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USB ground loop issue...can't find a fix or a good USB isolator! Help, I'm desperate!
Old 16th May 2018
  #1
Gear Maniac
 

USB ground loop issue...can't find a fix or a good USB isolator! Help, I'm desperate!

My USB ports have ground loop noise when powering my Focusrite Scarlett 2i4 2nd Gen. I currently use a hum destroyer filter box but I want to fix the root of the cause.

It seems like most of the USB isolators out there that power the 500mA requirments that I find are hundreds of dollars. Is there anything out there that is sufficient for my Scarlett sound card? It seems to me that the isolator needs to support 500mA power needs as well as the 24bit audio encoding of the focusrite interface. Please help, I'm desperate!
Old 16th May 2018
  #2
Gear Maniac
 

https://intona.eu/en/products

this seems to be the only product close to what I need.
Old 17th May 2018
  #3
Lives for gear
 
fireberd's Avatar
Do you get the hum with just the Scarlett plug in, but nothing plugged into the Scarlett?
Have you tried a self powered external USB hub (one that has its own power supply)? May be all that's needed if the USB port on the PC can't provide the needed power and thus causing the hum. I've seen problems posted on some forums of problems with USB powered recording interfaces. Providing power for the interfaces seems to be a fix for them.
Old 17th May 2018
  #4
Gear Maniac
 
ericzang's Avatar
 

If you are on a laptop does the noise disappear when it's power is disconnected and running on battery? If so then ebtech humx may likely solve it.
Old 17th May 2018
  #5
Lives for gear
 

I can tell you right off a ground loop requires different pieces of gear to be plugged into two different AC outlets to exist.
The hum is caused by AC flowing from one chassis to another seeking the shortest path to ground via shielding on the signal cables which radiats hum in the core signal wire.

I can also tell you anything that sounds like AC hum isn't coming from the USB data portion of the cable. The signal is already digital once it leaves or returns to the interface and there is no way in hell an AC wave is going to convert itself to a digital signal out of thin air and become part of that signal.

There may be contamination of the DC voltage that cable carries IF your interface runs on USB power. If you used a laptop with a crappy generic power source then maybe you could push the limits of it being contaminates DC, but even then it wouldn't be 60 cycles, it would be 120HZ ripple from poor quality smoothing caps.

I've also seen allot of complaints about bus powered interfaces not having enough current to properly power certain phantom powered condenser mics but they typically just don't power up or produce weak signals.

If you run your interface off a wall wart, the first thing most likely to cause hum is an improperly regulated wall wart. The Hum comes from the preamp not the USB cable and the wall wart needs to provide smooth AC voltage or any hum will be amplified to audible levels by the interface preamp.

Wall warts cant typically have ground loops because the SC they output comes off a transformer and the transformer itself provides a ground lift. Its still a good idea to keep the wall wart on the same outlet as the computer and any other gear connected to the interface.

From there troubleshooting is kindergarten stuff. Unplug all inputs to the interface, turn up the gains with no inputs. You can even record with no inputs. If you don't hear hum it has nothing to do with the interface connecting cable or computer. If you plug something in and hear hum, its coming from what you have plugged in. Period. There's one unlikely exception. If the input jack on the interface has a busted ground then your input cable might hum, but you also wouldn't get a signal without the completed ground.

What typically happens in these cases is people plug in to direct record and they hear loads of hum they never heard plugged straight into a guitar amp so they come to the wrong conclusions thinking its the recording gear. What they fail to realize is a guitar like a Fender with single coils has virtually no shielding. Its hums but a guitar amp has limited frequency response. Its a midrange frequency amp with no high frequency above 5K. An Interface has a flat frequency response from 20 to 20Khz. If that guitar produces hum you'll hear it sure enough.

Guitar cords are another culprit. Inexpensive cables may only have 70% shielding. You need 99% shielding to prevent hum. You don't need to spend megabucks on monster cables either, you simply have to look at the cable specs before you buy. You can buy high shielding cable at near budget costs. You simply have to know where to buy them.

As far as the guitars go. Humbuckers are best because they naturally cancel hum but you can still get hum with them if the rest of the wiring isn't beefy enough. Single coils with unshielded wiring like Fenders are the absolute worst. The only fix for those is to shield the instrument using copper foil or metallic paint or switch all wiring to shielded to make the wiring quieter. You can do things like shield the pickup covers too though it can be fairly tough to do well. Using noiseless pickups is another option if you don't mind the changes in tone. Beyond that using a noise gate can do wonders too. Hum is typically has a low noise floor compared to the signal so simply gating the noise away when you stop playing can do wonders.
Old 2nd July 2020
  #6
Lives for gear
 
ScottBrio's Avatar
Quote:
Originally Posted by fireberd View Post
Do you get the hum with just the Scarlett plug in, but nothing plugged into the Scarlett?
Have you tried a self powered external USB hub (one that has its own power supply)? May be all that's needed if the USB port on the PC can't provide the needed power and thus causing the hum. I've seen problems posted on some forums of problems with USB powered recording interfaces. Providing power for the interfaces seems to be a fix for them.
I know this is an old thread but this helped me. My SSL 2+ wasn't getting enough power from the USBs on my gaming motherboard (shockingly) and so I had to use a powered USB hub.

The ground noise was at a 7/10 loudness, now it's at a .5/10. Still not as quiet as my Scarlett 18i20 but I guess I shouldn't be surprised as it's USB powered vs the Scarlett which has it's own power supply.
Old 3rd July 2020
  #7
Gear Maniac
 
Trip Hop Mop's Avatar
I've been using this isolator [>link<] for near two years now with no problems at all. Was skeptical whether it'd work, so took the plunge and gave it a go. Glad to report that it works as expected.


Just note that a external power source needs to be plugged into the isolator for it to work. Otherwise it will rely on your computers power and grounding, which will defeat the purpose of the device.
Old 30th July 2020
  #8
Here for the gear
 

Hi guys. I have the same problem with my sound card. You can listen here, it sounds very similar to this, except in my situation there's less noise https://www.youtube.com/watch?v=xJxy...=youtu.be&t=24 but I can hear that repetitive 'blips' and it seems like they change a bit depending on the processor.
@ Trip Hop Mop What sound card do you have?
Old 10th August 2020
  #9
Here for the gear
 

Quote:
Originally Posted by RonnieM View Post
Hi guys. I have the same problem with my sound card. You can listen here, it sounds very similar to this, except in my situation there's less noise https://www.youtube.com/watch?v=xJxy...=youtu.be&t=24 but I can hear that repetitive 'blips' and it seems like they change a bit depending on the processor.
@ Trip Hop Mop What sound card do you have?
Yes, that's basically what my USB ground loop noise sounds like. It's why I run my H9 interfaces on bluetooth instead of USB. I'm about to buy an iDefender (like Trip Hop Mop linked) which should eliminate the issue. Most of the music stores carry them, also Amazon, ebay and such. About $50.
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