Phantom Power: The Definitive A-Z Guide

by ReverbLxnd in Mixing

Here's everything you need to know about phantom power in music production and audio work in one detailed Q&A guide.

Today we are going to talk about phantom power — what it is, what it is used for, where to get it, how it works… everything.

If you’ve ever come across an audio interface, or mic preamp that has a little button that says 48v on it, you might be wondering what the heck it does.

Well, you probably know that you have to switch it to use condenser or other powered microphones.

Phantom powering is a very important technique to understand so that you don’t damage mics.

Let’s jump right in.

What is Phantom Power?

Phantom power is a term used in the professional audio industry, particularly in the context of microphones.

Phantom power is an industry-standard method of transmitting DC voltage over an audio cable to provide power to professional audio equipment. It’s called phantom power because it works by transmitting power using the same cable carrying the audio signal.

It provides simultaneous transmission of both the audio signal and power to the microphone or audio device over a single cable.

Phantom power is used to power the electronics within a microphone as well as for the small preamp found in electric microphone capsules.

Other low power audio devices, such as DI boxes and preamps can also be powered by phantom power.

How Phantom Power Works

You probably also know that most audio interfaces come with a 48v phantom power switch. It’s very simple, v is for volts, so that would be a 48-volt phantom power switch.

If you have a closer look at the XLR 3-pin connector, on an audio interface or console channel, with a voltmeter, pin 1 is the ground (the earth connection). That connects the (-)ve or black meter lead.

When you connect pin 2 with the phantom power switched off, you’ll get a zero reading on the voltmeter. Same with the bottom pin (pin 3).

When you switch the 48v phantom power on, you should get a reading of ~48v on the voltmeter, on either pin 2 or pin 3.

When you hit the phantom power switch, power comes off the microphone preamp or audio interface, up the mic cable, into the mic, and it charges the capacitor inside so that the condenser mic can work.

On some older designs and some very expensive microphones, there will be a transformer inside in place of a capacitor but the concept is the same.

That is what it is, it’s just power to your mic.

Which Mics Need Phantom Power?

In 4 types of microphones, we saw that moving-coil or dynamic microphones don’t need phantom power because they generate their tiny audio current by simple mechanical means, whereas condenser or capacitor microphones do.

In dynamic mics, a coil vibrates in a magnetic field generating the audio signal. That’s just the way the technology is for these types of microphones.

They don’t require any kind of additional power, you plug-in your typical XLR 3-prong mic cable, plug it into the preamp or console, or your audio interface, and you’re hot.

But when we come to the more complicated compressor mics, there’s a problem. When you pick up a condenser microphone and plug it in, turn up the preamp gain, you’re not going to get any signal. It will be muted until you hit the phantom power button.

You need phantom power to use a condenser microphone. That’s because they have an amplifier inside them. The amplifier has to be supplied with some sort of power to make it work.

There are two ways to supply this power—

  1. Some microphones have batteries inside them to supply the power. Batteries go flat, they leak and can wreck your mic, they can go down in the middle of a recording, they need to be replaced ever so often, and so on.
  2. Phantom power.

There are microphones available on the market which can be powered by both internal batteries and phantom power. It always recommended removing these batteries if you’re going to use phantom power.

This avoids damaging your batteries, mic, or both.

You need phantom power if you’re going to use a condenser mic. And you probably are going to use a condenser mic in your studio.

A large-diaphragm condenser mic is the type of microphone I would recommend if you could only get one mic for recording in your home studio.

It’s great for vocals, it’s great for guitars, drum overheads, it’s great for recording almost anything.

Where to Get Phantom Power

Phantom power supplies are frequently built into microphone preamps, commercial mixer amps, and mixing consoles.

The good news is just about every audio interface in every budget (even the ultra-budget interfaces in the $50 - 100 range) comes with phantom power as a switch or button you can click either physically or in a piece of software that comes with the interface.

You’re not out of luck, it a simple normal thing you have to turn on and off to use a condenser mic.

Separate phantom power supplies are also available if your mixer, audio interface, or preamp doesn’t have one.

Why is Phantom Power 48v

The most common phantom power supplies will typically supply voltage within the range of 12 to 48 volts and will be present on a balanced 3-pin XLR connector.

When a mic requires a supply outside this range, they will typically use a Jack plug rather than an XLR connector.

Professional mics that require phantom power, should show their required voltage range within the product specifications. This should be checked to ensure your phantom power supply is compatible.

Can Phantom Power Damage a Dynamic or Ribbon Mic?

Remember the XLR connector pins we were checking with our voltmeter earlier.

Now, you might think that this phantom power voltage will damage a moving-coil or dynamic mic connected across pins 2 and 3. But if you check the voltage across pins 2 and 3, there won’t be any.

The voltage is only between pins 2 and 3 and the ground (pin 1). No voltage exists across the signal path. That is why it’s called phantom power.

What does that mean?

That means that if there isn’t a direct connection between the signal path and the ground, then the phantom power will only where it’s supposed to go, which is to power the capacitor.

The capacitor will block the direct current (DC) from getting to the wrong part of the microphone.

Pins 2 and 3, of course, carry the audio signal.

When you are using microphones with phantom power, make sure that the cables you’re using are properly balanced ones with a standard two inner conductors and the outer screen.

If you use, even accidentally, an unbalanced cable with one inner conductor, your microphone won’t work and your risk damaging both the microphone and the mixer or audio interface.

You also need to check that your cable is in good condition. Faulty cables can wreak havoc with phantom power.

Another thing you need to pay attention to when working with phantom power is whether it’s on or off. When you’re plugging a microphone in or out, you want phantom power to be off.

You always want to plug a microphone into a preamp that doesn’t have phantom power on. Then you apply phantom power with the volume down and give it a minute or so.

It’s best to have the mic fully powered, you might not necessarily damage it if you don’t, but that’s a good habit.

When you’re done using the mic, shut off the phantom power, wait a minute or two to make sure the phantom power drains out (it takes a few minutes to drain the power you supplied to the mic).

If you don’t wait, know that that cable is carrying a little bit of power still.

Passive ribbon mics don’t like phantom power. Turn it off when you use them. It’s possible to damage them with phantom power.

If you don’t turn phantom power off, you might not necessarily damage the passive ribbon mic but it can happen if you’re careful. A bad mic cable is perhaps a bigger culprit than this though.

Best just to leave it off and wait for phantom power to drain. Remember it takes a minute to drain. Knock the habit of plugging mics hot, just to be safe.

Does Phantom Power Affect Sound Quality?

You may wonder whether if sending power over the same cable as the audio signal is going to affect sound quality.

Phantom power won’t affect your audio signal quality at all. However, it is important to make sure that you don’t use a phantom power supply on a microphone which doesn’t require it such a dynamic microphone to avoid any incompatibility issues.

In Conclusion

Now you should a pretty good idea of how to properly power down phantom-powered microphones.

Phantom power can be a pretty big issue in AV if done wrong. It can mean that you’re damaging gear.

For dynamic mics, there is no use for phantom power. You might not damage a dynamic mic with phantom power but you don’t need it.

For passive ribbon mics which are very fragile, they don’t like phantom power.

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ReverbLxnd

I've been a musician and brought in my stuff for mixing and mastering, I've been my own producer where I wrote, recorded, mixed and sold my own stuff. Now, I'm *mostly* an audio engineer, where I only record and mix for clients. I'm currently based in Berlin, Germany, where I operate ReverbLand out of. Got a question? DM me on Instagram or Twitter @reverblxnd everywhere, or shoot me an email reverblxnd@reverbland.com. I'd love to hear from you.

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