Direct boxes aren't just for recording bass - check out these tips for guitar
By Jon Chappell
Here are two different scenarios involving guitar amps and recording, both with a common problem that can be solved with direct-box technology. We don't normally think of direct boxes for recording guitars (that's an onstage bass thing!), but it does come up, especially in the following two situations.
Scenario 1: You have a great vintage guitar and amp, but the amp has no master volume, so you really need to crank it to get the quality you want. The sound is so flippin' loud that it overwhelms your monitoring system, so you decide to put the amp in another room (down the hall, in the basement, etc.) and mic it, running the mic cable back to the recorder (where you are). You use headphones to monitor the miked sound, and the speaker volume doesn't shake you out of your chair.
Scenario 2: You're in a proper recording studio, with a separate live and control room, and you'd like to sit in the control room with the amp beyond the glass, because it's easier to run the session and talk to the engineer (you're doing a bunch of guitar overdubs). "No problem," says the engineer, "we'll put some close and ambient mics in the live room, and monitor you through these giant control-room monitors so you'll hear a full sound."
In both these situations, the guitar is separated from the amp by a considerable distance, and that means running an inadvisably long patch cord (greater than 30 feet) between the guitar and the amp. This isn't a good idea under any circumstance, but especially if you have passive or low-output pickups (as most vintage models are).
A neat way around the limitation of recording from the control room with a combo in the studio is to use Radial Engineering’s SGI (Studio Guitar Interface) system. These relatively inexpensive, no-frills, passive (non-powered) gizmos convert your guitar’s high impedance signal to low impedance and transports it to another box that converts it back to high impedance.
Here's how it works. The guitarist plugs a cable from the guitar into the first direct box, the SGI-TX (tx is the symbol for "transmitter"). Then the low-Z (three-pin) out is connected via a mic cable of whatever length (say 40 feet) is necessary to a second direct box. (Radial guarantees tone integrity up to 100 meters or 328 feet.) Because the signal has been converted to low impedance, it can travel a long distance without suffering degradation. The signal meets up and connects with to the low-Z input of the second Radial box, the SGI-RX (receiver). The second box should be placed right near the amp.
Fig. 1: Covering long distances with Radial Engineering’s SGI system--essentially two complementary-function direct boxes. The image in the foreground middle is a schematic showing the connections.
Then the high-Z, 1/4" output is used — along with a normal patch cord — to connect the second direct box to the amp, so that the amp's input gets the high-Z signal it's looking for. Fig. 1 shows the direct-box schematic in the foreground with a scale-looking illustration of how the setup looks in the recording studio.
Many studios have "tie lines" or wired jack plates on the walls that can get you into and out of the room you're in, but if you're at home, or in any other improvised environment where separating the guitar from the amp is advantageous, just the two boxes will do the trick.
Jon Chappell is a guitarist and Associate Editor at Harmony Central. He has contributed numerous musical pieces to film and TV, including Northern Exposure, Walker, Texas Ranger, All My Children, and the feature film Bleeding Hearts, directed by actor-dancer Gregory Hines. He is the author of The Recording Guitarist: A Guide for Home and Studio (Hal Leonard), Essential Scales & Modes (Backbeat Books), and Build Your Own PC Recording Studio (McGraw-Hill), and has written six books in the popular For Dummies series (Wiley Publishing).