You turn up at rehearsal and the tone sounds great. Then a sudden shriek tears through the room, and the culprit turns out to be your guitar, not the amp.
That squeal usually means a pickup has gone microphonic. It gets worse the louder you push, and it’s a different beast from ordinary amp feedback.
This guide explains why pickups turn microphonic and a little about how they work. We also walk through wax potting, the fix that actually makes the squeal stop for good.
So what sets a pickup off? Let’s start there.
Why Do Guitar Pickups Go Microphonic?
Like the name suggests, microphony happens when the different guitar pickups start behaving like microphones. They pick up unwanted sound from outside and mash it together with the signal coming from your guitar.
It’s this concoction that turns into a squealing screech as it travels down the signal chain and into your speakers.
So why exactly do guitar pickups go microphonic? To answer that properly, it helps to first look at how a guitar pickup works.
Once you understand the basic mechanics, the cause of microphonic feedback becomes obvious.
Anatomy of a Guitar Pickup
A guitar pickup is a transducer at its core - a device that converts energy from one form to another. It transforms the vibrational energy produced by guitar strings into a signal that can be amplified, recorded, or transmitted.
In that sense it’s a sonic transducer, the same family that includes microphones and speakers.
All sonic transducers are electromagnetic in operation, leveraging Faraday’s Law of Induction. This states that an electric conductor exposed to a changing magnetic field will have a current induced in it.
In other words, a wire wrapped around a magnet will have a current flowing inside it whenever there’s a disturbance nearby - a disturbance like the movement of a guitar string when you pluck it.
Of course, not every magnet-and-wire combo can capture that disturbance properly and turn it into the twangy sound you hear through the speakers. Guitar pickups use magnets made of alnico or ferrite.
You can read about how guitar pickups are made for the full process. Both materials produce strong magnetic fields and hold their potency even in harsh conditions.
The permanent magnet then has a finely enameled copper wire wound around it, in turns numbering in the thousands.
It’s this coil that registers the changes in the magnetic field that occur when you strum the strings. The resulting current is transmitted to the amp, where it’s boosted and sent down the chain.
For good measure, the strings are made of a ferromagnetic material like steel (one that becomes magnetized when exposed to another magnet). The result is an additional magnetic field that induces a current in the coil whenever the strings vibrate.
When Pickups Go Rogue: How the Squeal Starts
Remember that guitar pickups are classed as sonic transducers, and microphones are another member of the family. So you can expect a few similarities in anatomy - some types of mics use a setup similar to a guitar pickup, with a diaphragm that moves when hit by sound waves and a wire-wound magnet nearby.
There’s also some overlap on the functional side. Point a powered mic at your guitar amp as you play and it’ll definitely pick up sound you can then amplify.
That’s something you can take advantage of when playing an acoustic on stage by mounting the mic on a stand to free your hands. Or you can add a pickup to an acoustic guitar instead.
So could you swap a mic for a pickup? Afraid not.
While a microphone is designed to hear any kind of sound, guitar pickups are tailored to register only the intricate vibrations of guitar strings. Sound needs a medium to travel through (solid, liquid, or gas), but vibrations don’t.
That means a pickup will work even in a vacuum - something a microphone can’t do.
What gives pickups the ability to capture the strings’ subtle movements while shutting out other vibrations? It comes down to how they’re built.
Unlike microphones, pickups have no components that are meant to move while they operate. They’re often dipped in wax to fill the tiny spaces between the windings, leaving little (if any) room for movement.
And so microphonic feedback is usually a sign that your pickups are starting to lose their original shape. The windings become loose enough to vibrate under the influence of external forces.
These secondary vibrations disturb the magnetic field, creating a signal that gets sent through to your amp and loudspeaker. It comes out as a high-pitched howl because the wire in your pickups is extremely thin and vibrates at a very high frequency.
To add salt to the wound, that unwanted sound makes the coil vibrate even more, and you don’t have to be a genius to guess what happens next.
Why Microphonic Feedback Gets Worse With Volume
This also explains why microphonic feedback varies so wildly. When you’re playing at low to moderate volume, the sound waves coming off your speakers aren’t strong enough to start those secondary vibrations in the coil.
Crank the volume up, though, and the feedback turns into a screeching nightmare. At high volume the sound waves carry enough energy not only to start the vibration but to sustain it, which is why the squeal often won’t quit until you turn down or step away from the amp.
