Pro-Ject Amp Box S Mono This compact mono power amplifier achieves both a sound quality and SPL output that belies its small size. Designed around a Bi-Phase PWM (Pulse-Width Modulation) digital amplifier circuit, the Amp Box achieves a remarkable 80% operational efficiency and a highly dynamic 60 watts output into 4 ohms. This combination of small size and efficiency makes the Amp Box Mono ideal in Bi or Tri-amplification system applications. Additionally, a trigger signal can remotely switch the amplifier or amplifiers on/off and a Power-On cable is supplied for relaying on/off trigger action to additional units. The shielded metal chassis protects the circuitry from vibration and electromagnetic interference for the highest fidelity possible.