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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.
elberoth2

Showing 6 responses by simontju

simontju
257 posts
 
Hello,
I would respectfully disagree with Atmasphere words, if not all then vast majority. Class D designers and manufacturers are not for iPod and such alhgough I will admit that Spectron, for example, is designing, now, amplifier with 50 watts rms power with size less then postal stamp - as one of the project in professional audio. On other end of the spectrum Spectron is developing (compact!) 8000 rms amp for Inter-M, where Spectron won the contact against Bang and Olufsen (ICE), Philips (Hupex) and others.

No, class D was not design to work against heat. Spectron chief designer John Ulrick designed it in 1974 (so its not so young technology either!) to drive bass modules in his (and Nudell's) Infinity speakers - which I believe were accepted rather well ay that time.

I am AND engineer (digital signal processing) AND professional musician (graduated conservatory class piano centruries ago) and I can't imagine any audio designer who build amplifiers that cannot handle speakers with huge phase shifts and yet cause the chill down my spine when I hear the real piano sound in my listening room ( not heavenly piano glorified by 2nd and other even harmonic distortions nor one made out of steel or other metal with all non -existing details).

All The Best in Your search of perfection
simontju
257 posts
 
Hello Kijanki.
Excellent review of the review. I would point out only that

"Have thermal dissipation limitations due to the small power module size which means that thermal dynamic variations are present in the performance with time"

has a lot of sense and if designers did not so proper and extensive thermodynamic analyses then this is exactly what is occuring...with time.

Don't measure tmeperature outside the amp - measure it inside the small power module size and at not in one point... Nobody cheated physics yet

Simon
simontju
257 posts
 
Hello Art_t,

"To be perfectly honest, I have heard listeners say that our (switching) amps sound "very tube-like".

... and it is because in all probability they do. Most published measurments of switching amplifiers distortion patterns are very similar to....that of the tubes. Strong 2nd harmonics and strong even harmonics.

I personally love to read in Stereophile comments of reviewers on most of class D amps they review: "tube-like", warm, musical etc...and then glance to John Atkinson measurments with huuuuge 2nd harmonic distortion etc

I love expression "life-like" be it tubes, snakes or whatever...

All The best
Simon
simontju
257 posts
 
Kijanki:

"Simontju, Amp is close to 95% efficient and does not have to be large to do so."

1 - Even if efficiency would be 99.99% some heat would be generated and...dissipated somehow

2 - No heatsinks! I am talking NOT about chasses of the amp or whatever but inside the very small power module packed DENSLY with microscopic size electronics

3 - I can re-assure you that each responsible designer and manufacturer of class D module like Spectron, Bang & Olafsen, Philips did themselves or invited outside consultant(s) to make most comprehensive thermodynamic analyses.

4 - All The Best

Simon
simontju
257 posts
 
"Unfortunately companies are racing for best specifications. I would advise to take specifications, promtly discart[sic] them and just listen."

Hmmmmm.. these stupid people from Spectron wrote on their silly web site:

" BLA BLA BLA
BLA BLA BLA
YADDA, YADDA, YADDA,
BLA, BLA, BLA
BLA BLA BLA
YADDA, YADDA, YADDA,
BLA, BLA, BLA
BLA BLA BLA
Conclusion: We hear time and time again that the numbers on the data sheet do not predict an amplifier's sound quality. While largely true in the past, today more and more parameters, measured correctly and even more importantly - truthfully reported - do reflect well some very important amplifier sonic characteristics. When you are considering buying any amplifier, the first question must be if it can drive your speakers at all. If it can drive your speakers, then can it drive them well. Can it drive them, at the very least, without euphonic coloration, muted treble and veil etc? The right approach is to check the amplifier's distortion level and output impedance at high frequencies(* - for class D specifically - my comment here) . Also look for peak current and its duration, flatness of frequency response, noise level, bandwidth etc. Of course, Spectron also considers the speed of the feedback loop and inclusion of the output filter in the feedback loop to be of great importance, even if an audiophile cannot really check on this. Each and every one of these measurements contributes to a gorgeous musical experience, and each deficiency will be readily apparent to the critical listener."
simontju
257 posts
 
"perhaps you can enlighten me as to how i might acquire the taste."

...of life-like music reporduction I assume.
Well, attend concerts of acoustic music.
Good Luck in that
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