Specifically designed for telephone paging, the TPU Series of amplifiers offers a choice of rated power output from 15 to 250 W. Input terminals are provided for a 600-ohms balanced telephone line and a background music source, as well as a balanced low-impedance microphone in the TPU-250, TPU-100B, TPU-60B and TPU-35B. Bridging jacks which double your outputs are also provided. The built-in night ringer sounds a tone through the paging system speakers when triggered by an external contact closure. Voice-activated circuitry automatically mutes or fades music when paging, eliminating mechanical and background noise. The TPU amplifiers also feature the Aphex Aural Exciter circuit for increased presence and intelligibility, greater perceived loudness (with no increase in power) and reduced listener fatigue. The compact units mount easily on a wall and only a screwdriver is needed for all connections and adjustments. UL and CSA Listed.