If you have a guitar amp, it’s likely going to have a slight hum. Some will have it worse than others, but sometimes bad hum can indicate an issue. Let’s talk about potential causes and how to remove bad humming noises from your guitar amp.
Navigating unwanted noise in your signal chain is one of the most annoying problems a guitarist can face. Searching out and identifying the source of that noise can be even more troublesome.
In this article, we will dive into some common problems that cause amp hum, and all other sorts of awful noise. These issues might involve power sources, grounding issues, pickup selection or even bad components. Some issues we can resolve ourselves, but others will likely require the assistance of a skilled technician. Let’s dive in!
Guitar Amp Noise Troubleshooting
While we know the noise is coming from your amplifier, it is important to identify that the source of your noise is actually coming from the amplifier. The most common causes of buzz and hum actually come from your guitar, whether it’s the pickups, your internal wiring, or electronics.
For example, single-coil pickups often produce some sort of hum that increases as you turn up the volume or increase gain or overdrive. The initial reason for that noise, though, is that single-coil pickups are easily influenced by surrounding electrical interference.
To help with this, your guitar might need some improvements in shielding or grounding. Of course, the problem could also lie in your guitar’s other components, in your instrument cable or your effects.
So, before you pull your hair out trying to troubleshoot your amp, you have to rule out an issue with your other equipment first. This is easily done by unplugging everything from your amp except for the power cable. If you are still experiencing the issue, then it’s safe to say the source is actually your amp.
Editor’s Note: Amplifiers generally have large-value capacitors which can hold a charge for quite a while after the amp is turned off. Always make sure to turn the amp of AND UNPLUG IT from the wall before opening the casing. You should wait at least 15 minutes before doing any work to give the capacitors enough time to discharge. It is highly recommended to leave invasive repairs to the professionals (anything that involves opening the chassis of the amp).
Amp Hum With No Input
So, to be clear, if you’re getting a bad amp hum (or any other unwanted noise) with nothing plugged in, then you know the amplifier is the problem. However, if there is anything plugged into the input or the effects loop of the amp, then you will need to remove that first.
Amp hum will usually be the result of one of the following:
1. Check Your Speaker Cable
If you’re using a stack with a separate head and cabinet, or even with many combo amps, you’ll have speaker cable(s) connecting the amp and the speaker(s)/speaker cab. Ensure that you are using a properly shielded speaker cable and not an instrument cable to make this connection.
While they look the same, a speaker cable uses a heavier gauge wire, is built to handle more current is much better shielded. If you try to use an instrument cable, you’ll definitely have a bad hum. It could also do damage to the output transformers in your amp.
2. 60 Cycle Hum
60-cycle hum is also referred to as mains hum. Its name references the 60 Hz frequency of AC power that lives in the walls of your house (50 Hz in some countries). If that AC power is able to interfere with improperly shielded audio components, then it will produce an audible hum.
It can be caused by any sort of outside electronic device, from fluorescent lights and home appliances to computers or even phones. Try changing the position of your amplifier in the room or removing as many of the outside sources of interference as you can from your rehearsal space.
Assuming this didn’t work, figuring out the cause might be the job of a repair shop, but let’s look at some things you can do.
There is the possibility of your amp being designed with a cheap power supply, or even having a bad power cable. In this case, swapping out the power cable can be a quick troubleshoot to rule that out. Another option to rule out dirty power would be to purchase a noise filtering power conditioner.
It could also simply be a bad tube. If one of your power tubes goes out, the natural hum from your power transformer will no longer be canceled out. Turn your amp on and give each power tube a light tap with something nonconductive and forgiving (like a pencil). If you hear a ringing sound, you will need to replace your tubes.
In the next section, we’ll cover tubes a little more closely.
Now, there is another cause of 60-cycle hum we’ll talk about below which is easier to fix – Ground Loop Hum. You’ll see in a minute why this wouldn’t be a problem with the amp by itself though.
3. Tube Amp Noise Troubleshooting
Tube amps naturally produce more background noise than solid-state amplifiers. However, there are several reasons why a tube amp might be producing extraneous noises.
If your amplifier is making a hissing noise, has become heavily distorted or has significantly reduced in output, it is possible that it is time for new tubes. Tubes are like light bulbs. They do not last forever and need to be replaced when they go out.
Audible Signs Of Bad Tubes Include:
- Loss of high end
- Too much bass
- Loss of clarity/abnormal distortion
- Reduced headroom
- Reduced output
- No audio output at all
Visual Signs Of Bad Amp Tubes
If you have an indication that your issue could be tube-related, then there are a few visible signs to look out for. Keep in mind that power tubes are much harder working than preamp tubes and will need to be replaced more frequently.
You can carefully have a look at your amp tubes for the following signs:
- Are the filaments glowing? – No Glow, No Go. You need replacement tube(s).
- There should be a warm orange glow. Some filaments may be hidden and it will be hard to tell. In that case, see if the tube is warm (careful not burn yourself, they can get very hot).
- Is there anything broken off inside the tube? – Oftentimes, there are obvious metal fragments out of place.
