linuxaudio.org

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On Wed, Jul 25, 2007 at 10:58:07AM +0300, Sampo Savolainen wrote:

quoted text
> Quoting Ken Restivo :

>

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> > On Wed, Jul 25, 2007 at 08:55:19AM +0200, Malte Steiner wrote:

> > > I am still searching for the ultimate solution for the dreaded laptop

> > > hum and guess the only real one to end it all is to get a RME PCMCIA

> > > Card with Digiface and separate converters connected with optical ADAT,

> > or?

> > >

> >

> > The solution for me was to remove or lift the ground pin on the laptop's

> > power supply.

> >

> > After a lot of testing and asking questions on lists (including this

> > one), that was the solution.

>

> That is an extremely dangerous thing to do. Quoting

> http://www.epanorama.net/documents/groundloop/problem_solving.html:

>

> "Do not do this. Removing the ground connection isn't right. It is against

> electrical safety regulations and potentially very dangerous. Removing

> ground connection can defeat the actions of your noise filter or spike

> protectors inside the equipments. If the ground connection is cut then a

> fault in the isulation inside equipment will cause dangerous voltages to the

> equipment case instead of burning a fuse. Removing the ground connection

> from the equipments which have it is dangerous, against electronic safety

> regulations and you risk damaging your equipment. Running without a power

> ground will not automatically electrocute you but will make this much more

> propable if something goes wrong in your system."

>

> 

It's a laptop.
We're talking about 19VDC here. IANAEE, but I imagine that the $20 laptop power supply will sacrifice its life in case of lightning strike, horrible mains power fault, surge, or other disaster, leaving both the laptop and the performer intact.
Up until this year, I've never seen a laptop power supply with a ground pin anyway, at least here in the USA. They've all been two-pin AC, no ground. I've never had any kind of dangerous problem with them, in nearly over 15 years of using laptops. The grounding of laptop power supplies is a new thing.
Finally, I always run all my stuff off of a multi-outlet strip with a breaker. That thing is supposed to give its life as well too. 
There is no other solution. I've been told that the buzz/ground problem is *inside* the laptop and all of them have it. It's a cost-saving and space-saving measure that the PCB designers make.
I also need to point out that changing audio interfaces did not eliminate or even mitigate the buzz, and, I'm told could not have done so. I heard the buzz with USB and firewire interfaces.
I suppose if one is really safety counscious, one could run the laptop off of its battery. However, running out of battery in the middle of a show, is, um, disconcerting.
:-)
- -ken

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