Direct Digital Amplifiers

Peter,

Yes, Tact equipment employs this functionality. The tact S2150 digital amplifier paired up with the Tact 2.2XP preamp has really good digital equalization with a lot of flexability if you hook up the 2.2xp to a computer.

12-11-12: Willland
I am not sure if this is exactly what you are referring to ....

technically, a "direct digital amplifier" is a class-D amplifier that can accept, at its inputs, a digital pulse code modulated (PCM) data stream. Accepting a (digital) PCM data stream (which is the digital music stream) rather than accepting an analog version of the music stream is the real innovation of "direct digital amplifiers". Hence the "direct" in the name - you can directly connect the digital output of your computer or CD transport to this sort of amplifier & it will drive your loudspeakers. Internal to the direct digital amplifier, the PCM data stream is kept digital all the way & it is finally converted to analog at the output of the class-D output stage by the analog reconstruction filter/low-pass filter just before it drives the loudspeaker. The amplifier is still a class-D amplifier.
Today's class-D amplifiers accept an analog version (digital data converted to analog with an on-board or out-board DAC) of the music stream. The class-D amp converts this to a digital pulse wave modulated (PWM) signal & this is once again converted to analog by the reconstruction filter/low-pass filter just before it drives the loudspeaker.
Direct digital amplifiers do away with the initial conversion of the digital music stream to analog.
And, yes, like OP indicated, there are few direct digital amplifier products in the market today.
Hope that this helps some.

I share the OP's excitement about the technology. It seems to have so much potential for excellence by virtue of eliminating so much of the traditional signal chain.

Putting my money where my mouth is, I bought a C390DD to play with. I'm not ready to offer any final judgement, but I will say that it's very good sounding and it's probably not as good sounding as my traditional separates, which are much costlier. But its flexibility is mighty appealing. I still need to play with the analog input module, (RIAA applied digitally), and the subwoofer functions, as well as the room EQ, which I believe is still a pending feature. USB input is sub-par but is modular and likely to be upgraded in the future.

Bombaywalla, Class D amp doesn't convert anything to digital. It converts analog voltage to analog duty cycle of square wave and back to analog voltage thru filtering. Word "digital" would imply limit of resolution while it is unlimited - completely analog from input to output. People often confuse switching (where duty cycle is analog quantity) with digital.

Yes- class D amps operate in the analog domain. The 'D' is used because A, B and C were taken.

If you run a DAC directly into any traditional amplifier, the signal chain is actually simpler. Cass D amplifiers have considerably more processing to make things happen.