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Laptop + USB audio interface = annoying ground loop noise
Old 23rd December 2007
  #1
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Question Laptop + USB audio interface = annoying ground loop noise

Hi all,

I'm having a ground loop problem here (at least that's what I think it is), but after doing some research around the GS forum, and over the internet, I'm still not sure about how to fix it.

If my laptop's power supply is plugged in, I get some nasty noise, but it disappears when I unplugged it and the laptop is only running with the battery. I know this problem has been commented in a few other threads, and different solutions came up, but here comes my question, and something I still don't have clear.

Since I've already tried different cables, stripes, outlets, etc... and it still didn't work, I was thinking about getting a DI box, since it seems to be the solution to this kind problem for a lot of people. But the thing is:

- I'm using a Mini-Me via USB, and the noise goes through the USB cable (it would disappear if I unplug it too, but that's not what I want, obviously). Since the only analog output the Mini-Me has is a 1/8 output, that's what I'm using to send the signal to my monitors/headphones/etc...
So I thought about getting the DI box, and put it between the Mini-Me analog output, and the monitors/headphones amplifier/etc... But if I do that, would it remove the noise? I'm asking because, in that way (if it works) I'd be removing the noise from the signal that comes from the computer, through the USB and the Mini-Me, to the monitors/headphones, but what about the signal that comes from the Mini-Me (that means, any instrument/mic), through the USB, to the computer?
I don't know if that makes sense

More additional info:
- The monitors I'm using here are the HS50M
- Audio cables are not longer than 1,5m (like 60 inches?)
- I'm using a T cable (one stereo jack -from Mini-Me- to two mono jacks -to each monitor or to the headphones amplifier L and R mono inputs)


I'd really appreciate any help!


Thanks!!
Old 23rd December 2007
  #2
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Wavebourn's Avatar
 

Tascam US-122 + Dell Inspiron 9300 + Custom Linear PS == Deadly Quiet Setup.
Old 24th December 2007
  #3
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In short, if all your equipment is plugged in at the same electric circuit a DI with Groundlift could help.
If its not, plug it so that it gets fed by the same circuit.

You could also try to move your Audiocables around if you can, as the problem is never the ground loop itself but the electric unit inside that loop that injects unwanted stuff.
Old 24th December 2007
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Quote:
Originally Posted by sputnik View Post
In short, if all your equipment is plugged in at the same electric circuit a DI with Groundlift could help.
If its not, plug it so that it gets fed by the same circuit.

You could also try to move your Audiocables around if you can, as the problem is never the ground loop itself but the electric unit inside that loop that injects unwanted stuff.

The problem is voltage drops on a ground loop itself through which battery charging current goes. Ground of a switched mode PS can't be lifted up, but either an isolation transformer, or a linear PS may be used. I made a linear PS to silence the notebook, it works well, though huge (100W transformer + 20W heatsink).
Old 24th December 2007
  #5


The problem is the nasty, cheap SMPS that charges the battery. You need to break the ground between the computer and everything else.

I don't know if Mini-ME has a way to self power and isolate it fromt the computer ground, but that is the best technical solution...




-tINY

Old 25th December 2007
  #6
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I've ripped the ground pin out of my laptops power supply cable, and that's solve dthe problem.

have you tried a groundlift on the plug yet?
Old 25th December 2007
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Quote:
Originally Posted by Henchman View Post
I've ripped the ground pin out of my laptops power supply cable, and that's solve dthe problem.

have you tried a groundlift on the plug yet?
It's forbidden by safety rules.
Old 25th December 2007
  #8
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This is correct. A manufacturer will not get type certifications nor will they obtain UL or CE certifications. The problem here is that the things will meet codes but the ground loops that they set up are not spec'd for testing so they slip by. I suppose if you took this to an extreme, an insurance company might not honor a claim related to the laptop's failure if it was discovered that the safety ground had been defeated. Technically, they would have a case.

I hate to run my laptop this way but I do until I can build a 19VDC, 5 amp linear supply to replace the switch-mode brick power supply in my Dell. Seems like there's a 3rd party market here for someone to fill.....

Cheers,

David
Old 25th December 2007
  #9
Gear Head
 

I experienced some weird "electrical shock" from my mac book pro for a while. Come to find out, I wasnt the only one - i was using macs ungrounded plug plug vs. the 3-pin one that also came with it. Apparently the user is acting as the ground! I now use the grounded one for charging the laptop, but you may be having a similar problem. If your laptops power supply isnt grounded with a 3-pin connector, it may be trying to ground itself somwhere else, even by you touching it. Just a thought......
Old 25th December 2007
  #10
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When you lift the ground 60V AC stays on it because of couple of caps in series in EMI filter. It is enough to get a buzz touching a mic by lips.
Old 25th December 2007
  #11
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Thank you guys for all your responses! I have a few questions for you guys about some of your responses:

- "In short, if all your equipment is plugged in at the same electric circuit a DI with Groundlift could help. If its not, plug it so that it gets fed by the same circuit."

