Grounding (power) problems Imac 21.5"

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Level 1

8 points

Grounding (power) problems Imac 21.5"

Does anyone else have this problem with their intel Imac? I am hoping that under my applecare I will get a new computer or a repair. I use my computer for audio at my recording studio and have always used Mac's but this one had me stumped until I found more people that were finding "digital Hash" (digital noise) being recorded with audio signal.

I tore my studio apart only to find it was the computer that was the problem.

Intel Imac 21.5, Mac OS X (10.6)

Posted on Jan 5, 2011 4:02 PM

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Answer 1

cactusslim Author

Level 1

8 points

Jan 5, 2011 7:14 PM in response to cactusslim

The reason it didn't jump out before is because I did not use the computer with anything other than interface for a while but now I am setting up my full studio so it needs to work with other electrical equipment.

There are quite a few cases like this:

http://discussions.apple.com/thread.jspa?messageID=11006851&#11006851

So it does seem some Imacs have grounding issues, mine included.

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Answer 2

Jan 5, 2011 4:28 PM in response to cactusslim

Welcome to the Apple Discussions.

Could you tell us what you found? What is the problem? Your subject line says grounding, but in what way? Using an ungrounded power line to the iMac, a grounded system that seems to not be grounded? Are you sure you are not setting up ground loops in your studio? Not an uncommon problem with a lot of electronic equipment.

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Answer 3

cactusslim Author

Level 1

8 points

Jan 5, 2011 6:19 PM in response to Ralph Landry1

What I found was this. When I hooked up my Imac to a mixer via a Steinberg MR816 interface I got what I've seen described as "digital Hash". The sound of the computer processing was being recorded along with the signal I intended to record. I went through a lengthy process of checking each piece of equipment on it's own and in combination. Eventually I plugged a 1/4" cable into my interface and simply touched other equipment (on their metal chasis) to see which piece would generate this noise and create a ground loop. It made the noise with each piece of equipment I touched that had it's own power source and ground. It made the noise even if I touched a screw on my powered monitors. It did not make the noise if I simply plugged in an unpowered instrument like a guitar.

Everything was always plugged into one electrical outlet. I tried 6 different grounded outlets. If I plugged the Imac into a power bar which was not grounded the noise was gone and all the equipment sounded as it should. The Imac was the problem and it was the last place I looked.

But I only knocked out the ground for a moment as I do not wish to run the Imac ungrounded.

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Answer 4

Jan 5, 2011 6:52 PM in response to cactusslim

Fascinating problem, as an engineer would be loads of fun, but entirely too complex to try and sort out from a distance.

A very large electronic complex can be really trying to work on and eliminate ground loops. Best advice on this would be to bring in an electrical engineer and/or highly knowledgeable electrician to setup a good, properly grounded system for you. The idea of an ungrounded computer is scary.

I am very surprised this did not occur sooner from the way you describe the setup. Strange that it would now jump out at you.

Get back with what you end up doing, this is an interesting problem apart from the computer aspect.
Ralph

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Answer 5

Jan 6, 2011 3:32 AM in response to cactusslim

Wasn't aware of that, but, even though I've been a member of the discussions since 2000 or before, just got active again in September.

There are a lot resources on ground loops. A really good one is the Amateur Radio Relay League (arrl.org) because, as an amateur radio operator, we worry a lot about ground loops since we use very high voltages and power at radio frequencies. Safe grounding is a serious issue.

You might want to check out the arrl.org website and see what public resources are available. If I get a chance today, I'll log in there and see if I can find something that will help if you are inerested.

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