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