Switch from MacBook to iMac Created Ground Loop

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Rodan
Posts: 486
Joined: 14:33, 10 June 2006
Location: San Diego, USA

Switch from MacBook to iMac Created Ground Loop

Post by Rodan »

Just a little story here that will make old timers shake their head knowingly, but might help out people setting up equipment for the first time or making "improvements" to their current set-up.

I was finally able to upgrade from my trusty old PowerBook G4 to a new iMac (Woo Hoo!) and couldn't wait to get it all hooked together. Got the latest driver downloaded for my M-Audio Firewire Audiophile interface, hooked it all together, fumbled around with the Audiophile interface until I got everything back to where it should be, played a bit on my Fantom and was thinking everything was great. But wait! What is that background noise I hear now. That was never there with the PowerBood. And worse, when anything on the iMac screen changes, you can plainly hear it through the monitors. Could my beautiful new iMac have a bad power supply on the firewire cable?

Well, I did a number of things to trouble shoot the problem, but really the most likely thing in a situation like this is a ground loop. Not the easiest problem to find and fix, but the most likely. Tried cutting the shield on the firewire cable at the receiver end, didn't help.

Here is what did work. Moved the powered monitors up off ground with a three to two pin adaptor in the power cord. (Note that plugging everything into a single power strip did not work even though this often suggested.)

The lesson here is that if you are going to buy an audio interface, it may be worth the extra money to get one with balanced outputs rather than the RCA (single ended) jacks. That would allow you to set everything up without having to lift the safety ground on the monitors.

I am now older and wiser, and probably in the market for a different audio interface.

-Rodan
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Artemiy
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Joined: 13:00, 17 April 2003
Location: Ukraine
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Re: Switch from MacBook to iMac Created Ground Loop

Post by Artemiy »

Thanks for sharing your experience, Rodan!

BTW, try Apogee Duet, I hear extremely positive reviews about it. Planning to get it (or One) myself.
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