The AEA TDI Direct Box: We’re More Than Ribbon Mics

By: Paul Kobylensky

AEA is well known for our line of professional ribbon microphones, but our passion goes far beyond them. In truth, we are obsessed with capturing the purest, most musical, and pristine sound possible. A great mic is just one piece of that journey. Every piece of equipment in your signal chain contributes to that goal, even when not using a microphone at all.

We created the AEA TDI, our take on the perfect active direct injection (DI) box, with this philosophy in mind. Let’s explore what makes the TDI special, the inspiration behind its development, and how best to integrate it into your workflow. But first, a little background.

AEA, America, and the TDI

AEA’s goal of revitalizing the golden age of American audio manufacturing—and our commitment to clean, unhyped gain—has led us to develop our respected line of ribbon microphones and the best-in-class preamps to drive them. But, what about those times when you don’t need a microphone?

Today’s music technology is a world without limits. Many guitarists and bassists record and perform without an amplifier or other sound source anywhere to be seen. Countless reamping products and amplifier/processing plugins make it fast and simple to plug their instruments into a DI box, then straight to the board, and still achieve astounding results. That DI, however, can make or break their sound.

We wanted to create a DI box that honored the natural sound of those instruments at the source while living up to the AEA standard.

The result is the AEA TDI active direct injection box.

Fred Forssell’s Masterful DI Design

To achieve our goals, the TDI’s proprietary circuit design had to offer unmatched performance while remaining versatile enough for a wide range of use cases. For this challenge, we looked to Fred Forssell. Fred has designed every electronic circuit at AEA since 2006, and is known for his expertise in meticulous, high-performance circuit design. Most importantly, Fred’s relentless pursuit of sonic excellence matches our own. We had high expectations for the TDI and knew that Fred was the ideal collaborator.

The TDI Takes Shape

Fred’s design, the phantom-powered TDI, is an active DI box tailored for passive instruments. And, of course, it all starts with the input.

Fred gave the TDI an ultra-low-noise JFET input buffer. This design is ideal for handling delicate, high-impedance signals from passive pickups in guitars, basses, piezo pickups, and other similar sources.

Your audio then feeds into a super-clean Lehle step-down transformer, which balances and isolates the signal to reject noise and interference. This Lehle transformer preserves the inherent character of your instrument, minimizing distortion, and preventing signal degradation over long cable runs. It’s all then sent out the XLR output straight to your preamp, interface, or console.

How to Use Your AEA TDI

The TDI’s performance is only matched by its versatility. The perfect solution for direct recording of passive instruments, it also features a collection of appointments that prepare it for any recording studio or performance environment.

Recording Passive Instruments

Most electric guitar and bass pickups have a high output impedance. These instrument-level sources are highly susceptible to signal loss, especially considering the capacitance of longer cables. The TDI’s JFET input buffer acts as a bridge, converting that signal to a low-impedance, balanced signal suitable for the input on a preamp and audio interface. The TDI also offers outstanding performance with acoustic-electric guitars and other instruments with piezo pickups.

Recording Active Instruments

The TDI isn’t just for passive instruments, however. It also features a 20 dB pad, which allows you to confidently input hotter sources like active basses and synthesizers. It can even handle speaker level signals.

Engineer/mastering engineer Paul du Gré (Vitamin String Quartet, Leo Kottke, Los Lobos), said that it’s the TDI’s ability to handle these high input levels with minimal distortion that sold him on it.

“This new direct box designed by Fred Forssell is a thing of elegance in design and sonic beauty. With a ten megohm input impedance, this circuit has gobs of headroom.”

Splitting Your Signal

The DI also features a high-quality, passive THRU-put feature. Connected directly to the input jack of the TDI, it lets you simultaneously send the DI signal of your incoming instrument to your interface or preamp while a separate, completely unaffected signal drives your other devices, such as a guitar amplifier or pedalboard. This recording technique makes it easy to track the two sounds at the same time, greatly expanding your options during mixing.

Wet/Dry Rigs

This THRU-put, as discussed above, is particularly useful for crafting wet/dry rigs live and in the studio. Simply send the balanced, clean, direct signal to your front-of-house, preamp, or interface while sending the THRU-put’s unaffected signal to your desired effects chain. It’s a secret weapon of many bassists as it allows them to experiment with their tones while always maintaining their DI signal’s fat low end.

Live Performance

As an AEA product, you might be tempted to relegate the TDI to the studio environment. You won’t be disappointed! But we also ensured that its durable steel chassis, our straightforward design philosophy, and transparent sound make it equally valuable onstage. Whether running a complex live rig or needing a pristine DI for your acoustic guitar’s piezo, the TDI delivers studio-grade fidelity.

This versatility led songwriter, producer, engineer, and mixer Roger Alan Nichols (Hayley Williams, Steven Tyler, Tracy Nelson, Larkin Poe) to say, “It’s built like a tank, and it easily put my other DI’s in the bottom drawer.”

The AEA TDI Direct Injection Box

We want the TDI to combine every aspect of our company’s mission: American-made audio heritage, clean and pure sound, and professional, reliable quality. With Fred Forssell’s help, the TDI achieves this and more. Like our AEA ribbon mics and preamps, it is a tool built for discerning ears and is a testament to our unwavering belief in premium audio performance. We hope it will be a staple in your recording toolkit and your go-to DI box for years to come.