AOM Logo October 2006

The NuForce Reference 8.5 Class D Monoblock Amplifiers

Henry Wilkenson

Every so often, a relatively new manufacturer will come along and introduce a line of products that will make a major impact on the audiophile community. This is exactly what happened with the launch of NuForce’s line of class D amplifiers. NuForce was not the first to use class D amplifiers. Far from it, this class of amps has been around for quite some time, but never caught on for serious audiophile applications. While Bel Canto was the first manufacturer to bring a series of well received class D amps to market, NuForce has taken a somewhat different approach.


The class D designation does not stand for “digital” as is commonly thought. After class A, A/B and so on, it happens to be the next logical designation. What characterize class D amps are the high speed switching power supplies that they all employ. Most class D amplifiers use modules produced by Tripath, Philips or the ICE power by Bang and Olufsen. NuForce chose to go their own route and developed proprietary power supplies. According to NuForce, the heart of their amps, in part, use a high performance analog modulation technique and a closed –loop system. As a result, NuForce refers to its amp as an “Analog Switching Amplifier” TM. For this reason, they are not, strictly speaking, class “D” amps. Because of their unique circuitry, NuForce amplifiers offer ultra-wide bandwidth with virtually no phase shift in the audible frequency range. The output stage is fully regulated and has an extremely high damping factor (greater than 4000 at any audio frequency). Another claim for these amplifiers is near flat frequency response from 20 Hz to 50 KHz, with response out past 90 KHz. This response is much higher than that claimed for other amplifiers in their class. The Reference 8.5s are their lower power amps, rated at 100 watts RMS into 8, 4 or 2 ohms. Their peak power ratings (20 msec hold time), are 288 watts, 576 watts and 1152 watts for 8 ohm, 4 ohm and 2 ohm loads respectively.

Set Up

Weighing in at six pounds each and measuring only 8.5”W x 14”L x 1.8”D, installation is a snap. By the way, all of the NuForce amplifiers share the same size chassis and are made of high grade brushed aluminum. Their diminutive size is a welcome benefit, given how little valuable shelf space these amps require. Since the amps generate virtually no heat, you needn’t be concerned about ventilation. As you can see, the front panel of the 8.5 is clean and simple with only a blue LED at the center that lights when the power is on. Along the rear panel, from left to right, are the IEC power connector, the power on/off switch, the Eichmann Cable Pod speaker binding posts, the RCA/balanced selector switch, the RCA inputs and the balanced inputs. The RCA connectors can be upgraded to WBT Nextgen connectors for an additional $55.00 each. It is recommended that you opt for the WBTs. The benefits of the amp’s small size is somewhat offset by making speaker cable connections somewhat dicey. If you are using some of the heavier audiophile speaker cables terminated with spade lugs, you may find it quite difficult to make a secure connection, since, by necessity, these binding posts are very close together. The RCA/balanced inputs are better spaced and are as far away from the power cord as possible, which is not very far. One word of caution is in order here. When you install the RCA interconnects and, after connecting the speaker wire, double check the RCA/balanced selector switch. It is very easy to end up with an RCA interconnect attached and the switch inadvertently set to the balanced setting. Curiously, the amp will work under this condition, but you will hear a fairly loud buzz coming from your tweeter.

The Sound

The first thing that you will notice about these amps is the fact that they are dead quiet. Place your ear next to the tweeter and you will hear only silence. Put on a CD and the music will simply burst from that same black background. Conversely, you hear a constant hiss coming from the tweeters when the Bel Canto 200.2 amps are in the system. While this noise is not audible from the listening postiton, it is there nonetheless. The manufacturer recommends a burn-in period of at least 75 hours. However, many of the sonic goodies will be present at first listen. All during the burn-in period and for a while after, I noticed that these amps floated a large soundstage. At the same time, there was a timbral thinness and analytical quality that remained present. I had been told that these amps are highly sensitive to the type of speaker cables used with them. During the break-in period, I used Wasatch Cable Works Ultama Speaker Cables, which are constructed of a 50/50 mix of copper and silver. I swapped them out for a pair of Acoustic Zen Hologram speaker cables and presto, the analytical and thin qualities disappeared and were replaced by a full measure of warmth and timbral weight. In my system, these amps like cables constructed with copper, as opposed to ones with any silver content.

As I said previously, these amps continued to improve after the stated break-in period. One of the first things that I noticed was how revealing these amps are. On familiar disks, new musical information as well as micro details was revealed. For example, on “Miles Smiles” [Miles Davis Quintet, Columbia/Legacy CK 65682], Tony Williams’ drumming has much more clarity. The formerly buried micro rhythms he employs are there as never before. This quality is consistently present in disk after disk. I believe that the extremely low noise floor of these amps is in large part responsible for this level of resolution.

