Фонокорректоры — Pro-Ject Tube Box S2

The Tube Box S2 is a compact valve phono stage from Pro-Ject Audio Systems in Austria, and the company names it as its very first product with a fully discrete circuit free of op-amps and the first to ship with user-replaceable tubes. It handles MM and MC cartridges, carried an MSRP of EUR 449 including VAT and USD 499 in the US, and comes with a choice of a silver or a black case.

Key specs that matter

A pair of ECC83 (12AX7A) triodes forms the valve section. Gain is switchable in five steps - 40, 43, 50, 60 and 63 dB. Pro-Ject specifies a noise floor of 80 dB A-weighted and THD under 0.02% at 40 dB, falling to 75 dB and under 0.05% at the MC gain positions. RIAA accuracy is held to plus or minus 0.4 dB between 20 Hz and 20 kHz. Loading choices for low output coils run from 10 ohm to 2 kohm, next to a fixed 47 kohm setting, and capacitance can be selected in six values from 47 to 587 pF. The subsonic filter acts at 20 Hz with 18 dB per octave. The rear carries one RCA input pair and one RCA output pair, all gold-plated. The chassis is 103 x 73 x 131 mm and weighs 410 g, and power arrives from an outboard 18 V, 1,000 mA DC supply, with a draw of 470 mA in use and under 1 W in standby.

Engineering and use context

Low noise starts at a FET input stage, and equalisation is split into a passive and an active section. Each channel has its own circuit in a dual mono arrangement to keep crosstalk down. Polystyrene capacitors appear wherever the designers could fit them. Behind the external adaptor, several internal regulators feed the stages, and the high-voltage anode rail for the valves gets heavy filtering. Since the two ECC83s are socketed, a listener can fit alternative 12AX7 variants later, which Pro-Ject presents as tube rolling. Rumble filtering and gain are selected by front buttons. The aluminium and steel sandwich case was styled to match the DS2 range and damps vibration while shielding against electromagnetic interference.

Pairing

With its highest gain setting the stage suits low output moving coils, and the adjustable resistance lets owners follow the load their cartridge maker recommends. High output MC models can simply use the standard MM load position. Its line level signal goes into any spare high-level input of an amplifier, preamplifier or receiver. Width and height equal those of the Tube Box E, so the two cases take up identical shelf space.

Alternatives

The Pro-Ject Tube Box DS3 B moves up to a true balanced dual-mono design with two E88CC valves, two phono inputs and gain up to 65 dB.