Pro-Ject Amp Box RS2
Pro-Ject Class AB power amplifier with tube input stage, usable in stereo or bridged mono to drive demanding speakers.
Description
The Amp Box RS2 is a power amplifier from Pro-Ject's RS range, designed to be paired with a preamplifier or a source already featuring a preamplification stage. It operates either in classic stereo configuration or in bridged mode to form a mono amplifier, allowing it to be adapted to different hi-fi system architectures.
Its electronic design is based on a fully discrete Class AB architecture, combined with a tube buffer input stage. In stereo, it delivers 2 x 130 W at 4 ohms and 2 x 80 W at 8 ohms (1% THD), with peak power of 2 x 160 W and 2 x 100 W respectively. In bridged mode, power reaches 350 W at 8 ohms. Frequency response remains below -0.2 dB between 20 Hz and 20 kHz, with harmonic distortion below 0.08% at 20 W at 4 ohms. The signal-to-noise ratio stands at 97 dBV (100 dBV A-weighted), with channel separation of -58 dB at 10 kHz at 4 ohms.
The power supply plays a central role in the design: it relies on a large toroidal transformer, shielded between primary and secondary windings, forming an isolation transformer that limits interference from the mains. The fully metal chassis, available in silver or black finish, also contributes to the unit's heat dissipation.
In terms of connectivity, the Amp Box RS2 offers a pair of RCA inputs and a pair of XLR inputs, with input impedances of 47 kΩ and 20 kΩ respectively, and a gain of 27 dB. Speakers connect via terminals accepting 4 mm banana plugs, spade connectors or bare wire. A 3-pin RS232 terminal block is also present for integration into a controlled system.
This amplifier is aimed at users who already have a preamplifier or a source fitted with a line output, and who want a power stage capable of driving demanding speakers in stereo, or of forming a pair of monoblocks in a bi-amplified configuration thanks to the bridged mode.
Technical specifications
| Output power | 2 x 130 W / 80 W at 4 ohms / 8 ohms (1% THD) |
| Bridged mode power | 350 W / 8 ohms (1% THD) |
| Peak power | 2 x 160 W / 100 W at 4 ohms / 8 ohms |
| Noise level | -73 dBV (-76 dBV A-weighted) |
| Frequency response | 20 Hz - 20 kHz: < -0.2 dB |
| Channel separation | -58 dB at 10 kHz at 4 ohms |
| Signal to noise ratio | 97 dBV (100 dBV A-weighted) |
| THD | < 0.08% at 20 W / 4 ohms |
| Gain | 27 dB |
| RCA/XLR input impedance | 47 kΩ / 20 kΩ |
| Line level inputs | 1 pair RCA, 1 pair XLR |
| Speaker terminals | 4 mm diameter banana plug, spade or bare wire |
| RS232 | 3-pin plug-in terminal block |
What to check before buying used
The tube input stage is worth checking at power-on: a noisy or crackling sound, or a missing channel, may indicate a worn tube or one not making proper contact in its socket. With a toroidal transformer of this size, a slight hum at idle is not abnormal, but a pronounced buzz should raise concerns about possible saturation or an earthing issue. It is also worth testing operation in bridged mode, which is often less used by the previous owner, as well as the condition of the banana plug speaker terminals.
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