How to Fix a Guitar Amp Hum with No Input (Nothing Plugged in)

One thing that frustrates me the most, is when I’m setting up for a nice jam session, but then I notice an annoying hum coming from my amp even though there’s nothing even plugged into it.

We’re talking buzzing, hissing, or classic Fender-esque 60-cycle hum as soon as you switch from “Standby” to “On.” It happened to me the other night at rehearsal, and I was livid! Worst of all, the hum persisted in all the spaces between chords or notes.

It had to be fixed, as soon as possible.

I’m sure you’ve had a similar experience, and if you haven’t, I’d like to share how I fixed the amp hum with nothing plugged in, so that I can save you the frustration I’ve felt before.

Understanding Amp Hum

Before I get into how to fix amp hum, I think it’s important that we go over why amps hum and some of the things that can cause hum.

Firstly, all amps have a natural hum called ‘self-noise’. This is usually very low and often even unnoticeable, and will be drowned out by any playing. This hum can be made worse by a variety of factors.

Dirty Power

A common cause is something called dirty power. Basically, dirty power is when the electrical current in a circuit is flowing at a steady rate, yet fluctuating. I picture it as a straight line representing the steady electrical current, and a zig-zag or uneven line for dirty power.

Even small fluctuations can cause dirty power, leading to amp hum. This dirty power might be caused by the amps power cable or internal power being faulty, or even something else, like a TV, connected to the same circuit causing fluctuations.

Sometimes this effect comes from plugging too many things into one outlet. I’ve had it when running pedals and amplifiers from the same powerboard.

Dust

Another common cause, and the one I’ve come across quite often, is dust. Dust, either in the inputs or around connectors, can also cause interference that can cause the amp to hum more than it should.

It can come from anything in contact with the amp input. You know the unpleasant, loud buzz when you plug a guitar into a live amp?

Most of the time, amplifier hum without anything plugged in comes from damage or interference in the input. I’ve had this problem before!

Simple things like dust or even skin contact are enough. You can test it yourself by plugging one end of a lead into the amp and touching the other with the palm of your hand.

Funnily enough, Rage Against The Machine’s Tom Morello likes to do this live. I’ve tried it and it never looked as cool.

Signal Interference

Because amps are basically converting an electrical signal to an audio signal, they are often quite sensitive to interference. You’ve probably experienced the most common one where your cellphone was too close to the amp and made that weird morse code-sounding noise.

I counteract this by putting my phone in the neck compartment of my guitar case during rehearsal.

Anything that emits a signal can cause your amp to hum, like radios, TVs, and even fluorescent lights. Solid-state amps are usually susceptible to electrical interference since they have electronic parts.

However, even tube amps can be affected by the staccato sound of phone interference.

A shielded cable can help here.

Dead Capacitors or Tubes

Damaged or dead parts in the amp are often the culprits behind the amp hum. A broken or dead capacitor in a solid-state amp can create fluctuations in the current, similar to dirty power, or be more sensitive to outside electrical noise.

In a tube amp, a dead tube can result in the amp humming or amp noise. It’s not the dead tube causing the hum, but rather the tube isn’t canceling out the amp’s natural hum anymore.

I strongly advise against soldiering on if this is the case. Replace the tube, or get your local technician to do so. I’ve played with dead tubes before and it just meant the other tubes wore out faster.

Fixing Amp Hum

Now that we’ve gone over some of the main causes of amp hum, we can go over how to identify and fix the problem.

Whenever I have to figure out what the cause of a problem is with my gear, I go through a process of elimination to quickly and easily pinpoint the cause.

Step 1

The first thing I did was to move away or turn off any electronic devices close to the amp. Cellphones, TVs, Radios, fluorescent lights, anything that might produce a signal that could interfere with the amp.

Step 2

Switch between clean and overdrive channels on the amp and turn the volume and gain up and down. If the hum gets louder when you turn the volume and gain up, or is more noticeable on the drive channel, the inputs might just be dirty.

I sprayed some contact remover on a thin, clean cloth and wrapped it around a cable jack. Then plugged the jack in and out a few times. This helped clean the inputs, in theory helping get rid of the hum.

Step 3

Next, I tried plugging the amp’s power cable into a different power outlet that’s separate from other appliances. There was still a hum, so I swapped out the cable for a spare.

This should help you spot if the problem is being caused by dirty power and should also be an easy fix.

Step 4

If you’ve gone through steps 1 – 3 and you’re still getting amp hum, then the issue is likely internal.

On a solid state amp, check all the connections from the inputs to the speaker to the internal power supply. If a connection is loose, you should be able to simply resolder them. I would suggest you also clean all the connections with contact remover since dust can also cause trouble here.

I don’t mind using a soldering iron, but back when I wasn’t confident doing so, I would take my amps to my local guitar store. They usually have someone willing to fix things.

After checking the connections, also check the circuitry to see if any capacitors are broken. If you’re not that familiar with electronics or don’t want to risk further damage, you should rather take the amp to a professional.

Tube amps are similar with regards to the connections, but the big difference here is of course to check the tubes to make sure they’re still working. I would recommend checking the tubes regularly anyway since they only have a lifespan of around 1 – 3 years.

Final Thoughts

Even though there are many reasons why an amp is humming unnaturally or making too much noise, if you work your way from the easiest problem to fix to the most difficult, you should be able to quickly identify and fix the problem.

I’ve been able to fix the problem on the fly at rehearsal, but sometimes it’s just too big of a job for the rehearsal room, and demands a professional. Other than that, I hope I’ve been able to help you fix that annoying guitar amp hum when nothing is plugged in.