"Jon Noring" wrote in message


I'm curious as to what the "crystal ball" shows for the future of
digital amplifiers (aka "Class D") for high-end audio systems?

FWIW, my crystal ball shows them becoming more popular as they slowly
approach and beat the price/performance of more traditional kinds of
amplifiers.

After researching the topic last night on the Internet, it is
certainly intriguing. Surprisingly, though, I find little recent
discussion of the topic on this and related newsgroups.

That's because not a lot seems to have changed lately.

To aid discussion, here are a few links to overviews and reviews/
info on three example high-end digital amps (if you know of other
audiophile-grade digital amps to add to the list, do mention them!):

Overview of digital amplifiers:
http://www.embedded.com/europenews/OEG20020109S0073

One of the bigger sticking points with digital amplifiers is item 6 in
Figure 5, the L-C lowpass filter. The network in question is in the analog
domain, and is typically relatively large, heavy, and expensive if it's
effective at all. As a rule it dramatically raises the source impedance of
the amplifier in the highest octave(s) (i.e., 5-10 KHz and above). With many
speakers this results in a gratuitous treble boost that is surprisingly
large and potentially audible.

The current most common "digital amplifier" alternative is pretty widely
implemented and follows Figure 2, adding a traditional fully-analog power
amp.


An advocate:
http://www.classd.org/

Mostly "under construction, sorry".

TacT Millenium [review]:
http://www.soundstage.com/revequip/robert01.htm
http://www.tactaudio.com/ (TacT website)

Note that they don't quote numbers for output source impedance versus
frequency.

Spectron [review]:


http://www.positive-feedback.com/pfb...ctron.6n4.html
http://www.spectronav.com/tech1.html (Spectron website)

Note that they don't quote numbers for output source impedance versus
frequency at any frequency higher than 1 KHz.


Acoustic Reality [review]:
http://www.acoustic-reality.com/harmon.htm
http://www.acoustic-reality.com/ (Acoustic Reality website)

Note that they don't quote numbers for output source impedance versus
frequency at any frequency higher than 1 KHz.

The published reviews most likely to shed light on the output source
impedance issue are IME those published by Stereophile. Regrettably, I find
no online reviews at the Stereophile web site for products by these
manufacturers.