Digital Processor Reviews

Pro-Ject's "audiophile digital amplifier," the Pre Box S2 Digital, looks like something big that got shrunk down small enough that John Atkinson could carry one in his pocket on his way to my studio. "Herb, Ken Micallef reviewed this Pro-Ject DAC in our April issue. I'd like you to write a Follow-Up. I won't tell you what I think, but I'm curious what you'll make of it."

Then I remembered that Pro-Ject, an Austrian company, makes everything microsized—except their famous turntables, which are turntable-sized. On Pro-Ject's website, CEO Heinz Lichtenegger explains: "By shrinking the cabinets to a miniature size, we were able to save costs and offer our customers a true price to performance relation."

Yes, the Pro-Ject Pre Box S2 Digital D/A processor is small. A $399 giant killer? I wondered.

Auditions & Filters: You know that old vaudeville saying: Never follow a kid or a dog act (or Jimi Hendrix). Sequence is everything. If I were a tiny, fits-in-the-palm, $399 D/A processor and headphone amp, I wouldn't want to try replacing the ever-steady, pro-styled Mytek Brooklyn DAC ($1995, footnote 1) in my desktop reference system. I felt bad for the little Pre Box S2 Digital, but I had to start my auditions somewhere.

For me, the beauty of the Mytek Brooklyn is how it tames the ubiquitous but sometimes hard-sounding Sabre ES9028PRO converter chip. The Brooklyn, through its minimum-phase filter and with MQA disabled, sounds very un–sigma-delta, and remarkably nondigital. It plays with warm-blooded life, a good beat, and vivid sparkle. I've logged more listening hours with the Mytek Brooklyn than with any other DAC. Pro-Ject's Pre Box S2 Digital uses the ES9038Q2M standard version of the ES9038PRO chip; both DACs exploit the features and filters of this popular converter.

When the Pre Box S2 arrived, I'd just finished studying the stop-start rhythmic inventions and artfully planned tonal vicissitudes of French guitarist Noël Akchoté playing his arrangement of Meredith Monk's Nightfall (24-bit/44.1kHz FLAC, Rectangle/Tidal). The Mytek Brooklyn reproduces this recording with luxurious tone and vibrant, energy-charged, empty spaces. It produced a vivid see-into rendition of Nightfall's odd space. This brief work's six movements are performed in some sort of simple but clearly artificial acoustic space, with something like a vacuum cleaner running in the background. This unusual recording environment focuses the listener's attention on the weight, body, and percussive tones of Akchoté's acoustic guitar. The Mytek Brooklyn made all six tracks of Nightfall (total time 6:51) lush and exciting to listen to. Unfortunately, the Brooklyn sold for $1995 when new. I immediately wanted to hear if the $399 Pro-Ject could reproduce all the clever nuances of this mesmerizing recording.

When I played Nightfall through the Pre Box S2 Digital, I realized, for the umpteen-millionth time, just how completely different two DACs—even two DACs based on similar converter chips—can sound. The Pro-Ject conspicuously emphasized the attack of each note, way more than the Mytek. With the Pre Box S2, my ears—and eyes—were riveted on that sharp small place where Akchoté's pick touched the strings of his guitar. The Pre Box S2's stark immediacy dominated my Noël Akchoté experience, and its focused clarity let me hear more deeply than the Mytek had into the background—where, especially in Nightfall: No.5, P–R, that whining-hissing noise is most distinct. I was intrigued.

Through the Pre Box S2, the guitar and that strange background sound were equally clear and almost equally loud, but much farther apart in space than through the Mytek. With the Pro-Ject's Optimal Transient filter—Ken Micallef's favorite—engaged, Akchoté's guitar sounded closer to the microphone, the hissing farther in the background. (Isn't it funny how subtle changes in spectral balance can generate such radical differences in soundstage mapping?)

The Pre Box S2 Digital's reproduction of Nightfall emphasized the force and raw energy of this recording, while reducing the reverberant atmosphere. Bass had muscle, but midrange color was, to my painterly taste, insufficiently saturated. High frequencies seemed suppressed and/or nondescript.

The above comparison was made with the Mytek and Pro-Ject DACs feeding Rogue Audio's Stereo 100 power amplifier, which drove the spatially precise Harbeth P3ESR loudspeakers.

In hopes of a closer view, I switched to a higher-powered magnifier: HiFiMan's HE-1000 V2 headphones ($2999). Right away, they demonstrated that the Pre Box S2 Digital's headphone amp was incompatible with low-sensitivity (in this case, 90dB/mW) headphones—even if said headgear has a ruler-flat 32 ohm impedance, as do the HE-1000 V2s. The Pro-Ject's low gain forced me to listen to the HiFiMans with the Pre Box S2's volume turned all the way up. The sound was basically good, but Noël Akchoté's guitar became softer sounding. Formerly sharp note attacks were now blunted and less prominent. My mind's eye shifted its focus from pick and strings to the guitar's body and neck. That mysterious background noise became dull and distant. Obviously, the difficult load presented by the HiFiMans took the sharp edge off Akchoté's picking, but strangely, the Pre Box S2's headphone amp made its most enjoyable sounds at low volumes with just such expensive, insensitive headphones.

