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Class D = Trash?

So, I'm on my second class D amp. The first one, a Teac AI-301DA which claimed to use an ICE module, was unlistenable trash. I burned it in for a few weeks, it just couldn't perform, so I sent it back. Following that, I tried the new Emotiva A-300 (class A/B). It was significantly better, but lacking in too many ways for my tastes. So I changed gears, got an 845 SET from China -- and it was an immediate and massive improvement.

So, before I went further down the SET road, I wanted to try a better class D product using a modern class D module. I settled on the D-Sonic M3-800S with the Pascal module and custom input stage. I read from reviews that these things like to have big cables, so I picked up an eBay 8 gauge power cable (Maze Audio, el-cheapo Oyaide copy plugs, braided 4-wire cable) to go along with it.

Mid-range GONE.
Soundstage depth CRUSHED.
Euphonics DISAPPEARED.

Yes, resolution went up. Driver control went up, allowing me to play compressed rock/pop and orchestra with the speakers being able to render it all. But enjoyment in the sound is basically gone. Using my best power cable (LessLoss Original) improved performance, but didn't fundamentally change the amp's nature. I ran back to my headphones (Focal Utopias) to detox my ear canals.

So, how long does a class D need to burn-in? I want to give it a fair shake before writing the technology off forever. 
madavid0

Showing 5 responses by atmasphere

atmasphere's avatar
atmasphere
12,086 posts
 
1. Is there a consensus among amp designers that current switching frequencies (what I believe you're calling 'scan frequencies') being too low is the primary cause of 'inharmonic distortion'? If so, is there also a consensus that raising switching frequencies to the 3-5 MHz range would reduce 'inharmonic distortion'?

No.

2. Can you explain why I, and apparently many other class D amp users, do not perceive our class D amps as being cold or sterile? Do you think the ability to perceive the affects of 'inharmonic distortion' differs among individuals or do you think it's more likely the degree of 'inharmonic distortion' varies by amp?

A lot depends on what your reference is and different amps have differing amounts of distortion. Like anything else in this world, you have to try it. As a general rule of thumb though, if you can turn it up loud and it also **sounds** loud, then you know you have a problem. If your system is devoid of higher ordered harmonics and inharmonic artifacts, you won't know how loud the system is until you find that you have to yell at someone sitting right beside you to be heard. 

3. Are there any current methods of measuring 'inharmonic distortion'?

Of course! The best use is with spectrum analysis.
atmasphere's avatar
atmasphere
12,086 posts
 
^^ one of the artifacts of Class D is is that there can be intermodulations between the scan frequency and the the signal being amplified.

You can see this in the specs if the spectrum of distortions is graphed. So there isn't a lack of evidence!

In the digital world, they call this 'aliasing'. In the analog world (and since Class D is an analog process) we call it 'inharmonic distortion' to distinguish it from 'intermodulation distortion'; the latter being intermodulations between tones being amplified.

This is why the artifact of Class D is different from traditional solid state. The artifacts are similar to those of digital and you see many of the same complaints leveled against it- cold, sterile, that sort of thing.

Its a simple technology, and that seems in a way to belie the issues of how to correct the artifacts, which is rather tricky. Like digital though it is a rising star in high end audio (many think its already arrived but the fact that this thread exists is evidence that it has a ways to go, otherwise it would have completely supplanted tubes and traditional transistors; since it hasn't, we know without needing to know technical issues that its got a ways to go) and its potential can't be ignored (which is why we've been investigating and working on class D ourselves).
atmasphere's avatar
atmasphere
12,086 posts
 
  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.
atmasphere's avatar
atmasphere
12,086 posts
 
 Here's a link to what I was referring to in my last post about reading of faster switching mosfets:

http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html
Hmm. I'm a fan of class D amps (really expect them to bring home the bacon someday and am working on one myself) but not the 'digital' amps to which this article refers, because they don't exist. I expect the author really meant 'class D' or 'switching' when he must have accidentally used 'digital amps'... ya think?
atmasphere's avatar
atmasphere
12,086 posts
 
Personally I have lost all interest in hard to drive speakers because I find their total cost of ownership just too high for little value.
+1 on that!

When you can connect headphones to the power supply of any amplifier and hear the audio signal, you may count on the fact that the power supply is contributing to IMD. This is a very audible form of distortion! It is for this reason that we have a separate power supply for our driver circuits as opposed to our output circuits.

IMO this should be the case in a class D amp too, and I think that should pan out as the input circuitry usually has very different requirements as opposed to the output section.
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