Pro-Ject Pre Box S2 Digital Preamplifier


Pro-Ject Pre Box S2 Digital Preamplifier

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Pre Box S2 Digital marks a new era for our S-series components. For the very first time we are using a dual mono configuration with the highest class D/A converters of ESS Sabre. Their flagship DAC-chip ensures highest class audio in a small and affordable package. This DAC is capable of high resolution audio up to 32bit/768kHz PCM and DSD512! Pre Box S2 Digital is also the very first of our devices to support hardware MQA unfolding.

High Notes

MQA Delight

If you want to test out the joys of MQA (Master Quality Audio) on Tidal, look no further than the Pre Box S2 Digital. It’s a great DAC and will do very hi-res audio.

Tiny Box. Huge Feature Set.

MQA, can be a preamp, great headphone amp, super hi-res audio capabilities, very low jitter, DSD capable. Yes, you get all this in a very well made, yet tiny $400 box. Simply amazing.

Best Sound in its Category

We have not heard a DAC that sounds as good as this one for its price, period. Plus you can even carry it around when you travel.

Company & Product Overview

Pro-Ject Audio Systems was founded in 1990 by Heinz Lichtenegger. Their driving goal since their inception has been to provide music lovers with great value products. The Pro-Ject Debut Carbon is one shining example of this philosophy. It has become known as one of the best deals in high-performance audio and is the best selling turntable in the world under $400. Pro-Ject Audio has factories in the Czech Republic and Slovakia with their R&D headquarters outside of Mistelbach Austria.

The company has two divisions, one specializing in all things related to turntables and another division making small audio components that are known for over-delivering for their size.

While the team at Pro-Ject Audio Systems are friends of ours, we must admit that we think they have way too many products. Right now there are 33 different models of turntables and a full 7 different series of electronics. The sheer volume is overwhelming, making it easy to get numb to their product releases.

The downside is that when this happens, a real jewel may not get the attention that it deserves. One such jewel is their latest Digital Box design, the Pro-Ject Pre Box S2 Digital. It’s a digital micro preamplifier that can fully unfold MQA files.

If you aren’t familiar with MQA, it stands for Master Quality Audio, and has been gathering momentum over the past year for its ability to deliver very high-resolution audio over streaming. Tidal, for example, is currently offering a growing library of MQA audio files.

Design & Build Quality

Like most of the Pro-Ject Box designs, the Pre Box S2 Digital is tiny! It is 4” wide, 4” deep, and only around 1.25” tall. That is small enough to easily fit in a messenger bag. It is housed in a very nicely finished all aluminum box. Like most of the Box Designs, you get a choice of silver or black. 

The front panel has a full-sized headphone jack on one end and a small, but great feeling volume knob on the other end. In the middle is a tiny color display window flanked on either side by two buttons that let you select the input, get into the menu, and change the filters.

pro-ject pre box s2 digital

The rear panel has inputs for USB B, coaxial digital, optical digital and a USB micro power connection. On the other end is a pair of gold-plated RCA analog outputs. All of the connections feel very solid.

A small remote control is included in the box, which gives you control over most of the functions of the unit. In addition, you can access the play/pause/forward/back controls from the remote. When connected via USB, you can even control them while streaming music from your computer.

With its very small footprint, the Pre Box S2 Digital will probably find its way into many different listening situations. It can be at home on your desktop either as a headphone amp, or DAC for your computer speakers or both.

At the other end of the spectrum, it can hide out anywhere in your audio rack as a full-scale MQA capable DAC.

Finally, since it can even be powered off the USB input, you can use it on the go with a laptop. Even though you would think of it as a home-based component, it is actually smaller than some of the portable DACs that we carry.

pro-ject pre box s2 rear panel

Features & Technology

While it may be tiny, the Pre Box S2 Digital is packed with features! We popped the cover off to take a peek inside and found it to be totally stuffed with components. Upon closer examination, you’ll see that it’s a completely dual mono design, with each channel of the signal path mirrored. Pretty impressive for a $399 box!

Pro-Ject opted for the ESS Sabre ESS9038 dual DAC in the Pre Box S2 Digital -- the highest level DAC they have ever used. These dual DACs are capable of up to 32-bit PCM 768kHz and DSD512.

It’s important to point out that MQA unfolding and the higher resolution digital rates are only available on the USB input. The optical and coax digital inputs do not do MQA, but still go up to a very respectable 24/192. Pro-Ject made the decision to limit these two to keep the price down. If they made it available on all inputs, we would expect it to cost around twice the price. Most people are going to be using the desktop or laptop version of Tidal to play back MQA files, and the USB connection is best suited for that application.

