Mains hum in speakers after plugging in a cable

As soon as I plug in a standard 3.5mm jack cable into my speaker AUX IN port they produce a loud disturbing noise exactly as this one: https://en.wikipedia.org/wiki/File:MainsBrum50Hz.ogg. I don't even need to connect a cable to a computer, it's enough for it to be connected to speakers only. My speakers are Creative Inspire S2 Wireless. When I turn up volume, humming is louder. I tried connecting a power supply to another wall outlet, turning off my router but it didn't help. My current guess is that power adaptor is broken. I could get a new one where I live for a couple of dollars. It's worth mentioning that Bluetooth connectivity works completely fine, there is no humming when a device is connected to the speakers that way.

Does it make sense to get a new power adapter in such case?

user1042840

Posted 2015-09-09T21:30:52.153

Reputation: 141

Are you using an old-style "wall wart" linear supply? Modern switched-mode AC adapters are more compact and should not generate this kind of noise. – bwDraco – 2015-09-09T21:36:50.740

I am using Creative stock power adaptor: http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/mKIAAOSwBLlU8erR/%24_57.JPG. And would be the same one.

– user1042840 – 2015-09-09T21:39:01.117

Well, this definitely does not sound normal. What you showed is a switched-mode supply, and chances are good it's subpar quality allowing some small quantity of mains to reach the device. I'd want to replace the adapter, but don't get a cheap one. – bwDraco – 2015-09-09T21:42:47.280

@misha256: The problem is that these speakers used to work some time ago. What's strange here is that humming is produced as soon as a cable is plugged in the speaker, most people reported that they hear humming after connecting a cable on both ends – user1042840 – 2015-09-09T21:46:05.420

@DragonLord: I am not sure if it's possible to find a power supply with identical parameters and plug type and if it is how much more expensive it would be – user1042840 – 2015-09-09T21:47:26.617

I just connected the speakers in a different room to utterly eliminate radio waves interferences etc. but humming is still there. I really guess it's the power supply but I won't make sure until I buy a new one. – user1042840 – 2015-09-09T22:53:35.753

Answers

Why are you plugging a cable into the speakers without having the other end connected to anything?
That's the very definition of 'make a hum noise' - a game played by every guitarist who ever lived, at some point in their career.

It will get worse if you hold any single element of the plug at the other end & get better if you hold both elements with damp fingers, closing the circuit. If it doesn't stop when you do that, the cable or the speaker's socket is broken.

It has nothing to do with your PSU at all.

Tetsujin

Posted 2015-09-09T21:30:52.153

Reputation: 22 456

Why are you plugging a cable into the speakers without having the other end connected to anything? - I don't get it. In order to connect speakers to my new computer I need to plug a cable into the speakers first, right? – user1042840 – 2015-09-10T10:40:07.257

No. Plug into the source first, the destination last. Golden rule.... otherwise you get hum. – Tetsujin – 2015-09-10T10:42:26.610

You're right - humming is louder if I hold both ends with a finger and even louder after plugging in an other end into a computer. Do you think my speakers are just broken and a new PSU won't help? – user1042840 – 2015-09-10T10:43:43.670

There is still a loud humming if I plug a cable into computer first – user1042840 – 2015-09-10T10:45:10.010

As I said, first suspect the cable; then the socket. If the speakers are silent with nothing at all plugged in, they're the least likely to be at fault. – Tetsujin – 2015-09-10T10:58:00.247

I tried two cables, one of them being Creative stock cable. Level of humming is different on these cables but it's still there. I am not an electrician, I have no idea how to fix a speaker socket. As I said, I ordered a new PSU yesterday, if it won't help I will have to get a new set or check how much would it cost to fix it in authorized Creative customer service. Thank you for helping me here. – user1042840 – 2015-09-10T11:08:02.897

And of course speakers are perfectly silent without a cable plugged in – user1042840 – 2015-09-10T11:08:29.843

These speakers also have a headphone jack but there is no humming when I plug in a cable into this port. – user1042840 – 2015-09-10T11:32:17.753

There wouldn't be - it's an output – Tetsujin – 2015-09-10T11:46:50.570

Wait a minute - am I doing it right? Can AUX IN even be connected to a integrated sound card in a PC? Maybe I need a converter or something? – user1042840 – 2015-09-10T12:01:34.350

Try to plug both in the same wall outlet to see if the humming disappears. This post probably answers your question:

It's caused by the electrical ground on one piece of equipment being at a slightly different voltage than at other equipment. This causes something like a DC current between your equipment, which your speakers interpret as a hum. The quick and dirty fix is to use a long extension cord (with a 3-prong plug for ground) so your speaker system and computer are plugged into the same wall outlet.

Try to connect the plug to your phone. If the noise vanishes, it is probably the problem, since your phone is eletrically isolated.

You can also try shielded RCA cables to prevent some kind of interference, but it doesn't look like your problem.

neves

Posted 2015-09-09T21:30:52.153

Reputation: 287