Enhance Your Guitar's Sustain with Control-Room Feedback

Add a New Sound and Performance Element to Your Guitar through an Auxiliary Amp that Generates Feedback

by Jon Chappell

Every guitarist knows what it’s like to stand facing a stack of speakers with the guitar and amp turned up to feedback levels. It’s not only louder than heck, it increases the sustain of the notes themselves. It almost feels like the feedback is pushing you along, at times seeming to take over and make its own sound. Well, as far as the strings are concerned, it is.

What happens in a feedback situation with a guitar is that an endless loop forms between the amplified sound and the vibrating strings—but only if the strings are allowed to vibrate. You can make the strings vibrate either by picking them or by allowing the high-gain, close-range feedback to oscillate the strings for you. It’s this second, hands-free method that provides us with a neat performance trick to increase the sustain of the ringing strings without affecting the sound of the primary amp or the recorded signal.

All you need is an additional, small combo amp, and an available aux send on your mixer. (You could also accomplish this through an aux out of your preamp or main guitar amp.) We’ll use this aux send only to drive the smaller amp; we’re not recording the sound of the smaller amp.

SETUP FOR SQUEAL

Set up the amp and an aux send as shown in Figure 1 (which shows the line out as Aux Send 2). Run the line out from your mixer into the input of the smaller amp that you keep in the control room with you. It’s best to use a 10" or 12" combo with a clean sound. The idea is to play in the control room and use the small amp to generate feedback at desired spots during your solos or fills. We’ll be using the control-room amp to act as our “string exciter.”

Fig. 1. Running an aux send from the guitar channel to drive a small  amp in the control room allows you to selectively use feedback to  increase sustain without affecting the sound of the amp in the live  room.

Remember, we’re not actually going to be recording this amp; we’re just using it to move the guitar strings. We’re looking for additional sustain and perhaps some octave feedback at choice times. Set the amp controls with a little high cut, boosted mids, and a little added low end. If you have a parametric EQ, you can analyze down to the note/frequency which note will feed back. For example, if you have a 17th-fret A on the first string that you want to feed back, boost the frequency at 880Hz.

Put the amp on a chair or stool so that you can face your guitar into it when you want feedback. The position of the amp will vary according to the type of guitar you’re using, the pickup sensitivity, how loud the control-room monitors are, etc.

DIALING IT IN

There are two ways to initiate feedback: either by turning the face of the guitar into the pickups at the appropriate times, or by having someone actually turn up the amp's gain in time with the music when the desired feedback point comes. This way, as assistant “plays” the amp as you play the guitar. Again, no level change will be apparent in the recorded track, because this amp is not being recorded; it's merely acting as a string vibrator.

You should practice with the track and your assistant, until you get the right performance down as well as establishing the right settings on the feedback-inducing amp. Even a subtle application of this works wonders. A little sustain as the result of feedback will not only enhance your sound but inspire a performance!

Jon Chappell is a guitarist and the Senior Editor of 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 Dummies series (Wiley Publishing).