The NuForce 8.5s will produce a large soundstage. While the stage is well populated with stable, well-placed instrumental images, they have softer edges, with more rounded focus than you typically hear from transistor gear. In this sense, they are more reminiscent of vintage tube gear.

The midrange is much more difficult to describe. It would be easier for me to describe what these amps do not do with the midrange rather than what they do. As with the rest of the musical range, there is a startling amount of clarity without any brightness. With pianos, for example, there is a good balance between the fundamental note and the shimmer and decay. The decay of sustained notes seems to hang in the air longer than I have heard before and then simply fades into silence. There is a total lack of edge or hardness anywhere throughout the spectrum. These characteristics tend to make piano music in particular sound very realistic with regard to clarity and timbre. Additionally, the music comes through with all of the detail that you could ask for.

These amps are similar to vintage tube gear with respect to dynamics. For instance, drum beats on snare drums never come across with the usual pop. Rather, it’s more of a thud. Brass or plucked strings always have a soft attack. I never heard explosive dynamics from these amps. The razor sharp transients that transistor amps are generally known for were also missing.

The bass is extremely tight and extended, with no trace of bloat from the mid-bass down. Upright basses have good pitch definition along with good textural details. While the bass goes deep, you will have to live without the impact or slam factor that some larger and much more expensive amps will provide. It seems that I could never get the woofers pumping unless I cranked the volume up to very uncomfortable levels. These amps have a very high damping factor so they keep very tight control of the woofers. There was an instance where this was overdone. Marvin Gaye’s “Sexual Healing”, from the CD “Midnight Love” [Columbia CK 38197], has a bass line that includes drums, bass guitar and synthesizer. All of these instruments combine to produce a bass line that is somewhat heavy, with a good deal of bloom. With the 8.5s, the bass was so tight so as to be reduced to their bare parts. All of the bloom disappeared rendering the entire piece much too dry. I found the same thing happened with Bobby Bland’s “Greatest Hits” [MACD-11809]. The entire CD was treated in the same way. It seems that the 8.5s don’t distinguish between intentional bass bloom and woofer overhang. This could be a problem with many pop recordings’ heavy bass lines. Finally, the overall sound is very smooth. They are about the smoothest amps that I have ever heard. This smoothness does cost you in terms of instrumental textures. There are no rough edges in the sound even when this is the intention of the artist. SummaryThe NuForce 8.5 power amps are quite impressive sonically. I can easily see where they will have a very wide appeal, but they aren’t for everyone. If you are an audiophile that desires the golden glow of tubes in the mid-range, these are not the amps for you. If you must have the sheer midrange beauty that very good (also very expensive) SET amps are capable of, I’m afraid you need to look elsewhere. If you must have that “kick you in the chest” bass slam, you won’t find it here. You might find the “just the facts” presentation off putting. If, however, you are looking for a pair of small monoblocks that give you far more than a taste of the sonic qualities that audiophiles typically crave, then you have to seriously consider these amps. I know of no other power amps at this price point that can equal the performance of the Nuforce 8.5 monoblocks. Are they perfect? Of course not; what is? The quest for perfection involves a much higher price of admission (and even then, perfection will remain elusive). If you are in the market for a power amp at this price point or higher, you must give these a serious audition.

Associated Components

Analog Source: VPI HW-19 turntable, Grado Signature Tone Arm and Clearaudio Virtuoso Wood cartridge
Digital Sources: Sonic Frontiers SFT-1 Transport, ART DIO DAC (Modified), Lehman DAC+
Amplification: VAC LE Pre Amp, Bel Canto EVo 200.2 power amps bridged mono
Loudspeakers: Dynaudio 3.3
Cabling:Acoustic Zen and Von Gaylord Audio Chinchillia Interconnects and Speaker Wire
Accessories: P.S. Audio Power Plant P-300, Mapleshade Triple point Coupling Devices, DH Labs Isolation devices

The NuForce Reverence 8.5 Mono power amplifiers

Manufactured by NuForce
356 South Abbott Avenue, Milpitas, Ca. 95035

RMS power 100 watts at 8, 4 or 2 ohms
Peak Power (20 msec hold time) 288 watts @ 8 ohms
576 watts @ 4 ohms
115 watts @ 2 ohms
3 year limited warranty

MSRP USD$1,900 per pair

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