Mains Hum on iMac

Question

Mains Hum on iMac

When I send the audio out ie. head phone socket on my Intel iMac through an amplifier I get very loud mains hum. I thought it might be the sound card so I tried an external sound-card but the same hum appears.
The hum or buzz is so loud it makes it impossible to listen to anything.

Has anyone had this problem? Is the Imac faulty? Is there anything I can do or change?

Thanks

G4 Powerbook, intel imac, G4 iMac,intel mac mini, mac book, Mac OS X (10.4.9)

Posted on Sep 19, 2008 10:07 AM

Reply

Answer 1

den.thed

Level 10

91,654 points

Sep 19, 2008 11:25 AM in response to Alastair W Mclean

Hi Alastair

Are you using the correct 3.5mm Stereo jack to RCA cable or Adapter, and is it pushed all the way in?

Here's an example of a cable:
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=31700&doy=19m2

And one of an adapter:
http://www.cablestogo.com/product.asp?cat%5Fid=118&sku=40645

Dennis

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Answer 2

Sep 19, 2008 12:09 PM in response to den.thed

Hi, I am using a mini jack to RCA it is about 1.5m long and is factory made.
The amp and lead works fine with an ipod, iphone or powerbook it is just the Imac.

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Answer 3

den.thed

Level 10

91,654 points

Sep 19, 2008 12:33 PM in response to Alastair W Mclean

Next open and close GarageBand to see if resetting the Audio MIDI Setup will help!

Then if you still get the same results from the amp. and a set of 3.5mm headphones, take the iMac in for service!

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Answer 4

Sep 19, 2008 12:53 PM in response to den.thed

Hi is the reset in garage band preferences? Also I can not hear any hum on headphones plugged into the Imac mini jack socket,
I can sample the sound and upload it to my idisc and send you a link to it so you get an idea of the sound if that helps.

Thanks

Alastair.

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Answer 5

den.thed

Level 10

91,654 points

Sep 19, 2008 1:10 PM in response to Alastair W Mclean

No opening and closing it simply resets the iMac's Audio MIDI Setup to Default!

It's sounding more like ground loop hum from the equipment, check your grounding or try moving the amp. to a different (receptacle) outlet!

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Answer 6

Sep 19, 2008 2:03 PM in response to den.thed

Hi,
Ok I will try that and let you know
thanks for your help
Alastair

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Answer 7

den.thed

Level 10

91,654 points

Sep 19, 2008 2:47 PM in response to Alastair W Mclean

Your welcome, hope you can solve the problem!

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Answer 8

J.I.

Level 1

10 points

Sep 19, 2008 10:31 PM in response to Alastair W Mclean

I have the same issue with a 24" imac. Loud hum through the audio outs, going into a mixer. I had the power cable connected to a surge protector. I connected it to a wall outlet and that decreased the hum alot, I can still hear it alittle, its not as clean as my macbook, but connected to the wall reduced the hum.

So most of the noise was because of a grounding issue.

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