Getting rid of hum when connecting a computer to a stereo

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Sometimes, when you plug an audio line from a desktop computer into a stereo receiver or amplifier, an annoying hum comes through the speakers along with the music. You stop the music and the hum is still there.

I’ll leave the science behind all this to the links below.

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But I can report that it’s possible to get rid of that hum. Probably. Maybe.

More people are encountering the hum because more of us are listening to music using our computers through downloads or streaming services such as Apple Music and Spotify. Our electronic lives are also getting more complex, with a growing thicket of devices and cables bringing complexity and the threat of hum.

Hum might crop up in a situation like this:

The computer is plugged into a wall outlet or surge protector power strip.

The amplifier or receiver is plugged into a different outlet or power strip. A bunch of other stuff is plugged into both power strips. 

An audio line is connected to the computer via its headphone jack or USB port; it is linked to the “in” jacks of the amplifier. With this setup, you might get a hum.

What follows is the most common advice for troubleshooting this problem.

But safety first. Do not do this with wet hands or while standing in water. Make sure your electrical wiring is working properly and is grounded. You can check this by hiring an electrician. Or you can use an outlet tester, after reading the directions, of course. Don't tackle this unless you're reasonably confident about your abilities in safely handling electrical devices.

This is the main advice: Plug your computer and your ampifier into the same power strip. It might be that simple; the hum could go away. It was not that simple for me.

If there’s still a hum, unplug things one at a time from both the power strip and the amplifier and see if the hum goes away each time. Before unplugging, it might be wise to turn off the device first. In my case, when I disconnected an RCA audio cable between the cable box video recorder and the amplifier, the hum stopped. Linking a cable TV box and an amplifier turns out to be a common way to introduce hum. 

You can buy gear to try to silence the hum, such as a ground loop isolator. More information about that in the links below.

Another approach is to play your music from a smartphone or a laptop running on battery, connecting to the amplifier by audio cable or, if the feature is available, wirelessly using a technology such as Bluetooth. Or, use your desktop computer’s Bluetooth function to connect to a compatible amplifier.

The hum can happen when both the input and output devices are plugged into an electrical outlet. If one of the devices is not connected to an electrical outlet, a hum is unlikely.

Depending on your setup, it can get more complicated. Check the links below for more information, and search for “ground loop hum” or "stereo hum" using your favourite search engine.

Macintosh: Solutions for noise in the audio signal

Troubleshoot and eliminate AC hum on sound system (YouTube video)

Ground loops — eliminating system hum and buzz

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