That’s also why the problem tends to show up first in high-gain situations and on stage rather than at bedroom levels. The more energy you feed the pickup, the more a loose coil has to work with.
How to Fix Microphonic Guitar Pickups
We’ve already hinted that you can rein in squealing pickups by starving them of external energy - avoiding high-gain settings, turning the volume down, or stepping away from the speakers. These measures help in a pinch, but they aren’t always effective or practical, especially mid-gig.
For a real fix, you’re better off having the pickups repotted with wax. This may cost a bit if you pay a tech to do it, but it’s the only way to stop the problem from getting out of hand for good.
Wax Potting Pickups Explained
Wax potting, sometimes called “wax winding,” is a technique for tightening up a pickup and taming its resonance. It’s also used to give an electric guitar a more vintage character by saturating the pickup’s bobbin and coil with wax.
The wax fills the gaps in the coil and removes unwanted microphonic feedback from your pickups while adding sustain and definition to overdriven tones. Think of it as a built-in control that reins in the noisy, uncontrolled part of the signal.
Wax potting effectively does two things for the guitar: it lowers the frequency of resonance and increases dampening. These effects don’t occur in equal amounts.
It’s also worth noting that potting works on the electrical side of the equation rather than the magnetic output - in simple terms, it stops the physical windings from moving, which is what was generating the rogue signal in the first place.
The Downsides of Wax Potting
The main downside of wax potting is that it adds mass to the pickup. Pickups with a lot of wax in them can sound muddy and lose some definition, and they can be harder than unpotted pickups to play cleanly.
Heavily potted pickups can also become easy to clip or damage, so be careful when handling and moving them around. Because of this, wax potting is very much a personal choice - it’s something you may prefer or not prefer depending on the guitar you own, whether you play a Stratocaster, a Les Paul, or something else.
If you’re chasing high-output tones, our guide to the best guitar pickups for metal is a good next read.
Frequently Asked Questions
Is microphonic feedback the same as normal amp feedback?
Not quite. Normal feedback is the controllable howl you get when the string and amp resonate together, and many players use it on purpose.
Microphonic feedback is different - it comes from the pickup’s loose windings physically vibrating, so it’s harsh, sudden, and largely outside your control.
The giveaway is that microphonic feedback often appears even when you mute the strings or stop playing, because the noise is coming from the pickup itself rather than the strings.
Can I fix microphonic pickups myself?
You can, but wax potting takes care and the right materials, since melted wax and electronics are involved and overheating can ruin a pickup. Plenty of players do it at home successfully by following a detailed tutorial.
If you’re not comfortable removing and reinstalling pickups or working with hot wax, it’s worth paying a guitar tech. The job is relatively inexpensive compared with replacing the pickup entirely.
Do all pickups go microphonic eventually?
Not necessarily. Many factory pickups are potted from the start and stay quiet for the life of the guitar.
Microphony usually shows up in older, vintage, or unpotted pickups, or in ones where the wax has degraded or the windings have shifted over time.
High volume, heavy handling, and temperature swings can all speed things along, which is why gigging guitars tend to be more prone to it than instruments that stay home.
Will wax potting change my tone?
It can, slightly. Potting tames the resonant peak and adds a touch of dampening, so a heavily potted pickup may sound a little smoother or darker than the same pickup left unpotted.
If you also notice your pickups sound thin or quiet, that’s a separate issue covered in our guide on why guitar pickups sound weak.
For most players the change is subtle and well worth losing the squeal, but it’s why some vintage purists prefer lightly potted or unpotted pickups despite the feedback risk.
Final Thoughts
Microphonic feedback isn’t a mystery once you understand what a pickup actually is. It’s a coil of fine wire wrapped around a magnet, and the moment those windings come loose enough to vibrate on their own, they start acting like a microphone and feeding extra noise into your signal.
Crank the volume and that small problem becomes a stage-stopping shriek.
The good news is that it’s fixable. In the moment you can back off the gain, drop the volume, or move away from your speakers, but the lasting cure is wax potting, which locks the windings in place so they can’t move.
Just weigh the small tonal trade-offs before you commit.
Get familiar with how your pickups are built and behave, and a sudden squeal stops being a panic moment and becomes a quick, known diagnosis - one you can fix and get back to playing.
