Tech 21 designed the SansAmp XDI ($95) primarily as an interface for its PSA-1 Pro Tools plug-in — the software version of the company's popular PSA-1 guitar amplifier and speaker cabinet simulator — but it also functions as a standard direct-injection box when used with mixers and computer audio cards.
There are two high-impedance (1 M•) ¼-inch inputs labeled Normal and Bright, just as you'd find on a typical tube guitar amp. Unlike a guitar amp, however, you can use only one input jack at a time. A balanced XLR and an unbalanced ¼-inch low-impedance output jack are provided. The latter eliminates the need for an adapter when using the XDI with audio cards that have only unbalanced ¼-inch inputs. You can use both outputs simultaneously, though the manual advises against it with a warning that you could compromise the sound quality of the ¼-inch output.
In the Black
The XDI is housed in cast aluminum painted black with yellow labeling and measures 4.5 inches wide by 3.5 inches high by 1.5 inches deep. The casing feels sturdy, and the unit's four solidly attached audio connectors appear to be of high quality. Inside, the wiring and solder work is neat and clean. A hinged battery door on the bottom plate is a thoughtful addition.
The use of FET technology results in remarkably quiet operation. The circuitry accepts power from a 9V battery, a 9 VDC power supply such as the optional Tech 21 DC2 ($12.95), or 48V phantom power through the XLR output jack. The unit will operate with as little as 24V, making it compatible with many less expensive mixers and preamps. Conveniently, the unit overrides the battery when it detects phantom power.
I don't own a Pro Tools system, so I was unable to use the XDI with the PSA-1 plug-in. However, I did use it to drive the amp simulator in my Yamaha 03D digital mixer. The XDI made the mixer's rather lame amp simulator sound more realistic — an unexpected benefit. I patched the XDI between my PRS Custom 24 guitar and the 03D mixer using every possible configuration of inputs and outputs.
First, I connected the XDI to the 03D using the XLR output, powering the box with the mixer's 48V phantom power; then, I connected the XDI using the ¼-inch output, powering it with a 9V battery. Both methods yielded excellent results, and I could not perceive any differences in audio performance.
On the other end of the box, the XDI's Normal and Bright inputs offer distinctly different sounds, both of which will be familiar to guitarists who are used to playing through vintage and vintage-style tube amps. The equalized sound of the Bright input is particularly authentic sounding, providing the sort of transparent high-frequency sheen reminiscent of an old Vox AC30, for instance.
Next, I patched the XDI into one of the ¼inch inputs on my Mark of the Unicorn 2408mkII audio interface and recorded some guitar sounds directly into Digital Performer. The XDI sounded great in this application, functioning almost as a preamplifier in the way that it tightened up the sound overall and added high-end definition. The unit sounded the same when powered with a 9V battery as it did when powered with an external power supply.
There's really little more to say about the XDI. At $95 it's a great bargain for guitarists (or bassists) who want to plug their instruments in to a mixer or sound card, especially if you want your instrument to actually sound like a guitar without adding noise or undesirable distortion. You can never have too many direct boxes at your disposal, so check it out!