Class D = Trash?

A high-definition eGaN FET-based system with higher PWM switching frequency, reduced feedback, and higher bandwidth produces the sound that has the warmth and sonic quality that audiophiles demand;

For a quality Class D audio solution, it is possible to avoid these transitions all the way through the system to the final Output Filter

The key to great Class-d, is to get it’s LOW ORDER output filter to do it’s job of getting rid of ALL switching noise from the audio band before it get sent to the speakers, and without creating any phase shift.
The only way to do this successfully is to raise the switching frequency noise much higher so this low order output filter (without masses of feedback) can do it’s job properly without any residue effects or switching noise remnants being left within the audio band.

This is why Technics have led the way with the new SE-R1, have striven to DOUBLED the switching frequency with these new eGan Fet transistors, to get closer to the ideal above results.

Credit to Mark Levinson a couple of years ago tried to solve this problem with todays switching frequency, by using much lager (to take the amps power) higher order output filters and less feedback, but it was a bit of a flop, with their very expensive. (see the size of the 4 x chokes for the higher order output filter for each monoblock).

http://www.stereophile.com/content/mark-levinson-no53-reference-monoblock-power-
amplifier#rJEmkELOsfXsME4b.97
It’s 10khz!! (not 1khz) square wave without!!! the AP filter, is the best ever seen for a class-d amp (almost as good as a linear amp) because of it’s massive higher order output filter and less feeback, but this high order filter obviously created other problems, and was not received well, that’s why low order with low feedback is the way to go, but it must do it’s job properly, and the only way to do that is to raise the switching frequency noise much much higher.

Cheers George

Hi @georgehifi

I'm not sure that feedback in a digital amp works the same way, or has the same consequences as it does in a linear amplifier.

Do you have any data that indicates feedback is anything but a positive in a digital amplifier?


Best,


E

No but I believe from what others have said, the output filter in some Class-D’s is included into it’s global loop aiding it’s effectiveness? that's why I bought it up, just to cover all bases.

Cheers George

Ahhh, makes sense, and yes indeed it does. :)

Thanks for the clarification.

Hi atmasphere,

      I'm very interested in checking out your take on the first Atmasphere class D amp.
     Too early to share any insider details like modules chosen. type of power supply adopted, any customized components, target price and expected release date?  

     As to the Audiophile Review article describing class D amps as 'digital' amps, I think the author, Skip Taylor,was a bit inconsistent in the entire article. I think you're right, he was  all over the place on terminology and his knowledge base seemed outdated:

.1. He generically states "Class D Audio amplifiers" which is very close to the name of a class D company, Class D Audio.

 2. He talks about "Class D amplifiers" having to use high levels of negative feedback to compensate for poor open loop performance and meet target levels of TIM, not seeming to realize that the inventor of many recent class D breakthroughs such as UcD and Hypex NCore power modules, Bruno Putzeys, believes there's no such thing as too much feedback in his amp designs and considers TIM to be an irrelevant and meaningless measurement as far as class D amps are concerned. 

 3. The author states:"   By definition, large amounts of feedback introduce transient intermodulation distortion (TIM), which introduces a 'harshness' that hides the rich subtleties and color of the music that were intended for the listening experience."  
       His concept of feedback and TIM have more relevance for traditional linear amps than class D amps as far as 'harshness' is concerned and he doesn't appear to understand that high levels of feedback at all levels of the audible frequency spectrum are the key concept /tool that allow Hypex Ncore modules to sound so good over the entire spectrum, including a lack of 'harshness' and its high levels of detail that enables the rich subtleties and color of music to be reproduced so well.

4. I think the author's 'digital' experience is not primarily in home audio and it was reflected in his article.  
     His discussion about keeping the signal in digital format as long as possible, without converting it back and forth between analog and digital, is a concept I remember from the earlier days of class D when the confusion between switching and 'digital' amps seemed to begin.

     I think it's a good concept that kind of lost focus once it became clear that the adoption of the other system components that could make this concept a reality lagged considerably behind the adoption of class D switching amplifiers.  Components such as completely digital sources and preamps, that would allow digital signals to be inputted into the audio chain, remain in the digital domain while being routed by a purely digital preamp and sent along to a class D switching amp still in the digital domain, where it would be converted from a digital signal to an analog signal before being amplified and sent along to the speakers.

     Most of the early examples of class D amps were actually switching amps that were interchangeable with traditional linear amps but could easily accommodate the above with just the addition of digital inputs.

    The author made absolutely no mention of any of this.
     However, I should point out that, while I think keeping an audio signal in the digital domain as long as possible would likely be a good thing sound wise and with the possibility of enhanced functionality, I believe it also creates a boatload of issues that could be fairly complex, challenge manufacturers' flexibility and budgets, would require industry wide agreement/guidelines and negatively affect the number of customers willing to adopt this new technology/paradigm.   At this point, it may be more trouble than it's worth.
Tim                  ,