NuForce Icon-1 Amplifier and S-1 Speakers

The NuForce Icon-1 and S-1 system’s approach to high fidelity audio on the desktop doesn’t focus on big bass – evidenced by the fact that the system lacks a subwoofer. Instead, the focus is on component quality and sonic clarity. There’s also a decided simplicity in its design. Let’s take a look at how the two products’ feature set is designed to achieve synergy – a result that’s more than the sum of its parts.

NuForce’s claim to fame as a manufacturer of audiophile products is their efficient “Class-D” amplifiers. While ordinary amplifiers simply allow their output transistors to track the incoming audio signal, resulting in varying states that fall somewhere between completely ‘on’ and completely ‘off’ and a large amount of heat output from those partially-resistive states, a Class-D amplifier switches its output transistors completely ‘on’ or ‘off’ for varying lengths of time, resulting in an ‘average’ voltage output, which is smoothed into a consistent output signal by filtering circuitry that filters out the switching noise. It’s this completely ‘on’ or ‘off’ transistor operation that gives a Class-D amplifier its namesake – ‘digital’ operation.

A transistor that operates in a fully ‘on’ or ‘off’ state produces much less heat than a transistor that is partially resistive, so Class-D amplifiers can achieve extremely high efficiency, and can be packed into a far smaller enclosure than typical amplifiers – and indeed, the Icon-1 is tiny, at only six inches tall and an inch thick.

To control the amplifier, NuForce uses a circuit that self-resonates at 500kHz to ensure that any operating noise that isn’t filtered out of the final audio signal is well above the highest frequencies present in music, so it won’t create audible distortion. The Icon-1 embodies an extremely advanced approach to Class-D amplifiers, and the result is a stylish, compact amplifier module that will fit perfectly on any desk.

The front panel of the Icon-1 USB DAC/integrated amplifier is fairly simple, and the purpose of the controls is straight-forward both from their labeling and tactile feedback. The volume control turns smoothly, while the source selector knob moves from one position to another, and is labeled with a series of dots, which correspond to each of the Icon-1’s three inputs. A blue power LED indicates operation, while a black headphone jack virtually disappears against the amplifier’s flat-black faceplate. The knobs have a solid feel, reflecting the designers’ attention to detail.

The USB input port on the rear of the Icon-1 is our first indication that the Icon-1 isn’t your typical small solid-state amplifier – it’s designed with PC usage in mind, but that won’t stop you from using the Icon-1 with a variety of analog input sources as well. Each of the audio inputs are labeled with the same dot symbols that appear on the front panel’s input selector control, helping you make sense of which dial selection corresponds to each input. There’s also a line output jack on the rear of the Icon-1, which means you can connect additional amplifiers, or even a powered subwoofer.

The Icon-1’s speaker outputs are via a pair of RJ45 connectors, like the type that’s used on ordinary Ethernet cable. Included in the Icon-1’s hardware package, there are a pair of cables that have an RJ45 termination at one end, and banana plugs at the other end, for connecting third-party speakers. If you prefer to use binding posts, there’s an optional I/O module available from NuForce that converts the RJ45 speaker-level input to a binding post pair for each channel.

Also, while the included cables are only one meter in length, a set of two-meter cables is also available as an add-on. NuForce also offers a 45-watt power supply that enables the NuForce Icon-1 to drive low-impedance (4-ohm) speakers more effortlessly by supplying more current than the Icon-1’s stock power supply.

Delving into the guts of the amplifier itself, we can see that the Icon-1’s internal design is fairly simple, occupying a single circuit board. Near the USB input port, there’s a Texas Instruments Burr-Brown PCM2706 digital-to-analog converter – among the finest available. The amplifier’s output stage is controlled by a NuForce-designed Class D amplifier IC, instead of another off-the-shelf component. The NuForce IC (situated in the middle of four choke coils) is essentially the same as the one that’s used in the company’s high-end ‘audiophile’ products, though designed for far lower power output.

Also, we can see that a high-quality volume potentiometer and beefy input selector switch have been chosen, instead of cheaper alternatives. NuForce definitely didn’t scrimp on the quality of their internal components, further accentuating the point that NuForce didn’t intend to build a consumer electronics product with the Icon-1, but a desktop audio system for audiophiles.

To compliment the svelte Icon-1 USB DAC/integrated amplifier, NuForce designed the striking S-1 speakers. Each one features a single 3″-diameter full-range driver with a titanium cone, mated to a 6″ round waveguide. Single-driver speakers are preferred by some audiophiles because all of their acoustic output originates from a single point – the apex of the cone – and there’s no passive crossover network that could potentially harm coherence.

Single-driver speaker enthusiasts often cite a single-driver speaker’s uncanny ability to produce a near-holographic sonic image, with seamless integration of the midrange and treble ranges. In fact, the only area where single-driver speakers tend to fall short of multi-way speakers is in low frequency and high frequency extension at the very extremes of the driver’s frequency range.

To improve the speakers’ treble extension, NuForce selected a driver with a lightweight, paper-thin titanium cone and a compact yet potent magnetic structure using Neodymium. The result is a driver that boasts treble extension beyond the limits of human hearing. Also, the copper-anodized aluminum ‘beak’ in the center of the driver (called a ‘phase plug’) further improves high frequency performance by eliminating the drawbacks of the “dust dome” that’s at the center of many cone drivers. The round waveguide controls the speaker driver’s dispersion through the midrange, down to about 1.5 kHz, reducing distortion and preserving detail by preventing sound from bouncing off nearby surfaces (most notably your desktop).

The S-1 speakers use an RJ-45 input jack, which is designed to allow the use of typical Ethernet cable to carry voltage from the amplifier to the speaker. Not only is connection literally a ‘snap’, but you can use any Ethernet cable that you might already have available, if the included speaker cables aren’t long enough to get the job done. The Icon-1 amplifier uses six of the eight RJ-45 pins to transmit output voltage; the input jack of each S-1 speaker is wired to short the unused terminals together, signaling the Icon-1 to apply a gentle active equalization curve that compensates for the sonic effects of the S-1 speaker’s waveguide.

The NuForce S-1 speakers’ enclosures are made of 3/4″-thick fiberboard, which forms a solid and inert container for the speaker driver’s back wave. There’s no reflex loading of any sort – instead, the enclosure is partially stuffed with polyester batting to absorb the rear radiation of the cone. The wire used to connect the speaker driver to the input terminals looks thin and flimsy, but it’s solid copper – with very little insulation around it. I took care when reassembling the speaker to ensure that the leads would not touch when I reinstalled the speaker’s rear cover.

Thus far, we’ve seen that the NuForce Icon-1 and S-1 take an uncommon approach to PC audio through the use of high-quality components in a simple design. It’s a theme that’s common in many entry-level ‘audiophile’ high-fidelity music systems as well. Now that we’ve discussed the products’ feature set in detail, let’s see how the NuForce Icon-1 and S-1 perform when paired together.