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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 ?

[Chris Davis]

Simon Clayton wrote on Thu, 26 January 2006 18:26

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

As a matter of principle and good ethic, you don't want to get started lifting AC grounds.  In general this can have unexpected and lethal consequences.  So really your only choice is to just use them.  Using all your equipment as licensed by UL or CE will keep you "legit" in the event of an incident, investigation, and lawsuits...

Specifically, your laptop computer may or may not actually have continuity to the ground pin on the AC plug.  The ground may only be there for the sake of the high voltage inside your external power supply.  This would provide some protection in the event your laptop power supply or building wiring was inconsistent or faulty.

Like others, I recommend a product like the PCDi from Whirlwind to address the problem properly and safely.  

[Andrew Sharpe]

In my experience, many PC laptops have a high noise floor for the headphone output.  Depending on the make and model, some sound great, others are very noisy.  I would recommend, if it is possible, to use a cleaner output.  Since you are using laptops, some sort of PC card, for example the best price at Full Compass is the Echo INDIGO-I0, would be the most cost effective since you can pop it in and out of each laptop quickly.  You can also use a Firewire or USB audio device, which would defiantly give you a clean sound (Too many to do a quick price comparison, all depends on what you want).  Hope this helps!

[Josh Millward]

I have this very same problem. I have had it with Compaq and Dell laptops. It is NOT a functon of the AC ground. It is NOT an issue with the computer needing to be transformer isolated. It is NOT remedied by going to a USB audio interface. I use an M-Audio Moble-Pre USB audio interface. It seems to me that this is caused by one of two things.

1) The power supply brick, being of a switching type, injects this noise into the computer when it is plugged in. (I have tried putting ferrite clamps on the incomming DC power to no avail.)

2) The computer system (processor and chipset) changes settings when it is running on wall power vs. when it is running on battery power. These higher settings create noise in the system.

The best work around I have been able to come up with is either to just run the thing on batteries if at all possible, OR make sure the sound level coming out of the laptop is cranked all the way up to get the signal as far above the noise as possible. Yes, you will still hear the noise, but it shouldn't be as loud.

If anyone figures anything else out with this, please share it here so we all may benifit. I know this problem drives me insane all too often.

-Josh