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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
atmasphere's avatar
atmasphere
11,846 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.
randy-11
1,913 posts
 
no-bell - instead of wasting time on your verbose post above, you could simply use google to search for "inharmonic distortion"

try it

(and, no, I don't claim that Class D is good or bad -- I DO want to know if it offers any advantages for me)


noble100's avatar
noble100
2,419 posts
 
atmasphere,

      Thank you for replying to my questions.

    Your confirmation that current class D amp switching frequencies are not causing 'inharmonic distortion', along with class D Ice and Hypex NCore power module inventor Bruno Putzeys' statement that current class D switching frequencies in the mid-500kHz range are "completely reasonable", refutes the theory that they need to be raised to the 3-5mHz range (to not affect frequencies in the audible range) as far as I'm concerned.
     These confirmations make sense since they mirror the more subjective perceptions many class D users have, including myself, of the total lack of sonic anomalies and very high quality performance levels of class D amps..

    I'm looking forward to hearing the results of your first class D amp design effort.
   I suspect your class D amp will be transparent, detailed, with a very neutral overall quality while also having the extreme low noise and distortion levels that all seem to be common characteristics of good class D amp designs.  
   I believe you'll also find that an amp with the above traits will be a great match with high quality tube preamps since the amp will operate as the audio ideal of 'a straight wire with gain' which  will allow the sound qualities of your tube preamps to be amplified faithfully without any alterations. 

Tim
    
georgehifi's avatar
georgehifi
10,312 posts
 
This is a statement from Optoma USA customer help, a world wide company who I believe handled NuForce, maybe still do.
Digital Switching Amplifiers (commonly known as Class-D) have been around for years. Nevertheless, it is nearly impossible to engineer a conventional Class-D amplifier that handles the full requirement, 20-20,000Hz, for full-bandwidth music reproduction. A Class-D amplifier works by utilising a high-frequency saw-tooth waveform to modulate the music signal (to learn more about how Class-D amplifier works, click here).

The constant presence of the saw-tooth waveform, which is very high in frequency spectrum and its inevitable frequency jittering, can mask or corrupt low-level music signal. The output filter designed to filter out noise and overtones caused by the saw-tooth waveform adds a 180 degree phase shift to Class-D output stage, causing possible instability and adding distortion due to its own inherent non-linearities.

Additionally, the output filter presents frequency-variant output impedance that can interact with a speaker’s complex impedance. Variants of Class-D amplifiers with the addition of Digital Signal Processor claim to improve music reproductions.

However, because of their lack of close-loop design, especially from the speaker’s terminals, spurious interaction between the speaker’s complex impedance and back-EMF with the amplifier’s resonant output filter can result in harsh sound reproduction.

The fundamental flaws of conventional Class-D amplifiers remain unresolved.

Cheers George


tradeontheweb
43 posts
 
It's an interesting statement you posted George, and that’s from a large company that promotes/distributes Class-D amplification.
Kind of gels with what I hear with Class-D. I must admit I’m still waiting for it to come of age, 'till then I’ll also stick with my linear amps. I'd say the writings on the wall though, with the advancement of Class-D’s higher switching frequency, one that Technics have used with their SE-R1 (which I have not heard yet)
Great discussion nonetheless & hope to learn something from the various luminaries (and others) chiming in .... 

Regards

S
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