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Humm from the amp

alex-red

alex-red

Jan 9, 2023
12
11
New York
#1
Hi all,
it is another one about humming and buzzing amps....but I really do not know where to bang my head on this.

I have only one amp, it is a solid state simple cabinet. Since I moved to my new house it humms as I pull up the volume. Regardless of the level of gain, or whether the bass is plugged in or not. I thought it may be a ground loop and I tested multiple outlets around the floor. no change
I thought to see if the effect is linked to the ground pin itself, so I used a ground lift plug. no change....
Also I noticed that if I plug my XLR output in the interface, I can sometime hear interference (radio or tv conversations) at very low volume through the headphones, even if the power is off ... I guess whatever interference is coming through the powercord.
what options do I have? do I need to use an isolation transformer?
 
#2
Is your power source earthed? Can you try your amp in another building where the power source is known to be good? A missing or defective ground can cause these symptoms, and never lift the safety ground/earth because that's dangerous.

You can't possibly have a ground loop with only the amp plugged, that's impossible.
 
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#4
If it works fine in another building it’s the building not the amp.

Old homes don’t always have real 3 prongs. Some installers put in fake fronts and inspector's sign off without verifying.

Check your outlet. A cheap tester from the hardware store will do the trick. Worth it in the garage drawer if you don’t have one.

Edit: wanted to add playing ungrounded is dangerous! You may be fine by yourself but high five your guitar player or touch a mic with your lips with a hand on your strings and you’ll feel the ground loop close - I had a fun experience with ground lift on an old SVT and Deluxe Reverb at band practice.
 
Last edited:
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#6
uuuh, that's scary....I never thought of doubting the grounding in the sockets.
Anyway, the wiring is there, behind the plugs, I will bring the amp to a different building and check if it fixes it. if this is the case then I assume I will need to look into the grounding of the house.
I did not mean to give out bad ideas on using the ground lift, I only used it for a moment to test if that would make any change and debug the problem. Thank you all for the concern though 😍
 
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#7
alex-red said:
Hi all,
it is another one about humming and buzzing amps....but I really do not know where to bang my head on this.

I have only one amp, it is a solid state simple cabinet. Since I moved to my new house it humms as I pull up the volume. Regardless of the level of gain, or whether the bass is plugged in or not. I thought it may be a ground loop and I tested multiple outlets around the floor. no change
I thought to see if the effect is linked to the ground pin itself, so I used a ground lift plug. no change....
Also I noticed that if I plug my XLR output in the interface, I can sometime hear interference (radio or tv conversations) at very low volume through the headphones, even if the power is off ... I guess whatever interference is coming through the powercord.
what options do I have? do I need to use an isolation transformer?
Click to expand...

Can you explain more on what I have highlighted in bold italic? Do you have pedals in the signal chain or attached to a signal out/preamp out/speaker jack?
 
#8
The hum can also be caused by other stuff plugged into the same outlet as your amp. In my case, I get "additional" background hum in my home amp if it's sharing the same socket as my desktop PC, even if everything is properly grounded.
 
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#10
alex-red said:
uuuh, that's scary....I never thought of doubting the grounding in the sockets.
Anyway, the wiring is there, behind the plugs, I will bring the amp to a different building and check if it fixes it. if this is the case then I assume I will need to look into the grounding of the house.
I did not mean to give out bad ideas on using the ground lift, I only used it for a moment to test if that would make any change and debug the problem. Thank you all for the concern though 😍
Click to expand...
in the 100yr old house I referenced our solution was to put the music room on its own circuit on the panel. That made things nice and quiet… and blender proof.

YMMV but maybe you don’t have to fix the whole house just an outlet or two in the music room.
 
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#11
meisi said:
in the 100yr old house I referenced our solution was to put the music room on its own circuit on the panel. That made things nice and quiet… and blender proof.

YMMV but maybe you don’t have to fix the whole house just an outlet or two in the music room.
Click to expand...
In general, it's safer to fix the whole house...
 
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#12
B-string said:
Can you explain more on what I have highlighted in bold italic? Do you have pedals in the signal chain or attached to a signal out/preamp out/speaker jack?
Click to expand...
The setup here is as simple as it gets: bass - amp - interface - headphones (the result is identical if the bass is not connected). I can hear the interference coming through even if the amp is off but the xlr cable is still connected.
 
#13
Is the noise present in your amp without the interface plugged into the amp (not turned off, that's an entirely different thing electrically)?

Simple is bass ---> amp ---> headphones
 
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#14
the humm is there regardless of the presence of interface, and is only there with the amp on (both through the amp speaker or in the headphones through the interface if connected. The strange thing from my poor understanding was that I could hear a radio like interference through the headphones when the amp is connected to the interface even if the amp is off.
 
#16
alex-red said:
the humm is there regardless of the presence of interface, and is only there with the amp on (both through the amp speaker or in the headphones through the interface if connected. The strange thing from my poor understanding was that I could hear a radio like interference through the headphones when the amp is connected to the interface even if the amp is off.
Click to expand...
The "radio reception" might be a cable problem, but think about this; MP3 players that have an FM radio function use the wired headphone's wires as the antenna for the FM radio. If you try to listen to the FM radio function with Bluetooth wireless headphones you will get no radio stations.

Your hum in the amp could be a failed ground inside the amp or stray pickup from something in the home. Set your cell phone on top of the amp with it on and bass connected or not connected, if someone calls your phone you'll hear all kinds of fun things. Make sure your phone is off when you are trying to locate where this noise is coming from.
 
#18
I dont think it was damaged in the move.
Now I noticed that if I use a transformer at the wall outlet the humm is gone. in case this tells anything new.

The radio reception is still there if I connect the XLR cable to the amp and the interface, I guess I should change the cable, maybe the shielding mesh around the wires is damaged
 

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