Pro-Ject also spent a lot of time developing the clock used in the Pre Box S2 Digital. While digital audio can be great, jitter is one downside that we see often. If the digital signals are not put back together with the same timing as the original recording, the music seems to lack emotion, no matter how clear it may sound. The Pre Box S2 Digital has one of the lowest jitter rates we have ever seen, far surpassing some much more expensive units.

While it would have been easy for Pro-Ject to skimp on components, especially considering how inexpensive this unit is, they instead opted for some very high-end parts.  It is quite unusual to see organic polymer capacitors and thin film miniMELF resistors in the power supply inside a box selling for only $399! Pro-Ject even used a 4 layer gold plated circuit board with extra shielding.

Since Pro-Ject felt this unit would mainly be used in USB mode, they also spent a lot of R&D time coming up with a way to reduce all of the noise that is present on a typical computer USB connection. Many components use passive filtering, but Pro-Ject used a special combination of passive and active filtering which brought the noise levels to below -130db. This is a ridiculously low number! All of this translates into great sound with a super low noise floor. When listening to this unit, you never get any trace of background noise.

In a trend we are starting to see on some other DAC’s, the Pre Box S2 Digital also has some filter options that allow you to shape the sound. Like most we have tested, these are subtle and recording dependent, but can make a bright or edgy recording sound better. There are 7 choices that you can easily flip through.

The output of the analog jacks is right around 2 volts, so you can use this box as an audio DAC by just setting its output to 0, which is full gain on this unit. If you have a fairly sensitive power amplifier, it will even make a great digital preamp with its three inputs.

The headphone amp is another ESS design and it can support up to 600-ohm headphones.

Finally, for you Roon fanatics out there, the Pre Box S2 Digital is also Roon capable.


We set up the Pro-Ject Pre Box S2 Digital with a Windows 10, Windows 7, and Apple MacBook Pro.

We’ll start by talking about the PC setup, so you Mac users can jump ahead to the next paragraph.

If you are Windows-based, you will need to do a few things first if you want your Pre Box S2 Digital to work properly. We recommend that you skip the CD that comes with the unit and instead go straight to the Pro-Ject Audio website. From there, navigate to the product page for the Pre Box S2 Digital. You’ll have to enter in your serial number to be able to download the latest software and installing it takes a little time. You’ll have to confirm steps a few times to complete the process, so you can’t just set it to install and forget it, unfortunately. If you had already powered on your S2, you’ll also need to cycle power.

To take full advantage of the Pre Box S2 Digital, you will need a Tidal account. The web-based app will not let you do MQA, so you will need to download the full program from their site. You’ll get the best sound out of MQA if you let the unit do the unfolding, so there is another step inside Tidal you need to do. Then, there are a couple of more steps.

First, using the desktop app, click on the music quality button at the bottom, which will be labeled Standard, High, or HIFI. (For Mac users this is under settings in the menu bar) This will bring up a window where you will choose the S2 for the sound output and click on Master which will force Tidal to give you the best audio possible, no matter the coding. You’ll then want to hover your mouse over the words “S2 Output” until a settings icon pops up on the left end. Click on this and you will have three choices: Use Exclusive Mode, Force Volume, and Pass Thru MQA. Be sure to check all three boxes.

Once you have set all of this up correctly, the S2’s display will light up showing MQA when you are playing that type of file, and you’ll have a little blue light to indicate it is doing the unfolding. You’ll also see the bit rate of the file in the lower part of the display.

pro-ject pre box s2 on table next to laptop


We tested the unit with a few different headphones including the Grado RS2AudioQuest Night Owl, and Focal Elear. We felt these were probably representative of what people might be using with this cool little box. Just for fun, we grabbed an AudioQuest DragonFly Red for some comparisons as well. Connection to the S2 was made with a Transparent Audio USB cable.

In recent months, Tidal has added a ton of MQA content. In our testing, every single artist that we searched for (mostly classic rock, we must admit) had albums available that were done in MQA as well as the same identical album without MQA.

Our search included Jackson Browne, Tom Petty, The Eagles, The Beach Boys, The Rolling Stones, Elton John, Yes, Diana Krall, Tina Turner, The Doors, Van Halen, Chicago, America, Steely Dan, John Coltrane, McCoy Tyner, Charlie Parker, Duke Ellington, and Ella Fitzgerald, and I am sure we forgot a few as we gave this unit a long listen! For all of these artists, there are one or more MQA albums to play around with.

