These amps have the STEALTH front faceplatesFrom POSITIVE FEEDBACK Push these little guys to full power and you'll not hear a trace of hardness or brittleness, and not so much as a hint of compression or strain. My $16,000 Pass X 600s nearly drove me out of the room at high levels with the Avalons. The 9s intrigue while they pull you into the performance. They perform like $6000+ solid-state amps, and better than most of them. If you like your music powerful, neutral, slippery smooth, and super detailed, the 9s are your ticket. If you're looking for sweetness and love, warmth and liquidity, they're not for you. With the 9s, there is no direct link between volume and distortion. Almost every solid-state or hybrid amp I've heard gets edgy as you increase the volume. Some won't play above moderate volume without getting hard and glassy. Tube amps become compressed and less elegant. Even powerhouse amps (of all kinds) become congested as they reach their maximum levels. I used to blame this on room/speaker interaction, humidity, etc., but maybe, just maybe, it was the amps misbehaving. The 9s are unflappable, and that's that. I'm not always in the mood for completely neutral sound, but I do love the openness and lack of strain of the 9s. With a damping factor exceeding 4000, the 9s control the speaker drivers like iron fists, keeping them from distorting at higher volumes (or any volume). This would explain their amazing neutrality and lack of graininess. It might also explain their reduced richness and liquidity. The NuForce 9s show absolutely no sign of any digital artifacts. If you didn't know these amps were digitally based, you would never believe it. They are as smooth and musical as any analog amp, and superior to any digital amp I have heard to date. Many have compared them to tube amps, and I have to join that group. I also heard almost no discernible difference between the NuForce 9s and my AES Sixpacs (read that review here). The 9s produce a bit more bass and perhaps a slightly wider soundstage, while the Sixpacs have more detail and air, but it was almost too close to call. The workmanship of the Reference 9s is quite high. Although you might have heard that they are very light in weight, I found them perfect at 7 pounds each. While they are small enough to fit almost anywhere (8½ x 14 x 2 inches), unlike most digital amps they are heavy enough to stay in place with large speaker cables connected. NuForce is quick to point out that the Reference series amps are not digital switching class D. While their website proclaims them to be "analog switching," they don't disclose what class they are: NuForce amplifier technology is based upon the principle that a power oscillator can be modulated by an audio signal so that it produces an amplified audio signal obtained with a reconstruction filter, without the bandwidth limitation of a fixed frequency carrier-based conventional PWM control. It uses a high-performance analog modulation technique and a close-loop control system. Therefore NuForce refers to its audio amplifier as Analog Switching Amplifier…. Unlike some other Class-D amplifiers, NuForce's analog switching amplifier does not require a sawtooth waveform for modulation, but a proprietary naturally occurring modulating signal. In conjunction with taking the signal at the loudspeaker terminals thereby eliminating all distortions, NuForce's natural switching signal does not add noise into the system. NuForce amplifier also does not suffer from the 180-degree phase shift caused by the output filter. Notice they say "unlike some other class-D amplifiers," so are they or aren't they? A lot is also made of their switching speed of 500,000 Hz and their improved power supplies, but it sounds to me that the amp has a type of switching power supply that is very common in the computer world. Also interesting is the fact that the company proclaims that the amps have no phase shift, which may account for the unique sound. After many hours of listening to these amps, I can say that bass is their forte. It is prodigious, firm, and very well defined. To test bass, I always play the title track of Keiko Matsui's "Deep Blue." This track can cause extreme havoc if not under strict control by the amplifier(s) and speakers. Using this track, I switched between my Sixpacs, my DK Designs VS-1, and the NuForce units, using my Radio Shack dB meter to carefully set the volume control each time. (The NuForce amps were considerably louder at the same volume setting than the other amps.) The comparisons were interesting. The Sixpacs' bass actually sounded best, but did not go as deep as that of the VS-1 or the Reference 9s. The VS-1 and the NuForce were so close that I had to switch back and forth numerous times to hear a difference. They both went equally low, but the Reference 9s had a slight edge in controlling the bass notes and restricting their bloom. The Sixpacs had the best midrange, followed by the VS-1 and then the NuForces, by a tiny margin. The Reference 9s really came into their own on the top end, where they put the other two amplifiers to shame with respect to resolution and transparency. Another strong point is their soundstage, which is much wider than that of the Sixpacs, though I suspect that your mileage will vary depending upon your choice of speakers. When I tried my Von Schweikert VR-1s, the soundstage suddenly popped both forward and backward. I did notice that the NuForce amps benefited from extensive warmup. When I left them on overnight before listening, they sounded better by a fairly wide margin. By leaving them on, I also avoided those annoying pops when powering them up. As is my practice, I took the NuForce 9s out of my system for a week and returned to my reference system, then put the Reference 9s back just before finishing this review. The most apparent change was in the bass. It is quite astonishing how much bass these little amps produce—I never got completely used to it. I was quite pleased with the Reference 9s. Not only do they represent very good value for the money, but they also offer convenience, power, quality, but most importantly, extremely good sound. Ed Morawski Reference 9 v3.01 amplifiers
Retail: $2995 pair monoblocs Power/Load8 ohm4 ohm2 ohm Peak Power (20 msec hold time)325W650W 1300W RMS Power175W335W335W *RMS power denotes maximum continuous power. Peak power denotes an instantaneous power boost. Note that typical listening normally requires about 15W of power. These high power amplifiers provide more than sufficient power for just about any speakers on the market. Frequency Response: 20 Hz -0.3 dB – 120 kHz -3 dB
THD+N = 0.01%, 1kHz, 1W to 10W, A Weighted.
Input impedance: 22K ohm
Input sensitivity = 252mV, 1W @ 8 Ohm; 2.57V, 100W @ 8 Ohm; 1.81V, 100W @ 4 Ohm
Input sensitivity for maximum power: 3.33V
Gain: 21 db
SNR > 100 db at 100W Eichmann Cable Pod binding post for spade and banana plug (the plastic cap at the end of the binding post can be removed for connecting a banana plug)
Chassis is made of high-grade anodized brushed aluminum to reduce audio resonance
Dimension : 8.5″W x 16″D x 1.97″H (2.37″H include feet)
Weight : 9 lbs
Worldwide AC voltage (84VAC to 264V
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