In the past, NuForce offered one line of audio equipment targeted toward audiophiles and another line geared toward personal-audio/desktop-audio enthusiasts. Now, NuForce is introducing a third range of components that are affordably priced (only a bit more expensive than its personal-audio components), but whose performance aspirations fall squarely in the high-end camp. A good example would be NuForce’s new HAP-100 headphone amplifier/preamp ($595), which despite its modest price promises low noise, extraordinarily low distortion, wide bandwidth, and linear frequency response, plus a design aimed toward listeners “for whom quality headphone listening is a top priority.”
The HAP-100 is a half-rack-width-sized component that features single-ended, Class A, zero-negative-feedback preamplifier/headphone amplifier circuitry, a linear power supply, and a switched-resistor ladder-type volume control with 100 steps in 1dB increments. The NuForce also comeswith a handy remote that provides on/off switching, muting, input selection, and volume up/down controls. Unlike some headphone amp/preamps on the market, the HAP-100 can drive both its headphone and preamp outputs simultaneously, though it gives users the option of disengaging the preamp outputs if they wish. This capsule description of the HAP-100 sounds promising, but the key question is whether the NuForce sounds as good in real life as on paper. I will tackle that question by discussing the HAP-100 first as a headphone amplifier and then as a stereo preamplifier.
HAP-100 as a Headphone Amplifier
Ideally, headphone amps should be able to drive top-tier in-ear and full-size headphones equally well. Today’s best in-ear transducers are very revealing, high-sensitivity devices; they are not particularly taxing to drive, but they do require amps that are very quiet and that provide a great deal of inner detail and sonic finesse. Top-tier fullsize headphones, however, can be dauntingly difficult to drive, in part because they are often even more revealing of sonic nuances that their in-ear brethren, but also because their impedance and sensitivity ratings can potentially fall all over the map. Plainly, the challenge for designers is to build amps that deliver consistently excellent sound quality even when facing widely varying loads—something that is much easier said than done.
The HAP-100 offers three compelling benefits that can be appreciated no matter what type of headphones you use. First, the NuForce offers admirably low noise, which buys listeners freedom from unwanted grunge and helps unlock low-level details that could otherwise get lost in the noise floor. Second, in the best NuForce tradition, the amp emphasizes pristine cleanliness of reproduction with very good levels of detail and definition. Third, the amp’s precise, 100-step volume control allows listeners to dial in just-right amounts of output for virtually any earphone/headphone application (whereas many headphone amps appear to be optimized for low- or high-sensitivity ’phones, but not for both).
In my listening tests, the HAP-100 was at its best when driving high-performance in-ear headphones and custom-fit in-ear monitors. It succeeded in this context partly because it was inherently quiet, partly because its volume control worked perfectly with high-sensitivity in-ear devices, but primarily because it offered detail and definition aplenty.
To hear these qualities in action, try the beautiful title track of Gillian Welch’s Time (The Revelator), which centers on the voices and acoustic guitar of Welch and David Rawlings. The most evocative elements of the track (namely, Welch’s deceptively complex and delicately expressive vocals and clear, articulate guitar work) fell smack dab in the middle of the HAP-100’s sonic “wheelhouse,” creating a sort of sonic synergy that helped my top-class in-ear monitors really sing. Welch’s vocals were simply enchanting, made all the more lovely thanks to NuForce’s ability to capture very lowlevel inflections and harmonic details, while the guitars sounded at once tonally pure and dynamically lifelike—as if heard from only a few feet away. Underpinning these sonic qualities were the NuForce’s silent, jet-black backgrounds, which made subtle musical contrasts and shadings more apparent and enjoyable.
Still, the NuForce’s presentation was not without drawbacks. First, the amp’s tonal balance conveyed a touch of midrange/upper-midrange forwardness coupled with somewhat leansounding bass. Second, the amp sounded detailed and welldefined, but not entirely “continuous” or three-dimensional in its presentation. This tendency meant the HAP-100 gave good results in a “hi-fi checklist” sense, but was somewhat less musically engaging than it might have been.
Moving on, I tried the HAP-100 with many different top-tier full-size headphones (some with traditional dynamic drivers and others with planar-magnetic drivers), with mixed results. With certain ’phones, such as Sennheiser’s flagship HD-800, the HAP-100 gave an excellent account of itself, exhibiting sonic strengths similar to those I observed when listening through inear monitors. But with other ’phones, such as the Fischer Audio FA-002W High Edition or HiFiMAN HE-500, the HAP-100's tendencies toward midrange-forwardness and lean bass became more pronounced, yielding a somewhat brittle and strainedsounding presentation.
Why these variations in sound quality from headphone to headphone? I can’t say for sure, but I suspect the HAP-100 is optimized for “Hi-Z” or high-impedance loads (note that the Sennheiser HD-800 offers a relatively high 300-ohm load). The problem is that not all top-tier headphones offer high-impedance loads, and even those that do can be so power hungry that that they are still quite challenging to drive. The bottom line is that the HAP-100 can sound terrific with loads it can handle well, but its sonic weaknesses may become exaggerated when confronting less than optimal loads.