What is phantom power and why do I need it?
So often we receive a frantic call from a church sound tech or a parent at a school play, both of whom once got caught standing too close to the mixing console and are now the “the sound person,” advising that their new, upgraded microphone is not working. The old mic works, but the new one does not, so what’s wrong with the new mic? This would seem like a legitimate and logical question, and you cannot fault them for coming to the conclusion that the microphone is broken. But our team has found that 999 times out of 1,000 the problem is phantom power.
Before jumping into the discussion of phantom power, let’s talk about a couple of the many types of microphones. One of the most common types is the dynamic microphone. A dynamic microphone does not need any type of external power to operate. Another type of microphone is the condenser microphone. A condenser microphone needs external DC power to operate. Depending upon the design of the microphone, this power may be supplied by a battery, bus power from a computer, as well as several other methods, but quite commonly it is supplied by phantom power.
Phantom power is DC voltage sent down the microphone cable to power the preamplifier of a condenser mic capsule and/or to provide a polarization charge to the back plate of the element. Most modern mixing consoles provide phantom power, as do external audio interfaces, certain audio recorders and video cameras. Please note, though, that not all of these devices are guaranteed to provide phantom power. You will need to consult the owner’s manual for your device to determine if it does. On most devices, phantom power can be turned on or off via switch, button or software. You may find this labeled as “+48V” instead of “phantom power.”
In order for phantom power to work, a balanced microphone cable must be used. A balanced mic cable has three conductors: Pin 1 is ground, Pin 2 is audio positive, and Pin 3 is audio negative. Most microphones produce a positive voltage on Pin 2 when sound pressure is applied to the diaphragm.
Phantom power is 9–52V DC applied across Pin 1 and Pin 2, and at the same time applied across Pin 1 and Pin 3. The term “phantom power” was assigned because taking a measurement across the two audio lines – Pin 2 and Pin 3 – you find 0 Volts DC. Also, even though this voltage is present on the same pins as the audio signal, it does not affect the mic signal.
It is important to note that every condenser microphone has its own power requirement, while each audio input device provides different levels of phantom power.