This thread is humming along nicely - I hope others wont be too offended if I paste a few of the forum comments from elsewhere as I plan to address some of these when I return to this thread in 2 years time (!). Sounds like an eternity, but consider how long some of the other threads on Head-Fi have lasted - its always a shock to find the OP started the thread in 2009 ...
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Source: various threads on CanuckAudioMart and AudioKarma from 2009-2012:
(apologies if I seem to have singled out the comments specific to Nuforce, but they seem to have copped a particularly nasty hiding on the forums)
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If the OP is determined to buy a pair of Class-D monoblocks, I would suggest sticking to the ones based on the Hypex modules (Channel Islands, Kharma...), staying away from ones that employ the B&O ICE module (Wyred for Sound, Bel Canto, Jeff Rowland...). Some of the units using proprietary modules (Nuforce, Hephaestus) are quite good, but as I said in my original reply, a really good Class A/B linear amp, dollar for dollar, performs better in my opinion.
As a "family", Class-D amps have merits - bass control, transparency, and efficiency*. They also have their costs - cool/thin midrange, and strange highs (some call them "chalky"). Personally, I think it is the harmonics that they portray strangely, rather than the dominant tone itself, but that is another conversation entirely.
There are a couple of hidden costs with Class-D amps though. For starters, I am not convinced my the claims of efficiency (hence the * above). The serious listeners I know with Class-D monoblocks leave them turned on all the time. Why? Because they sound like a horse's face when cold. How efficient is that?
Second, Class-D amps are VERY sensitive to cabling, and you end up spending more on power cords, interconnects, and speaker cables than you might need to with a traditional linear amplifier.
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I have heard several of these designs (including the Axiom as well as the Bel Canto Ref 1000) and remain on the fence about them - I like the power that they can put out and the control they can manage over large drivers, making them a natural bass-amp for a 'vertical' bi- or tri - amping situation.
At higher frequencies though, they have, at least to my ears, always sounded a little dry and compressed. I am not sure I could live with them for very long if they were doing full-range duties.
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Put them beside a new Blue Circle SS chip amp and you'll never be able to listen to Class D again
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No one who has heard my system since I replaced the 300B Cary amp with the Red Dragons, has said the system is lacking anything.Or that they preferred the Cary, and these fellows all have tube amps from Acoustat, Nagra, Art Audio and Lumley.
No one has said they thought the tubed Cary was more musical.No one missed it or said they liked the sound before with the tubed unit.
And the Cary is a very nice amp.
No one has said the Dragons sound unnatural,digital, edgy sterile or any of the other negatives used by some on this thread.
Again I have to hammer it home that not all D amps sound the same.
The good ones, and I would say mine fits that description, do not sound alien.
They sound like a good solid state amp in some respects and a good tube amp in others.
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Yes I did hear the Nuforce amps.
I was eager to go up and have a listen.
Phil said to me "what do you think?"
I said they were the worst amps I have heard in a long time.
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I tried three different class D amps: Benefits; low energy usage, nice tight bass (they were originally invented for enclosure in subwoofers so no heat was important and bass was important), but I found they had a thin mid/high end and two dimensional sound stage; and have now thoroughly cured myself (for now) of this obsession with "being green". Class A/B thanks with a tube preamp.
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I owned the Bel Canto S300 and M300 series. Not to my liking at all. I owned some pretty good front end equipment at the time and I was so used of wide deep soundstage. That all but disappeared with the class D I owned.
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I have the Red Dragon Leviathan mono blocks, 500 watts into 8 ohms, 1000 into 4.
The closest to it would be the Bell Canto, same Ice power, upgraded from stock.
I have owned several power amps from tubes like Conrad Johnson, VTL,Michaelson Austin, Grant Lumley,Dynaco, Output transformerless tube amp from Atmasphere,and 300B SET from Cary. I have owned some Brystons,Bel Canto Evo,Spectral,Blue circle bc2 mono blocksHybrid)Meitner m100 mono blocks,Classe DR8 mono blocks,and others from the 1970's not worth mentioning.
After owning a lot of amps of all stripes,I would have to say that I don't think there are too many nits to pick with the Red Dragon or Ice amps in general.
