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Pro-Ject Pre Box S2 Digital

Micro-sized digital stereo preamp with built-in headphone amp (Silver)

Item # 252PBS2DS

Use this little gem for high-fidelity sound with your digital audio sources, including high-res audio tracks.

Use this little gem for high-fidelity sound with your digital audio sources, including high-res audio tracks.

Item # 252PBS2DS

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About the Pro-Ject Pre Box S2 Digital

Pint-sized audio precision

Use this little gem for high-fidelity sound with your digital audio sources, including high-res audio tracks. The Pro-Ject Pre Box S2 Digital measures barely over four inches wide, but it's big on flexibility. Use its stereo RCA outputs to feed pristine audio signals to a pair of powered desktop speakers or a power amp. Or connect your favorite set of headphones to the front-panel 1/4" jack.

Pint-sized audio precision

Use this little gem for high-fidelity sound with your digital audio sources, including high-res audio tracks. The Pro-Ject Pre Box S2 Digital measures barely over four inches wide, but it's big on flexibility. Use its stereo RCA outputs to feed pristine audio signals to a pair of powered desktop speakers or a power amp. Or connect your favorite set of headphones to the front-panel 1/4" jack.

Built to impress

The Pre Box S2 Digital sports a dual mono configuration, with two high-performance DACs (digital-to-analog converters) onboard. It can play just about any high-res audio track you send its way, including super-high-res DSD files. There's built-in hardware support for MQA (Master Quality Authenticated) files, such as those available through TIDAL's streaming audio service. Jitter — digital timing errors that can smear musical details — is reduced to vanishingly low levels. It all adds up to surprisingly robust sound, given the Pre Box S2's small size and reasonable price tag.

Praise for the Pro-Ject Pre Box S2 Digital from The Absolute Sound

"The Pro-Ject Pre Box S2 Digital offers audiophiles a very high-value DAC/digital preamp at an almost ridiculously low price. Not only does it include a plethora of important features, but it sounds good, has an elegantly designed control surface, and is expandable."

— From Steven Stone's January, 2019 review in The Absolute Sound Read the full review


Product highlights:

  • dual mono circuitry with two high-performance ESS Sabre DACs (ESS9038Q2M)
  • high-res audio playback, including PCM-based files up to 32-bit/768kHz and DSD512
  • full hardware-based MQA support
  • selectable digital filters
  • vanishingly low jitter (as low as 100 Femtoseconds)
  • frequency response: 20-20,000 Hz
  • total harmonic distortion: 0.0003%
  • headphone output power: 68 mW (32 ohms)
  • 1 coaxial digital
  • 1 optical digital (Toslink)
  • 1 USB Type-B for connection to a computer
  • RCA stereo output (rear-panel)
  • 1 front-panel 1/4" full-sized headphone output
Dimensions & Warranty:
  • 4-1/16"W x 1-7/16"H x 5-9/16"D
    • Crutchfield's in-house depth measurements are made with all relevant cables in place
  • weight: 21 oz. (without power supply)
  • warranty: 2 years
  • Our 60-day money-back guarantee
  • MFR # 9120065186424

What's in the box:

  • Micro preamplifier
  • AC adapter with attached 45" DC output cord and Micro-B USB plug (DC output: 5.0V 1.0A)
  • 3 AC plug adapters (US / EU / UK)
  • Wireless remote control (12-button)
  • CR2032 Coin cell battery (for remote)
  • CD with USB driver
  • Instructions for Use (English)
  • Instructions for Use (German)

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More details on the Pro-Ject Pre Box S2 Digital

Mark G.

Features & specs

Type Desktop/Component
Built-in Rechargable Battery No
Built-in DAC Yes
Amplifier Output Specs
Output Power 68mW
Output Impedance (Unbalanced) 32 ohms
Output Impedance (Balanced) Not given
Audio Specs
Bit Depth (USB) 32
Max Sampling Rate (USB) 768 kHz
Bit Depth (S/PDIF) 24
Max Sampling Rate S/PDIF 192 kHz
S/N Ratio (Unbalanced, in dB) 0
S/N Ratio (Balanced, in dB) 0
THD (Unbalanced) 0.0003%
THD (Balanced) Not given
Supported File Types
PCM Up to 768kHz
Total Inputs 3
USB Type B
Optical Digital 1
Coaxial Digital 1
3.5mm Digital None
Stereo RCA Analog None
Stereo 3.5mm Analog None
Stereo XLR Analog None
Headphone Outputs
3.5mm Unbalanced None
1/4-inch Unbalanced 1
4.4mm Balanced None
XLR4 Balanced None
Other Headphone Outs None
Line Level & Digital Outs
RCA Line Out 1
3.5mm Line Out None
XLR Line Out None
Subwoofer Out None
Optical Digital Out None
Coaxial Digital Out None
Wireless Connectivity
Bluetooth No
Wi-Fi No
Apple-compatible No
Android-compatible No
General Info
Width (inches) 4-1/16
Height (inches) 1-1/2
Depth (inches) 4-13/16
Weight 0.83 lbs.
Parts Warranty 2 Years
Labor Warranty 2 Years

