Power Amplifier Reviews

Price: $3,500 At A Glance: Enormous power output • Remarkably compact • Class D

Class D amplification has a narcotic-like hold on the audio electronics industry. These switching-mode designs mesmerize with a dazzling array of advantages: high efficiency, high power output, low weight, compact dimensions, and depending on implementation, enormous cost savings.

Invariably, advocates claim that late-generation Class D amplification has both solved the sonic problems heard on previous Class D amplifiers and sonically surpassed the best Class A/B designs.

Class D published specs can be attractive: nearly ruler-flat response from 20 hertz to 20 kilohertz, low harmonic (at 1 kHz) and intermodulation distortion, and low noise. As with the compact disc, when measured against the numbers put up by analog vinyl or tape playback (though Class D is not a digital format), Class D amplification seems to be a no-brainer. But hearing is believing, and while some listeners are sold on 16-bit digital audio, others can’t stand it—and that includes many well-respected audio engineers.

Clearly, Class D is enticing for a lot of reasons. Many manufacturers have taken the plunge. Some have gotten burned, but others, like two-channel specialist Audio Research, have managed respectful if not stellar results.

Without getting overly technical, in Class D operation the output transistors are either full on or full off instead of operating in a far less efficient linear mode. The huge increase in efficiency means the amplifier requires smaller heat sinks and power supplies. Small, lightweight, but surprisingly powerful Class D amplifiers can be found in virtually all of today’s home-theater-in-a-box systems and in car audio.

These amplifiers turn the analog sine wave input into a pulsewidth modulated square wave signal that is analog but appears digital. However, the higher the frequency reproduced, the higher the switching speed that’s required to process and filter out the square wave and re-create the analog output sine wave. This is where Class D amplifiers can run into trouble because of high-frequency harmonic distortion. That’s why Class D amplifiers are far easier to implement in powered subwoofers where the frequency response needn’t extend much above a few hundred hertz.

What’s most important to remember here is that, as with any system, there are both advantages and disadvantages. There are no miracles. Also, keep in mind that specifications can be made to look perfect by convenient omission. For instance, all but the vacant-eared true believers now admit that the severe brick-wall filters used in early digital audio had a deleterious effect on the final sound that was more objectionable to some ears than to others. Of course, such problems aren’t revealed in the specifications.

Over the past few years, Class D amplification has found its way into full-range high-performance audio designs with varying degrees of success. For the most part, audiophile reaction to music reproduced by Class D amplifiers has ranged from bad, to not bad, to pretty good at best. It should come as no surprise that a different and unique amplification technique might (or might not) produce different and unique sound, especially in relatively early implementations.

Anthem’s new $3,500 Class D monoblock amplifier is an extremely attractive-looking, robustly built, remarkably compact pancake of an amplifier capable of outputting an impressive 1,000 watts into 8 ohms, and an astonishing 2,000 watts into 4 ohms. If your speakers dip down to 3 ohms, the amp can supply it with more than 2,400 watts, limited only by voltage droop in your AC line.

While 20 pounds is not lightweight and 19 inches wide is not compact, these numbers are nothing short of miraculous for an amplifier capable of outputting 1,000 watts into 8 ohms. Though these amps are quite warm to the touch, even at idle, they can be stacked one atop the other in the same amount of space (or less) as a 5-x-200-watt amplifier to produce upward of 10,000 watts!

A front-panel status LED alerts you to various abnormal conditions such as out-of-range AC voltage, output-current excesses caused by short-circuited speaker wires, excessive temperature, and other faults.

Anthem claims its new amplifier is a “game-changing monaural powerhouse” that “annihilates conventional audiophile wisdom about Class D amplification.” Anthem literature also says it offers “flawless fidelity and full dynamic range across all volume levels, flat frequency response, and rock-solid stability into even the most difficult loads, no ‘dead time’ crossover distortion, and virtually no noise floor.”

Read between the lines of that verbiage, and the problems usually associated with Class D amplification should be obvious. Anthem claims it has made “radical improvements over previous Class D amplifier designs” that, of course, their manufacturers touted as being pretty much perfect.

How They Stack Up
While you can stack these amps five high (though not inside a front- closing cabinet environment unless you use a fan), Anthem recommends doing so with the surround channels sandwiched between the three front channels, with the center channel on top.

I drove the amp’s balanced inputs using the Marantz AV7005 surround processor (Home Theater, April 2011) with the front channels triple-stacked atop my A/V cabinet and the surround channel amps directly adjacent to the surround speakers. Later, I placed the front channel amps close to the L/C/R speakers and ran long lengths of balanced interconnect and short lengths of speaker cable.

How They Sounded
Many audio engineers and some listeners don’t believe in break-in for audio electronics—in which a piece of gear sounds one way cold out of the box but over time improves or at least changes, sometimes dramatically so.

Others clearly hear it and believe. The doubters say break-in really occurs in the brain, which becomes acclimated over time to a new sound.

For this review, I auditioned two sets of five of these Anthem amplifiers and an additional stereo pair, a few months apart from one another. To be perfectly blunt, out of the box, the first five were among the worst-sounding amplifiers I have ever heard. The sound was just plain wrong. I did everything I could to make them sound better including: 1) allowing a long break-in period, playing music all day every day; 2) swapping amps among the channels to hear if perhaps one or more than one might be defective; and 3) placing them close to the speakers and running long lengths of balanced interconnects and short speaker cables. But nothing made them sound better, and I was forced to write perhaps the most negative review I’ve ever written—one that was filled with very specific descriptions of what I heard from many familiar recordings.

Upon receiving the flaming copy, Home Theater editor Rob Sabin asked me to take a pair of the amps downstairs to my twochannel listening room just to be sure it wasn’t some kind of gear incompatibility. I complied, and with higher-resolution associated electronics and better speakers, the sound became even more disappointing.