Pro-Ject - Tube Box S2

Two ECC83 valves, five gain settings, front-panel loading switches and a regulated high-voltage anode supply, in a box you can hold in one hand.

The Tube Box S2 puts a pair of ECC83 double triodes — the same bottle you will see written as 12AX7 on American equipment — in the gain stage of a phono preamplifier, and gives them a properly filtered, regulated high-voltage anode supply rather than the running-on-fumes arrangement that lets some budget valve gear get away with the word ‘tube’ on the front.

Practically, the important difference from the solid-state Phono Boxes is that the loading switches are on the front panel. You do not need to unplug the box and turn it upside down to change impedance or capacitance; you reach round the front and change it while the record plays. For anyone who actually experiments with cartridge loading, that is worth a great deal.

Gain runs 40, 43, 50, 60 and 63dB, covering moving-magnet through low-output moving coil. Impedance and capacitance are both switchable, and there is a subsonic filter at 20Hz. The valves sit in sockets, so replacing them is straightforward when they eventually go soft — though Pro-Ject does not market or endorse valve rolling as such, and we would not encourage anyone to go chasing exotic New Old Stock on the assumption that it is a supported use.

We have to be straight with you about the published numbers on this one. Pro-Ject’s web page and their own PDF datasheet disagree with each other on more figures than on any other product in this range: the impedance step count, every capacitance value (by 3pF each), the signal-to-noise ratio, the distortion figure, the subsonic filter slope and one of the dimensions. Both are manufacturer sources. We have listed both values wherever they differ, rather than choosing one and presenting it as settled.

Features

• Two ECC83 / 12AX7 valves in the gain stage, in sockets
• Regulated, filtered high-voltage anode supply
• Loading and gain switches on the front panel — adjustable while playing
• Five gain settings from 40 to 63dB, covering MM through low-output MC
• Switchable input impedance and capacitance
• Subsonic filter at 20Hz
• Gold-plated RCA in and out

Specifications

• Type: Valve moving-magnet and moving-coil phono preamplifier
• Valves: 2 x ECC83 (12AX7A / 12AX7), socketed and user-replaceable. Pro-Ject does not explicitly market valve rolling as a supported feature
• Gain: 40 / 43 / 50 / 60 / 63dB per the PDF datasheet. The web page lists the same values in a garbled format
• Input impedance: The PDF gives 10 / 100 / 470 / 1k / 2kΩ plus a fixed 47kΩ. The web page omits the 470Ω step and lists 10 / 100Ω / 1k / 2kΩ plus fixed 47kΩ. The two manufacturer sources do not agree
• Input capacitance: The PDF gives 50 / 150 / 270 / 370 / 490 / 590pF. The web page gives 47 / 147 / 267 / 367 / 487 / 587pF. Every value differs by 3pF between Pro-Ject’s own two documents
• Where the controls are: Front panel, switchable while the unit is in use
• Signal-to-noise ratio: The web page gives 80dB A-weighted at 40dB gain and 75dB at 50 and 63dB gain. The PDF gives a single unqualified figure of 77dBA. The two do not agree
• THD: The web page gives less than 0.02% at 40dB gain and less than 0.05% at 50 and 63dB. The PDF gives a single figure of less than 0.0025%. This is a substantial disagreement between two manufacturer documents and we are not going to resolve it for them
• RIAA accuracy: ±0.4dB, 20Hz–20kHz. Both sources agree
• Subsonic filter: 20Hz. The web page gives 18dB per octave; the PDF gives 12dB per octave
• Alternate EQ curves: None. RIAA only
• Channel separation: Not published. Pro-Ject publishes no channel separation or crosstalk figure for any product in the Phono Box or Tube Box range.
• Inputs: 1 pair gold-plated RCA
• Outputs: 1 pair gold-plated RCA
• Power supply: External adapter, 18V DC / 1,000mA, feeding an internal regulated high-voltage anode supply for the valves
• Dimensions: 103 x 73 x 131 mm (W x H x D) on the web page; 103 x 73 x 119 mm in the PDF
• Weight: 410g without the power supply
• Country of manufacture: Not published for this model
• Warranty: Two years from date of purchase, extendable to three years by registering the product with Pro-Ject and subscribing to their newsletter. Pro-Ject states that warranty is administered by the local distributor and that terms can vary by region; no separate United States term is published. Coverage requires purchase from an authorised dealer — The ’In Groove is one.