Pro-Ject Head Box E black

Pro-Ject Head Box E: compact headphone amplifier

Plugging hi-fi headphones directly into the jack output 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 model in the Box series from Pro-Ject.

Fully discrete amplification

Pro-Ject chose a fully discrete amplification stage, without relying on the integrated circuits commonly found at this price point. The design is based on individual transistors and components assembled on a printed circuit board whose layout is intended to minimize signal paths and noise. The results show up in the measurements: total harmonic distortion below 0.005%, a signal-to-noise ratio of -105 dBV, and crosstalk of 65 dB. Frequency response covers 20 Hz to 80 kHz with a tolerance of ±0.2 dB. This approach offers another, more practical advantage: maintenance and repair remain possible over time, whereas a specific integrated component can become impossible to find once production has stopped.

Enough power for demanding headphones

665 mW into 32 ohms is comfortable for a device of this size. The supported impedance range goes from 8 to 600 ohms, covering almost the entire market: low-impedance portable models as well as high-impedance reference headphones that require an amplification stage capable of maintaining voltage. Output impedance stays below 1 ohm, which is useful for preserving the tonal signature of headphones whose impedance varies significantly with frequency (planar magnetic models and some high-end dynamic headphones are sensitive to this). The 11 dB gain is in a reasonable middle range and leaves comfortable room on the potentiometer, 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. The two outputs operate in parallel: you can therefore share listening 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 preamp, line output from an integrated amplifier.

An RCA loop for integration into a system

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

Metal chassis, aluminum finish

The enclosure is entirely metal, with a front panel and volume knob made of machined aluminum. This construction protects the electronics from electromagnetic interference and dampens vibrations likely to affect the signal. Dimensions remain modest: 103 mm wide, 37 mm high, 120 mm deep, for 390 g excluding the power supply. The unit fits easily next to a computer, DAC, or turntable. Two finishes are available, black or silver front panel, consistent with the Box series whose elements visually match 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 600-ohm headphones? Yes, the accepted impedance range goes up to 600 ohms. Very high-impedance headphones will require turning the potentiometer up higher, but the available power remains sufficient to reach comfortable listening levels with most of the relevant models.

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

What is the rear RCA loop output used for? 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 potentiometer only affects the headphone outputs, not the RCA loop, whose level remains constant for the next component.

Can you listen through headphones and speakers at the same time? Yes, since the RCA loop is in bypass and remains permanently active. Note that no automatic switching is provided: if the speaker amplifier remains powered on, sound will come out simultaneously from both sides. You must turn off the downstream amplifier to switch to headphone-only listening.

Do both headphone outputs deliver the same signal? Yes, the 6.35 mm jack and the 3.5 mm jack are wired in parallel to the same output stage. Connecting two headphones at the same time remains possible, keeping 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 buildup and power consumption, and allows the audio electronics to be kept away from a mains transformer, a potential source of noise.

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

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 sockets
• Analog loop outputs: 1 RCA / Cinch pair
• Headphone outputs: 1 6.35 mm jack, 1 3.5 mm jack
• Both headphone outputs can be used simultaneously

Headphone output characteristics

• 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
• Particularly low distortion
• RCA loop output (bypass) for additional amplifier

Power supply

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

Housing and design

• All-metal chassis, protection against electromagnetic interference and vibrations
• Front panel and controls in machined aluminum
• Compact footprint
• Color options: silver or black front panel
• Dimensions (w × h × d): 103 × 37 × 120 mm
• Weight: 390 g (without power supply)