The USB Dual Pre is powered via the USB bus. An internal 9 Volt battery, or optional external 12V power supply (or any combination of USB, battery & power supply) can be used depending on application. When running powered by battery alone, you should expect in excess of 50 hours of operation with phantom power off. Battery life will drop to approximately 20 hours (depending on microphone) when phantom powering is engaged (still enough time to get through an average session). The built-in low noise +48 Volt phantom power supply allows you to power up to 2 microphones as well as the preamplifier when running from any power sources including the USB bus. For monitoring, an 1/8-inch TRS mini headphone jack with level and monitor mix controls on the rear allow for latency free local monitoring of the inputs while recording as well as playback monitoring of the USB bus. The monitor mix is also routed to the 1/4-inch TRS balanced outputs. This lets you use the 1/4-inch outputs as either preamplifier outputs or as the monitor feed to your powered monitors. The USB interface is fully compliant with the USB 1.1 specification and uses USB adaptive mode for playback and USB asynchronous mode for record. It will work with the USB audio device drivers built into Windows 98SE/ME/2000/XP/Vista and Apple OS9.1/OSX computers with native USB support. No special drivers are needed.