NuForce Reference 9 Special Edition amplifier

Is Class D the Future of High-End Amplification?

Many of us dream of owning cost-no-object amplifiers such as the ASR Emitter II or the MBL 9011 monoblocks, but since few of us can afford those king-of-the-hill amps, some good real-world alternatives are plainly needed. Two of the finest sensibly-priced amplifiers I have found are the Reference 9 and Reference 9 Special Edition monoblocks from NuForce. I won’t tell you the NuForces equal ASR’s or MBL’s offerings (that would be unrealistic), but I will tell you they capture more than a little of the sonic flavor of those top-tier products.

The Reference 9s ($2610/pair) are compact, 160-watt, Class D monoblocks that feature switch-selectable balanced and single-ended inputs. NuForce VP Casey Ng stresses that these are “analog switching amplifiers” that offer wide bandwidth, minimal phase shift, and the ability to drive low-impedance loads. The Reference 9s were designed by NuForce chief technology officer Tranh Nguyen, who developed the power system for the Tomahawk missile and holds several patents relevant to Class D amplification. But enough background. What makes these amplifiers special?

The Reference 9s offer extraordinary resolution and transparency, shedding light on low-level musical details without imposing excess brightness. The Reference 9s gave me a taste of the whole-cloth integrity of the MBL 9011s and the focusgoes- on-forever clarity of the ASR Emitter II, rendering instrumental and vocal timbres with great purity. On good live recordings, such as Eva Cassidy’s Live at Blues Alley [Blix Street Records], the NuForces brought my system alive with the sort of crackling, electric intensity typically experienced only in live music venues— intensity heightened by the amps’ ability to capture the delicacy of Cassidy’s voice, the scorching heat of electric guitar solos, and the punch of the electric bass. No matter how complex material became, the Reference 9s never sounded congested. The amplifiers also produced wide, deep soundstages thanks to their uncanny ability to reproduce small reverberant details that help define the acoustics of recording spaces.

Next, the NuForces, whose damping factor is greater than 4000, delivered powerful and exceptionally well-defined low end. When the Ref 9s tell woofers to jump, the drive units simply salute and comply with no questions asked. As a result, the Ref 9s can extract great bass from ostensibly “hard-to-drive” speakers such as Magnepans, while making bass textures and details, as on acoustic bassist Dave Holland’s Emerald Tears [ECM, LP], intelligible as never before. One small caveat: The NuForces’ offer excellent low-frequency clarity and punch, but they do not compensate for recordings or loudspeakers that inherently lack bass.

Finally, the NuForces offer lively, expressive dynamics, which I appreciated both on leading-edge transients and on orchestral swells. The only catch is that it’s easy to forget these expressive amplifiers produce “only” 160Wpc, and when pushed hard the Ref 9s will run out of steam before 500Wpc blockbuster amplifiers might. But paradoxically, at reasonable volume levels the NuForces often sound more authoritative and alive than higher-powered amps do.

What about shortcomings? Well, the Reference 9s don’t easily present the sort of holographic, “glowing from within” midrange qualities that some fine tube amplifiers (e.g., the VTL Siegfrieds) do. They also show a certain accurateto- a-fault, garbage-in/garbage-out quality that can expose flaws in recordings and ancillary equipment alike (some listeners misinterpret this quality as excess brightness). But in the end faithfulness to the source is what makes these amplifiers so rewarding.

NuForce recently released $4200/pair Special Edition versions of the Reference 9s that incorporate better power-supply boards with “low-ESR capacitor” banks, improved input sections with dedicated power supplies, and pure, oxygen-free copper input wiring. The 150-watt SEs are slightly less powerful than their standard counterparts, though the difference is too small to hear. But what you can hear is the SE’s superior bass and upper-midrangeto- treble clarity, plus heightened focus and delicacy. Are the SEs worth the extra money? Let your system guide your decision. The more revealing your speakers and ancillary components are, the more you’ll appreciate what the SEs do.

Over the past year, NuForce improved the already good Reference 9 design, while pushing sound quality to the next level with the Special Edition model. Together, these monoblocks offer some of the best sound that sensible sums of money can buy in today’s high-end marketplace.