Audio Output Jack / AC - Distortion Feedback

I watched a movie on my laptop and connected my surround audio receiver to the audio out jack. At first, I heard feedback whining from the speakers. Once I disconnected the AC adapter power cord and used only the battery did the whine go away. Do you guys notice the same behavior?

It looks like the AC adapter is not fully shielded.

The audio, however, is amazing when using the SRS Utility and changing the output to Stereo.

Thanks.

 

E6400 - S... I've got the same problem. On batt all is ok. ON AC on my KOSS SPARK is bruuuuuuuuuuuuum...

Any solution ? Is it reason for return Latitude to DELL and take money back ???

 

I believe this is a Dell problem with most of their laptops - same issue with my M1330 - never could get a straight answer out of Dell. Never buy a Dell if you are using the headphone jack for anything broadcast wise or your listeners will have to get used to a 60hz hum. Glad you mentioned it was happening with your E6400 because I was close to biting the bullet and buying a Latitude to see if there was any difference.

 

As another test, I used another E6400 that we own and it duplicates the behavior. I thouht the power strip I was using might be the cause but when I removed it, the laptop still behaved the same way. It seems that the AC system leaks into the sound system. The behavior doesn't stop even if the battery is fully charged. In fact, removing the battery and running only on AC still presents the problem

It looks like this is a basic design issue. I don't think it is worth returning the unit on this issue but hopefully they have a solution in the future. This can get annoying when doing presentations and using external audio systems.

Current Solution: Use the battery only.

 

One thing I would question: Does anyone have a 90W adapter that does not have a ground plug? It could be possible that the ground plug is causing an isolation loop. If you have an adapter that doesn't have a ground plug and are having the issue I would be interested in hearing.

 

I have 90W without, problem is there too.

BUT TRY TAKE LAPTOP AND PUT ON YOUR NAKED LEGS !!!! BRUM IS GONE !!!!

So solution... Naked legs, latitude on legs, legs on the floor without carpet. o)))

DELL what's your solution ?? o)

 

WHAT!!! I don't think the folks at church will like me taking my pants off to present my presentation.

 

Ok after some research I have come up with more info on our issue:

Our laptops run on DC, and the power supplies for them are often fairly lousy switching supplies, so they're running on noisy DC. This often leaks so out onto analog ports, and causes the humming. It is called DC Hash and Dell power supplies are known for their cheap switching so this is the reason why we are experiencing the hum.

I tested a ground loop isolator unit tonight but this does not remove the hum - it isn't a grounding issue as I first suspected, it is indeed the product of a very low quality PS.

One interesting point - the new Aluminum Unibody Macbook or Macbook Pro was engineered with this issue in mind and has become a standard for musician application and PA application - Apple actually worked on this with their newest system. Wish Dell would!

 

It's some sort of current leakage which the bare legs helps to discharge. Is a work-around to run the computer on battery for the duration of the presentation?

John

 

Yes, John that is the only real solution.