All 3Dio FS series microphones contain a 9V battery inside as well as a 3.5mm stereo audio output jack. In addition to the 3.5mm output, the FS XLR & FS Pro II also contain 2 (two) XLR outputs, one for each ear.
9V Battery & 3.5mm Ouput - FS | FS XLR | FS Pro II
When using the 3.5mm output, the power switch of the 3Dio must be in the ON position. When the power switch is ON, the microphone capsules are powered by the 9V battery, which enables audio for the 3.5mm output only. When the power switch is turned OFF, the capsules no longer receive power from the 9V battery and therefore the audio for the 3.5mm output is disabled. The FS model will always require the power switch to be in the ON position because the 3.5mm output is the only output.
Phantom Power (48V) - FS XLR | FS Pro II
Phantom power is the name of a power source that comes from an external device. It is designed to provide continuous power (typically 48V or 24V) to a condenser type of microphone (like the 3Dio). Condenser mics, sometimes referred to as capacitor microphones, consist of a diaphragm that vibrates when sound waves hit it. As it vibrates, the distance between the diaphragm and the backing plate changes ever so slightly and these tiny changes in distance result in a varying capacitance. These tiny variations are converted into an electrical signal, which then requires power to boost the signal to an audible level. This is what phantom power does. It provides the necessary power to convert the tiny (but highly accurate) signal into a level that we can hear.
Most any device that accepts XLR inputs offers phantom power, including mixing consoles, audio interfaces, digital recorders and professional cameras. Although the audio signal travels from the microphone to the device, phantom power travels the opposite direction, from the device to the microphone. The XLR outputs of the 3Dio FS XLR & FS Pro II require phantom power in order to function. When using the XLR outputs, the 9V battery inside the mic is not used at all. When using the XLR outputs, we recommend turning the 3Dio power switch to the OFF position to preserve the battery life.
Even though some digital recorders and professional cameras offer phantom power, we do not recommend using the phantom power option with portable devices that run on battery because supplying phantom power wears down the batteries quickly. We only recommend using phantom power when the device providing the power can be plugged into a wall receptacle.