Grounding [buzz or hum] problem?

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Hey guys, how it going? Just back from a very short vacation and ready to pick up where I left off. The reason I created that "Basic Electricity" thread that some of you may know of, was to set the foundation for this problem I ran into a while back and no pc tech I talked to could come up with an answer.

I had bought a TV Tuner card to get the TV/Cable signal on my pc to record anything I wish and then burn to DVD. After connecting everything the only problem I ran into was/is there is a buzz or hum associated with the audio signal from the tv/cable and this noise is only present when coming into the pc so my TV/cable plays fine on it's own or even going through my Home Theatre System so there is nothing wrong on the tv or cable box end.

I was told that this is a "grounding" problem and should be taken care of "inside" the pc, called Dell but they couldn't help so I had to settle for using a Ground Loop Isolator which does the job effectively but I feel this only masks the problem, I want to not use the Isolator and fix the problem, especially later on if I should be fixing someone's pc that might have the same issue, I don't want to tell them I can't fix the problem.

So guys, this is a challenge, any ideas please? Thanks.

 

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Sorry, forgot to mention that I did all of the testing, exchanged power strips, cables and wall AC outlets and also pc's, the problem only occurs with this model [Dell Dimension 3000 and 2400], I don't get this problem when I connect my son's older Dell PIII pc so the problem is within the dell pcs which is why I am figuring that I have to do some sort of grounding "inside" the pc.

 

Audio hums are a common problem in sound amplifiers and other audio circuitry Mike. They are usually caused by electromagnetic radiation emanating from the power supply. The PSU has AC mains voltage as it's input. It's the frequency of the mains (50Hz in the UK) that causes this hum. 50Hz is in the audio spectrum i.e. you can hear it.

Proper grounding, positioning of looms and wires combined with good smoothing in the PSU usually prevents this but it is sometimes hard to resolve. In these cases a ground loop isolator can be used with good effect.

As far as I can tell from what you have said, is that you have fixed the issue already by installing the ground loop isolator.

So, be proud of yourself and move on to the next problem that will surely crop up soon, as this one is quite unusual

 

Appreciate the explanation, someone else has also suggested I try changing the PSU as the Dell PSU most likely will be a cheaper inferior unit, at least I know now where the problem is most likely to be, thanks!

 

The classic source of 'hum' is the use of multiple earths in an audio setup.

The usual fix is to ensure that all components are earthed at one point only. In my old HiFi days we used to see this when a separate turntable was hooked to an amplifier. The fix was to disconnect the earth wire on the mains cable for the turntable, and rely on the earth via the amplifier mains cable.

With computers this can be rather tricky - and when coupled to a Home Theatre system and a tuner it can be a pig!

So congrats on a solution.

I've seen comments that these isolators can cause a loss at the low end of the audio spectrum - but I've not had one in my hands so don't know whether it is noticeable or not.

Harry.

 

BTW - before you rush out and buy a new PSU for the Dell check that it isn't a non-standard size. I've seen many Dells where you couldn't change the PSU unless the replacement is bought from Dell.

Harry.

 

Very true - the one i have is a very strange flip flop type.

 

And they will cost you twice as much as a standard PSU