Ground loop / audio isolation transformer

[La Tenaille]

Hi,
I know this is not a problem specific to Usine, but I imagine a lot of you are using computers and various audio gears, so perhaps could you share informations about ground loop problems.

I'm wiring my future audio rack for stage (with a laptop and Usine of course), and have ground loop problems (especially when moving the mouse, HD activity...).

So I 'cut' the ground of my laptop transformer and no more noise... but recently I've read this article preventing people from doing such a thing (for human and equipment safety).
Then I read Senso writing 'sometime I use a ground isolator (cost 0.50€)' in this thread.

So, do you use audio isolation transformers like this one ?



Thanks for guiding me

[Clearscreen]

i've used these (http://www.amazon.com/Xitel-GLI1-X1-Gro ... B00023XDYA) before and they worked fine, but i'd start with the cheapest one possible and work up from there, as they can get *VERY* expensive.

[La Tenaille]

The trouble is I need XLR plugs... and I don't really understand were to plug this, I have 10 XLR line out!
About the laptop, I imagine the ground only protects the transformer... and if all my hardware is connected with balanced jacks/XLR, perhaps a single ground is enough ? I'm a bit confused

[cybercharles]

Hi la tenaille.

I have a simple question. How do you power supply your sound card ? Do you use an external power supply pluged in 220V or you power supply the sound card by the fire wire or USB wire ? Sometimes you can fix ground problem by the way of power supplying your sound card.

Charles

[amiga909]

check this first: run your laptop on battery. if the noise vanishes the grounding problem might not be solved without replacing the laptop's AC. I am really not sure about this, but I believe a line-isolator helps in some cases but not all!

then: check if your audio circuit is connected in any way to a device with an antenna terminal (radio, tv, video). disconnect all such devices. if the noise vanishes and u still want to connect these devices, a line-isolator or a mantelfilter (I dont know the english word) will help. it does not matter where u connect the line-isolator afaik, it just has to be connected to the audio circuit somewhere.

[La Tenaille]

cybercharles > I use external power supply and firewire.
Can't try the laptop on battery right now as I am rewiring everything (meters of cable, hours of soldering!), but as I mentioned, the noises disappear when I cut the laptop supply ground so I imagine it will also disappear if I use the battery.
I'd just like to do the best to prevent from future troubles, and cutting a ground doesn't seems to be a good idea...

[Clearscreen]

cybercharles > I use external power supply and firewire.
Can't try the laptop on battery right now as I am rewiring everything (meters of cable, hours of soldering!), but as I mentioned, the noises disappear when I cut the laptop supply ground so I imagine it will also disappear if I use the battery.
I'd just like to do the best to prevent from future troubles, and cutting a ground doesn't seems to be a good idea...

as it seems you're handy with a soldering iron i found this on another website (http://www.electronicskb.com/Uwe/Forum. ... -e-product) that might help:

A 10 Ohms resistor inserted somewhere in the ground loop will almost always cure a hum. Inserting this in the safety-ground at the mains connection could give a hazardous situation. But in the ground connection of the audio connection-cables will do fine. and absolutely no "loss of volume, tone or both."

i can't vouch for it, but it might be worth a try? otherwise unfortunately i think you're up for some expensive xlr ground lifts between your soundcard and whatever you're running it in to...

[La Tenaille]

Interesting tip, I'll try this.
I've also read that keeping a single power cord for the whole hardware was enough if the sound wiring was well made.
Perhaps I'll ask a pro to check my rack...
Thanks

[Clearscreen]

I've also read that keeping a single power cord for the whole hardware was enough if the sound wiring was well made.

i've heard that as well - i guess if everythings on the one ground there can't be a feedback loop...

[La Tenaille]

Hi,
I forgot a word, I meant "single power cord ground". Only one device keeps its plug-in power ground, and this ground flows from device to device, using the audio cables ground.
I've never heard about ground feedback loop...

[Clearscreen]

I've never heard about ground feedback loop...

i think we're actually talking about the same thing - what's happening is that having multiple grounds can somehow create a 60hz feedback loop in your electrical wiring and results in the hum you hear. basically if you have a single ground point there can't be a feedback loop, and one way to have a single ground point is to run everything off of the same power point (i think... bear in mind i'm no electrical engineer). if i'm wrong about this, let me know... always interested in finding stuff out