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Old 01-23-2014, 08:34 AM   #34
planetnine
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Join Date: Oct 2007
Location: Lincoln, UK
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If the laptop PSU has a three-pronged connector it is class1, ie an earthed device and needs that earth (ground) connecting.

If it has a two pronged connector and the "double-square" symbol on the case, it is class2, double-insulated, and doesn't need an earth (ground).


Class1 switch-mode PSUs have a nasty habit of putting electrical noise onto their outputs relative to ground potential, which ends up via the negative connector joining to the laptop's ground-plane and audio output connectors, which will create audible noise then if connected to another grounded device (ie monitors, amp, etc). The noise voltage will run to ground through the audio connection's ground and you'll hear it as crap (it really is horrible).

Don't remove the earth connection to the PSU!

It is there to protect you and your computer and other connected equipment if there is a fault in the PSU circuitry. It needs that earth connection to leak the current and trip RCDs/blow fuses.

Ways around the noise? Put a pair of DI boxes on the output (or other signal isolating device -usually containing isolating transformers), or replace your PSU with a class2 (double-insulated) one.

UK users -Maplin do a class2 universal laptop PSU for about £40 that will solve all this.

REPEAT. Don't disconnect the PSU earth connection. It's there for a reason. Yeah I know stuff is reliable now and faults like that never seemed to happen, but they can, and unless the manufacturer went for a more robust class2 design it is possible to hurt people and gear in a fault condition.

There, you've been told now...



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