NuForce Reference 9 Monoblock Power Amplifier

Several months ago I visited three members of The Absolute Sound team—Harry Pearson (founder and chairman of the Editorial Board), Jonathan Valin (associate editor), and Atul Kanagat (advisor to the “Cutting Edge” section) and had the opportunity to audition their superb reference audio systems. Many things stuck with me about those rich listening experiences, and one was the vivid memory of how excellent the respective system amplifiers were. At the time, Pearson’s system was powered by an ASR Emitter II amp, Valin’s by a pair of MBL 9011 monoblocks, and Kanagat’s by a pair of VTL Siegfried monoblocks. Then and now, I felt those three were among the finest amplifiers on the planet, but my enthusiasm was tempered by the sobering realization that each cost more than the car I drive; I could no more buy one of those amps than I could a fleet of Lear jets. Sighing, I made the rational choice to accept some cost-driven tradeoffs in my reference electronics, a decision that served me well right up until a pair of downright amazing and affordably priced giant-killer amplifiers came along and changed everything. Enter the NuForce Reference 9 monoblocks. Within a few hours of installing them in my system, I felt certain new benchmarks in affordable excellence had arrived.

NuForce’s Reference 9s are small, attractively (but not extravagantly) finished, 160 watt, Class D monoblocks priced from $1250 to $1305 each. The Reference 9s are equipped with switch selectable balanced and single-ended inputs (though users should run cabling to one input or the other, but not both at the same time). When I used the “Class D” descriptor some of you probably thought, “Oh, so the NuForces are digital amps,” but in fact they’re not. NuForce VP Casey Ng stresses that the Reference 9s are “analog switching amplifiers,” and the distinction involves more than mere semantics. In practice, the NuForces differ from many other Class D amplifiers in three important respects: First, they offer very wide bandwidth (20-50kHz); second, they can drive low impedance loads (350 watts @ 2 ohms); and third, they are based on proprietary circuit topologies developed by NuForce—not on any of the popular off-the-shelf Class D amp modules such as those offered by Tripath, Bang & Olufsen/ICEPower or Philips/Hypex UCD. Interestingly, the NuForce amps were designed by the company’s chief technology officer—an engineer named Tranh Nguyen, whose design accomplishments include development of the power system for the Tomahawk missile and who holds several patents relevant to Class D amplification. But enough technical background; let’s get to the heart of the matter. How do these amps sound?

Frankly, the NuForce Reference 9s do so many things right that I hardly know where to start, but let’s begin with the two qualities that grip most listeners first: resolution and transparency. The Ref 9s offer a truly extraordinary level of see-through transparency, and as an audiophile friend so aptly put it, “Their transparency is real, not a fake artifact caused by brightness.” That brings me to a second revelation: These little amplifiers not only deliver gobs of musically relevant detail, but do so without imposing the fingernails-on-a-chalkboard torture of excess brightness. In this respect, the Reference 9s combine some of the whole-cloth sonic integrity of the mighty MBL 9011s as well as a good bit of the focusgoes- on-forever clarity of the ASR Emitter II. How does this play out in musical terms? Well, for me it means falling in love with the timbres of individual instruments and voices all over again. As I write this, for example, I’m listening to the Quartetto Italiano perform the Dvorzak “American” String Quartet in F Major, Op. 96 [Philips, LP] savoring the way the NuForces reveal the profoundly complex voices of each individual instrument, as well as the interplay of those voices as they meld to form a greater whole (and isn’t that the real magic of great string quartets?). Similarly, on good live recordings, such as Eva Cassidy’s Live at Blues Alley [Blix Street Records], the NuForce’s bring my system alive with the sort of crackling, electric intensity you typically experience only in live music venues—an intensity heightened by the amplifier’s ability to capture, simultaneously, the delicacy of Cassidy’s voice, the scorching heat of electric guitar solos, and the giant-hearted punch of the electric bass. The word picture I’m hoping to paint, here, is one of an amplifier that essentially never sounds congested, regardless of the complexity of the material being played (a quality the the ASR exhibits to an even greater degree).