- You can also remove a tube and gently shake it to listen for a rattling sound.
- Is there a white discoloration on the getter (usually around the top)? – If so, he tube has lost its vacuum. That tube will need replacing.
- Is there a purple glow concentrated on an individual internal component? A purple glow will likely mean the tube has lost it’s vacuum and needs replacing.
- Keep in mind that a blue glow is often very normal, especially around the glass.
- Is the plate glowing cherry red? If so, this is referred to as “Red Plating”. You can just about guarantee that you’ll need to replace this tube, although the tube is rarely the cause of the problem in this case.
- If you notice this, turn your amp off immediately so there isn’t any further damage.
- Most likely your tubes need to be properly biased to prevent this from happening again. Otherwise, it could be an issue with your amp’s circuitry.
Tap Test For Microphonic Tubes
You can check for microphonic tubes by conducting a quick “tap test“.
- Turn your amp on.
- Make sure the volume is turned up.
- Lightly tap each tube with a pencil or chopstick
Microphonic tubes will produce a louder noise (out of the speaker) when tapped. Kind of like a ringing noise and sometimes even produce feedback. Good tubes will make more of a dull “thud” sound.
Most preamp tube issues will be microphonics.
Bonus Techniques for Isolating Bad Tubes
The following won’t tell you that the problem IS in fact tube related, but will help you narrow down what type of tube problem it could be if tube-related.
- Turn the volume up and down. If the unwanted noise gets louder, then it’s probably your preamp tubes. Otherwise, it’s a power tube.
- If your amp has multiple channels and you notice the problem only occurs on one channel, then you bet it will be a preamp tube.
- If you have a reverb tube, turn the reverb all the way down. If the issue goes away, then check your reverb tube.
* Continuing to use amps with bad tubes can cause damage to other components.
* Always replace power tubes in pairs. For more on tube replacement, check out this article.
4. Bad Capacitors
It is possible that the humming sound coming from your guitar amplifier is caused by a bad capacitor. Generally, if you suspect that capacitors are the problem, it is best to seek out a qualified repair person, but we will touch on it briefly.
There are generally four types of capacitors found in amplifiers:
- Power Supply Filter Capacitors
- Cathode Bypass Capacitors
- Stage Coupling Capacitors
- Tone Control Capacitors
Any one of these capacitors going bad comes with its own set of problems!
For example, if you have a bad power supply filter capacitor, it may be causing your amplifier to produce a bad humming sound. However, it can be difficult to diagnose this problem visually.
Power supply filter capacitors that are nearing the end of their lives may bulge or show other signs of deformity. You often won’t realize there is a problem until one blows, though.
Another issue is that they aren’t always easily accessible and sometimes they come
in the form of multisectional cans. In this case, the individual capacitors won’t be visible.
If you suspect a problem here, I strongly suggest taking it to a technician who can test for problems.
(The following sections will involve issues that might not necessarily originate in the amp itself.)
Ground Loop Hum
Ground loop hum is a 60-cycle hum that occurs when individual components in an audio signal chain are given multiple paths to ground. Most commonly, for guitarists, when 2 amps are plugged into separate wall outlets each having its own ground connection.
Ground loops exist all around us; they are so prevalent you probably don’t give them much thought on a daily basis. But, they can wreak havoc when introduced to an audio signal. When you have two or more devices plugged into separate outlets, you’ll likely produce a ground loop hum.
For example, let’s say you have your amplifier plugged into one outlet in your rehearsal space and your pedalboard plugged into a separate outlet across the room. If a strange humming sound emerges, this is likely a ground loop issue.
A simple way to solve this problem is to provide a single, stable power source for all of your gear.
The same phenomenon can occur with pedals or other equipment placed in your signal chain. Take a look at this example below. You’ll see that the audio components (the pedalboard in this case) are being powered by separate outlets, both leading to their own ground.
Try, in this case, to connect all the devices in your signal chain to one outlet. You could also try purchasing a hum eliminator (found here on Amazon), which is specifically used for ground loop hum.
Why Is My Amp Buzzing? – Amplifier Buzzing Noise
If your guitar amp is making more of a buzzing sound than a hum, it’s likely either a ground issue or it’s mechanical. The difference between a buzzing sound coming from the speaker and a buzzing sound coming from the other components should be apparent.
The grounding issue could be a crossed connection between your live wire and ground wire. Again, first, diagnose whether it is happening when nothing is plugged into the amp. Then add a single cable and your guitar. If the problem starts there, switch cables and so on.
Once you find the faulty component, check all your connections within that device. For instance, in your guitar, you’ll check the connections on your output jack, pots, selector switch, etc.
Mechanical noise will generally be coming from the amp itself, as in something is rattling. Examples of this include loose components such as screws, nuts, and bolts. Check the casing, the speaker and easily accessed areas first. Then move into the inner components.
Sometimes, amplifier components will only vibrate at specific frequencies. For example, a loose screw that buzzes every time you play the G on the 12th fret of the G string. This means that the component shares the same resonant frequency as the note you’re playing on the guitar. (You can see it happen with Tube Rattle also, which we’re about to touch on.)
