Phantom power: what it is, when you need it and how to use it

Perhaps you’re looking at the specs of a mic and you’ve noticed that it requires something called ‘phantom power’… Or maybe you’ve seen a button on your audio interface labelled ‘48v’ and you’re wondering what it does… In this lesson, we’ll learn what 48v phantom power is, when you need it and how to use it.

What is phantom power?

48v phantom power, sometimes referred to as 48v, is a means of sending direct current (DC) from an audio interface, mixing desk or pre amp to a piece of equipment which requires power to operate. The most common piece of equipment that we use in home studios which requires phantom power is a condenser microphone. There are also some DI boxes which require 48v. Phantom power is sent to the device from the interface via a balanced XLR cable, the same one used to send the audio signal from the device to the interface. Your interface will usually have a button labelled 48v which is used to switch phantom power on and off.

Phantom power and mics:

As we’ve already established, condenser mics require phantom to function. That’s because they contain active circuitry. The same is true of active ribbon mics which also require phantom power to operate. Because dynamic mics and passive ribbon mics do not contain active electronics, they do not require 48v.

So, what do you do if, like most of us, your audio interface only allows you to turn on 48v globally. In this case, you can either switch it on for all connections, or none at all. But how does this work if you want to use a combination of condensers, dynamics and/or ribbons at once? Let’s establish a few guidelines.

Old/vintage mics:

When it comes to old/vintage ribbon mics and even some older dynamic mics, sending phantom power to them could very likely cause damage. As such, it’s important to do some research into a specific vintage mic. Make sure it’s absolutely safe to use that mic with 48v switched on before connecting it. If you are in any doubt, don’t connect it, as the risk for damage is high, particularly with ribbon mics.

Modern mics:

With newer dynamic and ribbon mics, the vast majority are designed to accept 48v despite not requiring it to function. Their ability to handle 48v will usually be stated in their manual. So double check there if you have any concerns.

That said, there are a few instances when even a modern ribbon could be damaged if presented with 48v. Connections made through mis-wired cables, damaged/worn out cables, or damaged/worn out cable connectors are one cause. Additionally, a mic could be damaged if you connect or disconnect it from your interface with phantom power already switched on, rather than connecting/disconnecting the mic before switching phantom on or off. Also, making connections between mics and your interface/desk/preamp via a patch bay with phantom power switched on can cause damage. That’s because, when TRS cables are inserted or removed from the patch bay in order to route signals, power can momentarily be shorted (i.e. routed along an unintended path) to the ribbon mic’s element.

48v best practices:

With the above in mind, there are a few codes of best practice to follow to protect your mics when working with phantom power… Be sure that your cables are properly wired and in a good state of repair. Make sure that you turn phantom off before connecting or disconnecting mics. Not just ribbons, but condensers too. This will protect not only your mics, but also your speakers and your ears as well. Also, be sure that phantom power is switched off before you do any routing on a patch bay. Finally, when it comes to vintage ribbon mics or dynamic mics, do some research before connecting them to an interface which is outputting 48v to be absolutely sure that the mic can handle it. If in any doubt, don’t connect it.