Every guitarist knows and dreads the sound of static humming coming from an amplifier. You probably know by now that your guitar’s electronics must be grounded to stay silent. But what can you do if the amplifier hums, no matter which guitar you use?
To ground a guitar amplifier, you’ll first need to make sure that your electrical outlet and power cable are grounded. If those two are grounded, then you’ll have to open up your amplifier and make sure all ground wires are hooked up correctly. It’s also worth double-checking your guitar and cable.
This article will walk you through the steps of grounding a guitar amplifier, how to troubleshoot your noisy problem, and what to do about it. Let’s dive right into it!
Disclaimer: We are not responsible for any damages that occur to you or your property. Working with electricity is extremely dangerous without the proper knowledge. Any action you take upon the information in this article is at your own risk.
1. Check That the Electrical Outlet Is Grounded
Before you do anything, you should first rule out your outlet. It doesn’t matter how neat your grounding is in and around the amplifier if the ground in your outlet isn’t connected properly.
This would, unfortunately, land you on the receiving end of Metallica’s “Ride the Lightning” album.
Even though omitting the ground is a serious code violation, a concerning number of outlets and extension cords don’t have it hooked up. I’ve personally seen a DIY power strip that didn’t have the ground hooked up, and it both figuratively and literally shocked me.
This is especially common in basements because the problem is less likely to be caught.
Moreover, a ground wire that’s just hanging around behind the outlet always has a small chance of shorting something out and causing a house fire.
So, check the outlet you’re plugging your amp into first. It’s best to call an electrician to check this for you and fix it. If you have the proper know-how, you could use a multimeter to check the outlet.
If the outlet is properly grounded, connecting the probes to the hot and ground slots in the outlet should have the same reading as when you connect the hot to the neutral slot. This means that the electricity is flowing from the hot to the ground through your multimeter correctly.
All outlets in your house should be grounded regardless of your guitar amplifier. If you’re not sure, again, call up an electrician to avoid a potential fire hazard.
2. Double-Check if Your Guitar Amp Is Already Grounded
Before we move on to more complicated steps, are you sure that your amplifier needs to be grounded? Unless you bought the amplifier second-hand, it’s improbable that it’s not grounded.
Of course, there’s always a small chance of a manufacturing defect, in which case you should return the amplifier and replace it with a different one.
So, before you start a lengthy and complex troubleshooting procedure, just make sure that the amp indeed isn’t grounded.
Here’s how to do it:
- Grab your multimeter and set it to continuity.
- Touch one probe to the metal chassis or, even better, the ground sleeve inside the input jack.
- Touch the other probe to the ground prong on the power cable. The ground prong is the rounded third prong in the middle or at the top. In Europe and some other places, the ground pin is the railing on the side.
If there is continuity, your amplifier is grounded, and you can start looking for the problem elsewhere.
3. Make Sure the Power Cable Is Grounded
The power cable, also known as the mains cable, is the thick, usually black three-prong cable that connects your amplifier to the outlet. Virtually all power cables have a ground prong from the factory, but that doesn’t mean that the cable itself is grounded.
If the cable was bent in a funny way at one point, the ground wire inside might have broken.
To check the cable, simply set your multimeter to continuity, and touch one probe to the ground pin on one side and the other probe to the ground slot on the other side. Again, it’s the middle pin and slot. If it beeps or if the light on your multimeter turns on, it’s grounded.
If there’s no continuity, you could try repairing the cable, but you’re much better off replacing it altogether, as it’s probably not the only issue with the cable. They’re relatively cheap, anyway. Also, they’re mostly universal.
For example, the Amazon Basics Power Cord (Amazon.com) will work well with almost any amplifier. It’s super affordable and comes in any length you need.
4. Ground the Power Amplifier to the Power Socket
It’s finally time to open up the amplifier and get to work. The power amplifier is the actual meat of your amplifier — it takes your low-level guitar signal and the power from the mains cable to turn it into a strong, loud signal for the speaker to use.
The power amplifier is likely near the power cord, and the ground wire connects to the middle prong in the power socket. It’s usually green. If it’s been disconnected somehow, you’ve found the issue.
Simply solder it back in place and check for continuity with your multimeter. The other end of the ground wire is likely hooked soldered to the chassis or some piece of metal on the power amp.
The exact way it’s hooked up depends on your amp, so it’s best to find a schematic if that end isn’t firmly in place.
The solder joint for a ground wire doesn’t have to be perfect, and even a mechanical connection to the ground prong could work in theory. But, again, if the wire touches something else, it could cause a short and kill you and your amp.
So, if you don’t know how to solder, take it to an electrician.
5. Ground the Preamplifier to the Power Amplifier
Before we move on to the preamplifier, double-check that the power amplifier has been grounded properly. That’s because if you ground your preamp to the power amp and electricity has nowhere else to go, it’ll go directly back to your guitar and electrocute you.
Again, your best course of action would be to find the wiring diagram of your amplifier. This is because any grounding mistake in the preamplifier will lead to a ground loop, which happens when a circuit has more than one grounded point.
It’s highly unlikely that you have a grounding issue between the preamp and the power amp, but it’s worth checking.
Again, set your multimeter to continuity, and touch the back of any potentiometer with one probe and the ground pin in the power socket with the other. If there isn’t any continuity, you’ll have to check the schematics to see where the ground between the preamp and power amp should connect.
If you want to learn more, this YouTube video goes into extreme detail and also examines some factory errors in vintage Marshalls:
6. Ground the Input Jack
The input jack is the 1/4″ (6.3 mm) jack where you plug your guitar in.
The input jack is connected to the preamplifier through a pair of legs on the bottom side. Over the years, the legs can loosen up in their slots from vibrations and plugging the guitar cable in and out.
Thankfully, the solution is rather simple. You don’t even have to remove the board from the chassis. Simply take a bit of solder and heat it up on each leg with your soldering iron. The hot solder will fill in the gap between the PCB slot and the leg.
Check for continuity between the sleeve (the outer part of the jack) and the ground pin on the power socket.
If there’s continuity, congratulations because your amp is now grounded!
7. Double-Check the Ground on Your Pedals and Guitar
If you’re still getting noise even after properly grounding your amp, then it’s very likely that something is wrong with your guitar instead.
I once couldn’t figure out why my pickups were buzzing until I realized that my hot signal on the input jack was touching the copper shielding in the cavity.
Your issue might have something to do with an incorrectly wired pot, a cold solder joint, a broken wire, or something similar. Another issue that I encountered is that the ground wire on the pickup wasn’t soldered correctly, so it was losing contact as I moved the guitar around, causing a buzz.
The best way to know would be to either connect your guitar to another amplifier or to try a different guitar with your amplifier.
Again, a multimeter could save you a world of hurt if you use it to check for continuity. The hot wires mustn’t touch the ground at any point.
And if you’re looking to get the most out of your amplifier in the studio, check out my guide on How To Mic a Guitar Amp.
Hopefully, this guide has helped you understand how grounding inside a guitar amplifier works and how to troubleshoot and fix it correctly. Again, it’s best to have a professional check it if you don’t know your way around electronics.