Tips For Reducing Unwanted Feedback

By Mike Harian

All rock and metal guitarists have experienced it at one time or another. It's the middle of a gig. You're in a quiet passage in a song, or between songs. You shift your guitar position slightly, and to your chagrin the worst howling sound imaginable emanates from your amp. Yep, feedback. It's tough to escape at times, and unchecked, it can really mess with your tone not to mention your head!

Of course not all feedback is bad. Harmonically correct feedback can enrich your guitar sound, and is primarily responsible for those hanging lead notes that sing forever. Harmonically correct feedback can be used as a cool effect. Achieving it is simple. Push the gain on your amp, strike a note or chord then angle your guitar about 45 degrees into your amp speaker. Changing the angle from 45 degrees, to 90, then perhaps 180 degrees will at times shift the feedback from the tonic to the 4th or 5th, etc.

Now let's address "bad feedback". Many guitarists have been plagued with this problem at one time or another. Most feedback issues can usually be narrowed down to one of two culprits. Gain related problems, and/or pickup proximity. Let's discuss each:

Gain Related Problems

 Yep. Too much gain can be the root cause of a feedback problem. The solution is simple. Turn down your gain knob. Of course this may not produce results that are pleasing to your ear. If you are a metal player, the last thing you probably want to do is turn down your gain. If you are playing on solid state equipment the result is even less desirable, as you typically don't get the added gain from the post amp on solid state gear that you do on tube gear.

Here are a few things you can do to solve the gain problem. I'll list the items from cheapest and/or easiest to most difficult and/or most costly.

Step 1: Move farther away from your amp. Moving farther away tends to eliminate many feedback problems. Setting your amp on the ground (instead of placing it on a stand) may be enough.  An added benefit to placing your amp on the ground is that you'll get better bass response. Conversely (but far less desirable) you could lower the volume of your amp and put it up on a stand closer to you, so you could hear it better, then mic the amp (or use a direct box) such that the majority of the guitar volume is generated by the PA.

Step 2: Try another guitar or two. If the problem disappears see the section on pickups below.

Step 3: Check microphone interactivity with your amp. I had a mysterious feedback problem a short while ago. Seems that I was only having the problem when gigging. Because I typically don't mic my amp for rehearsals, I immediately began suspecting  the SM-57 we used to mic my amp. Turns out that my Peavey XXX doesn't play nice with any microphone! When it is not mic'd up it sounds great. Put a microphone in front of it (any mic) and I'm in feedback hell. I tried different mics with different positionings, all to no avail. Solution, a $35 Behringer direct box.  Yeah, I  know what you're thinking, but a direct box is still better than a microphone thrown hastily in front of your amp by a poorly paid sound-man who really doesn't have time to properly position your mic, or for that matter, who could care less about your sound.

Step 3: Try replacing your cord with a known good chord of high quality.

Step 4: Try replacing your preamp tubes. Bad tubes in multi-stage pre-amps may oscillate out of phase with each other, causing your amp to feedback.

Step 5: Place a noise gate between your guitar and your amp. Note: I have noted that placing the noise gate in the effects loop is less effective than placing it in front of your amp. I have used the little black MXR noise gate very successfully in this situation. The noise gate actually "mutes" your noisy/microphonic pickups, so if this cures the problem please see the section on pickups below.

Pickup Proximity

More often than not, pickup proximity is the most common cause of feedback. The biggest problem is setting the pickups too close to your strings. A good rule of thumb is to adjust your pickup height such that two nickels can easily fit between your pickup and low E string and one nickel can easily fit between your pickups and high E string. Reducing pickup height  solves 90% of the feedback problems plaguing guitarists! Also, setting a pickup too close to the strings will cause the magnetic field to dampen the string vibration, ultimately reducing your sustain.

Pickups can also be microphonic. When a pickup is microphonic it transmits external noise into the amplifier. The external noise can be sound from your PA, stage noise, your hand, pick, etc. Pickups are typically potted (dipped into wax or epoxy) to prevent them from being microphonic. If your pickup is severely microphonic you can speak into it (like a microphone) and hear your voice coming from your amplifier! A pickup doesn't have to be old or abused to be microphonic either. I recently purchased A Dimarzio Tone Zone (my favorite bridge pickup) for one of my guitars. Right out of the box the pickup was so microphonic that it would start to vibrate "sympathetically" while I was playing. I could actually feel and see the pickup vibrating in the pickup cavity of my guitar! Dimarzio remedied the problem quickly with a single call into their tech support department, but it's probably safe to say that not all new pickups are created equal...

Here are a few things you can do to solve a pickup related feedback problem. I'll list the items from cheapest and/or easiest to most difficult and/or most costly.

Step 1: Lower your pickup!

Step 2: Lower your pickup!!

Step 3: Lower your pickup!!!

Step 4: Insert some foam rubber in the pickup cavity behind your pickup. I do this on every guitar that I own, and it really keeps the sympathetic vibration down to a minimum.

Step 5: Try a couple of different guitars with your amp. If the problem still exists, see the gain troubleshooting steps above.

Step 6: If you are experiencing noise problems, ensure your pickup control cavity is adequately shielded and grounded.

Step 7: Replace the pickup. There are a number of good third party pickup manufacturers out there........ Bill Lawrence (www.billlawrence.com) Dimarzio (www.dimarzio.com) and Seymour Duncan (www.seymourduncan.com) to name a few. There are many others. Check Harmony Central (www.harmonycentral.com) for a complete listing. Young players - Don't always go for the "hottest" pickup you can find. Tone curves provided by a manufacturer on its web site will tell you much more than impedance and voltage specs. Also, hotter pickups tend to feedback more. This is especially true in high gain applications. Simply put, if hotter pickups were so great, every major endorsee of Dimarzio and Seymour Duncan would be playing Invaders and X2N's. Finally, hotter pickups typically produce a "muddier" sound. Personally, I like a pickup that is slightly hot, with some peak in the mid frequencies......but that's just me. Also, keep in mind that pickups will react differently with one another in the "combined" positions. My favorite pair is a Dimarzio Tone Zone in the bridge, coupled with an Air Zone in the neck. The two combined produce a spectacular out of phase sound that you just can't beat for clean and rhythm work. Ask around, and check the pickup reviews at Harmony Central before buying.