This article explains how to eliminate ground loops in your audio system setup. Ground loops are usually perceived as a hum or buzz in your audio signal. This can be caused by devices that introduce an electric potential to the ground connection, including peripheral devices connected to your computer.
Note: If you are a TRAKTOR Scratch turntable DJ, make sure to connect the grounding cable on the back of your turntable with the grounding screw on the back of your audio interface or hardware mixer. If either grounding cable or grounding screw are not provided, please consult the manufacturer of your hardware device for more information.
With this in mind, the following points should help to eliminate the ground loop:
A low quality power supply unit can lead to ground loop noise, particularly on laptops. Disconnect your computer from your power suppy so that it runs on AC power and verify if this resolves the issue. If you are going to use a replacement power supply unit, make sure that its specifications meet the ones required by your computer in order to avoid permanent damage.
Shared Power Outlet
Always connect your devices to the same power outlet (e.g. with a multi-outlet power strip). Note that even if the power supply of your laptop computer is not connected, your setup may still be vulnerable to ground noise from an external device with its own power supply. All devices that are physically connected to each other should share the same power outlet. You may also have to separate polarized plugs (two-prong) from grounded plugs (three prong), by connecting them to separate circuits.
Disconnecting your Devices
In order to find out where the ground loop arises, disconnect all devices from your computer and / or mixer, but not the amplifier and / or speakers. This also applies to other peripheral devices you may have connected to your computer (external data storage, CD burners). To check if the amplifier or active monitors create the ground loop, monitor your audio signal from the headphones output of your audio device (while the amplifier/active monitors are disconnected). If you find the device that introduces the ground loop, a ground lift of the audio connection may solve the issue. Never lift the ground of the power connection!
Note: Contact the manufacturer of your device before lifting the ground to find out if ground lifting is supported on your device. Some devices offer a switch for this whereas others may require a modified audio cable or a DI-Box (see below).
If possible, always use balanced audio cables to connect your audio device to your mixer or speakers. If your mixer provides both unbalanced and balanced inputs, always connect your balanced sources to the respective inputs on the mixer.
If you cannot fix the ground loop with the tips above, you can try to put DI boxes in between the connections of your audio devices, your mixer and/or your active loudspeakers. This will break the ground of the audio connection. With a DI box you can use balanced audio cables for unbalanced audio sources. Additionally, most of these Di boxes feature a Ground Lift switch.