Review: Audio Sprockets ToneDexter Preamp/DI Gives the Sound of a Mic with Convenience of a Pickup

In the world of acoustic instrument amplification, there’s long been a tradeoff between the handiness of pickups and the sonic superiority of microphones. Sure, the very best under-saddle systems sound very realistic these days, when compared to the earliest designs dating back to the 1970s, but to many ears it’s still the case that nothing beats the warmth and accuracy of a high-quality condenser mic.

Audio Sprockets’ ToneDexter addresses this conundrum with an ingenious solution. This preamp/DI, which the musicians and engineers James May, Andy Narrell, and Michael Seedman spent four years developing, is designed to give you the sound of a microphone with the convenience of a pickup. In effect, the ToneDexter learns how your guitar sounds through both a microphone and a pickup, and uses this information to produce a snapshot of your tone, called a WaveMap, for use onstage or in the studio.

Small and Flexible Package

Like many modern preamps, the ToneDexter is compact, taking up a footprint only slightly larger than a CD case, and has a sturdy metal chassis. It’s packed with features that are arranged straightforwardly. The top panel includes output level and pickup level trim knobs; notch, bass, treble, character, and WaveMap controls; and twin footswitches with multiple functions. On the right-side panel is a 1/4-inch in; on the left, a 1/4-inch out.

The rear panel includes an external power jack, and XLR input with 48 volts of phantom power (used when creating the presets); a 1/4-inch stereo out, with level control, for headphones; a 1/4-inch effects loop jack; an XLR DI out; a boost gain knob; and a phase switch. In other words, the ToneDexter has plenty of built-in flexibility to optimize the amplified sound of your guitar.

The Recommended Accessories

The acoustic guitarist is the obvious target audience of the ToneDexter, but its standard software is also intended for other acoustic instruments like baritone guitar, dobro, viola, cello, bouzouki, mandola, and mandocello. On Audio Sprockets’ website, you can download firmware for higher-pitched instruments like violin, banjo, mandolin, and ukulele, or for lower-pitched ones like acoustic bass guitar and upright bass.

The ToneDexter will work well with a range of piezo pickups, both passive and active—see Audio Sprockets’ website for a lists of recommended pickups, ones that can work with caveats, and those that are simply incompatible with the preamp/DI. For guitar electronics systems that include a pickup working in tandem with an internal mic, the company says it’s best to dial off the mic and use only the pickup signal in training the ToneDexter.

Audio Sprockets also recommends using a small-diaphragm condenser microphone, such as the MXL 600, Rode NT5, Shure SM81, or Sterling ST31, in a cardioid or omnidirectional pickup pattern. Large-diaphragm condensers and ribbon mics are also compatible, provided they’re carefully placed. Tube and dynamic mics, on the other hand, are not recommended.

Teaching the ToneDexter

To evaluate the ToneDexter, I used a recent Breedlove guitar with an L.R. Baggs Element Active System, an Audio-Technica AT4050 microphone, a pair of Grado headphones, and a Fender Acoustasonic amplifier. It was a cinch to get started: I just plugged the mic, the guitar, and the headphones into the ToneDexter, setting the mic in a cardioid pattern and positioning it (the company recommends six inches below the treble or above the bass side of the guitar, ten to 15 inches in front of the neck joint, or 12 to 15 inches above the nut).

I engaged the training mode with the boost switch, then strummed for a few measures, so that the ToneDexter could determine the levels of the microphone and the pickup, as designated by the indication LV on the machine’s screen. When the display showed TL, meaning that the learning phase had begun, I fingerpicked and strummed some random arpeggios and single-note lines, up and down the neck. This helped the ToneDexter fully analyze the sounds of the mic and the pickup. Over the span of about two minutes, the screen indicated a progression of training levels, from TL1 to TL9, and during this interval, I was able to isolate the mic sound by hitting the multifunction boost switch, to check that it had been well positioned.

After doing the recording at my office desk—the ToneDexter can be used pretty much anywhere, as it doesn’t pick up much room sound—I listened back on the headphones. Using the boost switch, it was easy to toggle between the isolated sounds of the pickup, the microphone, and the WaveMap. Though I wasn’t using a small-diaphragm mic—the AT4050 has a large diaphragm—I was pleased with the results. The Breedlove’s L.R. Baggs electronics perform very well as is, but combined with the ToneDexter’s simulation of the AT4050, the guitar sounded noticeably warmer and more detailed. At this stage of the process, you can trash the WaveMap and start over, but since I was satisfied with it, I used the WaveMap Select knob to find an empty memory slot, then pressed and held the boost to store the WaveMap (you can store up to a total of 22 presets, in two separate banks), ending the training session.

The differences between the raw pickup and the ToneDexter were even more appreciable when I played using my preset through the Acoustasonic amp. The guitar sounded—and felt—more natural with the WaveMap. If I had listened blindfolded, I would have sworn it was miked. What’s more, I found the ToneDexter’s EQ controls to have a useful sweep. The tuning and muting functions would definitely be handy in a live setting, and the notch filter was effective in attenuating a hint of feedback when I sat close to the amp and set it at a high volume level. When generating a WaveMap, though, the ToneDexter automatically improves a guitar’s resistance to feedback, and I did find the amp less prone to howling with the WaveMap than without.

Of course, the Breedlove/L.R. Baggs is quite a nice combo, and the Audio-Technica is a quality microphone. The catch is that the ToneDexter is only as good as its input sources. It won’t correct the shortcomings of inferior microphones, and, as with any live or recording situation, it can require some finesse with mic placement. And with all the fun of creating WaveMaps, it’s easy to forget that the ToneDexter is also an excellent preamp/DI. You can use it simply as such by selecting an empty slot in one of the WaveMap banks or by putting the unit on bypass.

The Bottom Line

It’s true that there are situations, such as in high-volume rock bands, where the penetrating sound of a piezoelectric pickup will do the trick—and might even be preferable to a miked sound. But in intimate settings, like solo performances or small ensembles with other acoustic instruments, Audio Sprockets’ ToneDexter is a total boon for the gigging acoustic guitarist. You get a convincing mic sound, without the hassle of having to bring one with you or being stuck behind it onstage, and a pro-level preamp and DI, all in one small package. 

SPECS

• Preamp/DI with microphone simulation
• Storage for 22 WaveMaps (microphone sounds)
• Output level, pickup level trim, notch, bass, treble, character, and WaveMap select controls
• Mute and boost buttons
• Built-in tuner
• 1/4″ and XLR (48V phantom power) inputs
• 1/4″ and XLR (DI) outputs
• 1/4″ headphone out with level control
• 1/4″ effects loop
• 9–15VDC power

PRICE: $399

This article originally appeared in the August 2018 issue of Acoustic Guitar magazine.