Sound quality of class D amps v Hiend references

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I didn't think that The Absolute Sound concealed the merits of these amps at all. They did describe each amp in detail. And certainly different reviewers saw some of the amps quite differently. Or for that matter, neither did the reviewers all see it the same way.

On the merits of the amps, the NuForce review for example, starts with "Two of the finest sensibly-priced amplifiers I have found are the Reference 9 and Reference 9 Special Edition monoblocks from NuForce".
Specific comments about the Reference 9SE include "startling dynamics, big and transparent soundstage and outstanding resolution". "Alive" is another descriptor. With regard to the Spectron, "the Musician III punched my clock like few other amps I've heard". Those are just two examples, but I can't see the idea that TAS is not openly admitting the merits of class D.

Now contrast the description of the NuForce above with the description of the Channel Islands D-200, which is said to be "polite", "falls off dynamically as music reaches its extremes", and "smooth". That supports Bruno's point about these amps sounding quite different.

TAS characterized Class-D amps as sounding different, which makes sense given the differences in the designs on the market. If you only look for whether the amps were viewed as "good" or "bad", well you can find either view in the Class D article. I suspect that class D sounds rather different from Class A/B as a general rule (though not always in the same way), and this difference leads to the mixed assessment of almost every amp TAS covered. And maybe the merits of class D are better revealed (or the flaws better masked) in some systems than in others?

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I deleted my initial post, because rereading it I thought it was a bit too bolt. As I said I have listened to Zappulse 2.3SE, Zappulse 700, UCD 400 and UCD 700 (generously offered by Hypex), Nuforce 9 and H2O Signature. I heard the Zap-modules on conventional speakers (Avalon Opus) and they were quite good. However I have extensive experience with classD amps on Apogee ribbon speakers: on three locations with 1ohm Scintillas and one location with 2-3 ohm Full Range and with different CD players and tube and solid state pre-amps. Having heard raves about classD I have given it serious auditioning. Some amps were someone’s DIY projects (ZAPpulse), ore assembled by the manufacturer (UCD, Nuforce and H2O).

What we heard on the Apogees was that there were differences, but more similarities. The amps were capable of driving these difficult loads with ease. That is remarkable for these relative small and not expensive amps. But what disappointed us was a strange, “stiff”, fatiguing sound in the higher mid and high frequencies, that lacks space around tones. The bass is very full and strong, but a bit exaggerated and doesn’t seem to integrate with the rest of the spectrum. However we compared them to 15 year old classA designs (ML-2, Classe DR3 VHC and Sphinx P16, that were way more expensive at the time. Maybe not a fair comparison, but these are the amps we use and you can buy for reasonable costs now and are capable of driving the Apogees on a musical way.

Given the price and new technology classD is very promising and I really like the idea of green amplification. My experience is with very difficult loads and classD seems to be more sensitive (at the moment) to speaker loads. I think it’s true you can’t speak of classD in general, the implementation of the total amp design must be very important, like the power supply and output stage and I really hope to hear a classD design that makes MY speakers sing. But I haven't heard it yet.

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Let me preface my comments by indicating that I respect the honesty of the TAS reviewers. However, the negative opinions of some reviewers are lacking in a couple of important respects (1) a failure to indicate the other equipment used in the review and (2) a failure to indicate what actions were taken to determine whether a reviewer’s impression resulted from poor equipment mating (or some significant flaw with the equipment being review).

I’ll pick on Jon Valin’s review of the ARC 300.2. Did he use the ARC Ref 3 in his review? Can he claim that the ARC’s preamp didn’t seem to mate well with its amp? How much break-in time did the amp have before he reviewed it? Did he experiment with alternative equipment mating to determine what the effect on sound would be? Were issues raised with the equipment manufacturer? I appreciate Jon Valin’s opinions, but the devil (and value of opinions) is always in the details. Perhaps the 300.2 is a giant killer with the proper mating, in the same sense that a set amp can sound gloriously musical with a proper set of speakers. Likewise, a solid-state (class a/b) amp can suffer (sonically) from a mating with the wrong cables, for example. TAS has heard of equipment/system synergies?

I raise these issues based on a couple of counterpoints. First, I’ve heard the ARC 150.2 (a smaller version of the 300.2) sound very musical (detailed, warm, full, not lacking in low or high frequencies, compared to the “absolute sound” standard) when mated with an ARC LS 17, Joseph Audio Pearls, Transparent cables, and a Krell disc spinner (in a dealer’s showroom). Second, some of these product manufacturers (ARC and Cary come to mind) have long histories of producing quality products (referring to sound quality, of course). Are the folks who voiced the Ref 3 and the Ref 210 likely to turn out an absolute clunker, as Valin seems to glibly conclude? That concern would certainly give me cause to examine the basis for the seemingly poor performance of the component, and the opinion of the reviewer.