When you say 'the same electric circuit', you mean the same outlet? Cause I'm using the same outlet for all the stuff I have plugged in. I'm using 3 of those things with plugs (I don't really know its name... 'stripes'?). I have one plugged in to the only outlet I'm using in the wall, and the two more plugged in to the first one, like a chain... to have enough plugs. I don't know if you know what I mean...


-"I don't know if Mini-ME has a way to self power and isolate it from the computer ground, but that is the best technical solution..."

The Mini-Me has its own power supply. It doesn't get powered by the USB. I don't know exactly what you mean when you say 'a way to isolate it from the computer ground'. The Mini-Me has one of those things to hook a wire and put it to the ground, you know what I mean?... and, if you do , is that what you mean?


- "I've ripped the ground pin out of my laptops power supply cable, and that's solve dthe problem.

have you tried a groundlift on the plug yet?"


I didn't want to rip the ground pin out of the power supply because of safety reasons. I've read something about it, and it's seem not to be recommended.

I didn't try a ground lift on the plug... it would be the same than a DI with a ground lift switch?


- "If your laptops power supply isnt grounded with a 3-pin connector, it may be trying to ground itself somwhere else, even by you touching it. Just a thought......"

This is a European plug, so it doesn't have 3 pins, but it has the equivalent system to ground.



Again, thanks a lot to all of you guys for your responses. I appreciate your help with this issue.


P.S. Merry Christmas!
Old 25th December 2007
  #12
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Quote:
Originally Posted by jacobo3d View Post
When you say 'the same electric circuit', you mean the same outlet? Cause I'm using the same outlet for all the stuff I have plugged in. I'm using 3 of those things with plugs (I don't really know its name... 'stripes'?). I have one plugged in to the only outlet I'm using in the wall, and the two more plugged in to the first one, like a chain... to have enough plugs. I don't know if you know what I mean...
Yes thats what I meant. Just to rule out another form of ground hum that can appear if different circuits are used.

I have to say I have no experience with ground hum on laptops. The way I understand things though a groundlift on the audiocable should do exactly the same thing as cutting the ground on the power supply. It breaks up the ground loop. Feel free to correct me if I'm wrong.

Merry Christmas
Old 26th December 2007
  #13
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Thanks for your reply!

I've found a new thing. I didn't realize until now, that the noise is coming through the headphones as well (at first, I thought it was only through the monitors). And that was something that didn't happen before. So, keeping the laptop's power supply plugged in, I've unplugged the monitors (HS50M), and the noise was gone.

Is this something about these monitors? Or it still would be a ground loop problem?


Thanks again!
Old 26th December 2007
  #14
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Quote:
Originally Posted by jacobo3d View Post
Thanks for your reply!

I've found a new thing. I didn't realize until now, that the noise is coming through the headphones as well (at first, I thought it was only through the monitors). And that was something that didn't happen before. So, keeping the laptop's power supply plugged in, I've unplugged the monitors (HS50M), and the noise was gone.

Is this something about these monitors? Or it still would be a ground loop problem?


Thanks again!
Yes, you've removed one ground loop.
Old 26th December 2007
  #15
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Quote:
Originally Posted by Wavebourn View Post
Yes, you've removed one ground loop.
Thanks for your response!

More ideas about how to remove that ground loop keeping everything plugged in are welcome
I keep trying different cables setups but I still didn't get rid of the ground loop.
Do you think that a ground loop isolator, or a DI box with a ground lift option, etc... would help to fix this in my case?

Sorry for so many dumb questions... but I don't know much about all this electric issues, and I'm getting crazy with this. I hope you understand. Thanks!!
Old 26th December 2007
  #16
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Quote:
Originally Posted by jacobo3d View Post
Thanks for your response!

More ideas about how to remove that ground loop keeping everything plugged in are welcome
I keep trying different cables setups but I still didn't get rid of the ground loop.
Do you think that a ground loop isolator, or a DI box with a ground lift option, etc... would help to fix this in my case?

