Laptop Grounding Issue

[electric1000]

Hi guys,

When I hook up my new headphones to my laptop I'm hearing a humming sound.
Headphones are connected directly to the laptop by aux, and there's also an external DAC+AMP for the HIFI connected by USB.

Multiple tests I've made shed light on the source of the issue:

1. Whenever I touch a metal surface on the laptop the hum stops.
2. If nothing is connected to the laptop (no charger as well), there is no hum.
3. If I connect anything to the laptop, including monitor via HDMI, DAC+AMP via usb, or the laptop charger, the hum resumes. (it could be any of the above, order does not matter).
4. Tried to connect the headphone by another external DAC, problem persists.

Seems like a grounding issue but I have no idea how to address it.

Any thoughts?

Thanks!

 

[static zap]

If you have another laptop charger try that .

( God forbid if it has a figure of 8 connector or 2 pin plug-- reverse that )
Don't go swapping any wires.

 

[Lucien Nunes]

It does seem like a grounding issue, especially as there is hum when the charger is not connected but something else is. That suggests either poor design or a fault in the laptop that makes it sensitive to hum being introduced by external connections, or the devices that you are connecting are themselves not being grounded, nor is the charger, because of missing or broken ground connections in your wiring.

Some brands and models of charger pass the ground from the wall outlet through to the laptop, either directly or via a resistor, others do not. Some need a ground for their own safety, others do not. Can you confirm the model of laptop and whether the charger is original and genuine?

You could test the outlet for the presence of a ground connection using a plug-in tester with indicator lights. Unfortunately these things, especially the cheap ones, are notoriously inaccurate as a means of testing for safety, but if there is enough of a ground connection to light the indicators, it should be curing the hum not creating it. If you have a multimeter you could test for continuity between the ground pin of the plug and the chassis of the laptop (e.g. via a plugged-in cable shield connection) or even just to the DC output of the charger, and likewise test whether any of the other outboard audio gear is grounded.