Phantom power is a power supply required by condenser microphones. The 48 volt DC power is transmitted through the microphone cable from the preamp — it does not impact the audio signal being returned from the mic.

The mic preamps found in most audio interfaces and mixing desks are capable of supplying phantom power. If you’re planning to use a condenser microphone and find that your audio interface doesn’t have phantom power, you should consider changing to an interface or mixing desk that does, or invest in standalone mic preamps and/or channel strips.

Why is phantom power needed?

Condenser mics are sometimes referred to as capacitor mics; this is because of the method they use to convert sound waves into an electrical signal

The capsule in a condenser mic (which is responsible for capturing audio signals) consists of two thin circular metal plates placed very close together.

Sound waves hitting these plates cause the gap between them to fluctuate in sympathy, and this in turn causes fluctuations in the electrical capacitance measured across the plates. This varying capacitance is then converted into the varying voltage of an audio signal. This only works if the plates are charged, hence the need for phantom power.

Is phantom power dangerous?

The maximum current phantom power can supply is 14.1mA. This is a very low current that’s not strong enough to give you a serious electric shock, but you should still treat it with the same caution and respect as you do all other power supplies.

For maximum safety, only engage phantom power when it’s needed, and when the mic cable is connected at both ends. Also, always disengage phantom power before disconnecting the mic cable.

Many of the devices we use in the studio — in particular digital gear such as synths and effect processors — can be badly damaged by 48v arriving at their output connectors. You should take great care to ensure phantom power never makes its way to these devices. The easiest way to do this is to never connect a line signal directly to an XLR mic input; when you have no choice, never use a jack-to-XLR cable and always go via a DI box, as this will block any phantom power from reaching the line device.

Also be aware that interfaces, preamps and similar gear that has combined XLR/jack input sockets have the potential to spill phantom power into the jack portion of the connector. They shouldn’t, but do you want to bet your classic Korg M1 on it? Proceed with caution and, if in doubt, connect via DI boxes.

My mic has its own power supply. Does it still need phantom power?

Some high-end and specialist mics need more than phantom power’s standard 48v, and these always come with their own power supply. When using such a mic, you should not need to engage phantom power on the mic’s input channel.

There’s also a mic design called back-electret that works similarly to a condenser mic, but requires much less power and so can usually be powered by a standard battery – the AKG C1000 is a well-known example. Such mics can also be powered by phantom power, and this is often the better option because, when running from a battery, mic responsiveness can change as the battery’s charge falls.

Learn more music technology terms in our Glossary.

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