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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
kijanki's avatar
kijanki
4,432 posts
 
Ar-t
I agree absolutely. Synergy is probably one of the most important things.

I respect people who can honestly say "I don't like it" even if it costs $500k, but I don't care much for blindsided people who try to present pseudo-sientific reasoning.

Being subscriber to Stereophile for many years I have a lot of respect for technical knowledge and integity of people there. They present detailed measurements but put more stress on impression with different co-equipment and different music pieces. Technical aspect is always interesting but is secondary to sonics.
kijanki's avatar
kijanki
4,432 posts
 
Simontju

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

"thermal dynamic variations are present in performance" - thermal dynamic variations of what? This is still jibrish to me.

Let me place here results of test made by somebody to 1kW icepower and 100W Icepower (same as mine). Notice that he tests 1kW amp with no hestsinks at all. If you take into consideration that average power in music i very low (only few percent) statements about "Thermal dynamic variations" are complete nonsense. Read below:

"Originally posted by dmfraser
I operated a sample 1000ASP on the bench delivering 350W average of pink noise into a 4 ohm load for over one hour with no additional heatsink and the metal case stayed below 55°C.

However, higher levels would make the power supply voltage go down to act as a thermal compensation. Much nicer than just shutting down.

However, with 1214W of sine wave, partly into clipping, after about 35 seconds, the output level would drop to about 600W by the protection circuitry. Remember this is with no additional heatsink.

The 200ASC, I was able to operate with sine wave at 100W into 4 ohms continuously. Turning it up, with sine wave, the module would shut down at about 214W.

However, with pink noise at 100Waverage and a 6 db crest factor, the 200ASC would run all day without shut down, until I was tired of tying up one of my Audio Precisions with it. It would also run all day with music, driven hard where the output limiter was set to a peak limit of 210W maximum. That is, the limiter would allow small amounts of clipping. Driven so the limit light in our external optical limiter was on essentially continuously.

We're quite satisfied and will be ordering production quantities of the 200ASC shortly."
rf_gumby
54 posts
 
Ar_t --- Excellent post. Classy, open, repsectful and
honest. Are you sure you're at the right forum? :)
atmasphere's avatar
atmasphere
11,901 posts
 
Kijanki, not to detract from your comments of the review of the review, but just so you know the numbers that are quoted are not speaker current. If it were:

First, reality:
For 100w into 8 ohms, the current would be about 3.54 Amps.
For 100w into 4 ohms I = 5Amps, for 2 ohms I = 7.1Amps

then the 'claim':
working it backwards, 50A into 4 ohms is 10,000 watts
into 2 ohms its 5000 watts.

So- 20Amps into 4 ohms is 1600 watts. But your amp does not make that kind of power!

I agree these numbers are common in a lot of amplifiers, the 'FWIW' part is that the numbers are *not* current in the speaker. I suspect they are power supply numbers, that number being the current output of the supply when shorted for 10ms. Our MA-2 amplifier which is an all-tube amplifier measures about 80 Amps using this technique...
kijanki's avatar
kijanki
4,432 posts
 
Atmasphere

Quoted current - as I said before is the peak current and has nothing to do with average power. It is used to show how well amplifier can respond to impulse.

Internally my 200ASC Icepower can deliver 48V to speaker what would make at 3 Ohm 16A current. Limiting circuitry is set to 11A. Power delivered to speaker will be 363W.

I don't know how long this pulse can be or what would be crest factor with multiple pulses but would like to point that Bel Canto rates the same module at 300W (10% thd)
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