NuForce Reference 9 V2 Special Edition Mono Power Amplifier 
Home Theater Power Amplifiers Mono Amplifiers
Written by Jim Swantko   
Friday, 01 February 2008

Introduction
In all my time as an audio enthusiast, I have never seen anything quite as polarizing as the words “switching amplifier.” In my experience, the overwhelming majority of audiophiles politely (or not so politely) dismiss them as a gimmick used to separate fools from their money. They firmly believe that bulk and heat generation are all indicators, which can be used to predict the competence of an amplifier’s performance. This idea is not as foolish as it may seem, as some of the most highly regarded amplifiers are behemoths, weighing in at over 100 pounds and producing enough heat to require a dedicated air-conditioning system.

There is, however, a burgeoning group who are singing the praises of some new switching amplifiers, calling them “giant killers.” But which side is correct? Switching amplification is nothing new; in fact, it’s been around for nearly 80 years. The advantages, which are obvious, include low weight, diminutive size, miserly power consumption and virtually zero heat production. These are all wonderful attributes, but they are meaningless to the audio enthusiast if the amplifier doesn’t sound good.

In the past, switching amplifiers were relegated primarily to sub-woofer duty due to their ridiculously high efficiency, damping factor and size, which were all ideal for burying them inside an enclosure without the need for massive heat sinks. They were also shunned from taking center stage, driving full-range loudspeakers, because they simply didn’t sound good, especially at high frequencies, and lost much of the detail contained in music.

Traditional digital switching amplifiers work by converting the input signal into a series of pulses. The average of these pulses corresponds to the instantaneous amplitude of the signal. The pulse is then compared typically to a saw-tooth waveform to create a pulse-width modulated (PWM) signal. This signal is then used to control the power stages to recreate the signal. A low pass filter is then used to remove the high-frequency saw-tooth waveform remnants.

NuForce has put its own patented twist on the switching amplifier. It has improved on the classical switching amplifier by replacing the saw-tooth waveform with a “naturally occurring” analog modulating signal. The saw-tooth waveform is said to cause jittering of the signal and ultimately a loss of the minute details that audiophiles so deeply cherish. The NuForce method is said to make the music sound … well, more like music and less like a digital recreation of music.

I received a pair of NuForce’s latest iteration of their Reference 9 Special Edition mono amplifiers, which are now designated as V2. V2 is an entirely new circuit from its predecessor and is reported to reduce noise by a staggering 20dB over the V1 design. It also cranks up the efficiency of the output stage to 85 percent and provides 190 watts into eight ohms and 300 watts into four. These top of the line V2 SEs sell for $5,000 a pair and come with a generous five-year warranty.

The SE’s add what they describe as “an improved power capacitor board with proprietary NuForce low ESR capacitor matrix and high-performance capacitors” to the standard Ref 9. According to the NuForce website, this should result in sweeter highs, smoother midrange, extra weight in the bass and a deeper and more coherent stage, which suits me just fine.

Set-up
As much as I tried to prepare myself for the size and weight of these amps, I was still shocked at just how light they are. A six-pack of beer weighs more than one of these amps. My wife immediately said, “I love them. Can the big thing in the middle of the floor go away now?” She was referring to my cherished 100-plus-pound Mark Levinson 336 amplifier.

The NuForce amps are about the size of a shoebox lid. The face of the copper-colored amp is clean and uncluttered, with only a single blue LED to tell you when they are powered up. The back panel has inputs for both single-ended and XLR inputs and a switch to determine which you are using. There are a pair of binding posts, a power switch and a receptacle for a power cord. I did notice that the binding posts are quite close together and they gave me a hard time while I was trying to cinch them down on my speaker cables, something I am very spoiled about by the Mark Levinson No. 336 with its wonderful binding posts. Banana connectors would make this a non-issue, but I prefer my spades.

With all the connections made, I flipped the switches and powered them up and began letting them break in with some music flowing through them as I went to bed.

My plan was to ignore them while I broke them in for at least a few days before I did any critical listening. This proved to be a problem, since my audio room is also my home office. I couldn’t help but give a quick listen every now and then between phone calls and emails. Even using the NuForce amps for background music, a few things became instantly obvious.

Music
First, the amps have the blackest background I have ever heard. I’m talking super-massive, black-hole black. In fact, it was a bit disorienting until I became accustomed to it. It was as if the outputs knew when a break in the music was coming and turned themselves off until they were asked to make another sound. This is not to say that notes didn’t have natural decay, because they did – it’s just that there was nothing else there besides the music, and I mean nothing. I was not accustomed to this added a sense of depth and separation.

If you have ever listened to the first track on disc two of Alison Krauss and Union Stations Live (Rounder/UMGD), you know how enchanting the dobra can sound, especially when played by someone as skilled as Jerry Douglas. Playing it through the Ref 9s re-created that feeling of “being there” better than my system ever has before. Each note, no matter how quickly they were played, and Jerry can play fast, was clearly distinguishable and had a life of its own. Never did the strings sound compressed or smeared on top of each other, as I have heard from lesser amps.