Product Research


Overview: The Pro-Ject Pre Box S2 Digital is a high-quality digital micro preamplifier with dual D/A converters built in. This tiny package has USB, optical, and coaxial digital inputs, RCA analog outputs on the back, and 1/4" headphone output on the front. The Pre Box S2 Digital is available in silver and black, and comes with a 12-button remote control. Dimensions: Width 4.057", Height 1.457", Depth 4.783", Weight 13.3 ounces (w/o AC adapter).

Construction: The Pre Box S2 Digital features a dual mono configuration with two high-performance ESS Sabre digital-to-analog converters (ESS9038Q2M), capable of high resolution audio up to 32-bit 768kHz PCM and DSD512. Its proprietary clock circuitry delivers jitter rates down to 100 Femtoseconds. The Pre Box S2 Digital supports MQA decoding, which enables hi-res audio streaming. It also has a high-quality ESS9602 headphone amplifier. All of this technology is housed in an extruded aluminum casing.

Connections: The Pro-Ject Pre Box S2 Digital offers three digital inputs. The USB input is for connecting the unit to your computer. A USB driver is supplied on the included CD, if needed. The Optical and Coaxial digital inputs allow you to connect to components, such as CD players, DVD players, TVs, Audio Streaming devices, etc. You can select the input from the front panel, and the selected input will be shown on the 1" OLED display. The Pre Box S2 Digital has a stereo RCA output on the back panel and a 1/4" (6.3mm) headphone output on the front. When headphones are connected to the unit, the rear output is muted.

Sampling Frequencies: The Pre Box S2 Digital supports 32-bit PCM, DSD, and full MQA unfolding. The USB input is capable of the following sampling rates: 32, 44.1, 48, 88.2, 96, 176.2, 192, 352.8, 384, and 768kHz. It also supports DSD64, DSD128, DSD256, and DSD512. The Optical and Coaxial Digital inputs will support PCM up to 24-bit/192kHz.

Power Requirements: The Pre Box S2 Digital provides two options for powering the unit. If you are not going to use the USB input, you can power the unit via the included 5V AC adapter. If you plan to use the USB input, you can power the unit directly from your computer via the USB input. In this case, you should unplug the AC adapter to avoid interference between the two power supplies.

Digital Filters: The Pre Box S2 Digital has eight selectable digital filters, including Pro-Ject's proprietary Optimum Transient Digital Filter. Other available filters includes: Fast Roll Off (Linear Phase), Slow Roll Off (Linear Phase), Minimum Phase Fast, Minimum Phase Slow, Linear Apodizing, Hybrid Filter, and Brickwall Filter. These filters can be accessed from the front panel or remote to let you shape the audio precisely to your liking.

Front Panel Controls: The unit has a rotary volume control with a range of -80dB to 0dB. Pressing the volume control instantly mutes the audio. There are separate volume settings stored for the headphone output and the RCA output. Two buttons let you select the input (USB, OPT, or COAX), while a single button is for cycling through the available digital filters. The Menu button gives you access to settings for Distortion Compensation and Audio Quality, and displays the software (SW) Version. You can change the values for the audio settings by turning the volume knob while in the menu.

Remote Control: The included credit card-sized remote control gives you basic playback control of your digital music files, including play/pause, forward, and reverse. You can also raise or lower the volume, mute/unmute, cycle through the Digital Filter selections, control the balance, and access the menu. The remote is 1.58"W x 3.4"H x 0.29"D, and powered by a CR2032 coin cell battery (included).


