Future of High-End Digital Amplifiers?

[Jon Noring]

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

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.

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

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

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

Spectron [review]:

http://www.positive-feedback.com/pfbackissues/0604/pappas.spectron.6n4.html
http://www.spectronav.com/tech1.html (Spectron website)

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


Jon Noring

[Andy Dee]

Jon Noring wrote:
> I'm curious as to what the "crystal ball" shows for the future of
> digital amplifiers (aka "Class D") for high-end audio systems?
>
> 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.
>
> 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
>
> An advocate:
> http://www.classd.org/
>
> TacT Millenium [review]:
> http://www.soundstage.com/revequip/robert01.htm
> http://www.tactaudio.com/ (TacT website)
>
> Spectron [review]:
>
> http://www.positive-feedback.com/pfbackissues/0604/pappas.spectron.6n4.html
> http://www.spectronav.com/tech1.html (Spectron website)
>
> Acoustic Reality [review]:
> http://www.acoustic-reality.com/harmon.htm
> http://www.acoustic-reality.com/ (Acoustic Reality website)
>
>
> Jon Noring
>
If you ever listen to Medium/Short wave radio, chances are you are
listening to a digital amplifier. For efficiency, a large number of AM
broadcast transmitters now use a digital modulator. Some use a high
power D/A convertor whilst others use a pulse width modulator.
Nothing new here, relatively old technology but done for efficiency not
for audio quality.
For me, the best place for the DAC is in the low power stages. The less
digital processing, the better.
Amplifiers should be class A for true fidelity but I can live with class
A/B. A class D audio amp would only add more RF pollution. I dont need
such effieciency for my few watts...

A

[Trevor Wilson]

"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?

**One does not require a crystal ball to make some reasonable predictions
about the future of such amplifiers. FWIW, here are mine:

* Class D amplifiers will begin falling in price rapidly. As a result,
within a few years (say: 5) almost all domestic amplifiers will be Class D.
* When Class D amplifiers operate at a suitably high switching speed (say:
7 - 10MHz), their use will be ubiquitous amongst even 'high end' systems.
Presently, Class D amplifiers operate at too low a switching speed to be
considered for _all_ systems.
* Class D amplifiers make perfect sense for subwoofer and other LF operation
right now.


--
Trevor Wilson
www.rageaudio.com.au

[Arny Krueger]

"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/pfbackissues/0604/pappas.spectron.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.