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Why does my amp hiss, hum or buzz?
Updated 8 min read1 knob panel8 sources
Hum is a steady low tone at twice the mains frequency, 100 Hz where the power is 50 Hz and 120 Hz where it is 60 Hz. It usually comes from single-coil pickups near transformers, dimmers or computers, or from a ground loop. Hiss is a high, steady rush that every amp makes, and it grows with gain, treble and presence. Buzz that fades when you touch the strings is your body acting as an antenna, and it is normal.
To find the source, work backwards: turn the guitar's volume to zero, then unplug the guitar, then take the pedals out. Whatever removes the noise is where it lives. Never take the earth off a plug to stop hum: Wikipedia's article on ground loops says that creates a shock hazard, and Marshall's handbook says never to operate an amp without an earth.
Hum, hiss, buzz or crackle: which one is it?
Thomann's guide to amp noise sorts it by sound. Humming is low and usually continuous, like the noise when a plug's tip touches the jack as you plug in. Hissing sits much higher and is also constant; Thomann likens it to waves on a beach. Crackling comes at irregular intervals.[1]
Mains hum has a pitch you can name. Wikipedia gives it as twice the mains frequency: 100 Hz where the power is 50 Hz, and 120 Hz where it is 60 Hz.[2] Fender calls single-coil hum 60 cycle hum,[3] after the mains in the United States. Buzz, in this guide, is the harsher noise from lights and dimmers, which DiMarzio says changes when you turn the guitar's tone control, while mains hum hardly changes at all.[4]
| Noise | Sounds like | Usual causes | Try first |
|---|---|---|---|
| Hum | A low, steady tone at 100 or 120 Hz | Single coils near transformers, dimmers or computers; a ground loop; a bad cable | Check the cables, then put all the gear on one outlet |
| Hiss | A high, steady rush | Gain, treble and presence; compressors and drive pedals | A step less gain, then a noise gate |
| Buzz | Harsh, and changes with the tone control | Fluorescent lights and dimmers | Move away; it fades when you touch the strings |
| Crackle | Irregular pops | A broken cable; scratchy pots | Swap the cable; have the pots cleaned |
How to find where the noise starts
1. Turn the guitar's volume to zero. If the noise stops, it is coming in through the pickups; if it stays, it starts after the guitar.
2. Unplug the cable from the amp's input. Noise that is still there comes from the amp itself or the power it runs on, so try another outlet, then another room.
3. Plug the guitar straight into the amp with one cable you trust. Thomann's first check for hum is a cable that is broken or not plugged in properly.[1] If it is quiet now, add the pedals back one at a time: the one that brings the noise back, or its power supply, is the culprit.
4. With single coils, select two pickups together. That is Thomann's test: if the noise goes, the single coil you had on its own is picking up interference.[1] Then turn and move around the room, because the noise changes with where you stand.
5. If the hum appears only when a second mains-powered unit is connected, such as mains-powered pedals or a second amp, it is likely a ground loop.[1]
- Guitar
- PickupsGuitar volume to zero
- CableSwap for one you trust
- PedalsAdd back one at a time
- AmpInput unplugged
- Outlet
Whatever removes the noise is where it lives.
Why do gain, treble and presence make an amp hiss?
Every amp makes some noise of its own. Thomann notes it becomes much more audible at higher volumes and higher gain, and that a compressor, booster, overdrive or distortion added in front can raise it drastically.[1] Premier Guitar gives the reason: the higher the gain, the more the signal and the noise are both amplified, and fuzzes and high-gain overdrives can generate noise of their own.[5]
Treble and presence do not create noise, but they turn up the high band where hiss lives, so a bright, high-gain setting hisses most. Before reaching for a gate, take the gain down a step and check the sound still works. The same goes for a compressor in front, which lifts the quiet noise between notes along with the quiet notes.
There is no easy fix for an amp's own hiss, Thomann says, but it matters less than it seems: it is mostly heard in the gaps when you are not playing, and a noise gate closes those.[1]
How do I stop single-coil hum?
Single coils pick up interference from alternating current. Thomann lists the usual sources: transformers in power supplies, stage lighting dimmers, neon lights and computers.[1] The closer you are, the louder the hum, and moving to another spot is the quickest cure. Humbuckers are designed to reduce it, as Wikipedia's article on mains hum says,[2] and Fender's noiseless single coils and Silent System exist for the same reason.[1][3]
Humbuckers do not stop everything. DiMarzio says they do not completely remove the higher-frequency noise from fluorescent lights and dimmers,[4] so a humbucker guitar can still buzz in a room lit that way. Wah pedals pick up interference too: Thomann's advice is to keep a wah away from the transformer in a pedalboard power supply.[1]
Why does the buzz stop when I touch the strings?
Premier Guitar explains it: your body works as an antenna and picks up noise, and touching the grounded strings sends it to ground.[5] DiMarzio describes the same thing from the other side: if the bridge is grounded, most of the noise disappears when either hand is touching the strings or the bridge.[4] So a guitar that buzzes when you let go and goes quiet when you touch it is working as designed.
