If you’re playing a gig on a big stage, outdoor festival, arena, or large venue, you’re probably going to be faced with having to run your guitar amp into the PA system.
The purpose of this, of course, is so that your guitar will be heard in a situation where the amp alone is not enough.
There are also times, even in a smaller, low volume venue, that running the guitar amp through the PA is a good idea, just to add some “presence”, and to fill out the overall mix of the band.
When you find yourself in this situation, you really have two options.
1. Run a “line out” of the amp to the PA
2. Place a microphone on the amp
Line Out
Many amplifiers will have an output jack in the back labeled “line out”, or something similar. This jack outputs a “line level”, non-powered signal that can be fed to a PA system or recording device.
This signal is “post” amplifier, but “pre” speaker and, as a result, the signal that is being fed to the PA or recording device represents the sound that is produced by the amp itself.
In other words, any distortions, reverbs or effects that are processed by the amp and/or pedals is the sound that is output at the “line” level – but not the actual sound that comes out of the speakers.
Obviously, the sound that ultimately comes out of the speakers is the “true” sound that is heard by the audience, so using the “line out” jack to feed a signal to the PA is the least desirable option.
Placing a Microphone on the Amp
Since the sound that comes out of the speakers is the most desirable sound, in most cases, placing a microphone on the amp is usually the best way to go.
When micing an amp, the first thing to decide is what kind of microphone to use.
A good “omni-directional” mic is most preferred, and the overall top choice of mics for sound engineers is the Shure SM-57.
This workhorse of a mic is an industry standard that has many instrument mic applications, and is hard to beat in sound replication and reliability.
Mic Placement
When placing the mic on a guitar amp, use a small boom or straight mic stand. Shine a flashlight into the front of the amp and locate the speaker face.
Place the mic against the grille cloth in an “off set” position toward the speaker edge, rather than directly in the middle of the speaker. This will give the “truest” sound of the amp through the mic.
When doing a sound check, turn the amp up to normal playing volume so that the sound engineer can tweak the guitar level and blend it properly with the rest of the band.
In Conclusion
Although there are times when using the “line out” feature of an amp is the only option – like when a mic is simply not available – the resounding choice of sound engineers and guitar players everywhere in a situation that requires an amp to be run through the PA system, is to put a mic on it!
