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Old 01-19-2019, 09:55 AM   #1
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Audio/Computer Equipment Ground Loop


Basically I want to install a second circuit so that I can get a little extra power for my gear. The easiest thing to do would be to install new pair of receptacles in a double gang box near the existing plugs.

I was thinking if I have audio/computer equipment connected to each other that is powered by two different circuits in two different boxes that there is a potential for a ground loop between them. It occurred to me that this could be reduced by having the two circuits pass through the same box at some point so that the grounds join closer to the equipment instead of way back at the panel.

I was thinking the best choice is to replace one of the existing boxes with a triple gang, having one receptacle from the old circuit and the two new ones in the same box to avoid creating a ground loop back to the panel.

Am I over thinking this?

thanks
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Old 01-19-2019, 10:18 AM   #2
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Not all that familiar with ground loops and audio, but it everything is on one circuit there should be no loop.
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Old 01-24-2019, 01:12 AM   #3
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Re: Audio/Computer Equipment Ground Loop


If the two circuits are fed from the same panel then you should not have a ground loop situation. If I wanted to be sure of clean power then I would use a line conditioner like the ones made by Oneac that have two transformers to isolate AC in from AC out. I would also verify that the ground circuit at the outlet is actually isolated which can be done at the receptacle with a volt meter.



Where I have experienced problems with audio equipment is from poor grounding of the cables (or unshielded cables) or where there is a long cable run which acts like an antenna and picks up RFI.



The power or line conditioners from Oneac truly protect against power quality and ground problems and are industrial grade. Their 100 VA unit weighs 27 lbs. and so not at all like the rubbish sold by audio shops like the special AC power plug filters.



A whole house surge protector costs under $100 and takes an hour for an electrician to install and this is added insurance for all the electronics in your house, and these days even coffee makers and washing machines can be damaged by surges.
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Old 01-24-2019, 07:10 AM   #4
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Re: Audio/Computer Equipment Ground Loop


Related - do they make a shielded romex for outlets?

(I'm going to be building a studio and running a new circuit from the fuse box for all my gear.)
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Old 01-24-2019, 07:36 AM   #5
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Re: Audio/Computer Equipment Ground Loop


Armoured cable comes to mind. Not sure what it would do in that case though.

Edit: looks like armoured cable (aka AC90) is a Canadian term. I think MC (Metal Clad) might be the American term?

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Old 01-24-2019, 08:10 AM   #6
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Re: Audio/Computer Equipment Ground Loop


@Jawster I'm not sure armored/metal encased would help for it, I think they just do that to protect the wires from penetration for exterior mounting and I think firestop applications.

As I understand it cable shielding needs to create a faraday cage with some form of conductive layer. Aluminum is good for that, but I'm not sure if you can create a faraday cage with corrugated metal or not. I know they can have holes (like a mesh) as long as the holes are smaller than the RFI waves "hitting" it, but I guess in my mind it needs to be "smooth" - I could be totally wrong.

Multiple searches have not turned up any kind of RFI shielded "romex" type cable, there's maybe some special name or letter designation for it.
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Old 01-24-2019, 11:58 AM   #7
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Re: Audio/Computer Equipment Ground Loop


Quote:
Originally Posted by Jawster View Post
Basically I want to install a second circuit so that I can get a little extra power for my gear. The easiest thing to do would be to install new pair of receptacles in a double gang box near the existing plugs.

I was thinking if I have audio/computer equipment connected to each other that is powered by two different circuits in two different boxes that there is a potential for a ground loop between them. It occurred to me that this could be reduced by having the two circuits pass through the same box at some point so that the grounds join closer to the equipment instead of way back at the panel.

I was thinking the best choice is to replace one of the existing boxes with a triple gang, having one receptacle from the old circuit and the two new ones in the same box to avoid creating a ground loop back to the panel.

Am I over thinking this?

thanks
You're unlikely to have ground loop problems if both circuits run from the same panel and follow roughly the same route to get there. However, your idea of joining the grounds near the receptacles is a good one and would help if you are getting some induced voltage between the grounds of the two circuits. There's no particular reason NOT to do it that way, except that it may be slightly more work to avoid a problem you are very unlikely to actually have.

Shielded NM cable? Not that I know of. But MC-AP cable would do the job. Regular MC may not actually behave like a shielded cable at high frequencies since the spiral armor has no bonding conductor, but MC-AP with its bare bonding wire ought to be well-shielded. It's probably totally unnecessary though. A modern recording studio does not rely on the AC line being low-noise (which is kind of silly anyway, since 60Hz is audio frequency).
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Old 01-24-2019, 09:44 PM   #8
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Re: Audio/Computer Equipment Ground Loop


Ground loops CAN be caused by having two different outlets, on two different legs in a single panel.


It's also pretty common with a coax connection.



See it all the time with a subwoofer plugged in off to the side in a room, but it's an easy fix with Muxlab or equivalent ground loop isolation.
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Old 01-24-2019, 11:32 PM   #9
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Re: Audio/Computer Equipment Ground Loop


Well.....unless you are running some really old power supplies, you have nothing to worry about.

Modern gear uses a power supply that is pretty much isolated from ground.

The only way you are going to have issues with ground loops is if you start connecting to commons on output devices.

You are worrying about the wrong things
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Old 01-25-2019, 12:33 AM   #10
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Re: Audio/Computer Equipment Ground Loop


I would recommend line conditioners, and 3 one-gang outlets instead of a two or three gang. The reason is that transformer aka wall-wart plugs cover up adjecent outlets. While 3 one gangs spaced a few inches apart adds space.
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