Class-D amps - a different re view


Martin Colloms, the editor of HiFi Critic (ad-free mag from the UK) have recently published the review of several different Class-D amps, together with an in depth technical analysys and measurments.

His conclusions were not favourable, to say at least:

"I regret that not a single model merits unqualified recommendation. Price is not the issue; the poor listening tests speak for themselves. (...)
At present we have to take the prudent view that good sound might be possible from switching amps, but we haven't heard it yet."

BelCanto REF1000 (ICEpower) - score 10.5 pooints
"The ICE power module used has a dependable reputation, and the design is well built and finished as a whole. While I would not suggest that you shouldn't try this amp, on sound quality grounds alone I cannot recommend it for audiophile use."

Channel Islands D100 (UcD) - score 13 pooints
"While I have reservations about a number of aspects of sound quality, and advise personal audition, given the solid lab results (...) the overall performance and the moderate price, these CA Audio monos do make it to the 'worth considering' cathegory."

NuForce 8.5V2 (proprietary technology) - score 9 pooints
"Yes, the price is good for the power output. Yes it's pretty, light, small and runs cool. However, the sound quality simply does not justify recommendation." (on top of that the NuForce amp measured very poorly - Elb)

Pro-Ject Amp Box (Flying Mole) - score 5 points
"I'm sorry to say that Project (...) was a real disappointment in the listening tests, and can't be recommended."

Just as a point of reference, recently reviewed Krell 700CX scored 100 points, CJ Premier 350 - 110 points and ARC Ref 110 - 135 points.

At least someone have had the balls to say it. This is why HiFi Critic is THE mag to subscribe.
128x128elberoth2
Vicdamone...The power which an amp can draw is limited by its power transformer. No matter what the audio circuits "want" only so many amps can squeeze through the transformer. Maybe the other changes had an effect which you describe.
We did an evaluation of class D about 2 years ago. At that time the technology was still immature. My guess is that it is still; the best of the class D stuff, while not bad, does not hold up to the state of the art.

Yet.

It seems to me that tube and transistor technologies are both in a mature state, while class D has still a ways to go, and showing a lot of promise. If you know about price/performance curves, the significance of the preceding statement will not be lost on you! Something that you all want to keep in mind is that one of the bigger promises is that Class D costs about 1/10th that of conventional transistor amps, while the industry gets to charge about 1/2 as much at retail. It takes barely more than the ability to chew gum and walk at the same time to get why they are really here. We have 100 watt/ch. module here that is complete with heatsinks and connectors that fits inside a pack of cigarettes. It is average in its sound with respect to all the class D amps out there, but- it costs $25 in quantities of one... all you add is a chassis and power supply. The incentive to work with this stuff is powerful.

The same sort of thing happened with transistors back in the 50s and 60s- they take about 1/10th as much as tubes to make an amp of the same power, yet the industry gets to charge the same price. Of course the industry had to create a story about how the new technology was better than the prior art, just as was done with the CD. I invite you to consider that the story was made up for reasons other than performance, although as in many fields of human endeavor, performance can always be gained.

Class D lacks many of the artifacts of traditional transistor design, and are already good enough that any designer who ignores that fact does so at his own peril. It appears that class D has already engulfed the common consumer gear market- its ideal for iPods, boom boxes, car stereo and cheap receivers.

A simple tweek for many of the amplifiers is the power supply. Class D being what it is, the power supplies are subject to quite a bit of noise. A very simple means to deal with that very effectively is to use batteries- gel cells- charged by an overgrown wall-wart. Its amazing how easily that can be used to improve things. Like the CD, class D has a lowest common denominator quality. The modules are all fairly close in performance- the big differences are all about the power supplies and noise suppression- at least for now.

I'm really wondering where this can all go. For example, the modules right now are fairly complete units. But what would be possible if the input or even the output could be done with tubes? To understand where I am going with this, imagine an amplifier with a single conventional 300b that could make 50 watts and didn't make any heat. Tubes do not have speed/slewing problems- they can switch at very high speeds. Its the impedance matching issues that slow them down... I predict that in 10 years conventional transistor amps will be all but gone.
To what benefit of the ice amps are the ones that use the Lundaul transformers in their amps?
Atmasphere, which one was in your view the sonically 'best' switching amp you heard 3 years ago?
My admittedly very modest experience is that -- like tubed or classic solid state gear -- tubed amps can sound exceedingly different.
Atmasphere...Since the output devices are simply ON/OFF switches, I see no point in using tubes here. The supposedly superior linear amplification characteristics of tubes would not be relevant. At the input, a tube could be used, but why not put it in the preamp.