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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.
128x128elberoth2
elberoth2's avatar
elberoth2 OP
1,223 posts
 
I've reread Colloms's review and found another interesting point. Martin speculates (since he does not have enough exhamples of different applications of Class-D technology to prove his point), that the above avarage CI Audio resoult may be due to the liniar PS used in this amp. He observed, that switching on the amps with switch mode PS actually degraded the sound of the other system components connected to the same grid ! It may be (or may not) the reason why H2O amps sound superior to other ICEpower based designs that uses SMPS.
nanotweeter
55 posts
 
Very interesting thread. My take is that unbiased, objective evaluations of which class of amplification sounds better is impossible. Hearing, like all of our senses, allows only subjective evaluations to be made. It can not be otherwise! No two pairs of ears are created equal.

While poor design, component failure or bad system synergy can make any type of amplification unsatisfying, the preference for amplification type with relatively equal quality components is totally personal and not open for argument. To do otherwise indicates a complete lack of understanding of this subject or implies the existance of a hidden agenda.
dotsystem
81 posts
 
Elberoth2

IMHO, the reasons for the mixed opinions on Icepower amps are the extent of RF present in a system, electrical isolation of the amp from the rest of the system, vibration isolation and impedance matching with the preamp.

Even the H20 with its linear power supply responds well to RF reduction measures. RF picked up by speaker cables can propogate backwards though the system. In the case of switching power supplies, there is potential to add more noise. I find that the Powerwraps are very effective at taming RF with the largest benefit on the player and preamp.

Power units that isolate the amp from other components are helpful.

For vibration control, isolate a module amp as you would a high quality front end component.

In the Rowland model reviewed by the TAS, a transformer is used to make preamp impedance matching less of an issue. The comments by TAS remind me of those made in ancient reviews of step up transformers for moving coil cartridges.

Once manufacturers consistently address this issues inside the amp, I believe that there will be little demand for traditional solid state designs.

At Dave Magnan's site he has many specific recommendations to improve the sound of Nuforce amps.

One advantage of the H20 is the roomy chassis. This means that there is room to add better bypass caps, replace the mediocre nickel plated binding posts, input connectors and improve the transformer damping. Not easy to do in small chassis amps or when the power supply is part of the module.

Bob
muralman1
1,527 posts
 
Points well taken, Bob. As an example that supports your observations, I just installed Sonicap Platinum bypass caps, and like what they have done. My speaker cables are short. I have found SC and IC insulation pollutes the signal significantly. I have yet to do binding posts or isolation. Any suggestions?
dob
577 posts
 
Elberoth - You are exactly right. The best sounding class D amplifiers - Spectron Musician III Signature and Kharma using linear traditional non-switching power supplies, and I been told by Spectron people - only due to the sound.

RF contamination indeed is a major source for sound degradation in class D - again Spectron people told me that when they re-designed RF filtering circuitry for Signature the sonic results were very impressive.
All The Best,
Rafael
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