I live in Germany and read most of the commercial German audio press. For those of you unfamiliar with these magazines, they focus on different "target markets": low to middle class hifi (Stereoplay, Stereo, Audio), high-end (Audiophile, Image HiFi). Although they are primarily marketing devices for German audio manufacturers and distributors, these magazines do occasionally review unusual components outside the German market and have the advantage of publishing technical data, specifications, and photos of the circuitry.
Although I am generalizing and my German audio friends will hate me for this, German high-end enthusiasts tend to like a very "analytic," rational sound from a component "built like a tank" ("wie ein Panzer gebaut," a cliche one hears over and over in German circles), with solid, dependable workmanship. In amplifiers, they tend to like high-power, solid-state designs, to drive very inefficient, large speaker systems (the most important part of an audio system in Germany is nearly always "die Boxen"). There are exceptions to this rule (a relatively large interest in tube amplification, SET, retro, etc. and there are some exceptional small German tube amplifier manufacturers that you will never hear about in the USA), but this is the general rule.
I mention all this, to provide you with the context for this review of the AudioPhysic Strada--a digital power amp coming from a large, well-known German manufacturer of relatively inefficient speakers, with a lot of capital tied up in the press. On the face of it, I can think of no better magazine for the Strada to be reviewed than Stereoplay or Stereo. Both magazines have been ranking digital preamp and amp products very high in the last few years (I am thinking of TACT Millenium review, Sharp review, and the reviews of Accuphase, TAG McLaren, Z-Systems digital amp / pre-amo products as well the praise lauded on the Gryphon Callisto 2200--an entirely OpAmp design, which is usually considered the #1 integrated amp by these magazines, 100% Klang-Qualität, as they put it.)
Despite all this, who can answer this simple question: Why haven't alot of manufacturers (besides Sharp, Tact, AudioPhysic, and a few others) brought out digital amplifiers, although the microchips for these have already been around for a long time? Looking at the specifications (which albert potter is right to point out as "pretty much meaningless"), why don't alot of manufacturers produce digital amplifiers?
Well, because the resultant interferencee from the digital coupling signals on other pieces of equipment is so high that in tandem with a complete system, one can no longer speak of high-end audio with digital amplifiers. With a typical digital amplifier, a digital coupling signal of at least 1 volt dances on the loudspeaker cables, with lots of power, and possible interference. The interference frequencies (even filtered with multiple capacitor networks) are often over 1 MHz in 3 Volt region, and many harmonics come on top of that. The portion of the interference that is reflected onto the mains results in large AC interferences that cannot be completely eliminated. Also the interference that is sent to other components are incalculable. And think of the following: one can isolate the sampling signals of a CD player from the mains by using a mains filter or isolation transformer or power gnerator, so that other equipment will not be loaded with it. This is measurable and controllable. The interference from a digital power amp has a power and reaches a value that makes rectification almost impossible. It is much higher than a CD player. EMV problems that are trully unsolvable result. The extent of interferejce is so high that all benefits, like higher efficiency annd lower distortion, are meaninglless and the succes--from a high-end standpoint--is entirely questionable.
