Pro-Ject Head Box E silver

Pro-Ject Head Box E: compact headphone amplifier

Plugging a hi-fi headphone directly into the headphone jack of a laptop or smartphone quickly reveals the limitations of these built-in outputs: insufficient power, audible background noise, compressed dynamics. The Head Box E sits between a line-level source and the headphones to provide the dedicated amplification these outputs cannot deliver. It is the entry-level headphone product in Pro-Ject’s Box series.

Fully discrete amplification

Pro-Ject has opted for a fully discrete amplification stage, without relying on the integrated circuits commonly found at this price point. The design is built around individual transistors and components assembled on a printed circuit board laid out to minimise signal paths and noise. The results show in the measurements: total harmonic distortion below 0.005%, a signal-to-noise ratio of -105 dBV, and channel separation of 65 dB. The frequency response covers 20 Hz to 80 kHz within ±0.2 dB. This approach also offers a more practical advantage: maintenance and repair remain possible over time, whereas a specific integrated component can become impossible to source once production has ceased.

Enough power for demanding headphones

665 mW into 32 ohms is comfortable for a device of this size. The supported impedance range runs from 8 to 600 ohms, covering virtually the entire market: low-impedance portable models as well as high-impedance reference headphones that require an amplification stage capable of sustaining voltage. The output impedance stays below 1 ohm, which is important for preserving the tonal character of headphones whose impedance varies significantly with frequency (planar magnetic models and certain high-end dynamic headphones are sensitive to this). The 11 dB gain sits at a reasonable average, leaving comfortable headroom on the volume control without clipping too early with standard line-level sources.

Two headphone outputs usable simultaneously

The front panel features a 6.35 mm jack for traditional hi-fi headphones and a 3.5 mm jack for modern-format headphones and earphones. Both outputs operate in parallel: listening can be shared between two people without an adapter or splitter box. A single line-level RCA input is provided on the rear, to be connected to the source of your choice: DAC, CD player, phono preamplifier, or the line output of an integrated amplifier.

An RCA loop for integration into a system

The rear panel also features a pair of RCA outputs, bypassing the input. This loop passes the signal on to another component: a power amplifier, active speakers, or a second preamplifier. The Head Box E can thus be inserted into an existing system without having to unplug cables every time you switch between headphone and speaker listening.

Metal chassis, aluminium finish

The enclosure is made entirely of metal, with a machined aluminium front panel and volume knob. This construction shields the electronics from electromagnetic interference and dampens vibrations that could affect the signal. The footprint remains modest: 103 mm wide, 37 mm tall, 120 mm deep, weighing 390 g without the power supply. The unit fits easily alongside a computer, a DAC, or a turntable. Two finishes are available — black or silver front panel — in keeping with the Box series, whose components are visually matched to one another. Power is supplied at 5 V / 0.5 A DC via an external adapter, and standby consumption remains below 0.5 W.

Frequently asked questions

Can the Head Box E drive a 600-ohm headphone? Yes, the accepted impedance range goes up to 600 ohms. Very high-impedance headphones will require turning the volume control higher, but the available power remains sufficient to reach comfortable listening levels with most models in this category.

What source should be connected to the input? Any line-level source with an RCA output: a USB DAC, CD player, the line output of a phono preamplifier, the “tape out” or “pre out” of an integrated amplifier, or certain game console or television line outputs. Headphone-level outputs and speaker outputs are not suitable.

What is the purpose of the RCA loop output on the rear? It reproduces the input signal without amplification. The Head Box E can therefore be placed between a source and an amplifier or active speakers. The volume control only affects the headphone outputs, not the RCA loop, whose level remains constant for the next component in the chain.

Can you listen on headphones and speakers at the same time? Yes, since the RCA loop is a bypass and remains active at all times. Note that no automatic switching is provided: if the speaker amplifier remains powered on, sound will come from both simultaneously. The downstream amplifier must be switched off to switch to headphone-only listening.

Do both headphone outputs carry the same signal? Yes, the 6.35 mm jack and the 3.5 mm jack are wired in parallel on the same output stage. Connecting two headphones at the same time is possible, bearing in mind that the power and impedance seen by the amplifier are then shared between the two transducers.

Is a specific power supply required? The unit uses a 5 V / 0.5 A DC power supply, provided by an external adapter included with the product. The low-voltage format limits heat generation and power consumption, and keeps the audio electronics away from a mains transformer, which is a potential source of noise.

Is the Head Box E suitable for use with a computer? Not via direct USB connection: the input is analogue, via RCA. For a computer source, a DAC must be placed upstream (USB to RCA) to handle the digital-to-analogue conversion. The Head Box E then takes over for the headphone amplification itself.

Technical Specifications

Audio Performance

• Output power: 665 mW (at 32 ohms)
• Signal-to-noise ratio: -105 dBV
• THD + N: < 0.005%
• Gain: 11 dB
• Crosstalk: 65 dB
• Frequency response: 20 Hz - 80 kHz (± 0.2 dB)

Connectivity

• Analog inputs: 1 pair of RCA / Cinch line-level connectors
• Analog loop outputs: 1 RCA / Cinch pair
• Headphone outputs: 1 × 6.35 mm jack, 1 × 3.5 mm jack
• Both headphone outputs usable simultaneously

Headphone Output Specifications

• Supported headphone impedance: 8 - 600 ohms
• Output impedance: < 1 ohm
• Suitable for demanding headphones

Electronic Design

• Fully discrete headphone amplifier (no cheap integrated circuits)
• Expertly designed printed circuit board
• Low-noise components
• Exceptionally low distortion
• RCA loop (bypass) output for additional amplifier

Power Supply

• Power supply: 5 V / 0.5 A DC
• Standby consumption: < 0.5 W

Enclosure and Design

• All-metal chassis, protection against electromagnetic interference and vibrations
• Machined aluminum front panel and controls
• Compact footprint
• Color options: silver or black front panel
• Dimensions (W × H × D): 103 × 37 × 120 mm
• Weight: 390 g (without power supply)