DI Boxes Explained: Active vs. Passive and When You Need One

The humble DI box is on almost every input list and is one of the most frequently forgotten items in a backline order. Here's what it does, which type to use, and how many you'll need.

What a DI box does

A DI (direct input) box takes an instrument-level or line-level signal — from a keyboard, bass, acoustic guitar, laptop or playback interface — and converts it into a balanced, mic-level signal the console can use. That does three things:

1. Lets the signal travel long distances. Balanced signals can run the length of a stage snake without picking up much noise.
2. Matches impedance. High-impedance instrument pickups sound thin and dull when plugged straight into low-impedance inputs. A DI presents the right load.
3. Isolates grounds. Many DIs include a ground lift switch that can break ground loops and stop hum.

Passive vs. active

Passive DI

A passive DI uses a transformer and needs no power.

• Great for line-level sources with healthy output: keyboards, laptops and playback interfaces
• Very rugged and simple
• The transformer provides good isolation, which helps with hum

Active DI

An active DI has electronics that need power — usually phantom power from the console, sometimes batteries.

• Best for weak or high-impedance sources: passive bass pickups, piezo acoustic guitar pickups
• Can add headroom and clarity for low-output instruments
• Needs phantom power turned on at the console

Quick guide

Stereo sources need two channels

Keyboards, playback and many electronic instruments are stereo. That means two DI channels per source — either two mono DIs or one stereo DI. A keyboard player using the Nord Stage 3 with all four outputs needs four channels.

Count DIs per position and add them to the order. Our Nord Stage 3 guide covers keyboard outputs in more detail.

Ground lift and hum

If you hear a constant hum when a laptop, keyboard or playback rig is connected, a ground loop is likely. The ground lift switch on a DI disconnects the ground connection on the output side, which can break the loop. Try it first before changing anything else.

Hum can also come from power problems — see stage power for backline. Never remove safety grounds from power cables to fix hum.

Pad switches

Many DIs have a pad that reduces signal level. Use it when a hot source — a keyboard at full volume, or a playback interface — overloads the DI or the console preamp.

Laptops and playback rigs

Laptop-based playback is one of the most common sources of noise on stage:

• Use a good audio interface instead of the laptop's headphone output
• Feed the interface outputs into passive DIs for isolation
• Keep laptop chargers on the same power as the rest of the position if possible
• Label each channel clearly: tracks, click, cues

Put DIs on the order

When you send a backline order, list DIs per position:

• Keys: number of outputs
• Bass: active or passive, and whether there's an amp line out too
• Playback: number of channels
• Acoustic instruments: active DIs

It's a small item, but it's often the last thing found at load-in. List it, and it'll be there.

Building a backline order for a show in Los Angeles? Send us your input list — we'll make sure the DIs, stands and cables are covered alongside the gear in our catalog.