A valve phono preamplifier for MM and MC cartridges, dual mono and balanced, built around two E88CC/6922 valves: it connects two turntables and sets gain, capacitance and load impedance from the front panel.
TUBE BOX DS3 B: valves and settings
With the TUBE BOX DS3 B, balanced inputs and outputs join the valve phono stage formula that Pro-Ject has had in its range for many years. The circuit, the work of Dr. Sykora, uses two E88CC (6922) valves, chosen for low noise and low microphony, together with audio-grade parts such as polypropylene capacitors. Pro-Ject describes the result as a detailed bass combined with warm treble.
Two turntables can stay connected and be called up from the front panel, with the settings of each input held in memory. Gain runs from 40 to 65 dB in six steps, enough to suit very different cartridges and to match the turntable's level to that of other sources such as a CD player or streamer. Capacitance has four values, while load impedance is adjusted steplessly from 10 to 1000 ohms by a potentiometer, even during listening, to find by ear the right load for a given MC cartridge.
The turntable connects by a 5-pin mini XLR lead, by two XLR cables or by RCA. In a balanced link the signal travels on two conductors, hot and cold, carrying the same musical content: the preamplifier takes the difference between them and rejects whatever noise was picked up along the cable. Both RCA and XLR outputs are provided, the latter giving 6 dB more. A subsonic filter acts at 20 Hz with an 18 dB per octave slope, and power comes from an external 18 V supply.
Specifications
- Valves: 2 x E88CC / 6922
- Input impedance: continuously adjustable from 10 to 1000 ohms, or fixed at 47 kohms
- Capacitance: 50, 150, 300 or 400 pF
- Gain: 40, 45, 50, 55, 60 or 65 dB; 6 dB more from the XLR outputs
- Typical output voltage: 500 mV at 1 kHz for a 5 mV input (40 dB gain)
- Signal-to-noise ratio: over 87 dBV A-weighted
- Distortion (THD): below 0.03%
- RIAA accuracy: ±0.5 dB from 20 Hz to 20 kHz
- Subsonic filter: 20 Hz, 18 dB per octave slope
- Inputs: one 5-pin mini XLR, one XLR pair, one RCA pair
- Outputs: one RCA pair and one XLR pair
- Trigger: 12 V input and output
- Power: 18 V / 1000 mA DC; maximum draw 750 mA, standby under 0.5 W
- Dimensions: 206 x 70 x 194 mm (width, height, depth)
- Weight: 1560 g, power supply excluded
- Finishes: black, silver
