Pro-Ject Pre Box S3 black

Concentrating an MM phono preamplifier, a DAC, an analog preamplifier, and a headphone amplifier into a chassis twenty centimeters wide: that is the brief of the Pro-Ject Pre Box S3. Thirteen inputs and outputs in total, a fully analog dual-mono design, and two additions in this generation: an eARC input for TV and an RS232 port for custom installation.

A fully analog dual-mono design

The Pre Box S3 comes in a compact 20.6 x 5.5 x 15.3 cm format (17.6 cm with connectors) and weighs 1,020 g excluding the power supply, in an S3 aluminum chassis that shields against electromagnetic interference. Manufacturing takes place in Europe.

The analog section adopts a dual-mono design: each channel has its own signal path. Channel separation reaches -72 dB at 10 kHz, the signal-to-noise ratio stands at 110 dB (120 dB A-weighted), total harmonic distortion remains below 0.007%, and the frequency response shows a deviation of less than -0.4 dB across the 20 Hz - 20 kHz band.

Volume control uses a motorized analog potentiometer, operable from the front panel or the supplied remote control. Level adjustment takes place in the analog domain, without intermediate digital conversion.

Three analog inputs with dedicated MM phono stage

On the analog side, the Pre Box S3 features two pairs of RCA line inputs (for a CD player, network player, tuner, or any other line-output device) and one MM phono input on RCA.

The phono stage accepts moving magnet cartridges with 45 dB of gain. The design prioritizes low background noise and high linearity, two parameters that weigh heavily on the playback quality of a vinyl record. A turntable fitted with an MM cartridge connects directly, without an external phono stage.

Digital section: Cirrus Logic DAC, asynchronous USB-C, and eARC input

Digital conversion is handled by a Cirrus Logic CS4344 with a Multi-bit Delta Sigma design, capable of accepting streams up to 24-bit / 192 kHz. Several digital inputs feed the DAC: one RCA coaxial S/PDIF and two optical Toslink inputs (useful for galvanically isolating the source), plus an asynchronous USB-C port mainly intended for use with a computer. Asynchronous mode, where the DAC clock drives the stream, reduces jitter compared with synchronous transmission.

The eARC input, new in this generation, allows a compatible TV to be connected directly via an HDMI cable. The TV’s sound (TV channels, streaming services, Blu-ray player connected to the TV) is then played through the hi-fi system, with centralized volume control via the TV remote in most cases.

Bluetooth 5.0 with aptX and aptX HD

The Pre Box S3 supports Bluetooth 5.0 with aptX and aptX HD codecs and the A2DP profile. aptX HD delivers 24-bit up to 48 kHz, with a higher bitrate than SBC, the default Bluetooth audio codec. Range and connection stability benefit from Bluetooth 5.0 compared with earlier versions. There is no wired network or Wi-Fi reception: for network streaming (Spotify Connect, Tidal, files on NAS), a dedicated player connects to one of the digital or line inputs.

Front-panel 6.3 mm headphone jack output

The integrated headphone amplifier delivers 2 x 70 mW into 32 ohms at 1% THD, with a compatible impedance range of 16 to 600 ohms. The output is on a front-panel 6.3 mm jack. This power is suitable for the majority of common headphones. For very high-impedance, low-sensitivity models that require greater dynamic headroom, a dedicated headphone amplifier connected to the fixed line output (3.5 mm jack) remains preferable.

Driving active speakers or a power amplifier

Two usage scenarios emerge. With a power amplifier and passive speakers, the Pre Box S3 provides volume control and source selection. The amplifier handles powering the speakers.

With active speakers, which incorporate their own amplification, the same variable RCA output is sufficient: the Pre Box S3 drives them directly. A dedicated RCA subwoofer output is also present. A fixed line output on a 3.5 mm jack completes the connectivity: it sends the selected signal, at a constant level, to an external headphone amplifier or a second listening zone.

12 V trigger and RS232 for custom installation

The 12 V DC trigger output (2.5 mm two-pole coaxial jack) triggers the simultaneous power on and off of other Pro-Ject devices equipped with a trigger input, such as the Amp Box S3, or any amplifier compatible with this protocol. The RS232 connection, on a detachable three-pin terminal block, accepts the control protocols of custom installation systems.

Standby power consumption remains below 0.5 W, in compliance with European energy efficiency requirements. The power supply is external: 18 V / 500 mA DC, with 100-240 V 50/60 Hz mains compatibility. Two finishes are available, silver or black.

Technical Specifications

Main functions

• All-in-one control center with 13 inputs and outputs in total
• MM phono preamplifier
• Digital-to-analog converter (DAC)
• Analog preamplifier
• TV eARC input
• Home automation / custom installation compatible
• Headphone amplifier
• Ideal control of power amplifiers and active speakers

Analog design

• Fully analog preamplifier with dual mono design
• Analog volume control with motorized potentiometer
• High-end MM phono stage with low noise, high gain, and exceptional linearity
• Premium aluminum S3 chassis protecting against interference

Audio performance

• Frequency response (20 Hz - 20 kHz): < -0.4 dB
• Line preamplifier gain: 4.5 dB
• Phono preamplifier gain: 45 dB
• Channel separation: -72 dB at 10 kHz
• Signal-to-noise ratio: 110 dB (120 dB A-weighted)
• Total harmonic distortion (THD): < 0.007%

Digital conversion

• Cirrus Logic CS4344 D / A converter, 24-bit / 192 kHz
• Multi-bit Delta Sigma architecture
• Asynchronous S / PDIF and USB C inputs up to 24-bit / 192 kHz

Wireless connectivity

• Bluetooth 5.0
• aptX and aptX HD codecs
• A2DP profile
• aptX HD audio quality: 24-bit up to 48 kHz

Inputs

• 9 inputs in total: 3 analog and 6 digital
• Analog inputs
  • 2 RCA line pairs
  • 1 MM phono input (RCA), low noise and high gain (45 dB)
• Digital inputs
  • 1 RCA coaxial S / PDIF
  • 2 optical Toslink
  • 1 asynchronous USB C
  • 1 eARC for TV
  • Bluetooth

Outputs

• 1 variable RCA output for power amplifier
• 1 fixed line output on 3.5 mm jack for external headphone amplifier or second zone
• 1 dedicated RCA subwoofer output
• 1 headphone output on 6.3 mm jack (16 - 600 ohms)

Headphone amplifier

• Power: 2 x 70 mW into 32 ohms (1% THD)
• Connector: 6.3 mm jack
• Compatible impedance: 16 to 600 ohms

Integration and home automation

• Trigger output: 12 V DC, 2-pole 2.5 mm coaxial jack, compatible with Amp Box S3 and other devices with trigger function for simultaneous power on and off
• RS232: detachable 3-pin terminal block for control protocol in custom integration
• Home automation and custom installation compatible

Power supply

• Power supply: 18 V / 500 mA DC; 100 - 240 V, 50 / 60 Hz
• Standby power consumption: < 0.5 W

Physical characteristics

• Dimensions (W x H x D): 20.6 x 5.5 x 15.3 cm (17.6 cm with connectors)
• Weight: 1020 g without power supply
• Available finishes: silver or black

Included accessories

• Remote control