PRO-JECT HEADPHONE AMP/DAC
MORE PEOPLE are listening to more diverse high-resolution audio formats through higher-quality headphones than ever before. But ideas about how to feed those headphones vary. The headphone amplifier/digital-toanalog converter, a popular hybrid product, is among the most tireless shape-shifters on the audio scene. I’ve reviewed AMP/DACS as compact as a USB stick and as big as a full-size rack component. At about 4 x 1.5 x 4 inches (WXHXD), Pro-ject’s Pre Box S2 Digital falls somewhere in between. You wouldn’t carry it in a pocket, but it doesn’t take up much space on a busy desk.
FEATURES AND SETUP
You might know Pro-ject as a purveyor of affordable turntables and other phono gear. But the 27-year-old Austrian company, distributed in North America by Sumiko, also offers what it calls the Box Designs line, which includes DACS, power amps, headphone amps, and various other devices. Pro-ject’s European arm also offers CD and streaming players.
As its name implies, the Pre Box S2 Digital can serve as a stereo preamplifier as well as a headphone amp and DAC. Pair it with a stereo power amp or a pair of powered speakers, and you’ll have a good starter system. Up to three digital sources— USB, coaxial, and optical— can plug into the back panel. There’s no analog input or Bluetooth connectivity, however, so turntables and tablets or smartphones are out of luck.
The quarter-inch headphone jack on the Pro-ject’s front panel suggests that this AMP/DAC is seeking to mate with full-size headphones. Also up front are a 1-inch color status display, a volume knob, and control buttons to select inputs, access the menu, and select between various digital filter options. The eight filter settings include Pro-ject’s proprietary Optimal transient digital filter. A small, plastic 12-button remote duplicates the front-panel controls, adding mute, balance, and transport. (A more substantial metal version is available for $79 extra.) The chassis, front panel, and even the buttons are all pale gray aluminum, giving the little box a solid feel.
Through its USB input, the Pre Box supports up to 32-bit/768khz files in PCM formats, and DSD via PCM up to DSD512, which covers any digital file you’re likely to buy or stream (and then some). The digital coaxial and optical inputs support files with resolutions up to 24/192. One of the Pre Box’s interesting features is MQA support, which I'll discuss in more detail later. When playing files with MQA, the display shows the MQA logo plus a blue dot in the upper right corner. MQA is supported only through the USB input; the company says implementing it through the other digital inputs would have increased the cost of parts and boosted the Pre Box’s price.
Unlike most DACS in this price range, the Pre Box features dual (ESS SABRE) DACS and separate left/right signal paths. Other differentiating features include a new proprietary clock design, ultra-low jitter, and a combination of active and passive filtering to eliminate noise from the USB output feeding the DAC.
The Pre Box can be powered directly via most USB connections, or you can use the included external power supply. MQA and DSD playback require installation of a computer driver from a supplied CD-R. Otherwise, the Pro-ject is
ready to go for Windows 10 and Linux. Most Mac OSX versions are supported except for El Capitan and Sierra.
Associated equipment that I used for my test included Hifiman Edition X V2, Sennheiser HD600, and Sony MDR-V6 headphones. I also used a Lenovo Windows 10 desktop PC running Foobar 2000 library software for file access, and Tidal Hifi for hi-res streaming.
During my listening, the Pre Box’s performance was characterized by an admirably clean and unfatiguing top end, though it could be frustratingly reticent with higher-end headphones. In a day spent with the Hifiman, for instance, it offered plenty of easy listening but not much sparkle. Flipping through the numerous filter modes did little to alter this first impression. The Pre Box didn’t hit its stride until I plugged in the Sennheiser and the Sony cans, whose distinct but vastly different sonic personalities were permitted to emerge.
I hadn’t expected much from the Sennheiser: it has a reticent top end of its own and I’d expected that the combination with the Pre Box would be overkill. Instead, their mutual smoothness in the presence region let me push the volume up enough to compensate for the Sennheiser’s modest bass, making the sound bigger and beefier than it normally would be in everything from symphonic staples like Beethoven’s Fifth (Carlos Kleiber, Vienna Philharmonic, 24/88.2 FLAC) to rock stompers like Led Zeppelin’s “Black Dog” (24/92 FLAC). Images, though not strongly outlined, were generously scaled, beautifully fleshed out, and darkly colorful, giving extra intensity to lushly arranged tracks like Nick Drake’s “Riverman” and “Hazy Jane II” (24/96 FLAC).
The Sennheiser HD600 was the least sensitive model I used and required the Pro-ject to play at the top of its volume range, usually – 15 to – 8 on a scale of
– 80 to 0. But I heard no sense of strain. Incidentally, the Pre Box and the Sennheiser share a list price of $399. Don’t make too much of that; I’ve heard expensive headphones sound great with inexpensive amps and inexpensive headphones sound great with expensive amps. The Sony MDR-V6, which costs only a quarter as much as the already reasonably priced Pre Box, has a treble-forward sound that formed a perfect yin-yang with the Pro-ject amp. Playing David Chesky’s “Ben’s Farm in Vermont” (24/192 FLAC), my go-to track for high-frequency finery, the chiming percussion instruments were not just audible, but integrated into a better musical flow than I can recall hearing with any pairing of headphones and amp, and I’ve played this track through many. The Nick Drake tracks were beautifully imaged, albeit in a differently balanced way. The Sony/pro-ject combo also shaved off the digital edges from Richard Thompson’s home-studio-recorded “They Tore the Hippodrome Down” (24/88.2 FLAC) to get at its bittersweet musical essence.
The Pre Box provided me with my first chance to do extended listening to MQA (Master Quality Authenticated) as delivered via Tidal streaming. MQA is a computationally intensive (and somewhat controversial) lossy audio codec that can “fold down” the ultrasonic content of bulky hi-res audio signals, resulting in Cd-sized files and streams. I tried to compare MQA streaming with non-mqa files, concentrating on tracks duplicated in Tidal and my hi-res music library. Of course, this was an apples-and-oranges comparison— I could never be certain that both were sourced from the same master. But one difference immediately obvious with all three headphones was level— the MQA tracks were invariably louder, even with volume controls maxed in both apps. I used the Pre Box’s volume control to roughly match levels. In a few cases where Tidal carried both MQA and non-mqa versions, the MQA versions were still louder.
While the stronger signal almost certainly gave the MQA streams a subjective advantage, the Pre Box always exhibited excellent behavior at the top end of its volume range. Sticking with the MQA versions, Kleiber’s Beethoven was warm yet up-close, a combination I don’t often hear, and I felt the world-class Vienna Philharmonic string sound was colorful, and realistic. Nick Drake’s vocal on “Hazy Jane II” and the backing vocals on Donald Fagen’s “Maxine” followed the same course, seeming less mechanical and more corporeal.
While these impressions held true for all three headphones, the main beneficiary was the Hifiman, whose performance progressed from just acceptable to truly involving. My past experience suggests that it often benefits from incremental improvements in hi-res audio formats. MQA got a better than passing grade from the Sennheiser and Sony, but with the Hifiman, it turned up aces.
The Pro-ject Pre Box S2 Digital offers a step up in performance with low- to medium-priced headphones, and it makes for an especially good match with those that have a treble emphasis. It also serves as an introduction to MQA. If it errs, it does so on the side of comfort and listenability. You’d have to spend a lot more to improve on Pro-ject’s Pre Box S2.