Electronics Gurus! iMac Grounding

[Trep]

I figured someone might be able to help me out with this because Im way over my head here, but have some idea what might be happening!

Im having issue with a loud grinding/Hum coming from my Profire 2626 outputs. After doing some research, I've isolated the problem down to my 2011 27" iMac, or its compatibility with my 2626. Ive heard of other people having similar issues with things like Firestudio's and iMacs.

It appears that the profire's TRS outputs are grounded to the Firewire 400 ports, which then is suppose to share ground with the computers ground via Firewire. I am running into a Firewire 800 port on the iMac via a converting cable, (which I noticed has a plastic plug on the 800 end and metal on the 400 end - not sure if this has any contributing factors.) The noise also varies with mouse scrolling and other computer activity.

I did a test to see where the problem was by using this setup chain however no signal, just to monitor the hum. No DAW open

Profire Outputs > Axefx > Monitors
Plus, Firewire cable plugged into my iMac.
(using the axefx so i could independently hear the hum from some kind of potential noise outputted from another place in the Profire)

As soon as the firewire cable was unplugged the noise stopped.

From this and my small amount of knowledge, It seems that the Profire Needs to be grounded alternatively. For those who don't know the unit, it has an external 2 pin power pack style DC adaptor not an IEC cable.

Any help GREATLY appreciated. Im at my whits end!!!!!

 

[006]

So weird. Another member on here was having a similar issue, he came to my house to try his iMac and 2626 on my outlets and the problem disappeared, which narrowed it down to the wiring at the place he was using. He moved to another place and as far as I know has not had the problem since. I have a 2011 27" iMac and 2626 as well, never had this issue.

 

[Trep]

Hmm, Strange.
Is you plug on your FW800 Side Plastic too?
Will a power conditioning unit have any affect helping poorly grounded mains if that is the Issue.??

 

[SethTheGreat]

I had exactly the same problem. It seems to be some sort of ground loop? But honestly I don't understand ground loops very well. I solved the problem by plugging my monitors into a plug strip with the ground plug removed. I know that's not very safe but it fixed the problem

 

[jeid]

Had the same issue, as have several other members here. I disconnected one of the pins in the monitor cable and it's been fine since.

 

[::XeS::]

It's a ground loop...I have a mac pro and the profire connected thru firewire and I have a buzz in the monitor... same thing with my macbook pro if I connect an external monitor.
It's not generated by the profire itself but probably as you said, having the trs grounded to the firewire port, if there is a ground loop you'll hear it.

 

[kev]

These things have been the bain of my life for years. I gave up on my latest one and removed the ground from my sub which was acting as the distribution point for all the crap I was getting. Highly unadvised though!

Mind you, in doing this, as the sub is connected to other things that are grounded I figure if something bad were to happen with the electrics it would find its path out through the other speakers connected through the sub and to ground. That might be totally wrong though.

 

[mickrich]

This works and is far safer than removing earths on your electrical gear.

http://www.soundonsound.com/sos/feb12/articles/art-dti.htm

I had the same thing with my Behringer ADA8000 that I use for click track and extra stereo returns (if needed) to my A&H Zed-R16 console.
Hum and even mouse movement and clicking noises.
Running balanced jacks into these then into desk solved the problem completely. One of these units will cover 2 channels of audio.

 

[Trep]

Thanks for all the Info.

Looks like I'm going to hit up some trial and error and see if I can solve the issue.

The firewire adaptor vs cable might be a good try

 

[kev]

Another thing I read on the internet after researching the issue for an age was actually snipping the ground wire from the firewire cable and then putting it back together again. I tried that, but it wouldnt work with my saffire. You might have varied results though.

 

[006]

The FW800 plug end is supposed to be plastic as far as I know, never seen one with metal like the 400. My 800>400 cable has plastic on the 800 end, metal on the 400 end.

 

[colton]

So weird. Another member on here was having a similar issue, he came to my house to try his iMac and 2626 on my outlets and the problem disappeared, which narrowed it down to the wiring at the place he was using. He moved to another place and as far as I know has not had the problem since. I have a 2011 27" iMac and 2626 as well, never had this issue.

Yep, everything is good here now. Really appreciate you helping me out.

I actually sent my Profire back and got a Saffire Pro 40 because I wanted to use the difference to get a Furman PL8C and everything worked out great. The only time I get some noise is when the dimmers in my living room are on, but that's an easy fix. Other than that it's your standard line noise that can be fixed with a gate or edited out. But yeah, I went through hell for an entire year chasing a ground loop/EMI interference and the only conclusion I could come to was dirty AC. I tried everything... different computer, interface, cables, guitars, monitors, headphones, ebtech hum-x, etc. Nothing worked. It was really bad at my old place. Good thing is I learned a lot about a bunch of stuff I otherwise would have had no interest in knowing. I hope you don't have to go through this for very long, no one should. Keep us posted if you want, I'm always interested in finding out what the culprit is when situations like this occur.

 

[Yhanthlei]

Had the same issue here, connected my monitors to a different outlet and everything's fine since then