Pro-Ject Amp Box S3
Ultra-compact class D stereo power amplifier, designed by Pro-Ject to drive desktop or small-room speakers.
Description
The Amp Box S3 is a stereo power amplifier from Pro-Ject, designed to take up as little space as possible while delivering sufficient power to drive compact speakers. It positions itself as a supplementary link or a minimalist amplification solution, rather than a full integrated amplifier, as it is limited to a single RCA stereo input and two speaker outputs.
Its operation relies on class D amplification, a technology recognised for its energy efficiency and compactness, combined with a TPA3221 chip recently integrated by the manufacturer. The circuit board has been redesigned, going from two to four layers, which shortens the signal path and results in improved crosstalk, an enhanced signal-to-noise ratio and reduced distortion. Rated power reaches 2 x 23 W at 8 ohms and 2 x 40 W at 4 ohms, with a frequency response of 20 Hz to 20 kHz and a total harmonic distortion rate below 0.02% at 10 W into 4 ohms.
The chassis is made of shielded aluminium, a design that protects the internal components from vibration and electromagnetic interference, contributing to the stability of the delivered signal.
This model is aimed at music enthusiasts looking for a discreet amplification solution for a desk, a small room or a supplementary system, particularly for driving active or passive speakers with low to medium power requirements.
Technical specifications
| Type | Stereo power amplifier |
| Power output | 2 x 23 W at 8 ohms, 2 x 40 W at 4 ohms |
| Amplifier class | Class D |
| Frequency response | 20 Hz to 20 kHz |
| Total harmonic distortion | < 0.02% (10 W at 4 ohms) |
| Signal to noise ratio | 87 dB (100 dB-A weighted)/4 ohms |
| Inputs | 1 RCA stereo input |
| Outputs | 2 speaker outputs |
| Input voltage | 20 V/3 A DC |
| Input impedance | 25 kohms |
| Output impedance | 8 ohms |
| Dimensions (H x W x D) | 36 x 103 x 118 mm |
What to check before buying used
The class D amplification chip and the external 20 V power stage do not cope well with electrical surges: an unsupplied or undersized power adapter may have worn down the capacitors. Check the volume potentiometer, which is often prone to crackling or track wear after several years of use. Also check the condition of the RCA input and speaker outputs, whose contacts can oxidise, as well as the aluminium chassis shielding, which must remain securely fixed to continue protecting the signal from interference.
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