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[Miguel Sousa Magalhães]

Hi
expirience noise when some laptops are connected to mains and to desk. Some times also occurs whem there is a video projector also connected.

Any way of wipe this noise?

Miguel

[Chris McDonald]

With my old laptop I had to run off the battery, the power supply was very noisy. Using a DI box to lift the ground might help. Also try USB or firewire sound interfaces rather than the onboard soundcard.

[Ken Freeman]

What kind of noise?  

Is this a Hum that stays with you? Try using a direct box with a transformer to isolate the signal grounds.

Do you have the input turned up while you are connecting?

ken

[Miguel Sousa Magalhães]

I believe it's not the typical hum noise generated by earth loop.
In hotels there are all kinds of stuff that makes interferences, air conditioned, electric motors etc.

What's is funny is that laptop transformers dont' have earth but noise stops when is running only with battery's

This don't happen in all rooms with all pc's.

We connect the phones out of the laptop to a DI ( usually in mono ) and then send it to desk as a mic.

Ground lift don't solve this. My DI don't have transformer isolation, should be it?

Miguel

[Ken Freeman]

I am familiar with the hotel environment.  At least, treat the computers like they are stage gear and keep them on the "Tech" power.  

Your note about how they do not make any noise on battery but do when plugged in A/C is a dead giveaway.  I suggest isolating the signal ground using a passive transformer based Direct Box.  I like Pro-Co's AV-1 the best as it can be multipurpose.

Do not, I repeat, Do not lift the A/C ground.  You are asking for trouble.

Ken

[Miguel Sousa Magalhães]

Well most of transformers don't have ground so no lift is possible. I was using a active DI but without transformer isolated. The ground lift did not do any effect.
I don't believe that i will have to carry a super cost Di for those creepy sounds of powerpoint. Well quality is everything

[Brian K Tennyson, CTS-D]

New product from RDL (but with RCA's)http://www.rdlnet.com/av-hk1.htm

Or try the Wirlwind pcDI. http://www.whirlwindusa.com/dirbox.html
or RLD STA-1 will balance your audio. If that doesn't do it you can lift the ground on the balanced out of the either of these boxes and it should kill that buggar.

[Ken Freeman]

Yes, these are very cool, but dedicated you can't use them as a DI the next day as the AV1 will.  I still think the single transformer based DI with a 1/4", rca and 1/8" input will still be the way to go.

http://www.procosound.com/downloads/av1.pdf

Ken

[Simon Clayton]

Ours do. I use a mains adapter that cuts the earth connection to the computer transformer. Works fine.

[Simon Clayton]

I routinely use an adapter to cut the AC earth in the quoted situation. Why do you reacon it's risky ?