New Digital Switching Amplifiers

I'm glad we could bring back this thread which was on its way to oblivion because it is an interesting topic.
Ar_t, maybe I didn't understand your question. I was refering to filtering the HF switching noise the amp itself produces.
Tvad, even the original distortion specs you mention are ridiculously low and probably people wonder how can audiophiles argue over such tiny changes in distortion. The actual printed graphs in Fig 2 however look a lot worse than numbers on a page.
Probably the worst Pioneer receiver is 75% accurate and the best Halcro is 90% accurate so any differences are small on an absolute scale. Nothing is perfectly accurate and you make a choice based on 1) your overall system, 2) preferences, and 3) what you find objectionable.
So if tpk123 is making a buying decision, then the objective is to weed out "bad" products, however small the differences, and buy the right product based on 1), 2), 3).
When I had the PS Audio, it gave me headaches like when I listen to CD's from the Cranberries. Could've been my system, room, CD's, or ears, but it didn't sound as good as "analog" S.S. amps IMS.
Even if they can filter out the HF noise, I'd rather not have a filter used at all. One more component in the chain to mess up the sound.

Also forgot to mention the specs were done with a steady 8 ohm simulated load. Real life loading would probably bring out the switching noise even more.
For an interesting read see the paragraph on "The Quest for that Old-time Religion " section:Hammer Dynamics Super 12. Dick Olsher talks about lowering the tweeter's x-over frequency. During *dynamic* passages "while such a solution results in a smoother frequency response, often the sound quality is far WORSE because of increased distortion. That poor tweeter is made to work much harder than it really wants to. In the end, it is reduced to painful screaming".
I'm saying this as an analogy to Stereophile's steady state 8 ohm load of the C-I amp versus real music.
Don't get me wrong, for the price, etc. I'm sure the C-I amp sounds really nice, it's just not perfect.

I understand that my digital amp output has some ultrasonic signal that would not be expected from a linear amp. Last time I checked "ultrasonic" means you can't hear it, but it does keep the bats away. :-)

There are 2 kinds of noise:

One that goes out on the speaker leads at the switching frequency. We'll say in the 500 kHz range. (I believe Tripath and Nuforce may be closer to 1 Mhz.) The other is all the crud in the 60-100 Mhz region that will mess up TV reception ans some other things. Two different issues, 2 different solutions.

As for distortion changing with warm-up:

You can get the distortion to drop if you increase the "stand-by" current drain. Problem is, you run the risk of destroying the switching transistors if you get it too high. There could be a thermal change in that parameter in the unit under review.