DiMarzio adds that shielding the control compartment and shortening excess wire in it reduces the noise further.[4] Beyond that, the fixes are the ones for single coils: distance from the source, where you stand, and two pickups together or humbuckers.
Ground loops: hum from two earths
A ground loop forms when the signal ground is earthed in two or more places.[1] Thomann gives the usual cases: a pedalboard with mains-powered effects, or a rig with more than one amp. Its fix is to plug all the guitar gear into one outlet through a power strip, not the amp into one outlet and the pedalboard into another, and where that is not enough, a ground loop isolator in the signal path, such as before the amp's input.[1]
One outlet does not cure every loop: Wikipedia's article notes that plugging everything into the same outlet does not by itself prevent one.[6] What you must never do is lift the safety earth with an adapter or a broken-off ground pin. Wikipedia says that creates a shock hazard,[6] and Marshall's JTM 30 handbook says never under any circumstances to operate the amplifier without an earth.[8]
What a noise gate fixes, and where it goes
A noise gate mutes the signal when it falls below a threshold, so it silences the gaps between phrases. Premier Guitar likens it to a door that slams shut when no playing is coming through, and warns that a gate set badly cuts off notes as they fade.[5] It does nothing about noise while you play, which, as Thomann says, is usually covered by the playing anyway.[1]
BOSS's NS-2 manual sets one up in a few moves. Switch on the noisy effects, then set Threshold so the Reduction indicator is lit at rest, while you are not playing. Leave Decay at MIN, turning it clockwise only if notes do not fade out naturally.[7] Set the mode switch to Reduction; Mute silences the guitar completely, for tuning.
The NS-2's Send and Return take the noisy pedals into its loop, and BOSS says not to connect delay or reverb there: connect them between the NS-2 and the amp,[7] which also keeps the gate from cutting off their tails. On a high-gain amp with an effects loop, Tonelify's pedal order guide suggests one gate before the drive and another in the loop.
- Threshold Lit at rest
- Decay MIN
- Mode Reduction
Threshold so the Reduction indicator is lit at rest. Noisy pedals in the Send and Return loop; delay and reverb between the NS-2 and the amp.
When the noise is the amp itself
If the amp hums or hisses with nothing plugged in, in more than one room, the amp is the suspect. Thomann describes worn tubes that start to feed back when you stop playing and later hum strongly before the amp falls silent. The fix is a new tube, and since power tubes should be calibrated by an expert, that is a job for a specialist.[1] Crackling as you turn a knob means a worn, scratchy pot, to be cleaned or replaced.[1]
Do not open the chassis yourself. Marshall's handbook says there are no user serviceable parts inside and to have the amp serviced or repaired by competent qualified personnel.[8]
When the noise is gone and the sound is still not the record's, Tonelify works out a song's settings for the amp and pedals you own.
Common questions
Why does my amp hum when nothing is plugged in?
Then the amp itself or its power is the cause. Try another outlet and another room. If it still hums, a worn tube is a common culprit, and Thomann advises having power tubes replaced by a specialist because they need calibrating. Never remove the plug's earth to stop it.
Why does my guitar stop buzzing when I touch the strings?
Your body acts as an antenna and picks up noise, and touching the grounded strings sends it to ground. Premier Guitar and DiMarzio both describe it, and it means the bridge is grounded as it should be.
Is it normal for a guitar amp to hiss?
Yes. Every amp has some noise of its own, and it gets much louder with gain, volume, treble and presence, and with compressors and drive pedals in front. A noise gate silences it between phrases, where it is most noticeable.
How do I stop single-coil hum?
Move away from transformers, dimmers, neon lights and computers, and try two pickups together: Thomann's test is that if the noise goes, the single coil was the cause. Humbuckers and noiseless single coils are designed to reduce hum, and a noise gate covers the gaps.
How do I fix a ground loop hum?
Plug the amp and all your mains-powered pedals into one outlet through a power strip. If that is not enough, put a ground loop isolator in the signal path. Never lift the safety earth: Wikipedia's article says that creates a shock hazard.
Where should a noise gate go?
After the noisy pedals, usually the drives, and before delay and reverb. BOSS's NS-2 manual puts the noisy effects in its Send and Return loop and says to connect delay or reverb between the NS-2 and the amp.
Does a noise gate remove hiss while I play?
No. It only closes when the signal drops below the threshold, so it silences the gaps. Hiss under the notes stays, which is why taking the gain down a step comes first.
Sources
The numbers in brackets in the text point to this list.
- Thomann: how to prevent humming and noise in a guitar amp
- Wikipedia: Mains hum
- Fender: the American Professional Classic and the Silent System
- DiMarzio: noise when you take your hand off the strings
- Premier Guitar: Silence is Golden, by Mitch Gallagher
- Wikipedia: Ground loop (electricity)
- BOSS: NS-2 owner's manual
- Marshall: JTM 30 handbook
Settings for your own amp
This guide covers what is true of every rig. For a specific song on a specific amp, Tonelify reads the documented chain behind the recording and returns gain, bass, middle, treble and presence values for the controls your amp actually has. A first plan starts with 7 days free, $0 today.
