The Grace ALiX Instrument Preamplifier squeezes the same technology as the company’s highly regarded studio preamps into an active DI box designed for a wide variety of acoustic musicians. The fully parametric midrange controls provide super-flexible EQ capability, and its three impedance switches are designed to accommodate virtually any type of pickup. The AC-powered device can also supply 9V 500 mA juice to other stompboxes. Photo by Mark Marshall

Other Cool Goodies
In addition to EQ and feedback controls, hybrid DI/preamp devices are typically loaded with features to help acoustic-electric guitarists get their music heard. Here’s what you’ll want to look for when shopping for an active DI.

Many have onboard tuners equipped with a footswitch that mutes the signal from the XLR and 1/4" outputs. Like clip-on or pedal tuners, these differ in style, but not in functionality. The Venue DI uses a circular array of LEDs to indicate whether a string is sharp, flat, or at pitch, while the Platinum PRO EQ uses a virtual needle to display this info.

Active DIs may also have a footswitchable boost that lets you set the amount of increased level you get when you stomp on it. For example, the Venue DI’s boost is adjustable up to +9 dB, and on the Platinum PRO EQ the range is from +3 to +12 dB. I use the boost for two things: The most obvious is to boost my signal for solos. But it also lets me balance the output of different pickups, when, say, I’m running two guitars through the same DI. First, I preset the levels for each guitar. Then when I switch from one to the other, all I have to do is hit the tuner/mute switch and make the swap. This spares me from having to bend over and fiddle with the preamp’s volume knob—very handy.

An active DI may have an onboard compressor. Although a few units offer separate knobs for level and compression amount, this is often a simple 1-knob affair with a fixed ratio, attack, and release—as on the Platinum PRO EQ, which also includes a multi-color LED to indicate both compression threshold and signal reduction. Even though its settings are basic, an active DI’s compressor will let you control your dynamics, and if it’s well designed, it can sound very natural.

To help you set the optimum gain for your instrument’s pickup, active DIs usually have a knob for adjusting input sensitivity (sometimes called a “trim” control), as well as some form of visual feedback if the input signal is clipping. On the Venue DI, a 4-segment LED meter indicates input level. On the Platinum PRO EQ, a single LED flashes to warn of input clipping.

The trick to using a notch filter is to get your guitar to start feeding back at soundcheck. Then, as it’s howling, turn the notch filter knob until the feedback disappears.

When an active DI can be powered by a battery, it’s supremely helpful if the device has a battery status light. This is usually a single LED, as on the Platinum PRO EQ, although the Venue DI coverts its 4-segment LED meter into a color-coded battery status display.

These days, it’s common to find an effects loop in an active DI. It works the same way as on a guitar amp: The send routes your signal (usually after EQ and compression) to whatever effect(s) you want to include in your signal chain, and the return brings the processed sound back into the preamp. On most devices, including the Platinum PRO EQ and Venue DI, the effects loop uses 1/4" jacks for the send and return, but some, like the Grace ALiX, require inserting a tip-ring-sleeve (TRS) Y cable. Of course, you can place any stompboxes before the DI’s input, but using the effects loop is usually a quieter option.

As on a passive DI, a ground-lift switch is also a useful feature on active boxes. Ground loops can occur when there’s more than one connection to your device; lifting the ground will eliminate the hum that results from such loops.

Some active DIs, including the Platinum PRO EQ, offer a pre/post EQ switch that affects the XLR output. In the “pre” setting, the DI sends a straight, low-Z signal to the mixing board; in the “post” setting, the signal is sent to the mixer after getting EQ’d and processed, yet before it reaches the onboard master volume.

The ModTone Acoustic Preamp does double-duty as an active DI and multi-effect stomp. Its bass, treble, volume, and gain dials are augmented with four knobs to tweak chorus speed and depth, and reverb dwell and level. Unlike many active DI devices, it also offers a headphone out for those late-night practice sessions. Photo by Mark Marshall

Onboard Effects
As you investigate various active DIs, you’ll find some that include other effects, such as reverb and chorus. The ModTone Acoustic Preamp ($229 street) is one example of this approach to an all-in-one design. A simple preamp with bass, treble, volume, and gain dials, as well as phase and ground-lift switches, the ModTone also provides two footswitchable effects: reverb (with dwell and level knobs) and chorus (with speed and depth).

Tech 21’s Acoustic Fly Rig ($299 street) takes the concept of onboard effects even further. In addition to its onboard SansAmp analog preamp with 3-band semi-parametric EQ, it packs a 750 ms analog delay (with time and repeat knobs, tap-tempo footswitch, and a preset chorus option) and an independently footswitchable reverb into its slim case. All the active DI goodies are here as well: a sweepable notch filter, low-pass filter, FET-based 2-knob compressor, footswitchable boost (up to +12 dB), tuner, headphone jack, phase-reverse button, ground-lift switch, and low-Z XLR and 1/4" outputs.

In addition to being a fully featured active DI with a 3-band semi-parametric EQ, boost switch, 2-knob compressor, and tuner, Tech 21’s Acoustic Fly Rig brings a tap-tempo analog delay and footswitchable reverb to the party. The idea is to shrink a DI and basic pedalboard into a device that slips into a gig bag—or even your back pocket. Photo by Andy Ellis

Color My World
We’ve talked a lot about the features in various active DI devices, but what about their sound? I believe no device is transparent—everything you plug into colors your tone. The question is, how? And do you like it? Studio engineers spend a lot of time testing different preamps with their favorite mics. Each mic pre has its own character—an API doesn’t sound like a Neve, and a Grace doesn’t sound like a Pendulum—and the only way you get to know these subtle differences is through A/B testing.

So it goes in the world of acoustic DI preamps. What sounds best is subjective, and you have to discover this for yourself. Bring your favorite acoustic-electric to your local music store, sequester yourself in their listening room, and get busy trying out some of the devices we’ve described here, as well as any other units you can get your mitts on. And—just like with any distortion or delay pedal—the user interface can impact your buying decision, so be sure to test as many DIs as you can. Using the info we’ve covered here, you’ll soon be ready to take the stage with your favorite acoustic DI.