  • Frequency Response: 20Hz to 20kHz
  • Output Voltage: 2.05 V (effective)
  • Headphone Output Power: 68mW (at 32 ohms)
  • Total Harmonic Distortion: 0.0003%
  • Dynamic Range: 124 dBA
  • Power Consumption: 5V, less than 1 watt

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Customer Q&A

7 questions already asked

Can I just use this as a DAC with a fixed output for my BlueSound Node 21?
[ Frederick  Dec 07, 2020 ]
1 answer
Yes. Currently using it as DAC only. Set volume to 0 level and you're all set.
[ ED  Dec 07, 2020 ]
Could I use the head phone out for a sub?
[ LOREN  Nov 16, 2020 ]
1 answer
I don't think so... if for no other reason that if you use the Headphone Out, it automatically mutes the stereo out in the back of the unit.
[ Larry  Nov 20, 2020 ]
Is this mono or stereo output? I thought I read it only outputs in mono. Thanks.
[ Jeremy  Aug 19, 2020 ]
6 answers
It has stereo output; look for the left and right analog outs on the back of the unit. These will connect to the appropriate inputs on your receiver or other device.
[ Edward P.  Aug 19, 2020 ]
It has R/L RCA output jacks. Since I am running Bose desktop speakers I have to use an adapter cord that plugs in to a single jack on the bose primary speaker. I get some sound, but very little stereo effect from the secondary Bose speaker that is noticeable. With different speakers the sound differential could be more distinct. My speakers are close together. The sound quality with the small bose speaker is excellent.
[ Thomas  Aug 19, 2020 ]
The Pre-box S2 is stereo. I assume your are referencing the mono outputs (one each for left and right channels). The 1/4' headphone connection definitely sends stereo output signals.
[ Shayne  Aug 19, 2020 ]
Yes it's stereo. It's a dual mono Design, which gives it's a cleaner signal. Hope this helps.
[ JAMES  Aug 19, 2020 ]
Stereo output.
[ Jeffrey  Aug 19, 2020 ]
It outputs 2-channel stereo via 2 rca connectors on the back. Works fine.
[ Thomas  Aug 19, 2020 ]
What type of power cord do you recommend?
[ Nicholas  Mar 10, 2020 ]
2 answers
FYI - If you use the USB In, you don't need a separate power cord. The USB will power the unit too.
[ Larry  Nov 20, 2020 ]
I use the standard one it comes with.
[ JONATHAN  Nov 16, 2020 ]
Does this work with an Ipad? Will it see it as an audio output over USB?
[ Joseph  Feb 16, 2020 ]
5 answers
Yes, i use my iPad Pro as an streaming device. The box will play tidal files as "mqb."
[ JONATHAN  Nov 16, 2020 ]
Hi Joseph, thank you for your question. You should not have any problem using an iPad as a connected USB source. Feel free to chat with us online or by phone at 1-800-324-9695. An Advisor will be happy to go over any additional questions you may have.
[ Jess  Mar 03, 2020 ]  Staff
Yes. I believe it will accept any usb source. I've only used my phone because that where my music is. iPad should work.
[ Marlon  Mar 02, 2020 ]
I have used this with my iPad Pro using an Apple Lightning to USB3 Camera Adapter. Works with no issues.
[ Anthony  Mar 02, 2020 ]
I don't think I can answer that question. I only used it as a preamp for a turntable.
[ Porscheman  Mar 02, 2020 ]
I read on one of the Audiophile forums that you can only unfold MQA files using the USB port. Is this correct? I was hoping to connect from my streamer via the coax input for MQA.
[ Jerry  Jan 20, 2020 ]
4 answers
I have not used the MQA function. However, what I read before purchasing the unit is that the MQA only functioned with the USB port. I am very happy with unit for its price. It was about half the size I thought it would be.
[ GREG  Jan 20, 2020 ]
I've only used it with the USB output so I don't have direct knowledge of the issue. However, the Stereophile online review seem to corroborate this: "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."
[ PHILLIP  Jan 20, 2020 ]
I often this S2 and I'm pretty sure it's only through USB.
[ David  Jan 20, 2020 ]
yes, that is correct, MQA is only available via USB
[ Bill  Jan 20, 2020 ]
Does inserting headphones mute the pre-out?
[ Justin  May 25, 2021 ]
4 answers
Yes. (Too bad, too. Many times I have use of a second audio out). But this is a great little unit I have three of them.
[ Peter  May 25, 2021 ]
Yes. The volume settings are also saved when switching between headphones and pre-out
[ FRANCESCO  May 25, 2021 ]
Yes, it will mute the pre out.
[ COLLIN H  May 25, 2021 ]
Yes. And I verified before replying.
[ ED  May 25, 2021 ]

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