They seem to walk the balancing line between the best of tubes and solid state and don't have any of those amps draw backs- not overly tubey sound, not sterile cold, and not inefficient
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I owned the Nuforce ref 9.02 for about a year and a half. They were phenomenal for ht due to their speed and dynamics. However, they lacked the harmonics for music. I demoed my current amps and it was an easy decision from there.
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I have listened to a number of them (2 channel only) and can only conclude that the D in Class D stands for depressing. They all sounded remakably similar to me, which leads me to believe that they were all built exactly per the application notes from the chip supplier with no added R&D. Perhaps there are some better sounding units out there, I dont know, but I heard enough to come to my own conclusions.
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Whoever said Class D amps haven't arrived must have gone to the wrong station or missed the train. This type of amp has evolved significantly over the last 15-20 years with the advent of faster signal devices, better materials for mosfets and improved designs. Its hard for me to look at a Class A or AB amp and not see all the wasted circuitry, metal and dollars going into heat dissipitation. The loss of audio energy must be in the realm of 50% for most of those A and AB amps and with it the onset of clipping at transients.
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I've heard several Class Ds, the Nuforce Reference, BelCanto Ref 1000s. I was impressed with both the Nuforce and really liked the BelCantos. I finally purchased an Axiom A-1400-2 after comparing it in side by side listening session to the BelCantos. The performance was very close though I thought the A-1400-2 produced a more natural tighter bass with the same transparent mid and detailed highs as the BelCantos.
Without the huge heat sinks necessary in conventional amps there is room for more important parts like bigger capacitors to provide fast abundant energy when needed. So clipping is virtually non-existent. And the Axiom also has the technology to dynamically allocate more power to the channel demanding it. So out went my pair of trusty Bryston 4BSSTs and in came the Axiom A1400-2 to take its place alongside my other favourite amp, a tubed McIntosh MC2102.
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I think one of the issues with class D is with type 3 in particular, and it relates to the power supplies as much as it does to the amplifier. Switching supplies have peculiar characteristics that are good in some ways, they behave like they are very stiff, up to a cliff-edge point, but may not be ideal for music playback. They also contribute to all the noise and interference.
What the article brushes aside are digital amps with no feedback, and those are, by a good margin, the best ones for me. Ironically, Martin Colloms is one of the great proponents of low or no negative feedback in amplifiers. I just wish he would listen to the NAD M2, John Atkinson (http://www.stereophile.com/solidpoweramps/nad_m2_direct_digital_integrated_amplifier/)gave it his pretty unqualified approval, and he's a man out of a similar mould.
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In our opinion, the real challenge now is not the audible performance, but confronting traditional attitudes about distortion in the specs. All of these designs can reach 1% or more at 20 KHz. In itself, although some would argue, it is not audible (What everyone ignores is that loudspeakers, no matter how good, exhibit far more distortion than that) If you address the other speaker interface problems then it comes down to audiophiles rethinking traditional wisdom.
The advantages of a properly designed class D are compelling: less weight and higher efficiency. In a world where the carbon footprint of electronics is becoming a big issue, this approach is compelling. However, we wouldn't move into an area that would degrade audible performance. For the record that no longer appears to be a barrier. We are getting close.
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Hypex are the one class D amp that I haven't heard, but I suspect it's the best of the analogue class D bunch.
For what its worth, I recently bought and compared an Emo XPA-5 and a few ICEPower amps. I thought the Emo was clearly better, though having said that my old NuForce MCH3C7 was very good in its own analytical and dramatic way.
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I can understand the distaste for such an amp from an engineers standpoint as I don't think there is any elegance to the design. It seems Class D exists through sheer brute force engineering. It is like a Rube Goldberg of amp design - an exceedingly complicated design to accomplish an otherwise simple task

. It is a layman's interpretation, but that's the way I see it.
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That's not to say that ICEPower amps are bad; I think they're a good solution for multi-channel receivers, but when you get up to separates quality gear, they're just not as transparent as the better linear amps, by which I mean Emotiva, Bryston, Arcam - amps with HiFi pedigree.
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