If the "Connect AC adaptor" warning is displayed on the top panel OLED, or the "USB current limit" warning (shown below) appears on the Mac desktop, connect the supplied AC adaptor between Duet's DC power input and a standard wall socket. The AC adaptor may be connected to any AC voltage between 100 and 240 volts AC, thus making it compatible with virtually any wall socket in the world. Also included with the AC adaptor are NEMA (North America), "Europlug" and British "BS 1363" plug adaptors.
Duet 2 is easily powered by any available USB port on your Mac in most applications. However there may be scenarios where connecting the external AC power adaptor is preferred or required.
There are two factors contributing to increased power consumption:
output volume into low impedance headphones
phantom power for condenser mics.
If you have Duet 2 set at a reasonable volume, you are not drawing that much power over the USB bus and you will be able to connect any microphones that require phantom power. When you are using low impedance headphones and your volume is very high you are drawing more power over the USB bus and may need the AC adaptor to use power hungry condenser mics.
Duet 2 has a sophisticated built-in power management system and will notify you with a message on its display when the use of the external power supply is recommended.
In extreme cases (fault conditions, like accidental full volume on headphones) Duet 2 will automatically reduce the headphone output in favor of continued use of phantom power such that a possible running recording session will not be interrupted.