Préamplificateur phono Pro-Ject Tube Box S2

Following the undeniable success of its compact Tube Box S tube phono preamp, the Austrian manufacturer is introducing an updated version of its best-seller.

Pro-Ject Tube Box S2: Chassis

At first glance, the Pro-Ject Tube Box S2 phono preamp doesn’t seem very different from its predecessor.

But a trained eye will immediately notice that the chassis has changed. The previous version featured a brushed aluminum front panel (black or natural) mounted on a black steel chassis.

The Tube Box S2, on the other hand, features a chassis made of a sandwich construction of anodized aluminum and steel.

Of course, this gives it a more “high-end” look, but it also provides better immunity to radio waves and various electromagnetic disturbances.

Pro-Ject Tube Box S2: Front Panel and Settings

The front panel features a power button, as well as a button to activate the subsonic filter (20 Hz at 12 dB/octave).

The major new feature compared to the previous Tube Box S is the inclusion of two switches on the front panel that allow you to select from six gain settings (40, 43, 50, 53, 60, 63 dB).

Part of the gain is provided by ECC83/12AX7 tubes (one per channel). These can be replaced with various models from different manufacturers to modify the preamplifier’s sound signature according to individual preferences.

Its adjustable gain, load impedance, and capacitance settings allow for a wide range of combinations with MM and MC cartridges, even those at the very high end… In fact, the Tube Box S2 is fully compatible with all moving-magnet (MM) cartridges and the majority of moving-coil (MC) cartridges.

Pro-Ject Tube Box S2 Switches

On its rear panel, you’ll find the standard gold-plated RCA input/output connectors and a knob for grounding.

Pro-Ject Tube Box S2: Electronics

The internal architecture is fully dual-mono, enabling highly precise stereo reproduction and a precise soundstage. The RIAA equalization is based on a dual-circuit design: one part is active, and the other is entirely passive.

The Tube Box S2 is the first Pro-Ject phono preamp designed entirely around discrete components. Pro-Ject has not used any integrated circuits (op-amps) here.

The input circuit relies on “FET” transistors selected for their extremely low noise and lack of distortion.

All capacitors are made with polystyrene technology.

No electrolytic capacitors were used in the audio signal path.

Pro-Ject Tube Box S2: Power Supply

The Tube Box S2 is powered by an external power supply providing a DC voltage of 18 V. This allows the unit to eliminate the need for a rectifier and filter circuit. However, several voltages are processed internally, regulated, and stabilized for the various parts of the circuit.

Pro-Ject Tube Box S2: Rear View

Pro-Ject Tube Box S2: Review and Listening Impressions

The initial measurements provide a fairly clear picture of the performance of this Tube Box S2 phono preamp.

It retains the tonal quality and definition of its predecessor. But the overall transparency and precision of the soundstage have improved significantly.

With complex recordings, it demonstrates authority while also offering plenty of nuance and finesse when needed.

There is no sense of frustration and, above all, no harshness or aggression in the high frequencies.

The tubes perform their role perfectly in terms of timbre and harmonic richness, without adding any coloration, as is often the case with this type of device.

Pro-Ject Tube Box S2: Unboxing

Setting up and adjusting this phono stage is very simple and poses no problems, as long as you have the specifications of the phono cartridge.

We recommend waiting about ten minutes after turning on the unit to fully appreciate its qualities.

Also, be careful not to be tempted to increase the gain more than necessary in an attempt to match the volume level of a digital source.

This will result in an aggressive sound and possibly even some distortion.

The Pro-Ject Tube Box S2 phono preamp is undoubtedly the current “best-seller.” In many respects, it performs just as well as many units costing twice as much.

FAQ: Everything you need to know before buying the Pro-Ject Tube Box S2

Which cartridges is the Tube Box S2 compatible with?

It is fully compatible with all moving magnet (MM) cartridges and with most moving coil (MC) cartridges, even high-end ones. To that end it offers six gain values selectable on the front panel (40, 43, 50, 53, 60 and 63 dB), plus adjustable loading and capacitance values, allowing a wide choice of pairings.

Can the preamplifier's sound be tailored?

Yes. Part of the gain comes from ECC83/12AX7 tubes, one per channel, which can be swapped for several models from different makers. Changing tubes lets you alter the sonic signature to taste. The rest of the input stage uses FET transistors chosen for very low noise and freedom from distortion.

How are the settings made?

The front panel gathers the essentials: a power button, a switchable subsonic filter (20 Hz at 12 dB/octave) and two switches to select the six gain values. The rear panel carries gold-plated RCA inputs and outputs plus a ground terminal. Setup stays simple once you know your cartridge's specifications.

Is a warm-up time needed before listening?

Yes. It is advised to wait around ten minutes after switch-on to fully appreciate its qualities. It is also recommended not to raise the gain more than necessary to match a digital source's level, as this can lead to an aggressive sound or even some distortion. The RIAA correction combines an active and a passive section, in a dual-mono layout.