Phantom Power Explained: What 48V Does and Which Mics Need It

What is phantom power?

Phantom power is a DC voltage, normally 48 V, that your interface sends to a microphone through the same XLR cable that carries the audio back. Shure defines it as the process of delivering DC to microphones that need power to drive active circuitry^[1].

It rides on the balanced audio lines without being heard. The same voltage is applied to both signal wires (pins 2 and 3) as a common-mode DC voltage and returns through the cable shield^[3]. A balanced input only amplifies the difference between pins 2 and 3, so the identical DC on both disappears from the audio. That invisibility is where the name comes from: Shure traces the term to the 1960s, when manufacturers developed a power supply that works but cannot be seen^[1].

The numbers are modest. Sound On Sound gives the professional standard as +48 V with a tolerance of 44-52 V, fed through 6k8 current-limiting resistors, with a maximum of 10 mA available to the mic^[2]. Most mics draw around 4 mA or less^[2]; Audio-Technica specifies 2 mA typical for the AT2020^[9]. That limit is why phantom power cannot push meaningful current into a sound source, and why a correctly wired dynamic mic ignores it.

Which microphones need phantom power?

Condenser microphones need phantom power, and so does anything with active electronics inside: active dynamics, active ribbons, inline mic boosters and active DI boxes. Focusrite lists condenser mics, inline mic preamps, active dynamic microphones and active DI boxes as the typical 48 V loads^[4].

Unsure which type you own? The spec sheet or manual will say "phantom power required", "P48" or "48V" if the mic needs it. The broader trade-offs between the two main mic families are covered in condenser vs dynamic microphones.

Is phantom power safe for dynamic mics?

Yes, for modern dynamic mics with balanced XLR outputs. Shure states that phantom power will not damage other microphones in the vast majority of cases, because modern dynamics are designed to accept it^[1].

Sound On Sound makes the same point from broadcast practice: in BBC studios, phantom power is permanently on at every wall box and cannot be turned off, and engineers plug dynamic and condenser mics in and out without trouble^[6]. The condition is proper wiring. Cables must be balanced, correctly pinned and well made, and decent XLR connectors mate the ground contact first^[6].

The exceptions are older and unusual designs. Sound On Sound warns that some vintage ribbon mics with center-tapped transformers, and mics wired for unbalanced operation, can be damaged unless they are modified^[6]. If a mic is decades old or came with an adapter cable, read its manual before you press 48V.

Can phantom power damage a ribbon mic?

Phantom power alone does not usually harm a modern passive ribbon mic, but a faulty cable or hot-patching can. Royer says its ribbon mics are not usually affected by phantom power, yet warns that if pin 1 is miswired or shorted to pin 2 or pin 3, damaging voltage can reach the ribbon element^[5].

Patch bays create the same fault for a split second. Royer explains that as a connector is inserted during cross-patching, it acts briefly like a miswired cable and applies phantom power to the wrong leads^[5]. Home studios rarely have patch bays, but a cheap XLR cable with a broken shield does the same job. A stretched ribbon means a trip to the repair bench, so treat these rules as habits.

1. Switch 48V off first
   Royer recommends turning phantom power off while a ribbon mic is connected or disconnected^[5]. Turning it on or off after the mic is connected is fine.
2. Use a tested cable
   Check the cable with a continuity tester or on a dynamic mic first. Pin 1 must be ground and never touch pins 2 or 3.
3. Mind shared phantom buttons
   On interfaces where one 48V button feeds several inputs, a condenser on input 1 means the ribbon on input 2 also gets 48 V.
4. Add protection if you want certainty
   An inline booster that does not pass phantom power, such as the Cloudlifter CL-1, protects ribbon and tube mics while adding gain^[8].
5. Check vintage mics before use
   Older ribbon designs with center-tapped transformers need modification before they meet 48 V^[6].

How do you turn on phantom power on an audio interface?

Press the button marked 48V or +48V on the interface or in its control software, after the mic is connected with an XLR cable. Many budget interfaces share one button across inputs. On the Scarlett 2i2 4th Gen, for example, 48V applies phantom power to both inputs at once^[4].

Phantom power only travels to XLR sockets. Focusrite notes that 48V is not sent to the 6.35 mm jack inputs^[4], so a condenser mic on a jack adapter will stay silent. If you are wiring a new setup from scratch, how to connect home studio gear walks through the full signal path.

1. Turn monitors and headphones down
   Switching phantom power can cause a thump. Shure recommends turning 48V off while plugging and unplugging to avoid pops and surges^[1].
2. Connect the mic by XLR
   Plug the XLR cable into the mic and the interface's rear or combo XLR socket.
3. Turn the input gain down
   Focusrite's own procedure starts with the preamp gain turned down to avoid pops and clicks^[4].
4. Press 48V
   The 48V light or on-screen icon should come on. Some condensers take a few seconds to settle before they pass clean audio.
5. Bring the gain up while you perform
   Speak or sing at performance volume and raise the gain until peaks sit comfortably below clipping.
6. Reverse the order to finish
   Gain down, 48V off, wait a moment, then unplug.

Why is my condenser mic not working with phantom power on?

Most silent-condenser problems come down to the signal path, not the mic: phantom power is not actually reaching the capsule, or the interface is listening to a different input. Work through these checks in order before you assume the mic is dead.

• 48V is on the wrong channel or off Confirm the 48V indicator is lit for the input you are using. On interfaces with per-channel phantom power, the button follows the selected input.
• A jack is plugged into the front On the Scarlett 2i2, connecting a jack to the front input disables the matching XLR input^[4]. Unplug the guitar or synth cable.
• A booster sits between mic and interface The Cloudlifter CL-1 does not pass phantom power^[8], so a condenser behind it gets none. Plug condensers straight into the interface.
• The XLR cable is faulty Swap the cable. A broken pin 2 or 3 kills the audio, and a broken shield kills the phantom power return path^[3].
• The interface is short of power Bus-powered interfaces can struggle on weak USB ports. Focusrite notes the 2i2's USB icon flashes red when the unit is not getting enough power^[4]. Try a different port or the optional power input.
• The supply is weak Schoeps warns that if a mic's reduced requirements are not met, maximum SPL can drop and distortion can increase^[3]. Portable recorders and some battery devices deliver less than the full standard.
• The DAW input is wrong Check that the track records from the same input number the mic is plugged into, and that the interface is the selected audio device.

If the mic is still silent after all of that, test it on another interface or test a known-good condenser on yours; that isolates the fault in two moves. For interface-side causes beyond phantom power, see no sound from your audio interface, and for hum and buzz rather than silence, see audio cables and ground loop fixes.