Hello,
I'm using a laptop with an Edirol UA-1Ex usb sound card, when my computer is plugged to AC I hear some noise on the speakers, I thought it could be due the unbalanced outputs, so I tried to put the cables far from the AC adapter, but the noise stills. Moreover when I do something cpu intensive tasks I hear more noises (while cpu is working hard). If the AC adapter is unplugged I don't hear any noises.
I want to know if using a balanced outputs will solve the problem, or any other suggestion.
Thanks in advance.

I’m afraid the PSU is very noisy and/or your sound card is susceptible to ripples in the power supply and/or EMI/RFI.
If the noise is affecting your sound card, a balanced output won’t cure this.
If you don’t have these problems running on battery power, replacing the PSU is probably the way to go

Not recommended solution: Cover AC adapter plug's earth/ground clip(s)/pin with duct tape or something.

I come across this quite frequently at the conference center where I work as we see many laptops on a daily basis. Roseval is right - the root cause is noise in the switching power supply, and as such lifting the AC ground on the laptop and/or destination device rarely fixes the problem (and, as Phoyo's response implies, introduces the possibility of electric shock in the case of equipment malfunction).

I've been able to completely eliminate the noise every time it's occurred by using isolation transformers between the laptop's (or USB audio interface's) audio output and the input of the powered speakers/mixer/etc.

Note that you don't need balanced connections to use isolation transformers - with unbalanced connections, just make sure that the cold (-) leg is shorted to ground on both the input and output of the transformer and then engage its ground lift switch.

I use Whirlwind's ISO-2 stereo isolation boxes, and they work and sound great, but they're a bit spendy from a consumer audio standpoint (~US$130). The cheapest ($65) stereo isolation transformer I've seen is the Ebtech H32PKG, which has 1/4" inputs and outputs (RCA-to-1/4" adapters are very easy to find).

The only caveat is that you often get what you pay for with transformers. I've never used the Ebtech, so I can't say whether or not it would have an audible effect on the sound (low-end roll-off being the most common artifact of inexpensive transformers), but that is a possibility...

I'll try to buy the Whirlwind (better pay a little bit more than waste my money).
Two more questions:
1) Can my speakers be damaged if I still using them with that noise?
2) when should i use ground lift button?

Thanks for the info!

No, it's just like any other sound that your speakers reproduce. There is often some DC offset present with such noise, but since the vast majority of modern amplifiers are AC-coupled (i.e. they block DC on their inputs), even a large amount (hundreds of millivolts) of DC offset would be eliminated at the amplifier's input.


Whenever you hear the noise. The whole point of the isolation transformers is to achieve complete physical isolation between your laptop and the speakers (or the amplifier driving the speakers). Since you will have solid grounds on each side of the transformer (through the power supply of your laptop on the input, and the power supply of the amplifier/powered speakers on the output), the ground does not need to be carried through. About the only time you need to connect the input and output grounds is if you're isolating a microphone or guitar pickup, i.e. sources that don't have their own electrical ground.

Edit: One other thing...to get from your Edirol interface into the ISO-2, you'll need RCA-to-1/4" adapters, as I mentioned. However, the ISO-2 only has XLR outputs, so you'll need appropriate adapters to get from XLR to whatever the inputs of your amplifier are (although you mentioned balanced connections, so perhaps your amplifier/powered speakers are already capable of that?). Remember, if the inputs of your amplifier are unbalanced, you need to make sure the XLR-to-whatever adapters short the cold (-) leg (pin 3 on an XLR) to ground (pin 1 on an XLR).

If an isolation transformer fixes your problem, you have the proverbial 'ground loop'. I assume you're still using the switching supply, just on the output side of the isolation transformer. Under that scenario, balanced line output from the computer _would_ fix the problem.

Ground loops come from large number of situations and are most often the building wiring particuarly if the source and destinations are on different circuits or worse, on different phases of the power company or worse, yet on different transformers in different buildings.

You CAN achieve nearly ALL the benefits of balanced line even from unbalanced outputs if the destination amp has balanced inputs. Connect the '-' inputs of both cannels to the ground shield of the source. Connect the '+' inputs of L/R to the L/R outputs and do NOT connect the XLR pin 1 shield.

G²

I have not dealt with the problem myself but I’ve read numerous complaints and suggested remedies. The problem is usually the basic design of the laptop power supply, but the fix seems to be quite variable. That is, repeated reports have said that what works with one model is sometimes useless with another. If users are telling the truth, committing much money before knowing that the equipment will actually work could be rather frustrating.

You might like to look at these threads and also consider a search on laptops and noise at the same forum.
http://www.audiomastersforum.net/amforum/i...pic,6168.0.html
http://www.audiomastersforum.net/amforum/i...pic,3809.0.html

Hi PaJaRo, before you spend any moeny on it you might want to try my very simple "fix".

I've seen situations similar to yours and the following usually makes the situation a lot better. It's obviously not a full fix but it may just make the situation tolerable. If it seems too simple and you think it cant work then give it a try anyway since it's free.

Turn all the volume sliders on your computer (software mixer and media player volume controls etc) up to maximum and turn down the volume control acordingly on your amplifier (or amplified speakers). In the case that you listen through headphones then you do the same thing and get an in-line volume control for the headphones to adjust the volume back down to an appropraite level. You'd be amazed at how much this simple advice reduces that annoying audio noise that some systems have.

Thanks for the idea.
I usually dont use software mixer so the output is max, as you said the noise is minimum with low amp on the speakers, but when I want to listening at loud volume and the songs goes quiet the noises are really disgusting
I think I'll have to spend some money.

http://www.maplin.co.uk/module.aspx?moduleno=223680

Hi

I had exactly the same issue; I bought one of these and now I have no noise what so ever.