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PROBLEM! - constant subwoofer humming

rp20010

Standard Member
Hi,

I have an active sub that hums the moment it's switched on. I've tried disconnecting the interconnect, changing power cable, powering on in different room etc.

NOTE: When I change the phase the hum changes tone slightly and then returns to normal, still humming that is. Also, changing the volume doesn't affect the amplitude of the hum.

Any advice on what could possibly have gone wrong. I really wana fix this!!

Thanks
 
Last edited:

hoppaz

Well-known Member
Hi,

I have an active sub that hums the moment it's switched on. I've tried disconnecting the interconnect, changing power cable, powering on in different room etc.

NOTE: When I change the phase the hum changes tone slightly and then returns to normal, still humming that is. Also, changing the volume doesn't affect the amplitude of the hum.

Any advice on what could possibly have gone wrong. I really wana fix this!!

Thanks
If the sub hums when it is not connected to anything but power then the amp could well be faulty. Is it new?
 

roncam29

Standard Member
I think most off them do I have a Mordaunt Short 409w it has a slight hum and a Monitor Audio rsw12 it hums when I switch it on but dies down a good bit when it has been on a while hope this helps.:thumbsup:
 

hoppaz

Well-known Member
no, it's not new. If it is the amp what components could I check?

Thanks
You haven't actually answered my first question, does it hum when plugged in to a wall without anything connected to it?

When I said amp I also meant the subwoofer amplifier not your av receiver. What sub is it?
 

hoppaz

Well-known Member
I think most off them do I have a Mordaunt Short 409w it has a slight hum and a Monitor Audio rsw12 it hums when I switch it on but dies down a good bit when it has been on a while hope this helps.:thumbsup:
No sub should hum even slightly to be honest.
 

rp20010

Standard Member
You haven't actually answered my first question, does it hum when plugged in to a wall without anything connected to it?

When I said amp I also meant the subwoofer amplifier not your av receiver. What sub is it?
Yes, it hums when only plugged into socket with nothing else connected. Its a PURE LIFE 4/10 SUB 10.
 

hoppaz

Well-known Member
What you have is a ground loop hum (google it).

To be sure it's definately the sub take it to a friends / relatives house and try pluggin it in. If it hums then I would be certain its the sub amp.

Only way to prevent it if the above works out true is to find a replacement or get it repaired.

You could try a ground loop isolator (google) which cost a few bob but it's not solving the problem totally.
 

markdj79

Novice Member
this should cure it

mark

edit....if it dont then its prob your sub amp
 

john_a

Standard Member
What you have is a ground loop hum (google it).
I don't think it is - if it hums when it's connected to the same wall socket as the receiver, there shouldn't be a ground loop (should there?) as there would presumably only be one earth path. Unless I am getting totally confused.
 

hoppaz

Well-known Member
I don't think it is - if it hums when it's connected to the same wall socket as the receiver, there shouldn't be a ground loop (should there?) as there would presumably only be one earth path. Unless I am getting totally confused.
There isn't just one ground path though when you consider all of the components and electrical items (all with different earth paths) that are plugged in to sockets in his home.

The reason why I asked him to try it at another house to eliminate the fact that something else isn't causing the hum in the sub in his home. If he takes the sub to another house and it's fine then he will definitely have a ground loop problem.

If the hum remains then it isn't a ground loop problem as such but a grounding issue with the sub itself so my statement that it is a ground loop hum was a incorrect John until the above is confirmed.

Mains conditioners didn't work for me. The problem is likely to be in the sub amp which outputs to the subwoofer speaker. A cleaner power supply is unlikely to do much here if the problem is occurring inside the subwoofer itself.
 

john_a

Standard Member
No but if you connect two pieces of equipment together that are powered from the same socket, I would have thought they would have shared an earth path and by removing the connection to the amp for example, would break the earth loop and the hum would go away? That would suggest that it's not a ground loop that is causing the hum - that's just a theory anyway and I am fully prepared for it to be proved wrong! :laugh:
 

hoppaz

Well-known Member
No but if you connect two pieces of equipment together that are powered from the same socket, I would have thought they would have shared an earth path and by removing the connection to the amp for example, would break the earth loop and the hum would go away? That would suggest that it's not a ground loop that is causing the hum - that's just a theory anyway and I am fully prepared for it to be proved wrong! :laugh:
They could well share an earth path. Unfortunately current sometimes find its own path to earth in order to ground and that is why you get ground loop problems. Sometimes this happens to be via another piece of electrical equipment.

So, it's either another piece of equipment grounding through the sub or the sub amp itself has a problem earthing hence the hum.

To test if its the latter he needs to try the sub simply plugged in at another house. If it hums then the sub amp needs fixing. If it works fine then I suggest he goes back to his house unplug/switch off everything including the fridge etc, put the sub on at the wall and start switching everything back on one at a time to detect which piece of equipment is causing the ground loop.
 

john_a

Standard Member
I just think that the loop is completed by linking the sub to the amp and that by breaking the loop (ie disconnecting the sub from the receiver), the hum would go away. If it hums when it is plugged into any socket in the house and no receiver connected, I would have thought there was a problem with the sub.
 

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