Усилители мощности стерео — Pro-Ject Amp Box RS

The Amp Box RS is a stereo power amp built by Austria's Pro-Ject Audio Systems, placed in its RS range of compact Box Design electronics. Pro-Ject lists four defining traits - a fully balanced double mono layout, energy-saving PWM output modules, a valve buffer at the input and an upgrade route to an external linear supply. The MSRP was EUR 899 including VAT, in black or silver finishes.

Key specs that matter

Output is 2 x 110 W into 8 ohm and 2 x 180 W into 4 ohm, and the amplifier is specified as able to drive 2 ohm loads. THD stays under 0.05% at 100 W, while the IEC-A weighted noise figure is better than 100 dB. Frequency response spans 10 Hz to 50 kHz inside minus 3 dB. The damping factor is 400 into 8 ohm and 200 into 4 ohm. Input sensitivity is 1.35 V and input impedance 22 kohm, on either RCA or XLR sockets. The case measures 206 x 72 x 200 mm, or 220 mm deep including the rear sockets, and weighs 2,120 g without the outboard 48 V, 2.5 A DC adaptor. Standby draw is below 1 W.

Engineering and use context

Two ECC88 (6922) double triodes form the buffer stage ahead of the switching modules, so the valves handle the incoming line signal while the PWM stages do the power work. Pro-Ject gives a conversion efficiency from mains to output of 92%, which keeps heat and energy use low for the power on offer. Surface mount components keep signal paths short, and each channel runs as a separate balanced circuit. The optional PS Box RS linear power supply raises the rating to 2 x 180 W into 8 ohm and 2 x 250 W into 4 ohm. Loudspeaker cables can end in 4 mm bananas, spades or simply stripped wire. The metal enclosure guards against vibration and interference, yet the maker warns that the heat it gives off means it should not be placed inside the Design Box Acryl cover. Mains input on the adaptor covers 100 to 240 V at 50 or 60 Hz.

Pairing

Pro-Ject names the Pre Box RS as the intended partner, and the XLR inputs allow a balanced link from any preamplifier that offers one. The low-impedance capability and high damping factor suit speakers with low impedance dips, and the company points to bi-amping or tri-amping, where two or three units drive separate driver sections of a speaker with split terminals.

Alternatives

The Pro-Ject Amp Box DS2 is another two-channel Box Design power amp with lower output.