Pro-Ject Head Box S3 B black
Pro-Ject Head Box S3 B: Fully Balanced Headphone Amplifier
The arrival of this amplifier marks the beginning of a new generation in Pro-Ject’s Box Design range, whose first entries (Micro and Mini) date back to the early 2000s. The Austrian manufacturer returns with two fully balanced models. The Head Box S3 B occupies the entry-level position and carries a straightforward promise: to apply a fully balanced architecture at an accessible price point, in order to get more out of the headphones connected at the end of the chain.
A Fully Balanced Topology from End to End
Pro-Ject makes a specific point: many so-called balanced headphone amplifiers are balanced only at the connector level, not in the internal circuitry. The Head Box S3 B applies the principle throughout the entire signal chain, RCA and XLR alike. The signal entering via the Cinch inputs is converted to balanced at the input stage and remains processed in differential mode all the way to the outputs. The expected benefits are well-established in balanced designs: better rejection of noise picked up along the signal path, increased separation between left and right channels, and a lower noise floor.
Two TPA6120A2 Chips and Usable Power Output
The power stage is built around two TPA6120A2 chips from Texas Instruments. The balanced output peaks at 820 mW into 32 Ω, with 480 mW into 8 Ω, 680 mW into 16 Ω, and 320 mW for high-impedance headphones at 300 Ω. The manufacturer’s position is deliberate: rather than chasing headline watt figures, the focus is on genuinely useful power — the kind that matches the headphones people actually use today. The measured figures support this approach. Signal-to-noise ratio exceeds 115 dB A-weighted. Total harmonic distortion below 0.002% at 1 kHz for 500 mV input. Crosstalk better than -81 dB at 10 kHz. Frequency response remains within -0.25 dB across the entire audible band.
Gain differs depending on the input used: 15 dB on RCA, 9 dB on XLR. The minimum accepted headphone impedance goes down to 8 Ω, covering virtually all sensitive in-ear monitors, including monitoring models.
Connectivity Suited to Mixed Systems
The rear panel offers a pair of RCA inputs and a pair of XLR inputs, along with an RCA loop output (bypass) to connect the unit to a speaker amplifier or extend the chain without unplugging anything. The headphone outputs are organised around four sockets: 4.4 mm Pentaconn and 4-pin XLR for balanced connections, 6.3 mm and 3.5 mm for unbalanced. The simultaneous presence of both Pentaconn and 4-pin XLR eliminates the need for adapters for owners of high-end headphones, which are supplied with one or the other cable termination depending on the brand.
Aluminium Chassis and European Manufacturing
The enclosure is made entirely from aluminium, a choice that combines mechanical rigidity with electromagnetic shielding of the internal circuitry. The front panel controls are also machined from the same material. The form factor remains compact (206 x 55 x 153 mm), and the moderate weight (950 g excluding the power supply) makes installation straightforward whether on a desk or in a hi-fi cabinet. Two finishes are available, silver or black. Production takes place in Europe.
The external 18 V DC power supply, included with the unit, accepts 110–240 V and keeps standby consumption below 0.5 W. Relocating the power supply outside the main chassis is standard practice at Pro-Ject, keeping stray electromagnetic radiation away from the audio circuitry.
Documentation
Technical specifications
Topology and power stage
- Unique fully balanced headphone amplifier topology
- Power stage implemented with two TPA6120A2 chips for a rich sound
- Fully balanced signal chain for RCA and XLR inputs
- Balanced output power up to 820 mW
- Redefines the class of balanced headphone amplifiers in its price range
Audio performance
- Maximum output power :
- 480 mW into 8 Ω
- 680 mW into 16 Ω
- 820 mW into 32 Ω
- 320 mW into 300 Ω
- Signal‑to‑noise ratio: > 115 dB A‑weighted at 1 kHz
- Total harmonic distortion: < 0.002 % at 1 kHz for 500 mV input
- Crosstalk: < –81 dB at 10 kHz
- Gain: 15 dB (RCA input) / 9 dB (XLR input)
- Frequency response: < –0.25 dB from 20 Hz to 20 kHz
- Minimum headphone impedance: 8 Ω
Connectivity
- Balanced headphone outputs: 4.4 mm Pentaconn, 4‑pin XLR
- Unbalanced headphone outputs: 3.5 mm, 6.3 mm
- Analog inputs: 1 pair RCA / Cinch, 1 pair XLR
- Analog loop (bypass) outputs: 1 pair RCA, for connecting an additional amplifier or extending the system
Construction and finish
- Fully aluminum chassis of premium quality ensuring mechanical stability and effective shielding
- High‑quality aluminum control elements and knobs
- Available in silver or black
Power supply and consumption
- Power supply: 18 V / 1 A DC, 110‑240 V, 50/60 Hz
- Standby power consumption: < 0.5 W
Dimensions and weight
- Dimensions (L x H x D): 206 × 55 × 153 (170) mm
- Weight: 950 g without power supply
Frequently Asked Questions
Does the Head Box S3 B replace an older model?
It inaugurates a new generation of the Box Design range, whose first entries (Micro and Mini) date back to the early 2000s. Rather than a direct replacement for a specific model, its arrival (alongside the DS3 B above it) marks a complete architectural overhaul, now centred on fully balanced signal processing throughout.
What is the difference from the Head Box DS3 B?
The DS3 B moves to a fully discrete topology (with no integrated circuits in the amplification stage) and delivers 1.5 W into 32 Ω, nearly double the power output. It is larger and provides the headroom needed for harder-to-drive headphones, such as certain low-sensitivity planar magnetic models.
Do you need a headphone with a balanced cable?
No. Both unbalanced outputs (3.5 mm and 6.3 mm) remain available and benefit from the same signal chain. Using a balanced connection brings a measurable improvement in channel separation and noise floor, but the S3 B remains fully worthwhile with a traditional headphone on a 6.3 mm jack.
What is the RCA loop output on the rear for?
This output takes the signal from the RCA input without any processing and sends it to another device — for example, an integrated amplifier driving speakers. It eliminates the need to unplug the source every time you switch between listening modes (headphones or speakers) and simplifies integration into an existing hi-fi system.
Is the gain switchable?
Gain depends on the input used, but no dedicated switch is provided: 15 dB for the RCA input, 9 dB for the XLR input. The choice of input therefore determines the available gain level. This difference is consistent with the higher output level delivered by a source with a balanced XLR output.
Which headphones can it drive properly?
The range is wide. The minimum accepted impedance goes down to 8 Ω, and 320 mW remain available into 300 Ω for high-impedance headphones. Mid-sensitivity dynamic models, headphones from 32 to 80 ohms, classic 250 and 300-ohm designs, and sensitive in-ear monitors all have comfortable headroom.
Can it be used as a preamplifier for active speakers?
Not directly. The RCA loop output is a bypass — its level is not controlled by the volume potentiometer, and there is no variable preamplifier output. To drive an active speaker system at the same volume level as the headphones, an additional component in the chain would be required.
- Eco-contribution of €0.12 included in the sale price.
- GTIN / EAN: 9120137901290