Is the CFB topology superior, and why? - Page 36 - diyAudio
 Is the CFB topology superior, and why?
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diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by AndrewT There seems to be a consensus that the most signal slew needed for a 100W into 8ohms amplifier is about 5V/us. If one then adjusts the amplifier to just be able to meet this slewrate then one finds that it distorts. From experiments it seems that by increasing the amplifiers slew rate up until it is about 10times the maximum signal slew that this added distortion reaches a minimum. End of consensus. That seems to imply that 50V/us is required for fast music signals, if one wants to reach that distortion minima for music reproduction.. And increasing beyond the 10times achieves little if anything of an improvement.
What if the input signal is sampled at 192khz like .. often ?That's means that the fastest rise/fall time between 2 consecutive points should be almost 5.2us .
Suposing that the soundcard,dac has a 6volts peak to peak which means exactly 2.1Volts rms as most of the soundcards,dac's has .That means that the SR of the soundcard dac is 6/5.2=1.15V/us .A typical gain of an100W amp is 33. To see the same transition on the amp output we must have the input multiplied with the gain in the same unity time like the input .So if the input has 1.15 V/us ,the output should have 33*1.15~40V/us . This value will be sufficient only if we don't want to have transient intermodulation distortion .But the neagative reaction takes exactly the same time to react to the output .So we should double the value to 80V/us.
But to have a lower TIM we should multiplied with 10
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"please try to listen to some music through the amplifier instead. Life is so short ..."

Last edited by catalin; 6th November 2012 at 02:29 PM.

diyAudio Member

Join Date: Nov 2009
Location: algeria/france
Quote:
 Originally Posted by catalin What if the input signal is sampled at 192khz like .. often ?That's means that the fastest rise/fall time between 2 consecutive points should be almost 5.2us .

You did compute the slew rate necessary for a 96khz sine at full power
not for a musical signal wich is limited to a fifth of this frequency so
your 200V/us should translate to 40V/us for a 200W amp , about
the number given by AndrewT.

 6th November 2012, 02:34 PM #353 diyAudio Member   Join Date: Jun 2007 Is there life .. __________________ "please try to listen to some music through the amplifier instead. Life is so short ..." Last edited by catalin; 6th November 2012 at 02:36 PM.
diyAudio Member

Join Date: Feb 2003
Location: Jakarta
Quote:
 Originally Posted by wahab Your point of view is interesting but since you have some maths formal training and are used to simulators why not try to check a few claims and bring a stone to the build that would have way more weight than subjective assumptions.
I'm not a precise person (by psychological test I'm a person who dominantly use the right brain, whatever that means). I mean, you can see that I often mention the wrong things and I still don't care, because it was not the point.

If you are referring to the 10X claim, of course, I have never taken it literally.

And unfortunately I don't rely on simulator to predict the relative quality between two amps of different topologies. Too difficult.

When around 2010 you created that thread about comparing sims of various amps, I thought you would soon learn and realize that it was not that simple. But it seems you still what you were then, fully trust basic simulation parameters to judge amp quality. That's okay of course. I just don't do it that way.

Quote:
 Originally Posted by wahab Electronics is a science backed field and in this respect it accept to be questionned with practical experiences so any claim can be checked and in the subject that interest us, CFB supporters still fall short of proving their claim of so called superiority of this topology using scientifical yet simple arguments.
Yes I think we all knew that. It takes courage to stand and say CFB is superior than VFB Just like in any other disciplines, some of us know that we have limitations, and at that border line we can just make assumptions, hypothesis, sometimes delusions.

diyAudio Member

Join Date: Nov 2009
Location: algeria/france
Quote:
 Originally Posted by catalin

Unless one listen to 192KHZ sampled crash cymbals at full volume,
assuming he has the speakers for the purpose , the paper
show that harmonics energy is barely more than two percent
of the total amount , so it s unlikely that there will be slew
rate limitation even at thoses frequencies with 30V/us amps....

 6th November 2012, 02:57 PM #356 Account disabled at member's request   Join Date: May 2006 [QUOTE=wahab;3230192]A story from the Arab world : When all animals reunited , they decided to ask the donkey female about who has the most beatifull children. The donkey answered that in all honnesty she found her own children to be the most awsome..... /QUOTE] Most excellent response.
diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by wahab Thank you but i know this article. Unless one listen to 192KHZ sampled crash cymbals at full volume, assuming he has the speakers for the purpose , the paper show that harmonics energy is barely more than two percent of the total amount , so it s unlikely that there will be slew rate limitation even at thoses frequencies with 30V/us amps....
You don't need to listen at full volume to have a peak to peak voltage swing !
Peaks in music are 5 to 10 times higher than the rms value .
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"please try to listen to some music through the amplifier instead. Life is so short ..."

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Location: ..
in digital audio signal reproduction just "conecting the dots" with straight lines doesn't give a valid audio band limited signal

no commercially distributed musical signals are recorded with substantial 192 k Nyquist content - virtually all studio ADC are delta-sigma and have brick wall internal digital filters below Nyquist

even the hotest source is recorded with slower mics

Quote:
 Originally Posted by jcx ... recorded music is band limited – Earthworks' fastest recording mics are limited to 50 kHz – and they have such poor S/N that their only use is close micing drum kit – capturing sound that never reaches the audience ears in reasonable live venues and that 50 kHz is still a small fraction of the closed loop bandwidth of typical modern audio power amps ...
the vast majority of studio mics have <25 kHz corner frequency, some classic vocal mics may only be 14 kHz

even mc cartridges can only track ~ 5 kHz power bandwidth - when people say records can have higher frequencies than CD you have to realize it is at much lower than mid band amplitudes - the slew rate limit is that ~ 5kHz

diyAudio Member

Join Date: Nov 2009
Location: algeria/france
Quote:
 Originally Posted by Jay And unfortunately I don't rely on simulator to predict the relative quality between two amps of different topologies. Too difficult.
What would be easier and more accurate ? Design by ears ?..

Quote:
 Originally Posted by Jay When around 2010 you created that thread about comparing sims of various amps, I thought you would soon learn and realize that it was not that simple. But it seems you still what you were then, fully trust basic simulation parameters to judge amp quality. That's okay of course. I just don't do it that way.
Processors with roughly one billion transistors are first simulated
and they work wich is the prove that simulators are accurate enough
to model real world behaviour of very complex electric devices , but still , here , there s lot of people that think that it s up to them to predict
the behavior of basic circuits using a handfull devices.

Indeed , had the sims displayed a superiority of CFB that its
promoters would have gladly embraced the conclusions
without even checking but alas , nothing of the sort did
happen , so what is left is to brand the simulations as not
significant....

 6th November 2012, 05:24 PM #360 diyAudio Member   Join Date: May 2005 Location: Denmark sure you can model what the circuits do, but not how they sound....simple as that...!!! Some of the fine amplifiers out there are based on tubes where you measure maybe 1% distortion, speakers are also measured in % and here we talk about 0.00something. It's pure nonsense..performance is not about distortion, something else is just much more important. CFB finds that something more often than VFB.. Question remains what and why...?? Quite sure simulators can find that difference too, and that could be the key to unlock more knowledge. but arguing in a way "I know more than you do" will never get us there. To gain knowledge we have to remain open and listen. Most here have something to contribute.. A least for me CFB is more than fashion. but in the End It may not be the final solution.

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