With the Phono Box S2 Ultra, Pro-Ject offers a phono preamplifier for MM and MC cartridges built purely from discrete parts, with no op-amps anywhere, and with switchable gain, input impedance and input capacitance.
Phono Box S2 Ultra: the circuit
Pro-Ject has brought the design first seen in the Phono Box Ultra 500 into its S2 range. The circuit does without operational amplifiers altogether and relies on discrete parts only, backed by polystyrene capacitors, a type held in high regard for phono stages. RIAA equalisation is split into two sections, which lets the unit track the curve to within 0.4 dB between 20 Hz and 20 kHz.
The adjustments make it a match for very different cartridges. Input impedance can be set to 10 ohms, 100 ohms, 1 kohm or 47 kohms, capacitance to 100 or 220 pF, and gain has four positions (40, 43, 60 and 63 dB) to move from MM to MC. A subsonic filter can be switched in, cutting 18 dB at 20 Hz.
The solid metal enclosure keeps interference away from the electronics. Connections are on RCA sockets and power comes from an external 18 V supply; those who wish can move up to the Accu Box S2, which Pro-Ject lists as the compatible upgrade supply. The maker quotes a signal-to-noise ratio of 89 dB for MM and harmonic distortion of 0.00052 %.
Specifications
- Type: discrete MM/MC phono preamplifier
- Signal/noise: 89 dBV (MM)
- Load impedance: 10 ohms, 100 ohms, 1 kohm or 47 kohms
- Input capacitance: 100 or 220 pF
- Gain: 40, 43, 60 or 63 dB
- Subsonic filter: switchable, -18 dB at 20 Hz
- Harmonic distortion: 0.00052 %
- RIAA accuracy: within 0.4 dB from 20 Hz to 20 kHz
- Connections: RCA input and output
- External power supply: 18 V DC, 500 mA
- Current draw: 80 mA at 18 V
- Weight: 570 g, power supply excluded
- Size (width x height x depth): 103 x 37 x 119 mm
- Finishes: black, silver
