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Music, Audio, and Podcasting Do you use your Mac to create music? This is the place for discussions on creating and editing music on the Mac!

Ground loop hum on Mac - can't record anything!


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Ulsterapple

 
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I'm sure this will have been covered before but can't find anything exactly relevant with a search, so please bear with me!
I'm using both Ableton 9 Live and Pro-Tools software to record music onto my Intel Mac via both firewire and USB. The USB device is an M-Audio Fast Track, very basic, so I've upgraded to a Profire 610 firewire recording system. I also use a Mackie Onyx Satellite firewire system.
Or, at least I would, if there wasn't a loud hum over everything. It's unbelievably loud and comes through on the recordings much louder than the actual music. If I hold anything metal - the Profire - or touch the Mac, it goes away. It's obviously an earth / grounding issue.
Suggested solutions are to plug the Apple into a different socket from the other items; difficult in a home setup with only two sockets in my study and probably a common earth for both. The interesting thing is that the USB inbox also hums now, which it never did before, not having a power source of its'*own.
I'm interested in this sort of thing: Ebtech - Audio Solutions
BUT: will it work on UK wiring? (Will it work at all???? )
Any other ideas to eliminate the hum? I have 400 software sitting idle because the hardware is letting me down... but I'm not a techie so soldering / wiring / diodes and transistors, as I've seen on other sites, wouldn't be feasible for me.
All help gratefully received!
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Seems to me there has been a post on a similar issue in the last six months to a year. Don't remember if it was resolved or not. If I can find it will post a link here.

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chscag

 
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Quote:
I'm interested in this sort of thing: Ebtech - Audio Solutions
BUT: will it work on UK wiring? (Will it work at all???? )
Any other ideas to eliminate the hum? I have 400 software sitting idle because the hardware is letting me down... but I'm not a techie so soldering / wiring / diodes and transistors, as I've seen on other sites, wouldn't be feasible for me.
All help gratefully received!
The Ebtech will not work on the UK power mains since it's only rated for 120V and does not have the proper connectors.

Having been in the electronic repair business for years, ground loop hum problems are some of the most difficult to overcome or eliminate. If your house wiring is at fault that will make it even harder. The best (and most expensive) way to eliminate hum and ground loops is to use isolation transformers; and not just any isolation transformer, but ones with filters.
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Ground loop problems are indeed difficult to overcome.

I would just call an electrician to come and inspect the place. If you're getting interference so bad that it reacts to touch, who knows what else is going on with your wiring. See if there are any electricians in your area that will do free inspections!

If you rent, then approach the landlord and let them know that you've come across some electrical wiring issues and see if they can get anyone out to inspect/fix it.
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Ulsterapple

 
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Thanks for the info on the Ebtech, that has saved me some cash as I'd have purchased it THEN found out later it didn't work!
The house was built in the 1980s so the wiring SHOULD be relatively modern, I had the circuit breaker setup replaced about ten years ago. The problem may be that there are only two sockets and all but the Mac - printer, PC, broadband etc runs from an adaptor in the same socket. Only the Mac has its' own socket but this is the other side of a two-socket outlet. Just a thought - would wireless broadband affect the signal in any way?
I had thought of connecting an earthing cable from the metal case of the Profire to the spare earth pin on one of the plugs - feasible? Many of these devices, the Profire and my Onyx Satellite use two-core cables so there is no separate earth cable as in UK wiring.
One other possible solution I have looked at is one of these:
ART DTI - Dual Transformer/Isolator Stereo DI Box - NEW | eBay
Any thoughts?
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The eBay offering may work since it provides a balanced and isolated output. It's certainly less expensive than a full line isolation transformer with filters. Here in the US a full line isolation transformer device could easily run $300 or more depending on capacity.

I'm not familiar with how the UK power mains are setup with respect to earth grounds and so forth, therefore it may be something that you might want to consult with a professional before spending money.
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Ulsterapple

 
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Got this one sorted with an isolation transformer from eBay at 64. It was built by an electronics shop for an individual and works perfectly for me.
The ART DTI didn’t work and is now gathering dust on my shelf...
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pendlewitch

 
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Ulsterapple there is a widely held rule for the avoidance of ground loop hum and it is that each piece of equipment should have only one earth current path between it and the rest of the system to which it is connected. (sorry for the sucking eggs lesson

so I've upgraded to a Profire 610 firewire recording system. I also use a Mackie Onyx Satellite firewire system.

If you didn't have the hum before then either of these devices could be the problem if the casings are touching a rack for example.Sometimes a fix can be to use the balanced inputs on your equipment although it can be bit more involved than that.

I only scratched the surface of the issues in my younger days by disconnecting everything and then plugging everything back in one by one until you find something that causes the hum. Start with the mixer and monitor amps and use the balanced inputs. There are other techniques that you can use such as placing resistors into cables but that is outside of my expertise. Go with standard cable first.

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Last edited by pendlewitch; 03-23-2014 at 07:23 AM.
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