humming speakers on iMac

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Hi all, i have a VERY annoying problem here. I have a 24" iMac9,1. The first one that uses ddr3 type memory. it works completely fine EXCEPT it generates a very consistent hum on my speakers. I am using a pair of Monsoon MM900 2.1 speakers. It is getting so bad that I have to power off the speakers except when I am listening to music(that drown out the hum). The speaker is not the problem as I plug it in my unibody Macbook and the problem gone away. Also, it didn't hum when I hooked it up with my Core 2 Quad desktop. All my equipment is protect with a UPS. I did some research and people was suggesting it is a ground problem. I bought an very expensive ebtech ground filter. Nothing helps so far. Has anybody got any ideas? tx
 
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Do you get the humming through your iMac speakers? Or just through the external speakers when you plug them in.
 
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humming speakers

Do you get the humming through your iMac speakers? Or just through the external speakers when you plug them in.

Just the external speakers. I hooked my macbook unibody and my thinkpad and the problem isn't there.
 
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filter

You may want to try a ground noise filter. I've seen them run anywhere from $14-20 online, but I did find one on Ebay with a BuyItNow price of $5.

eBay (US) : 3.5mm Headphone Jack Ground Loop Isolator Noise Filter (item 280594919631 end time Jun-24-11 08:30:06 )

I got one of these:

Ebtech HUM-X Exterminator Ground Loop AC Eliminator | eBay

and it didn't seem to help. I think I will try your suggestion. $ 7 is small change compared to my $ 68 that I spend already. tx

ps: will post the result once I try it
 
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Its definitely something with your audio jack, you could also try a different pair of speakers and see if its just a freak of nature with the ones you currently have.
 
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Its definitely something with your audio jack, you could also try a different pair of speakers and see if its just a freak of nature with the ones you currently have.

Yeah, but why would this problem not manifest in my macbook or thinkpad? I've another pair of speakers, i will try them today. tx
 
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Well, the audio output power could be different, just a thought and won't really hurt in testing
 
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Sounds silly, but make sure the speaker plug is seated in all the way. Some plugs seat harder than others.
 
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Hi all, i have a VERY annoying problem here. I have a 24" iMac9,1. The first one that uses ddr3 type memory. it works completely fine EXCEPT it generates a very consistent hum on my speakers. I am using a pair of Monsoon MM900 2.1 speakers. It is getting so bad that I have to power off the speakers except when I am listening to music(that drown out the hum). The speaker is not the problem as I plug it in my unibody Macbook and the problem gone away. Also, it didn't hum when I hooked it up with my Core 2 Quad desktop. All my equipment is protect with a UPS. I did some research and people was suggesting it is a ground problem. I bought an very expensive ebtech ground filter. Nothing helps so far. Has anybody got any ideas? tx

I've never felt the need for ext. speakers on any of my Macs!!

The inbuilt ones sound great to me - and I do like good audio
 
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well

I've never felt the need for ext. speakers on any of my Macs!!

The inbuilt ones sound great to me - and I do like good audio


well, these are monsoon flatpanel speakers. very good quality even that it hasn't been made in 6 years.
 
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Your problem sounds like an obvious earthing problem. The problem is most likely in the earthing of your speakers. Using a mains filter will have no effect on mains hum. The reason why you are not getting any hum when the speakers are connected to your laptop is because it is battery powered (and therefore isolated from the mains) and your iMac is obviously connected to the mains. Connecting your speakers to the iMac is obviously creating an earth loop.
 
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well, i think you probably are absolutely correct. what do you think is a good solution? I absolutely love these speakers.
 
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Come to think of it, I never had this problem when I was connected to my pc. Does the PC have better grounding than the iMac.
 

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Come to think of it, I never had this problem when I was connected to my pc. Does the PC have better grounding than the iMac.

It definitely sounds like a grounding issue - as has been pointed out. Have you tried a different outlet - for instance - the one that the PC was in that didn't exhibit the problem? Turn off lights - and any other appliance/electronics that may share that outlet's circuit.

It just wouldn't make any sense for the PC to have "better" grounding, not as a general statement, unless you happen to have a grounding issue with your particular iMac for some reason - or perhaps just your audio jack. Maybe your UPS is introducing the hum?? Try it without.
 
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Curing an earth loop can be a most frustrating problem if you don't know the circuit layout of the various components.

I would start, for the time being, by getting rid of the UPS. It's only confusing things for the moment and it may be causing some.

It's a case of a system of elimination....

You say you had no problem when the speakers were used via your PC. Did your PC have a two or three pin power plug? I'm not familiar with your speakers but assume they are of the powered variety i.e. they have their own inbuilt amplifier. Do they have a two or three pin power plug? Not all appliances have an earth connection at their power plug (they have a two pin plug) They are either completely isolated from the mains or pick up their earth connection via the appliance they are connected to.

Earthing problems with audio equipment often arise when two appliances, when fitted with their own earth connections are connected together - this forms a "loop" which results in a mains hum.

Therefore, should your speakers have a three pin plug this is where the problem could be. In order to check it, you'll need to disconnect the earth lead from this plug. They will still be grounded via the neutral lead to your iMac.

Hope this helps. As I said, locating an earth loop can be a tricky problem! :)
 
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Come to think of it, maybe the problem with the iMac and the speakers is because they are on different UPS. I will keep on trying until I find a solution. I will post results once I found it. Thanks!
 
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It definitely sounds like a grounding issue - as has been pointed out. Have you tried a different outlet - for instance - the one that the PC was in that didn't exhibit the problem? Turn off lights - and any other appliance/electronics that may share that outlet's circuit.

It just wouldn't make any sense for the PC to have "better" grounding, not as a general statement, unless you happen to have a grounding issue with your particular iMac for some reason - or perhaps just your audio jack. Maybe your UPS is introducing the hum?? Try it without.

hi, i finally fixed the problem. i plug the iMac and the speakers into the same UPS and the problem went away. Or at least, I can't hear it. Very happy man now!
 

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