What Does a DI Box Do?
Updated Nov 13, 2026 · By 
Jonah Mercer · Editorial policy
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A direct box, or DI box, takes the unbalanced, high-impedance signal from an instrument and turns it into a balanced, low-impedance signal a mixer or audio interface can accept over an XLR cable. That balanced signal travels over long cable runs with less noise picked up along the way.
What an instrument signal looks like
An electric guitar or bass sends its signal out on a 1/4-inch cable as an unbalanced signal. That signal is high impedance, which means it loses strength and picks up noise when the cable run gets long. A mixer or audio interface expects a balanced signal on an XLR input instead, so the instrument cannot plug straight in.
What the DI box changes
A DI box converts the unbalanced instrument signal into a balanced signal and sends it out on an XLR connector. The balanced signal resists noise over long cable runs. Many boxes also add a ground lift switch that breaks a ground loop and removes hum.
Active boxes and passive boxes
An active DI box needs power to run. The Samson MDA1 runs on 48V phantom power or a 9V battery. A passive DI box uses a transformer instead of power, as the Radial ProDI, ProD2 and Pro DI do. Choose an active box when your setup can supply 48V phantom power or a 9V battery, and a passive box when you want a box that needs no power at all.
How a DI box connects in a chain
Plug the instrument into the 1/4-inch input of the DI box. Use the thru jack to send the same signal on to an amplifier on stage, and run a balanced XLR cable from the DI box output to the mixer or interface. If the signal is too hot, engage the pad switch, and if hum appears, try the ground lift switch.
What you need
Samson MDA1 Mono Active Direct Box
An active direct box that runs on 48V phantom power or a 9V battery, with a 0dB/-15dB attenuation switch and a ground lift switch.
- Ground lift
- Pad switch
- Runs on batteries
- 48V phantom power
- 2-year warranty stated
Liquid Audio Radial Engineering ProDI Bundle
A passive direct box with a custom wound transformer, a 140kΩ input impedance, a 15dB pad switch and a ground lift switch, sold with a mic cable.
- Ground lift
- Pad switch
Radial ProD2 Passive 2 Channel Direct Box
A passive two-channel direct box with an isolation transformer, a lift switch and a 15dB pad.
- Pad switch
- 2-year warranty stated
Radial Pro DI Passive Direct Box
A compact passive direct box with a custom transformer, built to handle large transients without distortion.
- 2-year warranty stated
These come from our ranked list Best Direct Di Box, which compares them spec by spec.
Frequently asked questions
Do I need a DI box to plug a guitar into a mixer?
Yes, if the mixer only has XLR or balanced inputs. A DI box converts the guitar's unbalanced 1/4-inch signal to a balanced XLR signal the mixer accepts.
What is the difference between an active and a passive DI box?
An active DI box needs power, such as 48V phantom power or a 9V battery, while a passive DI box uses a transformer and needs no power.
What does the ground lift switch on a DI box do?
It breaks the ground connection between the instrument and the mixer, which can remove hum caused by a ground loop.
Ranked di boxes lists
More how-to guides
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