The TSD-PA20VG is a cost effective mono amplifier for 4? and distributed constant voltage speaker systems. Applications include hallways and classrooms. The TSD-PA20VG is also a cost effective alternative for small projector systems as it can be used with as many as (16) 25/70/100V ceiling speakers (tapped at 1W each), plus the extremely small footprint allows for easy mounting. For sound masking applications the TSD-PA20VG has the capacity to drive up to 34 masking speakers tapped at .5W each on a 70.7V line. Output is gain controlled from a potentiometer on the front panel with removable knob. Unit requires Power Supply that is sold separately for proper function, multiple TSDs can be powered with one power supply based on current requirements. You must use the TSD24V2500MA power supply. For multiple TSD applications use the TSD Power Calculator to determine the proper power supply needed. Features 4Ω/25V/70.7V/100V Output One (1) Balanced Input Removable Level Control with Set-It-And-Forget-It Security Cover Input Signal and Peak Indicator LEDs Cable Management System Removable Phoenix Style I/O Connectors Energy Efficient Compact Chassis Design Power Supply Sold Separately