Applies to all Focusrite preamps and interfaces

48V phantom power is 48 volts of electricity supplied through an audio cable that can power certain microphones as well as some other equipment that uses it.

Modern balanced microphones can broadly be separated into three categories: dynamic, condenser and ribbon. All condenser mics require electrical power to function, as do active ribbon mics, but normal dynamic mics do not.

On Focusrite preamps and interfaces, when you turn the 48V button on, phantom power is sent to the XLR mic inputs that the button controls.

48V phantom power is not sent to any 6.35mm (¼″) jack inputs or other inputs; these are instrument or line inputs.

Can 48V phantom power damage my equipment?

48V phantom power can damage your equipment if it is not designed to receive it:

• Equipment other than mics may be damaged by 48V if it is connected directly to your mic inputs.
• Older unbalanced mics will be damaged by 48V (modern, XLR coupled mics are largely balanced and protected against 48V).
• Supplying 48V power through non-XLR patch bay channels can potentially damage both the preamp and connected microphones.

Check the user guide or contact the manufacturer for any equipment if you do not know if it will be damaged by 48V.

What are the main types of microphone and do they use phantom power?

Dynamic

Dynamic mics convert sound energy into electrical energy using a diaphragm linked to a coil of wire that moves through a magnetic field. This movement through the magnetic field generates a voltage, which is proportional to the sound waves being received at the diaphragm.

This process does not require external electrical power like 48V phantom power. However, there are a few dynamic mics that have some amplification built into them that does require 48V in order to function.

Condenser

The capsules found in condenser mics — also sometimes referred to as capacitor or electrostatic microphones — consist of a thin membrane or diaphragm in close-proximity to a solid metal plate. Sound pressure waves move the diaphragm back and forth relative to the solid backplate.

As the capsule is too fragile to connect directly to other audio equipment, and it outputs almost no electrical current, active circuitry is needed to amplify the signal. Condenser mics require a DC power supply transmitted through an XLR cable in order to operate the active components used; therefore, a voltage is sent down the XLR cable to power the mic.

This voltage is referred to as phantom power, most commonly 48 volts. Note that the mic's signal will still need pre-amplification; the phantom power supply is simply there to power active electronic components.

Ribbon

Ribbon mics use a thin metal ‘ribbon’, often made of aluminium, placed between a pair of magnets that convert sound energy into electrical energy. In general, ribbon mics are passive so do not require phantom power. However, there are some active ribbon mics that do require phantom power.

Ribbon mics, especially vintage models, can be damaged by phantom power, so you should contact the mic manufacturer or check the user manual before connecting them.

What other uses for phantom power are there?

Besides mics, there are other types of equipment that may use 48V phantom power. This will be indicated on the equipment itself or in the user guide. 

Other equipment that might use 48V phantom power includes the following:

• Active DI boxes (direct boxes) — These are generally used to convert various signals into balanced mic level.
• Mic activators, inline preamps, and FET amps (e.g. Cloudlifters) — Used to provide additional amplification to low-sensitivity mics; occasionally they can be built-into a mic.
• Built-in guitar or bass preamps — These act like a DI box but often include more features.
• Acoustic-electric guitars (electro acoustic guitars) — Some acoustic guitars may have an XLR output through which 48V power can be supplied to a built-in mic or pickup.

What's best practice when using phantom power?

Best practice is to make sure phantom power is turned off before connecting or disconnecting your mics or other equipment from mic inputs, then only engage phantom power on mic channels that need it once they are connected.

If your mic preamp does not have a dedicated 48V button on each input, there may be a global phantom supply switch, or phantom might be switchable in banks, for example channels 1-4 and 5-8 on an eight-channel interface.

When phantom power is supplied in banks, you should take care to ensure that any equipment potentially vulnerable to it is not connected to an input within a bank receiving phantom power — bear in mind that only the XLR portion of the input is supplied with phantom power on Focusrite preamps and interfaces.

Using phantom power with a dynamic mic should not damage the mic, but it is rarely needed.

A condenser mic will not be damaged if phantom power is not engaged, though it will not produce any signal without it.

The Focusrite CM25 microphones from the Scarlett and iTrack Studio are condensers and will need phantom power. The Vocaster DM1 and DM14v are dynamic mics so they do not require phantom power.