µs is not more than enough on my point of view. Distortion and phase response will be greatly better with faster slewrates. See pictures in my previous post.
Easy to understand: The signal across the amp. If the amp is not fast enough (slew rate) to follow-it you will have a great differences between the original signal and the signal at the output. When you apply feed back, those errors will feed the amp with higher level correction error signal, that the amp will not be able to follow again, worsening the situation.

End of this endless controversial and useless discussion on this subject. Known from decades, and perfectly described by the authors you are referring too, among many others.
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Last edited by Esperado; 12th September 2012 at 11:39 AM.
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Old 12th September 2012, 11:53 AM   #1088
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Quote:
Originally Posted by Esperado View Post
I wrote OPEN LOOP Bandwith, you argue about Bandwith. Am-i not clear ?
Slew rate is just a method to evaluate the open loop bandwith of a closed loop amp. Done for that. To measure the slewrate, you need to over saturate the amp, for there is no influence of the gain factor. *Just the switching time*.

That's exactly what i said from the beginning: "Result of not fast enough Slewrate ... in a closed loop amp." (Consequence of delays, distortions and phase turn of the feedback signal due to slow response ).
In a ideal perfect amp with no feed back, and a limited slewrate and bandwidth, just high frequencies will be not reproduced. No IM generated.
To give an image, it is like in a car accident. Damage is caused with the speed in correlation with the slow response of the driver. More the speed is high (hf ), more you need fast (slewrate) reflexes ( feedback).

No, 50V/µs is not more than enough on my point of view. Distortion and phase response will be greatly better with faster slewrates. See pictures in my previous post.
Easy to understand: The signal across the amp. If the amp is not fast enough (slew rate) to follow-it you will have a great differences between the original signal and the signal at the output. When you apply feed back, those errors will feed the amp with higher level correction error signal, that the amp will not be able to follow again, worsening the situation.

End of this endless controversial and useless discussion on this subject. Known from decades, and perfectly described by the authors you are referring too, among many others.
I think youre very confused, go read the book as Sonnya suggested.
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Old 12th September 2012, 12:04 PM   #1089
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Esperado, i have looked at your modification of the Crescendo and you got lower distortion
after the modification.
Concerning if i have a priority of CFB against VFB that is not easy to answer in an absolute way out of context. My power amp and my preamp use current feedback, my phono has a current conveyer input stage with 75usec transimpedance and an active second stage with VFB. So i have at least one stage of voltgae feedback in the chain and it sounds great.
The TSSA though that i build gives me the best sound so far i had in my system.
Is it the speed, is it the spartanic simplicity, is the the PSU and how i build it ?
I can not tell. What i can tell is that it sounds very clean although it has distortion in the 0.1% range at higher level. I knew already that my hearing is not particular sensitive to low order harmonic distortion since i participated in the Klippel test. I scored in the middle group at around 1% TH low order weighted. Since then i know that the hunt for ultra low distortion is fruitless, especially when the amp gets very complex and a lot of PN junctions are in the chain.
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Old 12th September 2012, 12:11 PM   #1090
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The nomograph is from the Elliot sound pages and he is very concervative in terms of required slew rate. There are more examples when you google the article. He comes to the conclusion that a 10W amp needs only 2V per usec
to swing the highest audible tones.
I have some other ideas about speed. One of my teachers was Joseph Manger and the Manger driver resolves better when it is driven by a fast chain. It has to be a stable chain though. Incredible extention with oszillation is not good ether although such a chain can sound very exiting in terms of detailing. It is just too much and ultimatively tiring.

Last edited by Joachim Gerhard; 12th September 2012 at 12:14 PM.
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