Sorry for so many dumb questions... but I don't know much about all this electric issues, and I'm getting crazy with this. I hope you understand. Thanks!!
Yes, line level audio transformers will help, even if ins/outs are asymmetrical. I use Tascam US-122 that has asymmetrical line ins/outs so decided that it is cheaper to build a linear PS than to use 4 expensive line transformers, because any transformer in signal path degrade sound a bit, though it helps a lot to fight against interferences.
Old 27th December 2007
  #17
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The USB cable is still going to ground to the MiniMe to the laptop. I have a similar problem with my Edirol UA-25, fortunately I only use it for sending itunes to my DAC, so it's not an issue. While you can still lift the ground at the power supply, it's not an ideal solution. Now, does the USB connection work w/o a ground? I'm not sure.
Old 27th December 2007
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Quote:
Originally Posted by TAVD View Post
The USB cable is still going to ground to the MiniMe to the laptop. I have a similar problem with my Edirol UA-25, fortunately I only use it for sending itunes to my DAC, so it's not an issue. While you can still lift the ground at the power supply, it's not an ideal solution. Now, does the USB connection work w/o a ground? I'm not sure.
USB ground is THE ONE ground through which digits are walking, getting rid of a SMPS I've silenced my notebook completely.
Old 27th December 2007
  #19
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Thanks for your responses guys. I'll follow your advices and I'll see if I can finally fix this. I'll come back if I still have problems
Old 27th March 2011
  #20
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Quote:
Originally Posted by Wavebourn View Post
Tascam US-122 + Dell Inspiron 9300 + Custom Linear PS == Deadly Quiet Setup.
I am having the same problem, not at home but frequently when going around in small venues and reheasal rooms. I decided to go for both buying a DI and a better power supply, using the DI and its Ground Lift only when the PS still makes noise.

I just couldnt' find any information on where I can buy a Linear PS for my laptop, or how to build one... @Wavebourn: can you please point me in the right direction? My audio card is an Edirol UA-25, laptop is a Compaq HP, and the power supply has an "LPS" on it - but I don't thing it refers to "Linear Power Supply":

INPUT: 100-240V .6A 60-60Hz
OUTPUT: 18.5V --- 3.5A LPS

Seems like a Switching PS. Also, could a separate, good power supply for the audio card solve the issue?

Thanks!
Fabrizio
Old 27th March 2011
  #21
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here:
http://www.mastechpowersupply.com/dc...a/prod_65.html

This is what I use for my noisy computer stuff.
Old 27th March 2011
  #22
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Quote:
Originally Posted by drtechno View Post
That's a lab power supply! I never thought of using one of these to power a laptop I think I will look for one locally (I'm in Italy).

And what about the idea of powering the USB audio card with its own power supply? It should be cheaper, just 5V 2A via a self-powered USB hub (provided the hub doesn't use the power pins from the laptop at all)?
Old 27th March 2011
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Yeah, it probably may be better to buy a decent PS. I had some spare parts then, so I decided to build mine, deadly quiet one.
Old 28th March 2011
  #24
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Quote:
Originally Posted by drtechno View Post
That's a lab power supply! I had never thought of using one of these to power the laptop! I found one identical to that link but marked with a different brand, from a local ebay seller
Old 3rd April 2011
  #25
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@drtechno: I had never thought of using a lab power supply to power my notebook I found one identical to the one you posted, from a local eBay seller: I'm going to get one serious PS, and also a good DI with ground lift feature, just in case. Thanks!

Last edited by splisp; 3rd April 2011 at 01:06 PM.. Reason: typos
Old 3rd April 2011
  #26
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Quote:
Originally Posted by Wavebourn View Post
Yeah, it probably may be better to buy a decent PS. I had some spare parts then, so I decided to build mine, deadly quiet one.
Do you think a simple LM338-based (5A) Linear PS would be clean enough? Something like this? I have the same problem with a Netbook that requires 19v @ 2Amps.
Old 11th November 2011
  #27
In my experience , it's the DAC (soundcard) that needs to be isolated from ground loops to avoid the noise .. Leave your computer and it's power supply alone as grounding is very important for safety there ...

Just get one of these :

USB Isolator, Galvanic Isolated USB 2.0 - Electronics-shop.dk

and isolate the problem causing usb device/s

You are most welcome
Old 13th November 2011
  #28
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Quote:
Originally Posted by Murat Lahur View Post
In my experience , it's the DAC (soundcard) that needs to be isolated from ground loops to avoid the noise .. Leave your computer and it's power supply alone as grounding is very important for safety there ...

Just get one of these :

USB Isolator, Galvanic Isolated USB 2.0 - Electronics-shop.dk

and isolate the problem causing usb device/s

You are most welcome
You just power your notebook and USB connected device from different sources, isolating them galvanically. Should work, why not, it is one more possible solution, to break a ground loop in one more place.
Old 13th November 2011
  #29
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Quote:
Originally Posted by undertone View Post
Do you think a simple LM338-based (5A) Linear PS would be clean enough? Something like this? I have the same problem with a Netbook that requires 19v @ 2Amps.
I don't think that PS ripples are critical for a notebook PS, anyway it is a battery charger, and notebook contains all needed voltage stabilizers on it's motherboard.
Old 14th November 2011
  #30
Gear Nut
 

I don't even try to connect audio from a laptop without using a DI box.

It works and there is no down side. I also use one with MP3 players, I-phones ETC. just to protect the device.

Not always needed, but never hurts.

Frank
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