I first met Pro-Ject Audio Systems’ founder and president, Heinz Lichtenegger, in 2016, at the US launch of the Austrian company’s The Classic turntable. His passion for all things hi-fi was so intense I thought his head might explode. Gleeful in his mission to bring high-end audio to the people at less than typical high-end prices, Lichtenegger and Pro-Ject can fairly claim bragging rights for their entry-level Debut Carbon (DC) ($460 and up), one of the world’s best-selling turntables.

On Pro-Ject’s mammoth website, Lichtenegger bares his soul. “Our aim is to get as many people as possible into the wonderful hobby that is HiFi audio and to deliver a real stereo experience for the lowest cost possible,” that site states, below a photo of Lichtenegger taken in a moment of relative calm. “We want to give the customers back the right to choose what they need, without overblowing our products with unnecessary features.”

I began perusing the site, where I found a lurid display of audio porn to feed my addiction. I already own Pro-Ject’s Align it Cartridge Alignment Tool and Vinyl Cleaner VC-S record cleaner—compared to VPI’s HW-16.5, the latter does a better job of protecting the record label and avoiding contamination of the just-cleaned side, and its vacuum tube is made of aluminum rather than plastic—and now I was dazzled by dozens of components across several product categories, including four lines of digital source components. From Pro-Ject’s S2 line comes their Pre Box S2 Digital, a combination D/A processor and headphone amp that sells for a lean, mean $399.

Design
Manufactured in Slovakia and measuring 4.1″ square by 1.4″ high, the Pre Box S2 Digital embodies a number of firsts for Pro-Ject and its S2 line: its first dual-mono DAC using ESS Technology’s flagship Sabre Pro ES9038 dual chip, capable of resolution up to 32-bit/768kHz PCM and DSD512; the first implementation of Pro-Ject’s Optimum Transient Digital Filter; a new digital clock claimed to control jitter down to 100 femtoseconds (100 x 10–¹⁵ second); and its first component to support full hardware unfolding of MQA, via USB only.

The Pre Box S2 Digital also has eight filters for decoding PCM signals. According to the manual, these are: Optimal Transient (which Pro-Ject names as their preferred filter), Fast Rolloff (Linear Phase), Slow Rolloff (Linear Phase), Minimum Phase Fast, Minimum Phase Slow, Linear Apodizing, Hybrid, and Brickwall. (None of these filters are available during MQA playback.) Other goodies packed inside the Pre Box’s case, which is not much bigger than a tin of sardines, include Lelon organic polymer capacitors, Vishay thin-film Mini-MELF resistors, and a gold-plated, four-layer PCB.

Finished in powdered silver or black, the Pre Box S2 Digital’s little aluminum case feels reasonably solid. On its front panel are a ¼” (6.3mm) headphone jack and four buttons: two labeled Input, for cycling forward and back through the coax, USB, and optical inputs; Filter, to scroll through the eight filters; and Menu. At far right is a largish volume knob; press it to mute. At the center, a ½” by ¾” color screen displays the volume level, from silent (–80dB) to maximum (0dB), as well as icons for coax, USB, and optical, a green headphone icon, the bit rate and sampling frequency, and, when an MQA stream is detected, the MQA icon accompanied by a well-saturated blue dot.

On the rear panel are left- and right-channel analog output jacks (RCA), the USB (Type B) port, coaxial (RCA), and optical (TosLink) digital inputs, and a USB Micro B jack for the 5V wall-wart power supply. (The power supply is required when the USB digital input is not in use—otherwise, the Pro-Ject gets its 5V from the computer to which it’s connected.) The Pre Box S2 sits on four rounded rubber feet. All in all, it’s sturdy and well built.

Setup
I asked Buzz Goddard, Pro-Ject’s stateside rep, about the Pre Box S2 Digital’s Distortion Compensate/Disabled option and its Optimum Transient filter. He replied via e-mail:

“Tragically, so many people evaluate units like this based solely on measurements. The Distortion Compensate is to allow the measurement geeks to get the numbers that [get them excited], and the Disabled mode is for us more chill folk. Similarly, the Optimum Transient filter setting is focused on transients/edges of the waveform. Since the conversion from digital to analog involves filters, all of which have compromises, the option to invoke different filters allows the listener to explore these realms. Note that the differences are going to be at the upper limits of ideal human hearing.”

You might expect a minimal manual for such a small metal box, and sure enough, the Pre Box S2’s five-page manual is scant on important information. It explains that selecting Distortion Compensate/Disable in the menu will “enable/disable ESS on-chip distortion compensation feature,” but doesn’t explain how that or any of the filters affects the sound. After downloading the Windows driver from Pro-Ject’s website (I didn’t use the enclosed CD-ROM), installing it on my laptop PC was painless. The manual does include a good overview of the included plastic remote-control handset (add $75 for aluminum), which was greatly appreciated. And as far as setting up Master Quality Authenticated (MQA) unfolding—perhaps this tiny DAC-preamp-headphone amp’s main selling point—the manual gives no guidance whatsoever. You’re left to stumble around in Tidal, hoping to figure out how to actually hear unfolded MQA through the Pre Box S2.

Assuming that most folks will use Tidal to stream MQA, here’s the drill: On the Tidal home page, point your cursor to the head-and-torso profile icon in the upper-left corner. Open Settings, then Streaming. Under Streaming Audio Quality, below Normal, High, and HiFi, choose Master (“the best audio experience”). Then, below Sound, choose Sound Output, then More Settings, which will open your final window in the Tidal MQA maze. If you’ve gotten this far and have correctly configured your computer’s own Settings after installing the driver (not required for Macs), at the top of a new window will appear: Speakers (Pre Box S2 Digital). Use the sliders to choose Use Exclusive Mode and Passthrough MQA. Bingo! Now, when you play a Master album in Tidal, “MQA” should appear on the Pre Box S2’s display, and “Master” in the lower-right corner of the Tidal page, next to the volume indicator.