Next, as a bassist, I feel compelled to point out that the NuForces deliver the best doggone bass-pitch definition and control I’ve ever heard from any amplifier. Part of what’s going on is that the NuForces offer a damping factor greater than 4000 (no, that’s not a typo), so that when the Ref 9s tell woofers what to do, the drivers have little choice but to shut up and follow orders—precisely. The sonic results can be eyepopping in several ways. First, the Ref 9s seem to give some speakers (e.g., my Magnepans) about an extra half octave of bass extension they never had before. Second, the amps draw out layer upon layer of bass textures and detail you may never have heard before. A few nights back I put on master acoustic bassist Dave Holland’s Emerald Tears [ECM, LP] and listened in shocked amazement as the NuForces revealed one new subtlety after another (the intricacy of Holland’s solo work is just unbelievable!). The only word of caution I would offer is that the NuForces handle low frequencies with the utmost control, and therefore will not artificially “warm up” either recordings or loudspeakers that lack bass. But put these amps together with recordings and associated gear that can do bass well and it’s “fasten your seatbelts” time.

The NuForces offer lively and expressive dynamics, doing an especially good job with leading edge transients and moderate to large orchestral swells. One potential problem, though, is that the amps are so expressive that you tend to forget that they produce “only” 160Wpc; when pushed to their limits the Ref 9s eventually run out of steam before blockbusters such as Musical Fidelity’s kW500 would. When driven at less than “go-nuts” volume levels, however, the NuForces paradoxically sound more authoritative and dynamically alive than many higher-powered amps do.

Finally, I found the Ref 9s produced very wide and deep soundstages, though not quite on a par with the MBL 9011s or, especially, the ASR Emitter II (the ASR is, I think, in a class by itself in terms of soundstage depth and precision). Nevertheless, the NuForces can go toe-to-toe with amps several times their price and prevail by virtue of their uncanny ability to delineate layers of front-to-back depth in the soundstage, and to reproduce small reverberant details that suggest the acoustics of the recording venue.

What can’t the Reference 9s do? Well, one thing they don’t do, or at least don’t do easily, is to present the sort of holographic, “glowing from within” midrange qualities that the very finest tube amplifiers sometimes exhibit (the VTL Siegfrieds and certain WAVAC amplifiers would be good examples). Though I would never call the NuForces sterilesounding, they do have a certain accurate- to-a-fault, garbage-in/garbage-out quality. Basically, these amps will try and make speakers conform to the incoming music signals, for better or worse. But in a sense this very faithfulness to the signal is what makes the Reference 9 so rewarding on great recordings.

An open-ended question, and one that will bear further research, is whether other modern Class D amplifiers sound as good as the NuForces do. Thus far, I’ve briefly heard Class D amplifiers from Channel Islands Audio, Kharma, and Red Dragon Audio, and felt that each offered a lot of potential (though each sounded different from the others). I feel safe asserting that Class D technology has come of age, even for demanding audiophiles.

Prospective buyers should know that the NuForce amps have some minor quirks, which, to NuForce’s great credit, are mostly covered in the amps’ documentation. First, the amplifiers require about 75 hours of burn-in before sounding their best. Second, the amps must be connected to loudspeaker loads before being turned on. Third, the amps produce an annoying “scrritttch” when first powered up. Fourth, the NuForces sometimes exhibit a small but audible increase in background noise when preamp outputs are temporarily muted, though when preamp outputs are not muted the NuForces become dead quiet. Finally, the Ref 9s are very sensitive to ancillary cabling, input connectors, binding posts, and the like. For this reason I strongly recommend ordering your Reference 9s with the optional WBT NextGen RCA jacks (these will set you back an extra 55 bucks per amp, but they are worth every red cent).

Do you find it hard to swallow the idea that a $2610 pair of monoblocks can compete on a nearly equal footing with amplifiers many times their price? I certainly did, but after loaning the NuForces to a colleague whose reference system is far more exotic than my own, the verdict stayed the same: The Reference 9s really are that good. Therefore, I urge you to run, not walk, to the nearest NuForce dealer to audition a set ASAP. If your reactions are even half as favorable as mine, you’ll need your checkbook. Go, now.