You bought a condenser microphone and plugged it into your audio interface, but no sound comes in at all. When that happens, the first thing to check is whether “phantom power” is turned on. This article summarizes, for beginners and based on official materials from Focusrite and Audio-Technica, what phantom power (+48 V) is, why condenser microphones need it, and what to watch for when connecting.
Disclosure: This article contains affiliate links. If you buy through them, SoundBounty may earn a commission at no extra cost to you.
Key points
- Phantom power is electricity sent to the microphone through the microphone cable (XLR cable). It is usually 48 volts, and gear labels it “+48V” or “48V”.
- A condenser microphone needs electricity to work. Without phantom power, it produces no sound.
- An ordinary dynamic microphone does not need phantom power. Focusrite explains that sending phantom power to a dynamic microphone is very unlikely to damage it, but that it is almost never needed.
- The basic way to connect is to turn phantom power off, plug in the microphone, and only then turn it on for the channels that need it.
- Older ribbon microphones can be damaged by phantom power. Check the microphone’s manual before connecting.
What phantom power is
Focusrite describes phantom power as “48 volts sent through an audio cable that can power some microphones and other gear.” It is similar to getting power from a computer’s USB port, but here the power travels through the microphone cable from the interface to the microphone.
Audio-Technica explains the mechanism in a little more detail. Phantom power sends a DC voltage through the microphone cable. It is used to run the small circuit (preamp) inside a condenser microphone and to apply an electrical charge to the part that picks up the sound.
Audio-Technica explains that it is called “phantom” because the voltage appears to be 0 volts when you measure between the two wires that carry the audio signal. Electricity is flowing, but it does not get in the way of the audio signal.
To use phantom power, you need a balanced microphone cable (XLR cable) with three wires. Audio-Technica points this out.
Sources: Focusrite official help (What is 48V phantom power?), Audio-Technica official support (What Is Phantom Power and Why Do I Need It?)
Why condenser microphones need it
Microphones fall broadly into three types: dynamic, condenser and ribbon. Here is a plain-language summary of Focusrite’s explanation.
Condenser microphones: they need electricity
A condenser microphone is built with a thin diaphragm and a metal plate placed close together. When sound makes the diaphragm vibrate, the distance to the plate changes and an audio signal is produced. But this signal is very weak and cannot be sent out as it is, so a small circuit inside the microphone conditions it. That circuit needs electricity to run. Focusrite explains that this electricity is phantom power (often 48 volts).
Without power, a condenser microphone cannot produce sound. On the other hand, leaving phantom power off will not damage the microphone. Focusrite explains that “a condenser microphone is not harmed when phantom power is off, but it produces no signal.”
Note that some condenser microphones get power in other ways, such as batteries or a computer’s USB port (Audio-Technica’s explanation). However, an ordinary XLR condenser microphone is most often powered by phantom power.
Dynamic microphones: usually not needed
A dynamic microphone makes electricity when a coil attached to the diaphragm moves between magnets. Because the microphone itself generates electricity from the sound, it does not need phantom power. However, Focusrite explains that a few dynamic microphones have a small amplifier circuit inside and do need phantom power. Check your microphone’s manual to see whether yours is one of them.
Ribbon microphones: usually not needed, but take care
A ribbon microphone works by a thin metal ribbon moving between magnets. Focusrite explains that ordinary ribbon microphones need no power, but some “active” types do need phantom power. The points to watch are summarized in the section below.
The differences among the three are also covered in more detail in “Dynamic vs condenser microphones“.
Sources: Focusrite official help (What is 48V phantom power?), Audio-Technica official support
The “48V” button on an audio interface
Audio interfaces have a button or switch labeled “48V” or “+48V” for turning on phantom power. Some types switch it on a software screen. Audio-Technica explains that on some gear it is labeled “+48V” rather than “phantom power”.
- Where the power is sent: On Focusrite interfaces, turning on the 48V button sends power only to the XLR microphone inputs that the button covers. It is not sent to the 6.35 mm jacks (instrument and line inputs).
