A headphone amplifier with a balanced circuit throughout: RCA and XLR inputs, balanced outputs on 4.4 mm and 4-pin XLR, single-ended outputs on 3.5 and 6.3 mm, and up to 820 mW into 32 ohms.
Head Box S3 B: connections and power
Pro-Ject's Head Box S3 B is an amplifier dedicated to headphones, for the desk or for inclusion in a hi-fi system. The entire signal path is balanced, whether the source comes in through the XLR input or the RCA one: the aim is the greatest separation between channels with the least noise. Pro-Ject says it was designed by seeking an equilibrium between delivered power and perceived quality instead of chasing the power figure alone.
Balanced headphones plug into the 4.4 mm Pentaconn socket or the 4-pin XLR; conventional ones into the 3.5 mm and 6.3 mm sockets. Maximum power varies with the load: 480 mW into 8 ohms, 680 mW into 16 ohms, 820 mW into 32 ohms and 320 mW into 300 ohms, with headphones of 8 ohms upwards. The output stage uses two TPA6120A2 chips.
At the rear, next to the two inputs, an RCA loop pair passes the signal on to another component, so the amplifier slots between source and system without tying up an output. RS232 control is provided as well. The enclosure, aluminium all round, gives mechanical stability and screens the circuit. The power supply is an external 18 V unit.
Specifications
- Type: balanced headphone amplifier
- Maximum power: 480 mW into 8 ohms, 680 mW into 16 ohms, 820 mW into 32 ohms, 320 mW into 300 ohms
- Headphone outputs: 3.5 mm and 6.3 mm jacks, balanced 4.4 mm, balanced 4-pin XLR
- S/N ratio: above 115 dB A-weighted, at 1 kHz
- Distortion: below 0.002% at 1 kHz with a 500 mV input
- Crosstalk: better than -81 dB at 10 kHz
- Gain: 15 dB from the RCA input, 9 dB from the XLR input
- Bandwidth: 20 Hz to 20 kHz within 0.25 dB
- Analogue inputs: one RCA pair, one XLR pair
- Loop output: one RCA pair
- Headphone impedance: 8 ohms or higher
- Power supply: external 18 V / 1 A, mains 110-240 V at 50/60 Hz
- Standby consumption: under 0.5 W
- Size (WxHxD): 206 x 55 x 153 mm, 170 mm including sockets
- Weight: 950 g, power supply excluded
- Finishes: silver, black