As with many new technologies, there are two camps in the audio world regarding MQA. Some like it and some do not. We think you should listen and form your own opinion. MQA allows a higher bitrate file to be streamed than we have ever seen in the past. In some cases, we were able to listen to 192k files. One thing we did notice is that sometimes there seems to be “creative re-mixing” when the file gets converted to MQA. We noticed some instruments moved from their original location and on a couple of tracks a vocal passage that was originally in the far left, got moved to the far right. Interestingly enough, it seemed like the ones that were altered did not sound as good to us as the non-MQA file. When you do these comparisons yourself, be sure to also match the volume, as MQA is normally around 6-8 dB louder than the normal file.

All of that being said, we found some shining examples of MQA during our search that really show off its advantages in a big way. A few real winners include:

  • Doors, “Riders on the Storm”
  • Yes, “Mood for a Day” (off the album Fragile)
  • Diana Krall, “Like Someone in Love” (off the album, Turn Up the Quiet)

The improvement in the subtle nuances of the music, including extra warmth and a much larger soundstage, was really apparent in these cuts. Plus they all had what we felt to be closer to an analog sound. This tells us that the Pro-Ject Pre Box S2 Digital has one heck of a DAC in it.

The general presentation of the Pro-Ject Pre Box S2 Digital is very neutral with just a slight hint of lean -- but that is ever so slight. We listened to it for over 4 hours straight using both MQA and non-MQA and never had any sense of listening fatigue at all, which is a great sign. It truly is a very musical unit. When you have deep bass tracks they hit with a ton of impact and a clarity to the bass that we have never heard on a $400 DAC. Pro-ject’s circuitry to reduce jitter also works very well as we found ourselves tapping our toes on a lot of rhythmic tracks.

Next, we decided to compare the Pre Box S2 Digital against the Dragonfly Red, which can also do MQA. If you decide to do some comparing, make sure that you’re using the exact same recording. Some albums will have special remixed editions, so be sure the MQA and non-MQA come from the same album. While the Dragonfly Red is an absolutely amazing unit for $200, we definitely heard more subtle nuances and a bigger soundstage using the Pre Box S2 Digital. In our opinion, it’s well worth the extra $200.

Before we touch on this next observation, it’s time for an Audio Advice public service announcement. We are big believers in saving your ears. Your hearing is very important and trust our veterans when we say that you will still want to enjoy great audio well into retirement!

With that said, there are some of you out there that like to listen at high volume levels. For some of you, the Pre Box S2 Digital may not satisfy your demands, particularly if you are using headphones that are hard to drive. Using the Focal Elear, for example, we found a comfortable listening volume 2 clicks under full volume, but we recognize that this might not be loud enough for some of you. This is one area where the Dragonfly Red outmatches the Pre Box S2 Digital. It’s able to drive even the most inefficient headphones at a much higher level.

In summary, we have yet to hear anything that sounds as good as this little box does for $400 -- and it can handle MQA!

We know that some of you are going to ask how it compares to the Chord Mojo. At $579 we feel the Mojo has better pacing and a more effortless sound. The Mojo also has more output to drive a power amp directly and a more powerful headphone stage. With that said, $400 is an awesome value for the Pre Box S2 Digital.

Overall Recommendation

As we said, there are several use cases for this great little box. We feel the typical case will be at someone’s desk, driving either a pair of headphones or a pair of powered speakers like the Audioengine A5+.

It will let you discover the very cool world of MQA without breaking the bank. You could also use it as a travel DAC, powering it off of your laptop. This is a shade less convenient than some of the DAC’s that have rechargeable batteries or can run off of your smartphone, but it’s an option.

In a nutshell, if you are interested in checking out MQA or want to upgrade your computer audio setup, the Pro-Ject Pre Box S2 Digital is a steal!

Details & Specs
  • Dual mono construction
  • High end ESS Sabre ESS9038 dual DAC
  • Proprietary clock circuity design
  • Organic polymer capacitors and thin film miniMELF resistors
  • MQA hardware decoding
  • DSD64, DSD128, DSD256 & DSD512 (DSD over PCM)
  • Up to 32bit/192kHz for optical & coax inputs
  • 7 selectable digital filter characteristics
  • 1 proprietary optimum transient digital filter
  • Headphone output on the front (6.3mm)
  • Synchronization of all internal oscillators
  • Jitter as low as 100 Femtoseconds!
  • Gold plated four layer PCB
More Information
Series S2 Line
Total Harmonic Distortion 0.0003%
Frequency Response 20Hz - 20kHz
Product Manual Download
Roon Status Roon Tested
Customer Reviews
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