- Number of buttons: Some have a button for each input, while others have a single switch for everything, or switch inputs together in groups such as two channels at a time.
- Not every interface has it: Audio-Technica advises checking the manual, because whether a device can supply phantom power depends on the device.
Audio-Technica also explains that if you connect a condenser microphone such as the AT2020 through an ordinary XLR-to-USB adapter cable, many such cables supply no phantom power and the microphone often will not work. The difference between USB and XLR microphones is compared in “USB microphones vs XLR microphones with an interface“.
Sources: Focusrite official help (What is 48V phantom power?), Audio-Technica official support
Connection order and cautions
The basic order
Focusrite describes the best practice as follows.
- Make sure phantom power is off.
- Connect the microphone or other gear to the input.
- After connecting, turn phantom power on only for the channels that need it.
The same idea applies when you disconnect a microphone: turn phantom power off first, then unplug it.
Some gear must not receive it
Phantom power can damage gear that does not support it. Focusrite gives these examples.
- Connecting a line output, an instrument output, a headphone output and so on directly to a microphone input can cause damage with 48 V.
- Old unbalanced microphones (two wires only) are damaged by 48 V. Most XLR microphones sold normally today are balanced and built to withstand 48 V.
- Sending 48 V through a patch bay that is not XLR can damage both the preamp and the microphone.
If you are unsure, Focusrite advises checking the equipment’s manual or contacting the manufacturer.
Cautions for ribbon microphones
Focusrite explains that ribbon microphones, especially older models, can be damaged by phantom power. It advises contacting the microphone’s manufacturer or checking the manual before connecting. Also, by default, Focusrite interfaces turn phantom power (48V) back off when the interface is powered off. Focusrite explains that this is a safety feature to prevent accidentally damaging older ribbon microphones. When you use a ribbon microphone, Focusrite recommends leaving this setting as it is, so that phantom power returns to off.
Power requirements differ by microphone
Audio-Technica explains that the power requirements differ from one condenser microphone to another, and that the amount of power gear can supply also differs. If you get no sound or a low level, compare the requirements in the microphone’s manual with the interface’s specifications.
Audio-Technica also explains that some microphones use a dedicated module to step 48 V down to a lower voltage. If you remove the module from such a microphone and connect 48 V directly, it will almost certainly be damaged. If your microphone has a removable part, do not take it off on your own.
Sources: Focusrite official help (What is 48V phantom power?, After restarting my interface 48V Phantom Power turns off), Audio-Technica official support
What to check when there is no sound
- Is the microphone a condenser microphone? If so, turn on the 48V button.
- Are you using an XLR cable (and not an adapter cable or a jack-only connection)?
- Does the 48V button cover the input you are using? On types that switch several inputs together, check the manual to see which inputs are affected.
- Did 48V turn off after you restarted the interface? On Focusrite models, the default is that 48V returns to off when the power is turned off.
- Is the gain knob at zero? Phantom power only runs the microphone; the volume has to be raised separately with gain.
Phantom power is electricity to run the microphone and does not make the sound louder. Focusrite also explains that a microphone signal still needs further amplification (a preamp). For preamps, see “What is a microphone preamp?“.
Frequently asked questions
Q. Is it okay to turn on phantom power for a dynamic microphone?
Focusrite explains that using phantom power with a dynamic microphone should not damage it, but that it is almost never needed. If you do not need it, it is safer to leave it off. For ribbon microphones, follow the cautions in the section above.
Q. Should I turn off 48V when I am not using a condenser microphone?
Focusrite recommends turning it off first when you swap microphones or other gear. When you use a microphone that needs no power, such as a dynamic microphone, leaving it off when it is not needed is also a safe approach.
Q. Can I not use a condenser microphone with an interface that has no phantom power?
One option is to put in between a device that can supply phantom power. Audio-Technica explains that an external audio interface or a mixer can supply phantom power. When choosing, look for models that list “48V”. A comparison is collected in “Audio interface comparison“.
Comments