Advice Needed Humming subwoofer

Captain Jack

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A bit of advice needed. I have some relatively old but good PC speakers*, which come with an active (powered) subwoofer. The problem I have is that the subwoofer is constantly humming - even without any audio sources or cables connected (except the power cable, obviously).

I haven't taken it apart yet but was wondering what could potentially cause this. It's clearly a mains hum - but how is this usually isolated from audio components? Knackered inductors? Or a grounding issue?

* Teac Powermax 1300
 
PaulR

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If you have any ferrite rings handy you could pop a couple onto the leads.
 
Captain Jack

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Nothing lying around but definitely a thing to try. Could it be a transformer?
 
Captain Jack

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Not convinced on RF - I've had this in several houses that I lived in, in different rooms. Not sure if that's a definitive elimination?!
 
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Captain Jack said:
Not convinced on RF - I've had this in several houses that I lived in, in different rooms. Not sure if that's a definitive elimination?!
Click to expand...

RF can come at any time from many sources, I am not saying it is that but subwoofers are prone for it, if it was me I would do as Paul says and put ferrite rings on it and plug it in at various points around your home to start with.
 
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Thanks all, will obtain some rings and wrap the cord around them (assuming it's the power cord?).
 
PaulR

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Any and every cord!
 
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Get a RFI attenuating surge cube and make the turns of cord close to the point the cable enters the device.

Belt and braces. :)
 
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I'd say a duff earth or RFi

turn flat screens, tv's and computers off and see if it still hums
 
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I have a subwoofer here.
Even with the amp turned off, you could hear a local radio station on it!
Bloody annoying at "quite times" on the TV.

But with a bit of earthing, (cable from the woofer to the earth on a wallplug) and the noise from the radio station reduced dramatically, now you can hardly hear it, although it is still there.
 
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If it's humming (50/60 Hz buzz) it could be a ground loop on the audio lead to the speaker, a bad audio connection (missing or broken shield) can do this.

Another possibility is if it has it's own internal power supply you could have some bad caps in the power supply, if it does have an internal power supply is the power cord on the same AC power buss as the audio source?

Another thing to look at is if the AC power plug is polarized or not, (one blade has a slight flare out on it) some of the older ones didn't have a polarized AC plug, if this is the case try reversing the power plug, and see what happens, if it had a 3 prong plug on it did you cut, bypass with an adapter or remove the ground prong?

My bet is if it is a self power unit and it's old then the AC power supply electrolytic filter caps may have dried out.
 
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Not really helpful but have you checked there isn't some old cheese stuck in the back? I find that really hums......
 
Terryl

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Engineering definitions:

Hummer, a device that plugs into the AC wall outlet or uses battery's to power it.
Puppy, anything else that does not us any form of AC, DC or dark matter to power it. (can also be used to describe a unknown hummer, such as "Whats that puppy do?)







Sorry........My fault, found the half full bottle of scotch left over from last night........
 
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Terryl said:
Another thing to look at is if the AC power plug is polarized or not, (one blade has a slight flare out on it)
Click to expand...

Doesn't quite apply to us brits that... :D

uk-plugs-and-sockets.jpg
 
Terryl

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2cvbloke said:
Doesn't quite apply to us brits that... :D

uk-plugs-and-sockets.jpg
Click to expand...


Well yes, but I have seen them cut the ground blade off, just to make it fit in some cases.
 
2cvbloke

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Terryl said:
Well yes, but I have seen them cut the ground blade off, just to make it fit in some cases.
Click to expand...

Do that to a british plug and you can't plug it in at all as the earth/ground pin opens a safety shutter that sits over the live & neutral connections... :D

But in the case of this amp, I'm on the side of bad wiring internally or bad smoothing caps... :)
 
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