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Old 27th January 2004, 12:01 PM   #21
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Maybe to analyze the design. Seems he knows a bit about class d, and if you check his site, you can see where he discusses the different merits and demerits of each topology.

Why would wanting details (of any sort) make him biased? Obviously many others felt comfortable providing himwith information, as there are at least 10 other class d companies discussed on his web site. Why don't you consider him independant? He doesn't work for any of the companies discussed on his web site, and he isn't in business himself. What's the problem?
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Old 27th January 2004, 12:14 PM   #22
km is offline km
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hi.

>Maybe to analyze the design> yes maybe.

>Obviously many others felt comfortable providing him with information>

dont know about that , do you?

>He doesn't work for any of the companies discussed on his web site>

dont know about that either , do you?

if you perform a listening test i suggest that you listen

if you look at schematics and thd specs im afraid you "can hear what you see" , got it?

best rgds karsten madsen - cadaudio.dk
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Old 27th January 2004, 12:32 PM   #23
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You really need to read the web site....As to judging sound from the design and specs, he says:

"How can I infer sound quality from measurement data?
The best way to determine the sound quality of an amplifier is to hook up a source and a pair of good speakers and listen. Some even go so far as to claim measurements are uncorrelated with audible quality. The reality is "yes and no".
Yes, there are amplifiers with excellent figures that put out a perfectly foul sound. And yes, there are amplifiers with very mediocre figures that sound quite fabulous. But no, there are some important things to be learned from measurements. Firstly, it is true that absolute distortion figures tell little about how an amp will sound. The behaviour of distortion versus frequency does."

Which is what you are saying, if I understand you correctly.

Furthermore, as to his motives:

"This site tries to provide maximally objective information for people who want to build class D amplifiers. Originally the target audience was companies producing consumer appliances containing class D amplifiers. I have no financial interest in this whole affair..." and "I'm now 53 and retired."

So, while I don't know FOR SURE, taking him at face value, I have no reason to question his integrity or honesty. If you have some valid, first hand information that contradicts his statements, then spell it out. Otherwise, it looks like you have an axe to grind, and your inferences are in poor form.
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Old 27th January 2004, 12:36 PM   #24
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Quote:
Why would wanting details (of any sort) make him biased? Obviously many others felt comfortable providing himwith information, as there are at least 10 other class d companies discussed on his web site. Why don't you consider him independant? He doesn't work for any of the companies discussed on his web site, and he isn't in business himself. What's the problem?
I think this is generally quite a good site but I also doubt that it is really unbiased (but whose opinion is unbiased anyway).
Just a small hint: He is also Belgian like Bruno Putzeys.

But there are also some informations that are incorrect: Sigma-delta amps (like the Sharp) can use almost the full supply voltage swing, like any other switching amp (and not only 50 % as he claims). They are less efficient than a PWM amp at low output power due to the high idle switching frequency, but this will improve significantly at higher output levels. He is critisising Sharp for the feedback takeoff before the output filter. It isn't that complicated at all to take feedback from the filter (I tried really hard with several topologies that were designed by intuitition UNTIL I sat down to do the PROPER math ) but it is also a matter of personal taste. I by myself prefer feedback takeoff after the filter but I also admit that it has some disadvantages: Degraded load stability (I have seeen measurements of the Sharp SM-SX100 that were excellent in this respect) and more susceptibility to TIM. I know of a mixed solution (that is new to my knowledge, but I may err) that should be a quite useable tradeoff between both worlds but I am afraid of publishing it because someone might go and patent it


Quote:
in my mind patents can be used to establish a stronger basis for discussions with other parties and i know of at least one example where it was used to try to keep others out of the market (im talking about class-d patents here)
Are you talking about a well-known Californian company that patented a general description of a switching amplifier with a double feedback loop (which was as much prior art as can be, at least from the drawing on the first page !) ?


Regards

Charles
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Old 27th January 2004, 12:49 PM   #25
km is offline km
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hi.

kuribo , whether i/we trust tip voigt is our decision i think and i think we can disagree about his objectivity as well.

charles , no i wasnt referring to that one but im sure there are more than one example of this......

the icepower does actually have 2 feedback loops , one before and one after the output filter , right?

i also think that to make a good comparison of audio equipment you would normally have more than one listener , right?

again i would welcome a qualified and unbiased comparison of pwm amplifiers , preferably compared with class a (or ab) amplifiers , but i dont know of any, just too bad we all live so far part

rgds karsten madsen - cadaudio.dk
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Old 27th January 2004, 12:51 PM   #26
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He was born in South Africa, and now lives in Belgium part of the year, and in South Africa the other. I don't think he is a Belgian citizen. Regardless, I think infering he is biased because of his place of residence is in the same country is a bit of a stretch. He doesn't seem too impressed with the Icepower amp, which is from....a Belgian company!

In any case, he seems to give solid reasons for his ranking of the UcD design. Of course we all have bias, but he does start off his web site by saying "maximally objective information", so I take him at face value. He isn't trying to sell anything.
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Old 27th January 2004, 01:01 PM   #27
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Quote:
He doesn't seem too impressed with the Icepower amp, which is from....a Belgian company!
They are actually from the "class-d heaven": Denmark.

Quote:
the icepower does actually have 2 feedback loops , one before and one after the output filter , right?
In the patent I have in mind they use a topology with a double-feedback loop before the output filter (using two integrators).
The hybrid solution I also mentioned isn't a nested configuration like that either but much simpler and easier to implement and calculate.

Regards

Charles
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Old 27th January 2004, 08:24 PM   #28
Steven is offline Steven  Netherlands
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Quote:
Originally posted by phase_accurate

...But there are also some informations that are incorrect: Sigma-delta amps (like the Sharp) can use almost the full supply voltage swing, like any other switching amp (and not only 50 % as he claims). They are less efficient than a PWM amp at low output power due to the high idle switching frequency, but this will improve significantly at higher output levels....

Isn't it that sigma delta modulators need to be of high order to keep the noise low while employing a moderate oversampling ratio? I think because of loop stability of these modulators often a 3dB margin to full scale is adhered to, and noise and distortion rise sharply (excuse the pun) if modulated above that level. If this is the case for the Sharp and THDN increases above -3dB of maximum (voltage), then this would equal 50% of maximum power.

Steven
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