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[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