Old 01-08-2014, 12:44 PM   #1
Quexoz
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Default Audio Interface Ground Loop? Scarlett 2i4

Not really Reaper related, but I figure a lot of folks using Reaper, like me, are also using audio interfaces, so here goes...

Video of problem (may need to crank volume a bit, there are no sudden LOUD parts): http://www.youtube.com/watch?v=v_gpV5jf_As

This hum is much louder than it appears in the video but it does well enough to make the point. The drone can be heard loud an clear over any audio played via the Scarlett 2i4. My camcorder mic doesn't seem to pick up really low frequency well.

I just got a new Focusrite Scarlett 2i4 to replace my M-Audio Fast Track USB 2 and have this hum/buzz out of my sub-woofer any time it is plugged in. If it is going to the main speakers, it must be too low frequency to play on them, I don't really hear it anywhere but the sub-woofer.

The hum continues even when the receiver is powered down or the sub-woofer volume is turned all the way down. It seems greatly reduced if I toggle the 48v phantom power (not in use) on/off a time or two.

The Focusrite folks have suggested ground loop isolators, and/or a ground lift adapter (3 prong to two) on the sub-woofer. I don't see how this is a ground loop though. Everything is in the same power source and my Fast Track sitting in the exact same setup, same cables and all, works perfectly. Why does it not have a 'ground loop'?

Thanks.

TLDR version: New Focusrite Scarlett 2i4 connected via Sony Receiver/amp hums loudly through sub-woofer. M-Audio Fast Track does not. What the....?
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Old 01-08-2014, 01:44 PM   #2
jerome_oneil
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Is everything plugged into the same circuit? If you run off of two different circuits, sometimes ground will be at two different potentials, causing a hum.

I'd plug everything into Giant Power Strip and see if that doesn't calm things down a bit. Then work out from there.
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Old 01-08-2014, 02:03 PM   #3
Quexoz
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There are two power strips/surge protectors plugged into the two ports/sockets/whateveryoucall'em in the same wall outlet, so everything is on the same supply/ground. If I am not mistaken, both those outlets are on the same wire in the wall. It's right behind the desk, under the Sony receiver in the video.

What has me skeptical of a ground loop other than them being on the same ground, is why would toggling the phantom power reduce the hum? Why does the M-Audio Fast Track not have the same problem when plugged in to the exact same USB/RCA wires in exactly the same setup? Why does everything work fine when playing movies/audio on my PC and only act up when the 2i4 is plugged in since it gets it's power from the PC, same as my onboard sound card? Wouldn't a ground loop do this all the time, even if the 2i4 was not involved?

Edit: I guess I should remove/replace the surge protectors and try running an extension cord from another outlet to the sub-woofer and see how that plays out too. But first...there is much snow to be shoveled today. Thanks again for your time.

Last edited by Quexoz; 01-08-2014 at 02:35 PM.
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Old 01-08-2014, 03:10 PM   #4
jerome_oneil
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Quote:
Originally Posted by Quexoz View Post
Edit: I guess I should remove/replace the surge protectors and try running an extension cord from another outlet to the sub-woofer and see how that plays out too. But first...there is much snow to be shoveled today. Thanks again for your time.
Yeah, that would be the next place I looked.
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Old 01-08-2014, 03:19 PM   #5
Mink99
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You might suffer from a ground loop that is induced by the USB port. Some devices have no shielded USB ports and then a hum or even a distorted noise might be the result...
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Old 01-09-2014, 03:34 PM   #6
Quexoz
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Quote:
Originally Posted by Mink99 View Post
Some devices have no shielded USB ports and then a hum or even a distorted noise might be the result...
You might be onto it here. I tried a different power outlet with no joy. Same result.

Another thing I've found is if I power everything down, plug in the 2i4, then power everything back up I don't seem to get the hum. If I have everything powered up and then plug the 2i2 usb power in, it immediately starts the humming.

