The D SERIES-HPA3 is a high efficiency 3.5 W power amplifier with one line input, an amplified output to drive a 4 or 8 ohm speaker and a separate headphone amplifier. The -HPA3 features a balanced line level input that may be connected unbalanced. The gain range will accommodate standard unbalanced levels as well as professional balanced levels. The amplified output levels are controlled by a front-panel volume control.The amplifier features a Mini-Jack headphone output on the front panel. When a headset is plugged in, the power amplifier may be switched off. Two recessed slide switches located on the top of the rear enclosure are set prior to mounting the module. One switch is provided for setting the input sensitivity. The mute switch determines whether the power amplifier operates when headphones are plugged in.Amplification for the speaker output is provided by a high-efficiency Class D power stage with audio filtering tailored for crisp, pleasant audio clarity. The high-efficiency Class D output stage produces negligible heat for all levels of expected voice or music modulation.The D SERIES-HPA3 is designed to be mounted in a wall box. The front panel does not include any illuminated indicators, making the -HPA3 ideally suited to installation in dark rooms or areas. Wiring is connected through a rear-panel detachable terminal block. Module operation is from a 24 Vdc ground-referenced power supply.