Field Test: Radial Studio Guitar Interface

Sep 1, 2007 12:00 PM, By Kevin Becka



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Combo guitar amps are great for live gigs, but not necessarily for studio recording. This is because the player has to reside in the same high-SPL space as the device. The ear-saving alternative is to run an extra-long, high-impedance guitar cable from the control room to the amp, losing tone and punch in the process. The Studio Guitar Interface (SGI) from Radial Engineering offers an affordable solution, allowing a guitar signal to travel 328 feet over a standard, balanced, low-impedance XLR mic cable with a very small sonic trade-off (more later). It can also be used in a live situation to get your signal from a wireless system to an effects rack or amp.


The system breaks down to two palm-sized interfaces: the SGI-TX transmitter and the SGI-RX receiver. Keep in mind that this system isn't wireless, and that's the beauty: You don't have to pay for the transportation cost with tone. There's also a nice feature that lets you add an impedance load (Drag) to your pickups that you'd normally lose by running it through a transformer or two, which is how the SGI does its voodoo. The Drag control lets you dial out top and add low-end punch, which makes up for variations in tone changed in the process.

To make the long-distance run, plug your guitar into the (wall wart-powered) SGI-TX interface using a guitar cable, make your long run to the SGI-RX receiver using standard mic cable and then back from the SGI-RX to your amp using another guitar cable. Your results may vary with different cables, but for this test I made the high-impedance runs using a Canare Star-Quad guitar cable and the XLR run with a 25-foot Monster ProLink Standard 100 microphone cable. The SGI-TX is an active device with 100-percent discrete, Class-A circuitry and Drag control load correction to ensure the most natural sound. The SGI-RX is completely passive.


I ran the system using four different guitars and a bass, providing a wide range of pickups, loads and tonal variations. I first played the guitars with the SGI in place and then without it, making assessments along the way. For starters, I tried a Fender American Deluxe Telecaster with SI switching and two stock single-coil pickups. I immediately had to employ the RX's ground lift to get rid of a nasty hum, but after that it was smooth sailing. This setup provided the least amount of variation in tone; there was little difference between A/Bs with and without the SGI. The Vox AC30 CC2X with two 12-inch Celestion Blue Alnico speakers — the amp for all the guitars tested — rendered the Tele's punchy and clean tone with and without the SGI, with little or no audible volume change.

Next I tried a Gibson ES137 with standard dual humbuckers. When A/B'd with and without the SGI, the humbuckers were a bit louder without, slightly altering the tone so that it sounded a bit less punchy and had a bit less low end. Even with the drop in level, I could easily match the tonal variations using the Drag control, which let me dial in less top and more low-end punch. The Drag control is altered using a small, knurled rotary knob that has a quality feel, and can either be hand-tweaked or turned with a screwdriver. It's a bit hard to turn, which may be a good thing if you're looking to lock in a setting that's not easily changed over a series of gigs. The screening on the box in reference to Drag is a bit of an enigma marked “Less” and “More,” yet the rotary doesn't seem to correspond to the printing because the knob itself is not marked, making it hard to reset accurately. Nonetheless, I could use my ear to dial in exactly what I needed from one setup to the next.

Next I next played a Heritage Golden Eagle with a Johnny Smith-style floating humbucker and flat-wound strings. Once again, as with the last humbucking pickup, the overall volume and tone altered ever so slightly when the guitar was run through the SGI, but I was able to compensate with the Drag control.

For something completely different, I tried an Epiphone Chet Atkins steel string with piezo pickups, which traditionally can sound rather thin. This guitar's tone was enhanced when running through the SGI. The Drag control offered some degree of EQ that took some of the brash high end out of the piezo and added some warmth — an unexpected plus. Last, I tried a Modulus 5-string Quantum 5 with a graphite neck and stock EMG active pickups. A/B testing with and without the SGI was the same as with the guitars; there was a slight drop in volume and bottom, but once again the Drag control did its job by restoring the tone changed in the process.


The Radial SGI offers an elegant, simple and affordable solution for recording combo guitar amps at a distance. The only audible trade-off was a bit of lost level and subsequent tone when I used it with some of the guitars, especially with humbucking pickups. In all cases, the variations in tone and volume were minute and I was able to dial in and match the tone quite accurately using the Drag control. At $275, the SGI is an affordable, great sounding and ear-saving no-brainer that should be in every studio.

Radial Engineering,, 604/942-1001.

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