As a reader, I’m left to wonder whether there is an issue with the component, an issue of a rash opinion, or the issue of an audio reviewer trying to balance a grain of sand on the head of a pin. If my statements offend anyone, I apologize. I mean them to be direct *and* respectful.

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ossocao wrote:

"Shure there are a lot A/B and tubes will kill digital gear."

I disagree. Exotic linear designs are used in systems whose function is conspicuous consumption (in which case the system sounds like crap) or that have been carefully tuned around the fundamental distortions of linear amps.

The TAS reports do not indicate that the audition systems were tuned around the switching amps with equivalent care. This may require attention to RF noise, or simply undoing the introduced compensating distortions.

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I don't really have anything new to add to this discussion. I appreciate Bruno's take on the situation, which, IMO, is just. No one is writing off Class D/T. Contrarily, that does not mean it is fully competitive with the best Class AB (and some affordable Class AB). And that doesn't mean that there aren't exceptions, like Bruno's own MP150.

In the case of the ARC 300.2...I tried the amp with the Ref 3, which one would think would be a perfect combo, and with the MBL 6010D. Allowing for the differences in the two preamps--and they are the two best I've heard--the amp displayed the same set of virtues and flaws. I've also heard the ARC 150 in a five-channel version. Indeed, I used it for some time in my home theater, along with the Krell Theater Standard controller. Despite a little upper midrange elevation (and perhaps because of it and the clarifying effect it had on dialogue), I thought the 150.5 was a great home-theater amp. But then again, it wasn't being called upon to work full-range (I was using the Krell MRS sub at the tiime) and it wasn't being fed a high-res signal (strictly Dobly Digital and DTS 5.1).

In response to jba's queries, the 300.2 came to me from another reviewer who had thoroughly "broken it in." I let the amp warm up for better than a day before listening to it (having been advised to do so). And left it on throughout my auditions.

BTW, I dont need to be lectured by jba about the glorious history of ARC. I think I have probably reviewed more ARC gear than any TAS reviewer (starting with the SP10MkII and D79B), have owned more ARC gear than any other marque, and currently use as my reference an entirely ARC-powered system (Ref 3, PH7, Ref 610T). Its current offerings are, in many ways, as good as hi-fi gets. That said, the 300.2 simply doesn't compare, sonically, to current ARC Class AB amplification, and I don't think ARC would claim that it does.

More importantly and essentially here, my comparisons weren't just made to higher-priced equipment (in the current issue of TAS, I compare a moderately-priced Class AB amp, designed by John Curl for Paraound, to Class D/T); I also compared the Class D/T amps I reviewed to the absolute sound--just as I always try to do with any piece of gear. The 300.2's fell short of that (unreachable) standard by a wide margin.

As for the question of value for dollar, personally I found the treble range response of the Class D/T amps I reviewed to be uniformly weird and for that reason alone wouldn't dream of using any of them, as they currently stand, in my system. (The Kharma MP150 is the sole exception.) However, the Rowland 201 had an absolutely amazing midrange, as bloomy and detailed as amps that cost many times as much as it does. If Rowland could extend those midrange qualities into the treble, he would have a gem (albeit a gem that sounds like a Rowland).

We will certainly be revisiting Class D amplifiers. We'll need to. They are growing like mushrooms in the shade, and by next year there will be a whole new crop to harvest.

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Hi, thanx for that classD group review, i've noted interesting point about really different bass D vs AB amps. Do you have some explanations about nature of the tighter bass from the all class D amps in the test? Actually, the tight bass isn't bad at all, isn't it? :?:

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tuckers is correct. Power amps allow speakers to damp themselves by the amount of impedance the amps present to the speakers. Switching amps present the lowest practical amount of impedance of any amplifier type, so they give the best bass performance with speakers designed for negligible amplifier output impedance.

The speaker is a motor that acts like a generator once it is in motion. The current from the generator action is what provides the damping force in the moving speaker parts. Too little amplifier output impedance causes too much generated current and too much damping force, while too much amplifier output impedance does the opposite. Underdamped speakers are boomy, while overdamped are anemic.

For analogy, consider 'shock absorbers' on a car. If the shocks are too weak, the car wheels bounce around and the steering control is sloppy. If the shocks are too strong, the ride is awful!

This was all understood and explained in a hobbyist article in 1954. See

http://www.paulspeltz.com/tomcik/index.html

for a posting of this article with permission from the author and publisher.

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Typical Class AB amps use feedback, which compromises the damping behavior in actual use. Switching amps do not use analog feedback and so have low output impedances determined by their power supplies and the residual parasitic resistances of the switching transistors.

Your perception of bass depends on uniform amplifier performance across the audio spectrum, not just at low frequencies. This makes the feedback network design critical in linear amps.

On the mechanical side of things, it is easier to support and isolate a switching amp to avoid acoustic feedback. This may make more difference for bass tightness than the circuit considerations in a particular comparison.

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