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NuForce HAP-100 Headphone Amplifier/Preamplifier

NuForce HAP-100 Headphone Amplifier/Preamplifier

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.


To better understand the foregoing comments, try listening to the HAP-100 with a variety of headphones on a bellwether track such as “Angel of Darkness” from Hot Tuna’s Steady As She Goes [Red House Records]. This enjoyable but non-audiophilegrade recording presents midrange content that is energetic and somewhat prominent to begin with, so that the need for midrange and upper midrange neutrality and for counterbalancing bass weight and body becomes critically important. The HAP-100 displayed its signature sonic virtues on “Angel of Darkness” when driving the Sennheiser HD-800s, but with harder-to-drive ’phones the amp often pushed Jorma Kaukonen’s vocals and electric guitar too far forward in the mix, giving them a borderline shrill quality. Similarly, when driving difficult loads, the amp undercut Jack Cassady’s normally vigorous-sounding, syncopated bass guitar lines, making them sound thin and insubstantial, thus robbing the song of its low-frequency foundation.

For comparison purposes, I tried the same track with the same group of test headphones, but using competing amps from CEntrance (the DACmini, $799) and Burson Audio (the Soloist, $999). What I learned was that both of these admittedly more costly competitors could match or surpass the HAP-100’s sonic strengths, while consistently delivering more balanced tonal response across a broad range of headphones.

All things considered, the NuForce has much to offer when it is used with in-ear monitors or with the right full-size headphones. But the fact is that the amp does appear to be load-sensitive, meaning that it would be a good idea to try the HAP-100 with your preferred headphones before making a purchase.

HAP-100 as a Preamplifier

I tested the HAP-100’s capabilities in a high-end system comprising an Oppo BDP-93 NE (NuForce Edition), a pair of NuForce Reference 9 V2 SE monoblock amps, and a pair of PSB Imagine T2 floorstanders. I also had on hand a sample of NuForce’s exotic, two-chassis Reference P-9 preamplifier ($3150) to use for comparison.

Very early on, I came to think the HAP-100 was well suited to its role as a preamplifier. I say this because the HAP-100’s output capabilities seemed well matched to the task of driving power amplifiers, thus allowing the NuForce’s best sonic qualities to shine through while minimizing possible sonic weakness. The result, then, was a preamp that, while not perfect, offered really impressive performance in light of its price.

To observe some of the HAP-100’s strengths in action, check out the track “Satori in Chicago” from Noah Wotherspoon & The Stratocats’ Buzz Me [APO Records], which is a very well recorded, jazz-inflected, electric-blues cut. Wotherspoon demonstrates a command of all of the usual Fender Stratocaster pyrotechnics plus a few of his own, so that the song offers a masterful display of soulful electric-blues guitar chops. But the song also offers something more—namely, the unmistakable sound of a highly skilled band that is absolutely locked into its collective groove. The NuForce does its part in several ways, first by revealing the leading edges of transients in a clear, powerful, and incisive way, and then by focusing on tonal purity and inner details. As a result, Wotherspoon’s guitar really does sound like a Stratocaster merrily howling away through a fine guitar amp, while the electric bass has the visceral, deeply grounded drive of the real thing. But perhaps one of the biggest treats of all is the HAP-100’s rendition of the drums, which have a just-right amount of snap and “pop,” and of the hi-hats and cymbals, which shimmer with rich layers of delicate, understated detail. This is awfully fine sound from a $595 preamp.

How does the HAP-100 compare to the far more costly Reference P-9. In simple terms, I think many listeners would report the two preamps sound more alike than not, though discerning listeners would find small but significant differences. First, the P-9 offers smoother and more grain-free mid and highs. Next, the P-9 offers better-weighted and more powerful bass, though in fairness the HAP-100 sometimes seems to offer a more taut low-end presentation. Finally, the P-9 offers a heightened degree of threedimensionality— perhaps because it is even quieter than the HAP-100 and provides superior resolution of lowlevel details.

Collectively, these differences become apparent on a track such as the “Aphrodite” movement of Robert Paterson’s The Book of Goddesses [American Modern Recordings], which highlights flute, harp, and percussion as captured in a reverberant recording space. The HAP-100 gave a good, clear, detailed rendition of “Aphrodite,” but the P-9 makes the three-dimensional character of the recording space (and of the instruments’ interactions within the space) much more apparent. Still, the important point to bear in mind is that the HAP-100 captures a significant percentage of the P-9’s sonic goodness and overall character for less than one-fifth its price.

Summing up, I would say the HAP-100 offers terrific value as a preamplifier; it is in no way embarrassed in the company of more expensive units. It is quiet, detailed, and well defined, and come with a handy remote that’s a joy to use. Moreover, the HAP-100 is a thoroughly viable headphone amplifier, one that’s at its best with in-ear transducers, but can also give highly satisfying results with some (though not all) of today’s best full-size headphones. Viewed as a complete package, the HAP-100 offers an awful lot to like at a down-to-earth price.


Inputs: Four stereo analog inputs (RCA)
Outputs: One variable-level stereo analog output (RCA), one 1/4-inch headphone jack
Accessories: Power cord, full-featured remote
Frequency response: 20Hz–20kHz, +0/-0.1dB
Distortion: <0.002% @ 20Hz–20kHz (3V RMS output at RCA jacks)
Signal-to-noise ratio: >100dB
Preamp output: 7.8V RMS, RCA, maximum
Headphone output: 5.2V RMS, Hi-Z, maximum 5.1V RMS @ 300 Ohms, 1.81V RMS @ 32 Ohms, 0.91V RMS @ 16 Ohms
Weight: Not specified
Dimensions: 8.5″ x 1.875″ x 10″
Price: $595

NuForce, Inc.
382 South Abbott Ave.
Milpitas, CA 95035
(408) 890-6840, East;
(408) 240-0746, West

Full-Size Headphones: Audeze LCD 3; Fischer Audio FA-002W High Edition; HiFiMAN HE- 400, HE-500, and HE-6; and Sennheiser HD-800
Custom-Fit In-Ear Monitors: JH Audio JH 16 PRO s; Ultimate Ears In-Ear Reference Monitors and Personal Reference Monitors; and Westone Elite Series ES -5 Monitors
Headphone Amps, Amp/Preamps, and Amp/DACs: Audio Electronics by Cary Audio Nighthawk, Burson Audio Soloist, CEntrance DACmini, and HiFiMAN EF-5 and EF-6.
Sources: AudioQuest DragonFly DAC with Mac Mini, CEntrance DACmini with Mac Mini, NuForce-modified Oppo BDP-93SE universal/Blu-ray player, and Oppo Digital BDP-95 universal/Blu-ray player
Preamps: Burson Audio Soloist, NuForce Reference P9
Power Amps: NuForce Reference 9 V3 Special Edition monoblocks
Loudspeakers: PSB Imagine T2
Interconnects/Speaker Cables: Nordost Blue Heaven and Ultralink
Room treatments: RPB Binary Absorber/Diffsorber panels

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