Also, I get lots of USB noise all the time that I do not get from my M-Audio Fast Track. Meaning ANY activity on the PC causes little noises through the speakers, sub-woofer mainly. Just moving my mouse on screen within Reaper or scrolling the mouse wheel, for example, makes a "bvvvvvvt" noise. It's not a problem because these sounds are not recorded though.
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Old 10-10-2014, 05:39 PM   #7
Rcs
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Default 2i4 problems

I have the same problem, this is my second one now the first developed a hardware problem and wouldn't connect after one use, this is the replacement and it has what seems like a ground loop, don't waste your time just get a replacement,it's not your gear or set up, my set up is the same as with the 2i2 I used to have, worked fine, and the old 2i4 worked fine until it broke, I will be sending it back on Monday, phone focusrite and they will tell you to send it back through the supplier.

Cheers, Rob.
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Old 10-10-2014, 06:17 PM   #8
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Quote:
Originally Posted by Quexoz View Post
...a ground lift adapter (3 prong to two) on the sub-woofer...
This is NEVER the right answer! Focusrite reps should be slapped for even suggesting such a potentially dangerous "fix". These are NOT "ground lift" adapters. They are meant to connect a 3-prong device to a 2-prong outlet, but you're supposed to screw that little tab to the outlet itself, which is supposed to connect it to the grounded outlet box.
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Old Today, 05:28 AM   #9
drumphil
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If you have devices connected with unbalanced audio cables that also have ground pins on their power cables, then you have a ground loop (audio ground and power ground, which are ultimately connected.) Two ground paths between devices is all it takes. Balanced connections are the ultimate solution, but if that isn't practical, then isolating transformers are the next best solution that can promise hum free performance.

The problem can be better or worse depending on a bunch of factors, but balacing, or short of that, transformer isolation are the only guaranteed solutions.

You can still have problems with balanced systems if you have the shield connected at both ends depending on exactly how your gear works internally (as the shield connects the chassis ground of each box together which is often connected to the audio ground in each box, plus your power grounds for each box = ground loop). This wouldn't happen if all gear was designed properly, but reality is as it is.

Quote:
I have the same problem, this is my second one now the first developed a hardware problem and wouldn't connect after one use, this is the replacement and it has what seems like a ground loop, don't waste your time just get a replacement,it's not your gear or set up, my set up is the same as with the 2i2 I used to have, worked fine, and the old 2i4 worked fine until it broke, I will be sending it back on Monday, phone focusrite and they will tell you to send it back through the supplier.

Cheers, Rob.
This is not necessarily true. Depends on exactly what is causing the problem.

Sigh.. ground loops, something I know a lot more about since becoming a technician for a radio station.

Read this:

Sound System Interconnection: http://www.rane.com/note110.html

Grounding a Shielding Audio Devices: http://www.rane.com/note151.html

Thanks to Rane for their excellent resources on this issue.

"If you are unable to do things correctly (i.e. use fully balanced wiring with shields tied to the chassis at the point of entry, or transformer isolate all unbalanced signals from balanced signals) then there is no guarantee that a hum free interconnect can be achieved, nor is there a definite scheme that will assure noise free operation in all configurations."

"Winning the Wiring Wars

Use balanced connections whenever possible, with the shield bonded to the metal chassis at both ends.
Transformer isolate all unbalanced connections from balanced connections.
Use special cable assemblies when unbalanced lines cannot be transformer isolated.
Any unbalanced cable must be kept under ten feet (three meters) in length. Lengths longer than this will amplify all the nasty side effects of unbalanced circuitry's ground loops.
When all else fails, digitize everything, use fiber optic cable and enter a whole new realm of problems."

Last edited by drumphil; Today at 05:47 AM.
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Old Today, 11:33 AM   #10
SamuelC
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If you are playing guitar directly in front of your Pc ( very close) you will get ground hum

If your interface is near the tower same thing.

Some interfaces have a ground screw on the Back to bring a ground wire to the ground( mine does the Edirol Fa101) which helps by grounding the Interface.

Some interfaces will not have that.


Keep some distance between your interface and the PC tower. Cheap USB cables are famous for ground loops.
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