The absolute silence of the background was also obvious as I listened to Alan Jackson’s album Drive (Arista). Alan likes to stack backing vocals on top of his lead vocals, which are sometimes very difficult to separate from one another. “Bring on the Night” is a track that illustrates this well throughout the chorus. I have played this on various systems and it is always obvious that something changes during the chorus, but it’s hard to tell if it’s another vocalist, or simply a little reverb or delay on Jackson’s vocals. With the Ref 9s, it was obvious that it was indeed another voice, but there was also such separation that now each voice was clearly distinguishable from another, which was very impressive.

Secondly, the bass these little amps produced was nothing short of astounding. I was not prepared for just how completely and effortlessly they controlled my Aerial 10Ts. I should note that my Aerials are not the most efficient speakers, with their 86dB efficiency rating, and pairing them with an amplifier without an iron grip on the 10-or-so-inch woofer will result in sloppy and boomy bass. This was a non-issue with the Ref 9s; in fact, I have never heard better bass from them. Drum impacts were lighting fast, with fantastic weight and impact.

I found myself listening to the opening bass lines of Diana Krall’s “Temptation” from her album The Girl in the Other Room (Verve) over and over again, marveling at the speed and depth that the NuForces recreated. The strings created a snap with each pluck of the strings, which was not only heard, but also felt. My No. 336 was clearly outclassed and I have never had a complaint with its bass performance before.

Vocals through the Ref 9s were very natural and textured. On Mark Knopfler’s “Back to Tupelo” from the album Shangri-La (Universal), his voice is alone through most of the track. It came through with texture and grit and floated at the front of the soundstage. There is a nice touch of warmth, but not too much.

Shangri-la is one of those albums that I have on constant rotation, so I know it well. I felt myself drawn more into the music with the NuForce amps than with any other amp that has passed through my system. I also picked out new details, such as the distinct sound of Knopfler’s lips separating and a breath before he begins to sing on “Back to Tupelo.” Acoustic cues abound and it was quite easy for my mind’s eye to virtually recreate the recording studio.

The upper frequencies were where I expected to hear a chink in the armor of these little amps. Expecting to hear a rolled-off top end and a loss of detail, I was relieved when I listened to “Songs for Sonny Liston” off the same Knopfler disc. It’s a bluesy track with a rhythm that will get anyone’s feet tapping. However, there are several instances where lone cymbal strikes are played. These were natural and shimmered for what seemed like an eternity, decaying naturally.

Miles Davis’ trumpet on “Kind of Blue” from his album of the same name (Sony) makes huge dynamic swings throughout the disk. At times, it is soft and sweet and at others, it genuinely rips the air, such as on “Flamenco Sketches.” The Ref 9s never got out of line and became harsh; they simply passed the music with all its textures and resonances. The cymbal work in “All Blues” was wide open, lifelike and occupied its own distinct space. The saxophones growled and the wonderful reed work came through clearly.

The Downside
I found it very difficult to find faults with these little amplifiers. However, I would like to see a better set of binding posts on the back. The fact that they were small and a close together only exacerbated the issue of struggling to get the speaker cables firmly connected. Cardas-style posts, which allow you to clamp both terminals with a single large knob, would be perfect – I know they were offered on previous versions of NuForce monos. Why they are no longer available, I have no idea.

I also noticed that these amplifiers don’t like to be powered off. When powered down for extended periods, I found that it took four to five hours to get them back to sounding their best. When cold, they were not as open as I had come to expect. The stage shrunk in all dimensions, though it gradually reopened as time passed. This only happened once, however, as I am a quick learner and never powered them off again, which wasn’t a problem, considering how miserly they are with electricity.

The other downside I can see, if you can call this a downside at all, is that anyone who wants to use these amps needs to be sure their front end is up to snuff. The Ref 9s pass absolutely every bit of detail, good or bad. If you are providing the amps good-sounding audio, they will be very happy. If you have weaknesses in your system, you will be made aware of them very quickly, probably triggering another round of upgrades.

Conclusion
I must admit that, prior to my time with the NuForce Ref 9 V2 SEs, I was firmly ensconced in the camp that dismissed switching amplifiers. I felt they had no business in the world of true “high end.” I am man enough to admit when I am wrong. I simply cannot recommend these amplifiers highly enough to those who appreciate the very best. They are small, energy efficient and cool running. They are smooth from top to bottom, with an open, airy top end, beautifully textured midrange and a bottom end to die for. If you still aren’t a believer, maybe you should audition a pair for yourself. NuForce is so confident in these amplifiers that they are offering home auditions for a buck. You read that correctly, a measly dollar will get a pair of these wonderful amplifiers to you to experience for yourself. I now see how this seemingly crazy offer isn’t really that crazy after all.
Manufacturer NuForce
Model Reference 9 V2 Special Edition Mono Power Amplifier
Reviewer Jim Swantko





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