Class D = Trash?

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 I think you're right, he was  all over the place on terminology and his knowledge base seemed outdated: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                  , 

  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?  

We're doing our own circuit, so no modules, at this point we are using traditional power supplies.

Hi atmasphere,

     Proprietary power modules and supply?  Wow!  Very cool and very interesting.


Good luck,
   Tim

seanheis1
  I started a thread about it and it appears that the switching frequencies aren't currently high enough to avoid degrading the signal. If it was a simple break in issue, they would be broken in at the factory.

Don't give up on Class D though. When the switching frequencies improve, they will become the solid state amps of choice. Some folks don't hear what we hear and they are fortunate to enjoy these small and efficient power houses. More power to them.

Well said the day will come with much higher switching frequencies, as I also posted to Randy's question

randy-11I always thought the gentle filter slope was b/c steep "brick wall" filtering caused caused audible distortions...

It’s because a simple low order output filter can take the amps full power, but it’s effects reach down into the audio band and still leave some switching noise left overs, hence the need to take it up much higher as Technics did with far higher switching frequencies, so they can be effectively removed, without effecting the audio band.

These days when Stereophile tests a Class-d amp, they put on an external output filter, the Audio Precision’s AP0025 filter, which has a -50db rolloff after the audio band so the 1khz square waves look half decent without the switching noise embedded right across it, (good for sales) 10khz square wave still looks a mangled mess though, trouble is this AP filter can only take very low power, would be real nice to leave it in to listen to, but it would blow up in a micro second.

http://www.stereophile.com/content/class%C3%A9-sigma-2200i-integrated-amplifier-measurements#31YFAPfYVDGeowzZ.97  
And yes steeper filters as you said do have their own set of problems re sound, as ML found out with their No.53 monoblocks.

Cheers George