However, in terms of gain, punch, and boogie, the Pro-Ject preferred sensitive, easy-to-drive headphones such as AudioQuest's NightHawks ($299), with their impedance of 25 ohms and sensitivity of 100dB/mW. This combo made a wide variety of recordings sound lively, smooth, and very musical—even through the S2's Brickwall filter.

Through the NightHawks I listened to a remastering of the Julie London chestnut Julie Is Her Name (24/44.1 FLAC, Liberty/Rev-Ola/Qobuz). I was taken aback by how soft and supple her voice sounded through the S2 Digital's Brickwall and Fast Rolloff (Linear Phase) filters. That worried me—since when does a brick wall feel soft?—so I switched to the headphones I use most with the Mytek Brooklyn: Sony's MDR-Z1Rs. With this album the Sonys sounded much less soft and more transparent than the NightHawks—but Pro-Ject's Brickwall, Fast Rolloff (Linear Phase), and Minimum Phase Slow filters sounded almost identical.

Julie London gave the most pleasure through my beloved Audeze LCD-X headphones ($1699). The very sensitive LCD-Xes (103dB/mW, 20 ohms) made the cleanest, most tuneful, most lively bass of any headphones I tried with the Pro-Ject. Midrange detail was most specific and natural. The LCD-Xes gave me an enhanced view of the Pre Box S2's transparency. But the sound still leaned slightly toward the gray and detached.

The Pre Box S2 delivered its most open, transparent, and flat-out pleasurable sound with (don't laugh) JPS Labs' Abyss AB-1266 Phi headphones ($4995), which have an impedance of 42 ohms and are totally insensitive at 88dB/mW—which meant that I could play them only at low volumes. But drive and dynamics were surprisingly good, and the Abysses' extremely natural and detailed sound gave me a more revealing view of the Pre Box S2's eight filters. I tried them all, but even through the electron-microscope resolution of the AB-1266 Phis, I occasionally struggled to detect when, precisely, I'd switched filters, let alone which filter was doing what to my music.

The only filter that caught my attention in a positive way was Pro-Ject's own Optimal Transient, which I used most often. Fast Rolloff (Linear Phase) gave music the most solid body, while Slow Rolloff (Linear Phase) added a hint of suppleness to Fast Rolloff's stiff corpus. Minimum Phase Fast brought that background noise in Nightfall somewhat more to the fore, but made it softer, less odd-order-harmonic sounding. Minimum Phase Slow increased the gentleness factor, but only by a teensy-weensy bit. For some reason, of all the filters, Linear Apodizing made Nightfall's motor-fan noise sound loudest and closest to the mike. The Hybrid filter seemed more unaffected (or less effective) than the rest, but I don't know why. Brickwall sounded as artificial as Fast Rolloff (Linear Phase). Switching from Brickwall to Optimal Transient was a slight but noticeable step in the direction of relaxation and naturalness.

These struggles force me to ask: Why does a DAC need eight filters? What purpose do they serve? Have filters become the digital equivalent of analog tone controls? Which filter measures best? Which is the most accurate? If one of these filters is right . . . which one am I supposed to like? Most important, why am I being forced to choose?

Conclusion: No matter which filter I did choose, the overall sound quality of Pro-Ject's Pre Box S2 Digital was mainly affectless. It did nothing noticeably wrong. Many audiophiles would call this "neutral."

The Pre Box S2 Digital's clarity was distinctly good, its punch and drive distinctly strong, its ability to separate sounds and instruments on a soundstage obvious, its bass resolution above average—all very good, right? Unfortunately, in my floor and desk systems, the Pre Box S2 substituted a digital-artificial blankness for transparency. It diminished atmospheric effects. It never fully "disappeared" from the sound of the recording, or stopped being a digital device. Its headphone amp was gain-challenged.

I know—the Pre Box S2 costs only $399 and is USB bus-powered when used with a computer. But folks, no matter the price, I have a strong need for audio equipment to disappear into some amount of music-like beauty. Most important, I need some sense-oriented (as opposed to measurements-oriented) reasons to like a digital product.

The Pro-Ject Pre Box S2 Digital's main sense-oriented effects were its impact and its beat-emphasizing drive, both of which I regard as distinctly masculine traits. What was missing was a radiant, sensuous, feminine side. To me, the Pre Box S2 Digital is simply a good DAC-headphone amplifier at its price point but it didn't kill any giants.—Herb Reichert