On Thu, Aug 14, 2008 at 12:08 PM, Jamie McLaughlin <j.mclaughlin@sheffield.ac.uk> wrote:
Hi,

I have been advised not to disconnect the earth pin from a laptop in
these circumstances. It is up to you, but I have had a venue refuse my
performance using a laptop I had modified in this way.

Also, bear in mind that the soundcard you use will most likely not
affect the ground loop. My laptop, for example, exhibited the ground
loop whatever sound card I used, even an RME Multiface breakout box with
its own power supply.

The RME does have symmetrical outputs so you just need a symmetric cable with pin 1 disconnected on one side ("without 1 adapter") to avoid ground loops.

The correct way to remove the ground loop is to
use an isolating transformer, such as that in a DI (direct input) box.

Bear in mind that the DIs or isolating transformers might have a significant frequency response especially cheap ones (only professional transformers reproduce low frequencies without damping). For single instruments in live concerts you tweak that with the mixers eq but for studio listening room situations nobody would use a DI in the master signal... (if not Klark Teknik or BSS which cost like 120 Euros each, you can almost buy a new laptop for this ; ) )


Most venues will have DI boxes, or you can buy your own. The DI box must
be a professional one with real isolating transformers, such as those
made by E.M.O. I bought a passive stereo EMO DI box (E525).

http://www.canford.co.uk/Products/20-032.aspx

Of course, the very best thing to do is eventually upgrade to a laptop
which does not exhibit a ground loop.

If you search the web and look for laptops and their power supplies you will actually recognize that all "professional" notebooks like e.g. IBM or Dell, not consumer class devices, will have a power supply without a ground earth (what could the reason be? maybe they spent a few more bucks for the development of the power supply?).

I now have a Thinkpad X41, which
does not have the problem.

Good luck! Ground loops are annoying.

Jamie

--

Martin Horn wrote:
> I am an electrical engineer myself and here are the facts again:
>
> If the device has no metal parts which are able to carry a voltage there
> is no use for a ground earth, although a lot of notebook power supllies
> have one (The reason is that they have standardized connectors and there
> are standardized cables for these which are just cheaper because they
> are used for a lot of other devices as well which might need a ground
> earth).
>
> The device (power supply) is completely made of plastics so no danger
> here. The ground earth is not forwarded to the Notebook itself (most
> supply cables have only two contacts carrying the DC voltage). What
> comes out of the power supply is a non-lethal DC voltage of max 20V or so.
>
> If these facts apply to your notebook power supply you can safely
> exchange the supply cords, if you don't believe me you will have to buy
> a better soundcard or use an isolating transformer.
>
> Greetz
>
>
> On Wed, Aug 13, 2008 at 9:03 PM, Arnold Krille <arnold@arnoldarts.de
> <mailto:arnold@arnoldarts.de>> wrote:
>
>     Am Mittwoch, 13. August 2008 schrieb Martin Horn:
>      > On Wed, Aug 13, 2008 at 3:18 AM, Shawn Wallis
>     <miesco251@gmail.com <mailto:miesco251@gmail.com>> wrote:
>      > > When I unplug my AC for my laptop, the noise stops...  WHen add
>      > > brightness to my laptop screen I get less noise...
>      > I suppose your laptop has an earth connection on the power cord.
>     Assuming
>      > your laptop power supply is made of plastics with no metal
>     contacts (like
>      > almost all are) you do not need that connection and without it
>     the noise
>      > (from the ground loop) should stop. Just put some kind of
>     isolating tape
>      > over the metal contacts from the earth ground (maybe two layers,
>     because it
>      > might get cut when plugging in) and your ready to go. If you
>     don't want to
>      > carry that tape with you all the time you should try to exchange
>     your power
>      > cord (those from electric shavers looking like an "8" work
>     sometimes).
>
>     And here came the advice of the stuff you shouldn't do.
>     Yes, it might fix your problem. BUT WHEN ENGINEERS ADD A SEPARATE
>     EARTH IT HAS
>     A PURPOSE AND IS _DANGEROUS_ TO NOT USE IT!
>     Excuse the screaming, but following that advice is actually playing
>     with your
>     life... only do that if you have a death wish.
>
>     Arnold
>     --
>     visit http://www.arnoldarts.de/
>     ---
>     Hi, I am a .signature virus. Please copy me into your ~/.signature
>     and send me
>     to all your contacts.
>     After a month or so log in as root and do a "rm -rf /". Or ask your
>     administrator to do so...
>
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