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.
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Showing 9 responses by eldartford

Interesting that the reviewer rated only the UcD amp (CI D200) as worth considering. I agree with the ICE/UcD finding, but lack of an assessment of a Tripath amp is too bad. My Tripath CarverPro ZR1600s are right up there with my CI D200s. However, the rating gap between all the digital amps and the conventional amps is so absurd that it calls into question the validity of the entire review.
Warrensomebody...That "power from the wall" theory does not make sense to me. Say what you like about the way they sound, but digital amps make very low demand on input power. They are typically 85 percent efficient in converting wall power to audio power, whereas the typical SS amp runs 30 to 40 percent. Don't ask about tube amps!
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.
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.
Muralman1...You said "Never will class D emulate the fantasyland of tube amps" but I suggest that your descriptions of your H2O amp come darned close :-)
Atmasphere...When transponders (radar response avionics for planes) were first introduced they were all transistorized except for the output device which was a traveling wave tube. The high RF frequency used by the transponder was cited as the reason for the TWT. The TWT was a frequent failure item. Thank God it has now been universally replaced by transistors.

The switching frequency of digital audio amps is well below 2 MHz, and solid state power devices have no problem at such frequency. My CI D200s (UcD) switch at around 400 KHz and my CarverPro ZR1600s (TriPath) are up to about 1.5 MHz.

I wish I could afford one of your OTL amps, which I believe exploit the benefits of tubes without their drawbacks (except cost).
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Mrtennis...Not an absolute predictor, but a useful indication. Why else do we contribute opinions, pro or con, on this web site?
We go on and on about the subtle "sonic character" of amps, but it is all insignificant compared with the great variability of microphones, about which we can do nothing on playback. (Well maybe a bit with an equalizer).
Atmasphere...I agree that the specs we measure are intended to verify that a unit is performing as per its design (ain't broken) and do not necessarily correlate with sonic quality. (Although high IM distortion is very anoying to me). However, if the ideal amplifier is a "straight wire with gain" why don't we just compare the output, adjusted for gain, with the input while playing some complex waveform like music, and over a range of amplitudes. "Total Error" would be the parameter...who cares if it's harmonic,IM, or noise. I submit that many SS amps would score well, and many tube amps not. However the tube amp fans would say that the ideal amp is not a straight wire with gain, but rather is a harmonic synthesizer, with gain. To each his own.