NuForce is a brand that will by now be familiar to many Playback readers because we have used their excellent Icon Mobile portable headphone amp as a value-priced reference for several years. NuForce has recently released a headphone amp with a built in DAC for desktop use, called the Icon HDP, which is the subject of this review.
NuForce claims that the HDP’s analog headphone circuit has a high current design with a simple circuit. The analog section is separated from the digital section on a different circuit board and features its own separate, isolated power supply regulator.
The digital section uses four 24/192kHz DACs that provide a fully differential and balanced output to avoid the need for coupling capacitors. While the USB input is limited to 24-bit, 96 kHz inputs as is normal, the coaxial input, consistent with the DAC design, can handle 24-bit, 192 kHz data streams.
For this test, we used the Sennheiser HD 800s, HD 650s, the Denon AHD-5000s and the Beyerdynamic DT 990 headphones as our listening references. We also compared the DAC section of the Icon HDP to the DAC section of our reference Esoteric DV-60 universal player.
Consider this headphone amp if: you want an amp with a lively tonal balance and superb delineation of musical lines.
Look elsewhere if: treble warmth or bass extension is of paramount importance.
Ratings (compared to similarly-priced headphone amp/DACs):
Given the subtleties of different headphone amp designs, along with the wide variations in frequency response of headphones themselves, inevitably a certain amount of what we hear with headphone amps and DACs is conditioned by what is connected to them. That said, there are several basic characteristics of the Icon HDP that seem to be consistent across a variety of headphones.
The HDP’s standout characteristic is what we normally call instrumental separation, by which we mean that you can hear each member of an ensemble or band quite clearly and distinctly. Backing vocals are clearly delineated, as just one example, as are instruments like guitars (where several musicians can be playing similar instruments simultaneously). Once you’ve heard delineation done right by the Icon HDP, you start to see that many competing amps have a certain smearing effect on the sound. While this smearing can lend a false sense of coherence to the music, it is a form of noise or distortion.
Related to this, the Icon HDP does a fine job of following instrumental transients as they decay. This, as we’ve pointed out before, is very helpful in establishing a realistic and flowing sense of ambience on many types of recordings, and especially on orchestral pieces.
In the bass, the HDP renders notes with high definition, as it does elsewhere in the frequency spectrum, but I didn’t sense quite the low-frequency depth or dynamism that I’ve heard with some more expensive amps. The approach taken by the HDP does, however, suit somewhat bass-heavy headphones, such as the Denon 5000s, rather well.
At the other end of the frequency spectrum, I felt the Icon HDP had ever so slightly elevated upper midrange and lower treble. This isn’t the kind of thing you notice as “upturned highs” per se, but rather is more a matter of shaping instrumental transients so that they are slightly sharper-sounding than they would be in live music. Again, this very subtle shift in rendering works well with some headphones. I am, for example, sensitive to a slight upper-midrange depression that I’ve observed in my Sennheiser HD800s, one that can normally make vocals sound somewhat “hooded.” But with the Icon HDP in the circuit I found that typical problems with hooded vocals were ameliorated quite nicely.
I have attributed the performance characteristics above to the Icon HDP amplifier circuit because I heard these characteristics whether using the built-in DAC of the HDP or the DAC section of Playback’s Estoteric DV-60 universal player. That isn’t to suggest that the DAC on the HDP makes no difference. On the contrary, I’d say the HDP’s DAC is quite good, exhibiting only minor differences from the DAC in our multi-thousand-dollar reference player. In fact, there are ways in which the HDP’s internal DAC is preferable to the Esoteric’s DAC. These chiefly consist in shifting treble transient errors up to a higher frequency, which to my ear makes them less noticeable. In short, the Icon HDP exhibits much lower than average levels of digital grunge.