"Crackle" when using a Laptop

[whitefieldgarrick]

I have changed my USB soundcard to an Maudio pro. This suffered unacceptable background noise. I noticed that this only happened when
the laptop was charging - To run a two hour show this is a requirement. I have tried ferrite rings in all possible locations. Moving the transformer as far from the sound card as practical. Using a separate power supply for the sound card (With Ferrite ring) tweaking settings on the sound board etc. I then borrowed another transformer (I have to return this) and it was quiet enough to run a show if volumes were moderate. I have purchased a new Toshiba 19v transformer
and this is as bad as the original !! Is this a common problem ?? does any one produce an up spec transformer (At moderate cost) that tackles this problem.

Any other suggestionsI would appreciate replies that a self taught operator can understand !!

PS a laptop is used for security reasons.

[Martin]

Sounds like a problem I have had (and I think it's fairly common) when the laptop is connected to the mains rather than running off the battery. The Behringer HD400 2-Channel Hum Destroyer fixes it for me - I carry a couple of them with me all the time. About 25 UK pounds and easy to source.
A word of warning - the jack sockets are a bit close together so if you're using the fat, metal-cased jack plugs then they can touch each other and make matters worse. A bit of LX tape wrapped around the jack plugs deals with it.

[jmgordon]

There are two aspects to this ground loop problem, the usual mains hum and the noise from the power supply. Although you describe the latter for your Toshiba as a transformer, in all likelihood it is a switch-mode power supply, which produces a high frequency screech that isn't always adequately filtered out. It is, I suspect, skimping on the filters that enables them to be sold at "moderate" cost (although the Sony one is anything but moderate). Finding a transformer-based power supply with the right voltage and current capacity may not be easy.

I encountered this for the first time this year when I had to replace my Toshiba laptop, which had a 2-core mains supply, with a Sony with a 3-core lead. Taking the headphone out into a small mixer produced unacceptable intererence, both low and high frequency. Using an ART Ground Loop Isolator removed the hum but not the HF, to the extent that I assumed that both it and/or the Sony power supply were faulty and arranged to change them, but without improvement. However, the Maplin Ground Loop Isolator, which is intended for car radios and thus is designed to filter out ignition noise, produces almost complete silence (from interference). A support guy at ART in the USA said that theirs was not designed to take out that amount of HF and that fidelity would suffer.

An alternative approach I have used is to make use of the laptop's mini-TOSlink optical output and an optical converter. This can be USB powered, but that immediately re-creates the ground loop. However, using the provided separate power supply maintains the isolation.

Getting rid of the noise in any particular set-up can be a bit of a black art, depending upon whether the signal earth is floating in the various components. Your new M-Audio may differ in this respect from your previous arrangement. Removing the mains earth is not, of course, a safe option.

[Eric Snodgrass]

As the other two posters stated, this is not an unusual problem with laptops when they are plugged in to mains power rather than running on battery.
What M-Audio USB interface are you using?

[Richard]

We've had this problem too with all sorts of laptops, PC and Mac. Switched mode power supplies dump all sorts of rubbish to earth, which I think causes the problem. One thing I've found which can help reduce the problem is to plug the laptops PSU into a different mains supply to the PA (traditionally a good way to create ground loop hum, which shows how desperate I was at the time). It doesn't cure the problem completely but it can help.
In the end we bought a Presonus Audiobox just for when someone turns up with a laptop, problem solved.

Cheers
Richard

[derick]

Normally a good stereo di with groundlift engaged should take care of this problem

[Eric Snodgrass]

I use a Rolls HE18 Buzz Off when I interface my laptop with an audio system. It works perfectly every time for eliminating noise.

[Richard]

another thing that can cause noise is using the wrong USB port.
when I plug our audiobox into the port that it was plugged into when the drivers were installed everything works fine using the correct driver and no noise.
But if it's plugged into a different port the computer uses a generic microsoft driver which sounds awful, lots of high pitch digital noise.

see here
http://support.presonus.com/entries/211 ... bile-setup

cheers
Richard