How do Digital Amps Mfrs. compare in sound?

hmmm, me thinks last time I heard 'em voices I was 16. . . right in the middle of the Sturm und Drang of adolescence. . . now I'm only a crotchety old prankster foolin' 'round with words and audio components.

Hi Coffeey, small design improvements can make large changes in sound quality in any design. Class D amps have always been good, maybe not great but good. UCD in the last year and a half has redesigned their boards and have chosen some better components. Class D amps use allot of surface mount parts and that is the reason most companies buy modules from B&O (ICE) or Hypex (UCD) and then design and build their own power supply. Now that class D production has picked up, many surface mount component manufacturers are willing to set aside the better parts for these designs. Most, if not all of the sound differences between tube and solid state amps are the parts and power supply. The same applies to Class D. Circuit topology for tube and solid state haven't changed much in decades. So how is it possible for a manufacturer of these amps to make their product sound better then last years or even 10 years ago? Parts, board layout, isolation and power supply.

Excellent points Stereo. I would like to add that at least 2 manufacturers (Bel Canto and JRDG) have started to add pre power supply current rectification in some models. This means that the power supply is essentially fed DC from a current reservoir of capacitors. The idea is the DC current is expected to:

1. largely eliminate 2 way AC line noise in and out of the amp.
2. Keep internal capacitors more optimally charged.
3. Be able to draw power for large transient from the DC reservoire regardless of the current state of AC 50/60 Hz phase.
4. Increase overall power conversion efficiency.

Some of these amps do sound amazingly musical to my ears. . . if and when more devices adopt various form of rectification prior to power supply, we may eventually be able to determine if there truly exists a correlation between input current rectification and sound quality.

I probably won't be adding much to the discussion by simply suggesting (as another poster did) that it depends on the manufacturer. For the past 2 weeks I've been listening to an ARC 150.2 which I swapped into my system in place of a tubed ARC D90B. The 150.2 is a tripath class T amp, which is really just another name for class D. I'm feeding it with a tubed ARC SP-8, and it sounds as good as, if not better than, the tubed amp it replaced. I also have the TAS issue which compared a number of class D amps, and if you read the review of the ARC 300.2 (the bigger brother of my amp) you see two opposite opinions - the assigned reviewer loved it (as I understand, he actually bought one after reviewing it) but Jonathan Valin, another TAS reviewer, definitely didn't like it. It seems to me that when you have two professional reviewers for the same publication disagreeing, it certainly points up that there is no "easy answer" to the question of class D sound.

SONICS
"Immediately good/refreshing sound" (how Class D is commonly described... at first) can be a very superficial thing. How many times was the sound of some gear (or music) you are long term happy with NOT necessarily so good at first ?

B. NEW TEAM - SUSPICIOUS NEWBISM
"Good" (sic) Class D is a massive Analog/audio/RF/Digital engineering tangle problem, & analog engineers are sage enough to know to leave such a vipers' nest alone. Seriously clever people and the biggest corporations have all thrown "brains and bucks" at, and into Class D, since the early 1960s. Over 40 years of trying! With still very few results on the high end stage, and, very late results all round.
People playing with overly-mathemeticised plans of reality may need to write out 1000 lines :
"Digital knowledge is not power amplifier engineering." !
Not a single master of analogue power amplifier engineering has turned to Class D. Shouldn't one know this, and, ask 'Why?’
By their nature, electronic engineers are usually eager to "migrate into the future technology".

C. Because the people who make Class D amplifiers are somewhat "ignorant", let alone their advertising copy-writers, they forget that the ACTUAL efficiency of an amp has to be multiplied by the power supply's efficiency, to arrive at the nett, realistic sum. This down-plays their rather spurious/overstated claims of high efficiency, once the comparison is made on an apples/apples basis.
In other words, taking best case practical round figures, an analog amp (70% efficient) is only a tad less efficient than a Class D amplifier (90%), whether they both use a mains frequency power supply of nominally 70% efficiency (70% x 70% = 49%; 70% x 90% = 63%); Here, Class D's 63% is only "28% ahead" of 49%.
Or, if both amps use a high-frequency (switching) power supply, then 70% x 90%, and 90% x 90%, are 63% & 81%. Again, 'D' is only some "28%" better. Do you wreck high-end sound for that? But, even the average 63% (of both) is FAR more than 200% more efficient than the most efficient car or indeed, power station.
If we dare include the power station efficiency (circa 28%), then any eco benefit from just one final part of the total energy loop, acting efficiently in Class D, is further reduced!

D. To anyone with an understanding of what makes existing good high-end hi-fi amplifiers, it is hard to see WHAT Class D achieves, that is useful. No one has ever announced it or written it down. It is not a logical next step. ONLY IF manufacturing convenience, cost, and material usage were put at the head of the list, before sonic quality.
This is from Ben Duncan , prominent audio designer.