In order to run your electric acoustic guitar into most professional P.A. systems, you need to plug into a direct box, which is also commonly referred to as a D.I. box or line transformer.
The direct box convert your high impedance guitar signal into a low impedance one as use by most professional mixing boards.
There are benefits of using a low impedance sign, one of which is you are able to run much longer cables without near as much signal derogation as a high impedance line. Think about all those arena shows you have been to and seeing the front of house mixing board on the floor more than a hundred feet away from the stage and it starts to make sense. Another benefit is XLR cable can easily be linked together since one end is male and the other is female.
(Here is as good as place as any for a let info on XLR plugs and jacks. The male, the one with the three pins, points the way the signal is headed: something to keep in mind before using a male to male or a female to female converter. This was the intention, since XLR cables are also used to connect power amps to speakers and monitors.)
Most direct boxes, while having only one input, will have two outputs: an XLR and a standard ¼” output jack. This allows the guitar to run to both the p.a. and an on stage acoustic amplifier if desired. Many guitarist use the ¼” output for their tuner, where it won’t degrade the signal…however, this renders the tuner’s mute switch (if it has one) useless, as the XLR signal is not in that path. If you want to have your guitar muted when you tune (and the audience does), you’ll need to run your guitar into the tuner and the tuner’s output into the direct box.
Most stand alone direct boxes, as opposed to a preamp with an XLR out that functions as a direct box, are devoid of controls aside from a ground lift switch and maybe a pad switch. If there’s a hum in the line (usually caused by running your guitar into an amp and the P.A. at the same time), the soundman may ask you to flip the ground or ground lift, and 9 times out of 10 that will solve the problem.
If your guitar has a preamp, or you’re using one in line, and your signal is running too hot, you may be asked to either turn down some or flick on the pad switch that will attenuate the signal to an acceptable level.
There are both active and passive direct boxes. For some reason, active signals “like” passive direct boxes and passive signals “like” active direct boxes for optimum performance, though both will do the job. Of course, active preamps require power, which will usually be phantom power provided by the board, but may need to be powered by batteries if being used with a semi-pro sound system.
If your guitar is equipped with more than one pickup or a pickup and a mic, and you want to send the signals separately to the P.A. you’ll either need two direct boxes or a stereo direct box (basically two direct boxes in one).
All that being said: direct boxes are usually provided by the sound company or club. But, there are those players that are really picky about their sound and consider every aspect of their sound chain essential, and they bring their own direct box to the gig.
Jake Kelly is a man on the constant search for enlightenment, if anyone finds it let him know so he can get some. For more of this hombre’s ramblings and the rest of L2P check out L2Pbandspace and L2Pnet.com.