Class-D amps - a different re view

hi audioperv:

the objections i raised are reasons not to want to listen to solid state amps. what ever faults lie in the design of tube amps do not deter me from wanting to listen to them.

subtractive coloration of some tube designs does not bother me. additive colorations of solid state amps is annoying.

i have heard class d amps at ces many times. i have no desire to listen to them on panel speakers.

ralph, what say you ?

That's interesting MRT. . . roaming the halls and suites at RMAF I was actually dismaied by how so many tube designs at all price points were trying to out-solid-state solid state designers. . . and succeeding admirably, tizziness (additive flaw presumably) and vanishing harmonic structure (subtractive flaw I presume) included. The difference apparently is that. . . if such flaws are heard on classic solid state or switching technology--which I did hear in spades as well--the problem is with the technology or the design, but if any apparent 'solidstatification' of tubes is perceived, the culprit is supposed to be only the wild and utterly uncontrollable acoustics of the suite. . . go figure!

Oh yes, let's not forget that flabby bass, or conversely that magic vanishing bass, or that sudden hard clipping: these are apparently more artifacts that plague room acoustics where some tube designs are featured. . . Yet, if switching amps or solid state amps are present instead, 'tis always safe to point an accusing finger at the designer.

Mrtennis, Class D should not be confused with solid state. They don't even sound similar.

You would not like to hear class D on panel speakers? You obviously have not heard my panel speakers.

If a room sounds good at a show, I pay attention, but if it does not sound good, I don't let that deter me. I've had my own room sound lousy plenty of times... its really tricky to come into a room, set up a high end stereo and have it sounding convincing in a day or a day and a half (which is the timing that the shows give you).

If people keep coming back and wanting to hear more tracks I take that as a good thing, but I've never had a room sound as good as my system at home, nor have I heard *any* system at a show sound as good as what I have at home. I'm pretty sure I have a lot of company!

So we're back to the same deal- you have to audition this stuff. I've had the opportunity to do just that, and tweak the circuits as well. From that, and the feedback of customers, come my comments. My conclusion has been that while class D lacks many of the traditional solid state artifacts, that they do have artifacts of their own, but not ones that are common to class D in general (IOW very unlike traditional transistors in that regard; every transistor amp I've ever heard has identified itself as a transistor amp, class D does not identify itself as 'class D'), instead the artifacts seem to associate themselves with the specific product. That, by itself is a very good sign- it suggests that as the technology evolves, a truly neutral implementation could emerge.

Our auditions and customer input show that its not there yet, that we (as Atma-Sphere) have some breathing room for now. By no means has our own line of work been exhausted- the circuit is always suggesting new ways for it to be improved. So it will be interesting to see where things are in say, five years.

One thing that I have been intrigued with is that it is possible to build class D amps that lack the traditional style of feedback loop- a deadly sin as far as the human ear is concerned (and part of the 'traditional' transistor sound). That suggests that the amplifier can be designed around the rules of human hearing rather than the arbitrary standard of 'constant voltage' output. From what I have seen though, the open loop distortion is going to have to go down a bit yet...