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Diving into DI Units

By Al Fernald. There’s seemingly endless variations on the units themselves, and not merely between brands.

The “I” in DI Unit is variously said to stand for input, or injection, or induction or interface. If that seems like a lot of variation on a basic theme, it’s quite fitting because there’s seemingly endless variations on the units themselves, and not merely between brands. Whether you’re looking for active or passive, something for your bass or for your laptop, whether for the studio or for the stage, there’s a specialized DI out there that will suit your needs. Here’s a brief rundown of just a handful of available DI models, drawing from all different kinds across the market.

Avalon Mono Instrument & DI Preamp

You’re judged by the company you keep, and the U5 keeps good company—we spotted at least a half-dozen of them around the stage on Paul McCartney’s last tour. Intended for bass guitar and acoustic instruments, electric guitars, keyboards, synthesizers and low-output pickups, the unit offers a high-input impedance input stage for reportedly zero load effect on sensitive pickups and keyboards, and 100 percent discrete, Class A signal amplifiers. A half-dozen passive tone-EQ curves are included to accommodate various acoustic and electric instruments; a high-cut switch eliminates unwanted acoustic pickup and high-frequency noise; and a ground isolation switch eliminates potential earth loop and AC buzz problems.

Avalon Design •

BAE PDIS 2-Channel DI

Introduced at last year’s AES Convention, BAE’s PDIS is a passive DI stereo box that utilizes an OEP/Carnhill transformer and Neutrik connectors, sporting 1/4” inputs and low-impedance XLR outputs for each channel on one side, while a pair of through outputs for each channel can be found on the reverse side. The PDIS can be used as a DI for stereo instruments, or act as two independent, separate instrument DI channels for separate mono instruments. The PDIS is hand-wired in California and has 100 percent through-hole components.


Countryman Type 85 Active DI

A staple of the industry, the Type 85 connects a high-impedance instrument pickup to a balanced XLR mic input. Because it’s active (i.e., powered), the box runs on 48V phantom power, but if that’s not available, you can still use the unit with a 9V battery, which should last for roughly 400 hours. Countryman says it uses only hand-selected, high-quality discrete components to create the Type 85’s single-ended Class A circuit. Keeping it simple, there’s no roll-off switches or effects, leaving frequency decisions to the engineers instead.

Countryman •

Mackie MDB Series DIs

The newest offerings on this list, Mackie’s MDB Series debuted at this year’s NAMM Show. The line consists of four models: the MDB-1P passive DI, the MDB-2P passive stereo DI, the MDB-1A active DI and the MDB-USB stereo DI. The 1P and 2P both offer a high-impedance 1/4” input with Thru output, a balanced male XLR output connector with ground lift, and a -15 dB pad for connecting to high-output sources. The 1A, intended for instruments like guitars and basses with active pickups and preamps, offers increased headroom, a -20 dB pad and a Merge switch that turns the Thru jack into a second input. The USB stereo DI brings audio from a computer into analog gear, offering output level control, headphone output, mono sum and dual XLR analog outputs with ground lift.

Mackie •

Radial JDI Passive Direct Box

An industry standard if ever there was one, the JDI is a passive direct box equipped with a Jensen audio transformer to handle high-to-low impedance conversion and signal balancing at the same time. The transformer also uses a magnetic bridge that passes signal while rejecting stray DC voltage, helping the unit eliminate hum and buzz caused by ground loops. Some of the JDI’s features include input and throughput 1/4” connectors, a -15 dB input pad, and 180° polarity reverse to help phase-align the instrument with the PA. A secondary circuit is added for direct interfacing with high-output devices, and a Merge function sums stereo sources to mono.

Radial Engineering •

RapcoHorizon DBBLOX Direct Box

As a one-channel passive instrument direct box, the DBBLOX is diminutive in size but gets the job done handily. Roughly 3 1/2” x 1 1/4” x 1”, the DBBLOX converts a high-impedance source to a low-impedance load. The unit sports a 1/4” input, an XLR male output and a DBT Transformer. For those who need to head the other way around, the DBBLOXF version can be used to convert a low-impedance source to high-impedance load, with an XLR female input and 1/4” output.

RapcoHorizon •

Rupert Neve Designs RNDI Stereo Active Transformer Direct Box

Rupert Neve has designed some of the most legendary studio gear in existence, so it’s no surprise that the RNDI has its fans. The unit’s sound is based around custom Rupert Neve-designed transformers, and Class A biased, discrete FET amplifiers, powered by 48V phantom power on the XLR connection, creating high-impedance input of 2 megohm. RND claims there is no crossover distortion added to the signal. Likewise, there are no ICs or digital components in the design. In instrument mode, the RNDI offers input headroom of +21.5 dBU, allowing it to handle instruments, interfaces, CD players and drum machines without a pad.

Rupert Neve Designs •

Switchcraft 370DI Mini AudioStix DI

As many of our audio sources get smaller—smartphones, laptops and the like—it makes sense that people want equally portable DIs to go with them (even though the average DI isn’t exactly titanic to begin with). With that in mind, Switchcraft has the 370DI Mini AudioStix DI, a pocket-sized DI that melds together the company’s SC700CT DI Box and 318 Inline Audio Adapter. Sporting a 3.5mm input jack, dual RCA inputs, a DE Series male XLR, ground lift switch and a 20 dB pad, the 370DI sums and converts the unbalanced stereo outputs of smartphones, tablets, laptops and consumer gear to a balanced mono line level so that they can be connected to consoles or house systems.

Switchcraft •

Whirlwind Director Passive DI

While Whirlwind offers the IMP2—its basic DI with a TRHL transformer, parallel input and Thru jacks, and a ground lift switch—the Director builds on the IMP2’s features, bringing to the table a specialized metal shield around its TRHL-M transformer; a lowpass filter switch; and a 30 dB pad switch. If that’s not enough, there’s the version that builds on the Director: MultiDirector is essentially a 4-channel rackmount version.

Whirlwind •