The phenomenon of a sympathetic frequency buzz or rattle can even occur with something else in the room, that has nothing to do with your amp. Sometimes it’s difficult to track down an object that’s vibrating at a specific sympathetic frequency.
If you suspect it to be an outside item, you can confirm that by taking the amp to a different part of the building or even outside before tearing the room apart!
If you’re using a tube amp, you could be experiencing tube rattle. Combo amps are particularly hard on tubes because they sit right behind the speakers. More often than not, changing your tubes is going to be the solution.
Some people claim to have luck using tube dampers. Tube dampers are rubber rings that you’ll place around the center of your tubes to reduce the resonant vibration from your speakers.
For more on troubleshooting tubes, scroll back up to the tube section.
Why Do I Get Static When Turning Volume Knob?
If you hear a gritty, static noise when you turn the volume knob on your amplifier you’re most likely the victim of either a dirty or worn potentiometer. Dirty potentiometers are easily cleaned, but worn potentiometers will need replacing.
Airborne dust and dirt can settle inside your amplifier over time, eventually causing static noise. Oftentimes, you can quickly rock the knob back and forth to free up grime inside the pot. You might find that will do the job.
If not, this problem can easily be fixed by cleaning your potentiometers using some contact cleaner (found here on Amazon). You can use this on both your amplifier and guitar pots if needed. It’s even safe on vintage gear.
For thorough cleaning, you can open up the pot and clean it well with isopropyl alcohol. This is the best method, but certainly not the most popular method.
If the problem is not solved by cleaning the potentiometer, then it is possible you’ll have to replace it.
The Hail Mary – Check For Bad Solder Joints
It is impressive the number of faulty electronics you can fix by just poor connections. Reflowing solder joints can work for unwanted noise issues as well as many other problems (including no sound at all). Cracked solder joints are quite common. However, this is the “when all else fails” type of fix and you refuse to take your amp to the shop.
While this probably shouldn’t be recommended but it often is. And I’ve seen results from it.
There are a lot of people who might not be deeply knowledgeable in electronics but have still had to do a little soldering before at some point. If you are interested in exploring this, start by examining all the solder joints around potentiometers. Afterward, proceed to inspect the rest of the amp.
Take your time to examine for cracks. Using a bright light and a magnifying glass will help you check each connection. Aside from cracks, also look for dull, whitish, convex or deformed solder joints.
Some people even make practice of carefully touching up all the solder joints in discarded or older equipment as soon as they get their hands on it. This isn’t bad as long as you know what you’re doing. If not, you can quickly do even more damage.
If you haven’t touched a soldering iron since shop class in high school, it is advisable to practice on something else first. You’ll want to avoid mistakes on a piece of equipment you’d like to use again at some point.
If your issue is something this easy, though, a professional repair shouldn’t cost you that much. Plus, you can hold SOMEONE ELSE accountable if they do a bad job! Otherwise, if you mess things up more it is going to end up costing you more in the long run.
Products For Amp Hum And Noise Mitigation
Morley Hum Eliminator
If you’re struggling to navigate ground loop hum, you may consider purchasing a hum eliminator. You might want to keep one in your gig bag if you’re playing out much – especially with 2 amps.
A hum eliminator is a simple adapter that is designed specifically to combat ground loop hum. So, understand that it won’t help with other causes of unwanted noise.
Noise Gate Options
Another gear-based option for solving unwanted noise in your setup is a noise gate. A noise gate works by establishing a volume threshold just above the background noise. If your signal doesn’t exceed that threshold it won’t make it past the gate.
Many guitarists would strongly recommend trying to solve unwanted noise at the source, rather than resorting to a noise gate. The argument is that the organic integrity of your tone, sustain, attack and decay are compromised when using a noise gate.
Metal guitarists usually swear by them, though. In the case that you play with extremely high gain, a noise gate may become essential. At these settings, you’re also less likely to notice any negative change in tone.
If you fall into that latter category, we recommend the following 2 pedals:
ISP Technologies Decimator II G String
A simple pedal with a single threshold knob, the ISP Technologies Decimator II G string is an industry leader in noise suppression technology. This is the go-to noise reduction pedal for metalheads everywhere.
MXR M135 Smart Gate
The MXR M135 Smart Gate offers a little more fine-tuning than the ISP noise gate. With three adjustable noise reduction stages and a trigger level control knob, you can dial in the perfect threshold for your setup. The Smart Gate is designed to preserve sustain and react instantly to threshold triggers.
Excessive noise can be one of the most frustrating and annoying scenarios for guitarists. Humming, buzzing, hissing, or whatever the case may be, it doesn’t belong in your amplifier. At least at above acceptable levels.
Whether you are on a gig, at a rehearsal, or in a recording session, having a newfound amp hum is a quick way to ruin your day. Fortunately, most humming noises can be easily remedied with a few quick methods.
This always starts with locating the root problem. This way you can eliminate the real cause instead of applying a bandaid fix.