Усилители мощности моно — Pro-Ject Amp Box S3

The Amp Box S3 is a micro stereo power amplifier by Pro-Ject Audio Systems, designed and produced in Europe. Lacking any volume knob or input selector, it is meant to follow a preamplifier, streamer or DAC with variable output, driving a pair of loudspeakers from a box small enough to hide on a shelf. Pro-Ject based it on a new circuit board concept with what the maker describes as a sophisticated topology, and the casing is metal so that vibration and interference are kept away from the circuit. Two case colours exist, black and silver.

Key specs that matter

Continuous output is 2 x 23 W into 8 ohm and 2 x 40 W into 4 ohm, with a peak figure of 2 x 50 W into 4 ohm. Gain is 31 dB and the input impedance is 25 kOhm. Frequency response covers 20 Hz to 20 kHz within 0.7 dB into 4 ohm, and total harmonic distortion stays below 0.02 percent at 10 W into 4 ohm. Noise is rated at 87 dBV below signal, or 100 dBV A-weighted, and channel separation better than 68 dB at 20 kHz. The chassis is 103 x 36 x 118 mm and weighs 385 g, external supply excluded.

Engineering and use context

Signal enters through one RCA pair only. Speaker terminals take 4 mm bananas, spade lugs, pins and bare wire, which covers most cable terminations without adapters. A 12 V trigger input and output on 2.5 mm two-pole jack sockets make the amplifier start and stop along with a source or preamplifier and pass that command further along the chain. Power comes from an external universal supply rated at 20 V and 3 A, which keeps mains transformers out of the small case. With a width of just over 10 cm, the unit stacks with other components of the Box series that share the same footprint, and it can sit behind a display or inside a cabinet where a full-width amplifier would not fit.

Pairing

The fixed gain means the Amp Box S3 relies on an upstream component to regulate volume, such as a Box-line preamplifier, a network player whose output level is adjustable or a DAC fitted with a volume stage. The trigger link is useful when that source supports it, so the whole chain wakes together. Since the rated power rises markedly into the lower load, compact bookshelf speakers rated at the lower impedance suit it well, and higher sensitivity models make better use of the modest output in a room of around 20 m2.

Alternatives

The Pro-Ject Amp Box DS2 is another ultra-compact power amplifier from the same maker, placed in the DS line above the S3 series.