Do You Need a DI Box if You Have a Preamp?

A direct injection (DI) box is one of the most misunderstood yet critical pieces of equipment in audio engineering. If you search the web, you’ll come across countless debates on whether this piece of musical gear is necessary when you already have a preamp. You may have seen the forums and might be wondering who is right. So, do you need a DI?

You need a DI box if you have a preamp, as it protects audio signals from external interference, preventing any hums that may impede your audience’s listening experience. It also enables you to use longer cables at venues with bigger stages without deteriorating sound quality.

Read on for a detailed explanation of the role of a direct injection box, the types on the market, and what to look for in one.

DI Box from Radial Engineering
JDI, a superb DI box from Radial Engineering

Why You Need a DI Box

A direct injection box comes in handy in audio production in two primary ways: matching your mixing desk and instruments’ impedance and balancing signals.

Here’s a breakdown of how your DI box helps in these:

Impedance Matching

A DI box is a critical tool for impedance matching. Notably, a typical guitar amp has an input impedance of 1MΩ, while that of a mixing desk is about 10kΩ. This type of impedance mismatch can cause problems during music production.

Suppose your mixing desk’s impedance drops below the guitar’s. In that case, you’re likely to experience thin, lifeless sounds with background noises each time you play the guitar. That can be irritating, especially in a live concert.

A DI box is a device that prevents your guitar’s audio signal from producing those irritating noises on its way to the mixing board. Notably, it acts as a transformer, taking guitar signals at their native impedance and delivering them at a level your mixing desk can handle.

Having a preamp doesn’t mean you should do away with your DI. Instead, combining the two is a sure-fire way of adding some pretty nice warmth and saturation to audio signals.

In other words, using a DI and a preamp helps to tilt the sounds towards the lower frequencies; the bass and vocals begin to stand out while the higher sounds get quieter and subdued. Use the two to get a cleaner sound with better harmonics.

To Balance Audio Signals

You may ask: “Why do I need to balance audio signals?”

To answer this question (and consequently point out the importance of a DI box in this regard), let’s take a look at the two primary types of audio cables.

Unbalanced Cable

This cable type comprises two wires wrapped in a plastic casing. It takes audio signals from audio equipment, like your guitar, and passes them to a receiver device such as the mixer, without manipulation. Although this simplifies things, there’s a high chance of audio distortion.

Balanced Cable

This comes with three wires: a ground wire and two signal wires. Each signal wire passes an identical signal, although one is usually inverted. When the two signals reach the receiver, the inverted signal is “put in phase,” producing the initial sound. However, there’s a likelihood of the signals getting distorted during transmission, leading to the production of a signal that’s “out of phase” on the receiving end.

How DI Boxes Help

Since both types of cables are susceptible to distortion, it’s best to have a device that balances the audio signals at the receiving end, and that’s where a DI box performs a highly valuable role. It balances all unbalanced signals, eliminating all humming, buzzing, or signal interference that may distort the sound.

Additionally, DI boxes are indispensable when transmitting signals over a long distance. That’s because the longer a cable is, the more it’s susceptible to signal interference. In other words, using longer cables increases the chances of producing unbalanced audio signals, which can hurt your listening experience.

Although you may try to avoid that, chances are you’ll need longer cables, especially when performing high-capacity concert venues. As a result, it’s advisable to use a device that allows you to send signals without risking audio degradation, and a DI box does precisely that.

For more information, I recommend that you watch the following YouTube video on what a DI box can do:

What Are the Different Types of DI Boxes?

Having discussed how DI boxes help in the production of clean sound, let’s dive into the types of devices you’ll come across when looking for one.

They are:

  • Active DI box: This type of DI box requires an external power source. Some of them use 9-volt batteries; others use a 48-volt phantom power transmitted through XLR cables. Still, some use dedicated AC power supply units.
  • Passive DI box: Unlike an active box, this type of direct injector doesn’t need a power source. Instead, it’s a transformer that matches your audio equipment impedance through electromagnetic induction.

Although these boxes perform the same function, their performance, and the kinds of instruments they pair well with, vary. Therefore, it’s critical to determine the type that will work best with your equipment before spending your hard-earned cash.

Here’s some information to help you make the best choice:

  • A passive DI box is better for creating saturated sounds. As I mentioned earlier, this box type is a transformer, making it a great choice if you want to create saturated sound using powerful signals. It can take the high-input impedance of powerful equipment, like your electronic keyboard, and convert it into an incredibly pleasant, slightly saturated signal.
  • A passive box comes with a ground lift switch. This feature helps to remove ground loops, especially from instruments that have ground paths for electrical signals, such as electric keyboards. A ground loop can cause humming noise, which can be an issue to your audience.
  • An active DI box can serve as a preamp. Because this type of box can inject some electricity into audio signals, you can use them to boost high-frequency signals, making it a worthwhile companion to your studio console.
  • An active box works best with passive equipment. During live sound production, an active DI box performs better with a passive instrument. For the best results, pair your active DI box with instruments with lower output, like electric basses and acoustic guitars that lack battery-powered output.
  • Passive boxes work best with active instruments. Suppose your input equipment produces high-intensity signals. In that case, a passive DI box would be a perfect choice. For example, you can pair these boxes with an electronic keyboard or an acoustic guitar with battery-powered output.

What To Look For in a DI Box

Regardless of whether you pick an active or a passive DI box, here are some of the features to consider to get the best deal on the market:

Multiple Channels

Arguably, you want to use a DI box without much hassle. It would be best to pick the one with two or more channels for your keyboard, guitar, and other instruments. Also, some boxes come with channels for computers and media players, making it easy to use your PC or mobile devices in audio production.


This feature splits an input instrument-level signal into a separate output. It allows unprocessed signals to be sent to an amp on stage and the PA through a balanced XLR output. As a result, the bass player can use the amp for onstage monitoring, dramatically reducing stage volume.


Some DI boxes come with an attenuator that prevents incoming signals from overloading your setup’s circuitry. Notably, these pads decrease incoming signals by 15 dB to 20 dB, allowing the circuitry to accommodate the output of unbalanced line equipment like electronic keyboards. Therefore, boxes with this feature help protect your equipment.

Tip: If you need an active DI box, I recommend this high-quality model (link to Amazon). It’s a professional direct box, built like a tank, and it can handle most situations resulting in amazing sound. On the other hand, if you need a passive box, I recommend this lovely piece of engineering (link to Amazon), which is one of the best passive DI boxes on the market.

Bottom Line

The goal of any audio engineer is to offer the audience the best listening experience. However, this can be a challenge, mainly due to the possibility of the distortion of sound during transmission. Whether you use balanced or unbalanced cables, chances are there’ll be some interference, which may result in a nasty background hum.

Therefore, a DI box is a worthwhile addition to your audio equipment. It ensures that the impedance of your input instrument matches that of the mixer, preventing distortions and balances all audio signals, providing clean, noise-free sound.