The Tube Box S2 is a valve phono preamplifier for MM and MC cartridges: two replaceable ECC83s, a discrete dual-mono circuit free of op-amps, and gain and subsonic filter controls on the front panel.
Tube Box S2: valves and adjustments
Pro-Ject presents it as its first unit with an entirely discrete circuit, with no operational amplifiers, and as the first whose valves the owner can swap: the two ECC83s (12AX7A) may be replaced with others of the same type to steer the character of the sound. The maker describes a full, relaxed presentation with a rich midrange.
The input stage uses low-noise FETs and the layout is dual mono, to keep the two channels apart. RIAA equalisation is done in two parts, one passive and one active, and stays within 0.4 dB between 20 Hz and 20 kHz; polystyrene capacitors are fitted wherever possible. Power starts at an external 18 V adaptor and continues through several internal sections, among them a well-filtered high-voltage anode supply.
The range of adjustment is wide. Gain is set on the front to 40, 43, 50, 60 or 63 dB; the input load can be 10 ohms, 100 ohms, 1 kohm or 2 kohms besides 47 kohms, and capacitance has six values lying between 47 and 587 pF. The subsonic filter, also on the front, acts at 20 Hz, 18 dB per octave. The RCA inputs and outputs are gold-plated and the aluminium and metal sandwich case keeps out vibration and electromagnetic interference.
Specifications
- Type: valve MM/MC phono preamplifier
- Valves: 2 x ECC83 (12AX7A), replaceable
- Load impedance: 10 ohms, 100 ohms, 1 kohm, 2 kohms or 47 kohms
- Input capacitance: 47, 147, 267, 367, 487 or 587 pF
- Gain: 40, 43, 50, 60 or 63 dB
- Noise: 80 dB(A) at 40 dB of gain, 75 dB(A) at 50 and 63 dB
- Harmonic distortion: under 0.02 % at 40 dB, under 0.05 % at 50 and 63 dB
- RIAA accuracy: ±0.4 dB from 20 Hz to 20 kHz
- Subsonic filter: 20 Hz, 18 dB per octave
- Input: one pair of gold-plated RCA sockets
- Line output: one pair of gold-plated RCA sockets
- External power supply: 18 V DC, 1000 mA
- Current draw: 470 mA DC, under 1 W on standby
- Weight: 410 g, power supply excluded
- Size (width x height x depth): 103 x 73 x 131 mm including sockets
- Finishes: black, silver
