My recent introduction to NuForce amplifiers and my subsequent review of the Reference 8 and 8B amplifiers has been a romantic adventure of sorts. I was so enamored of the Reference 8 series that they became my reference amps of choice.

When the production version of the Reference 9 amplifiers became available, NuForce’s Jason Lim intimated to me that it might be possible for him to send me one of two pairs of the amps that he had available in the gold-anodized finish. Upon my agreement, the amps arrived, and I must say that the gold finish is absolutely gorgeous!

  

At about the same time, I noticed a lot of talk/fuss on the Internet about the Benchmark DAC1. Benchmark Media Systems, Inc. is a company that focuses mainly on the Pro-sound market, but seems to have captured the interest of audiophiles with its DAC1— a stereo, 24-bit, 192-kHz Digital-to-Analog audio converter.

The main features of the DAC1, are its UltraLockTM circuitry (which Benchmark claims makes it 100% immune to jitter), balanced (XLR) and unbalanced (RCA) outputs that can be configured for either a fixed or variable output level, and two HPA2TM high-current, quarter-inch headphone jacks. The DAC1 has 3 digital inputs, TOSLINK, XLR, and a coaxial BNC connector; and includes a BNC to RCA adapter. All inputs accept both AES/EBU and S/PDIF digital audio formats. There is a female AC IEC receptacle for your choice of power cord (a shielded cord is provided), and the DAC1 is switchable for 110 or 220VAC operation.

Benchmark is very proud of the performance they have achieved with the DAC1 and provides copious graphs in the owner’s manual to illustrate its extremely low distortion, immunity to jitter, frequency response linearity, and ultra-low noise floor. So would this translate into superior subjective audio performance? We shall see.

Getting back to the NuForce Reference 9s, these amps use the same basic amplification circuit of the Reference 8 series, but with a considerably larger power supply. The higher capacity power supply necessitates a larger chassis—both to physically contain the components and to effectively dissipate the extra heat that higher power generates. The Reference 9 amplifiers are rated at 160 watts rms into 8 ohms and 300 watts into 4 ohms, with 676 watts of short-term peak power available at 4 ohms.

While the NuForce Reference 8 amplifiers are available in either balanced or unbalanced versions, the Reference 9 amps include both. A small rear-panel toggle switch facilitates this choice. Now standard on the Reference 9s are the Eichmann Speakerpods, which seem to be an improvement over the previous Cardas Uni-clamp design. NuForce also offers a couple of low-cost upgrades, which include WBT NextGen RCA input jacks and extra input decoupling capacitance for extended bass (recommended for the Ref 9 driving bass driver in a bi-amping configuration).

With the 9.02 version, all the previous little bugs appear to have been addressed and worked out. These include reduced turn-on transient noise, reduced RFI interference, and a circuit that makes the amps stable in a no-load condition. NuForce has accordingly extended the limited warranty to 3 years.

The Reference 9 amps come in three attractive standard finishes—black, silver, or gold, and may be ordered in custom-color anodized finishes at extra cost and waiting time. Some intriguing color samples are located on the NuForce website for curious and fashion-conscious ‘philes to peruse.

When I first received the NuForce Reference 9 amplifiers, I was using a Rega Planet CD player as my source, which provides very good performance on its own. But I was seeking a more state-of-the-art digital source for my VMPS RM30 speaker system. My hope was that the combination of the Benchmark DAC1 feeding the NuForce Reference 9 amplifiers would yield a very high performance, cost-effective solution. Consequently I contacted Benchmark Media and they kindly agreed to send the DAC1 for evaluation and review. The particular DAC1 I received was the silver-faced model and the accompanying owner’s manual and the version appears to be “Revision H,” which was initiated in May, 2005. The following changes have been incorporated into the DAC1 since its original introduction:

1) RCA output impedance changed from 1.25K Ohms to 30 Ohms
2) RCA output level calibrated to 2Vrms at 0 dBFS (old levels were higher)
3) 20 dB pads enabled at factory on XLR outputs
4) Lower DC offset at all outputs
5) Lower DC offsets internally
6) Quiet gain control pots
7) Detented gain control (front panel)
8) 192 kHz input rates
9) Higher internal sample rate
10) Reduced brightness of Blue LED
11) Added gain balance trim (factory adjustment)
12) Brushed aluminum anodized finish on face plate (old finish was anodized polished aluminum)

Listen, and you will hear…
My first listening session with the production version of the Reference 9 amplifiers proved very interesting. If I could choose just one word to describe the sound of the Ref 9s, that word would be “relaxed.” The Reference 9 amps immediately flexed their collective muscles and allowed me to play my system comfortably at average levels a few decibels louder than I had been able to manage with the Reference 8s and other amps I had tried (excepting the PS Audio GCC-250, which played as loud but didn’t sound quite as musical).

I’d characterize the sound of the stock Reference 9s as warm and smooth, with deep, articulate, punchy bass. Yes, they played louder, and sounded more “at-ease” than the Reference 8s; and there appeared to be no lack of bass extension. Yet, at the end of the day, I didn’t think they sounded quite as fast and transparent as the Reference 8s. To my ear, the original Reference 9s had a more rounded and slightly less incisive character than the Reference 8s, more like what one might hear from a decent tube amplifier. That said, the difference between the Ref 8s and Ref 9s was not large and a family resemblance was unmistakable. But in high-end audio, it’s the small differences that count and these minor contrasts between amps had me scratching my head and splitting hairs as to which model I preferred.

As fate would have it, a couple of weeks of my vacillating passed and I received an e-mail from Jason Lim who said he had a few improvements for the Reference 9s if I cared to send them back. And from that point, my amps made a few additional trips back to NuForce for subsequent upgrades. Indeed, I believe NuForce regards me as part of their extended R&D team. Since I was having some fun trying successive versions and evaluating how the sound had changed with each revision, I was a willing participant. Consequently, I know a lot about the evolution of the design and how each change affected the sound of the amplifier. I won’t try to cover that experience here, because it would make this article unduly lengthy and would not represent current production.

The result of this developmental process is the Reference 9, version 9.02. NuForce had added some safety features to the circuitry to make the amps more stable and to increase their long-term reliability. In Addition, they increased the bandwidth out to 100kHz, which is the main performance enhancement of the 9.02 version. My Reference 9s contain all presently available factory options, including doubling of the input capacitance, the now-standard Eichmann Speaker Pods, and finally, the gold-plated copper WBT NextGen input jacks. Happily, all these options are available from NuForce at very reasonable extra cost. This is the version I will be commenting on for the remainder of this review. It represents, in my view, their best sounding production model to date.

As it happened, the Benchmark DAC1 arrived just before the NuForce 9.02 update. However, I initially tried the 9.02 version with the stock Rega Planet CD player so that I could compare apples to apples before the DAC1 was added to the system.