A valve phono preamplifier for MM and MC cartridges, using two ECC83s and a balanced circuit: a 5-pin mini XLR input alongside RCA, XLR and RCA outputs, with impedance, capacitance and gain selectable on the front panel.
Tube Box S3 B: valves and balanced input
The Tube Box S3 B entrusts the turntable signal to two ECC83 valves, also known as 12AX7, and aims for the warmth typical of this technology. The B in the name indicates balancing: the gain stage is symmetrical and discrete, the input is a 5-pin mini XLR and the outputs are on XLR, with RCA sockets as the alternative both in and out.
In a balanced link the same musical information runs along two conductors, one positive and one negative. The gain stage recovers the music from the difference between them and cancels any noise that was added to both on the journey. This requires two distinct amplifying sections for every channel, an uncommon choice in equipment of this class. With a Pro-Ject True Balanced phono cable and an MC cartridge the advantage is exploited in full.
Gain runs from 40 to 65 dB in four steps, making it possible to even out the turntable volume against a CD player or a streamer. Loading spans impedances from 10 ohms to 47 kohms and capacitances from 50 to 400 pF: the lowest values help in particular cases, such as leads with high capacitance. The settings for each input stay in memory. The chassis is steel and aluminium and the power supply is an external 18 V unit.
Specifications
- Type: balanced valve MM/MC phono preamplifier
- Valves: two ECC83 (12AX7 type)
- Input impedance: 10, 50, 100 ohms, 1 kohm, 47 kohms
- Input capacitance: 50, 150, 300, 400 pF
- Gain: 40, 45, 60 or 65 dB (6 dB more from the XLR outputs)
- S/N ratio, MM at 40 dB: 97 dBV, 105 dBV A-weighted
- S/N ratio, MC at 60 dB: 83 dBV, 88 dBV A-weighted
- Distortion at 1 kHz: below 0.005% (MM) and 0.01% (MC)
- Distortion 20 Hz - 20 kHz: below 0.1% (MM) and 0.03% (MC)
- RIAA accuracy: within 0.4 dB from 20 Hz to 20 kHz
- Subsonic filter: 20 Hz, 18 dB per octave
- Inputs: one 5-pin mini XLR, one RCA pair
- Line outputs: one RCA pair, one XLR pair
- Power supply: external, 18 V / 1000 mA DC
- Consumption: 800 mA at 18 V; standby under 0.5 W
- Size (WxHxD): 206 x 81 x 153 mm, 164 mm including sockets
- Weight: 1.01 kg, power supply excluded
- Finishes: black, silver
