The Basics of Phantom Power for Microphones

If you've used any condenser mics in your home recording studio, you probably already know of the importance of phantom power. While a small number of condenser mics can be powered by other means (i.e. a battery), almost all used in studios use phantom power.

Those working with condenser mics may also have learned (the hard way) that not all audio interfaces and mixers have built-in phantom power. So we wanted to take a closer look at what phantom power is, how to use it and how it will affect your studio.

1. What is Phantom Power?

While we won’t go too far into the technical aspects of phantom power, the basics are that it is a positive voltage (from 12 volts to 48 volts DC) that runs on pins 2 and 3 in an XLR cable. The word phantom is used because the power source is essentially invisible, running through the same cord that the audio signal flows through. Many audio interfaces include a switch labeled P48 that turns phantom power on and off – the 48 standing for the highest voltage rating.

2. Why Do Condenser Mics Need Phantom Power?

Put simply, condenser microphones have active electronics that need an external power source, while dynamic mics are passive and therefore do not need phantom power. Because of the way condenser mics work, their output is very high impedance, and therefore requires a powered circuit to reduce that impedance.

3. Can You Use Phantom Power on Dynamic Mics?

Technically yes, but that doesn’t mean you should.

If you are running live sound, you probably won’t notice much of a difference if you have phantom power switched on for a dynamic mic. However, if you are recording, you may find that you pick up some additional hum due to the phantom power.

Additionally, because of the way the power flows through the pins of an XLR cord, a normally working mic and cable will not result in a dynamic mic being damaged by having phantom power turned on. However, if there happens to be an imbalance in the amount phantom power voltage being applied to each pin, the power can damage or destroy a dynamic mic. This is particularly true with ribbon mics (a type of dynamic mic), where an imbalance of power flow can destroy the ribbon in the mic.

4. Should You Turn Off Phantom Power Before Plugging in a Microphone

Yes, and you should also turn off power before disconnecting a mic. The loud pop that is produced when you do either of these actions can result in damage to your equipment (not just the microphones, but possibly your speakers, as well).

5. What Supplies Phantom Power?

Many audio interfaces and mixers have phantom power built in, though – as mentioned previously – some do not. If your audio interface does not include phantom power, you have a few options.

Among the most common is using a microphone pre-amp that supplies phantom power. This has the advantage of not only providing phantom power, but you also tend to have better quality inputs than many audio interfaces. Another option is to use an external power supply. You can check with your mics manufacturer to see what product they recommend, and they may make a power supply specifically for your mic.