Unwanted machine noise

[nix808]

Hey all,
I've been trying to use my laptop as my instrument, then into my PC for effects. The snag I've run into is that I get horrible machine noise when using the RCA outs on my soundcard(M-Audio Audiophile USB). Previously I've used the digital outs to get around this, but I want to route in a different order (I've got 2 Creative soundcards in my PC). It also means that I don't have to run SynthMaker as a router on my lappy which adds another 9ms latency. Any help with this would be much appreciated, eh. Using different leads affects the amount of noise, but none run clean. I've tried the RCA outs on 3 stereos, and one doesn't have this noise, so I tried running an out from this after the lappy and into the PC, but the noise recurs.
Thanks very much, wishing you good times making music,
nix

[JonathanDragonDJ]

so you can run from laptop to stereo without the noise? can you run from stereo to desktop with no noise?

[BertKoor]

What happens if you run the laptop on batteries instead of mains power?

[nix808]

Thanks for your reply Jonathan,
Yeah, I can run fine from the stereo to the PC, and from PC to stereo. I think it's something to do with the M-Audio soundcard, eh. A funny thing about this is that if I run a line from the card's headphone out, turning the volume doesn't affect the noise signal, only the audio.
Cheers, nix

[nix808]

Thanks very much Bert,
You've sussed it there, eh. Can it be remedied at all? I think my battery is on it's last legs, so. Thanks so much for your help again, I can play clean for a time at least.
Cheers, nix

[BertKoor]

Well, if running on batteries helped then you're probably the victim of a ground loop: http://en.wikipedia.org/wiki/Ground_loo ... tricity%29

You can fix it by cutting the ground connection either of the power or of the audio cables. Using an ungrounded power extension cord for the laptop power may work fine without putting your safety ak risk.

[nix808]

Thanks a lot Bert,
I'll use my battery for recording and a little ground loop filter which cuts 90 % of the noise for most of the time. I'm a bit shy of losing my laptop to a power surge, eh.
Cheers, nix

[Lunch Money]

The ground connection won't save your computer from a power surge. And plugging a 2-prong connector (mine's 2-prong already, no ground even if I wanted it!) into a surge-protecting device of some sort will work just as well as with a 3-prong connector!

[nix808]

OK, maybe the shop just wanted to sell something. When I talked to them they told me that wasn't the case, that I needed to have 3 pins to use a surge protector. Lots of countries only run 2 pin connections anyway, is this the same as using my equipment in Finland or the US?
Thanks for your help, nix

[BertKoor]

Apart from providing a common ground, 3 pins power is only needed for ground fault leak protection. That is, when a certain amount of current is detected on the ground lead, then everything is switched off. This can only happen when there's a short circuit with the ground that shouldn't be there.

This is an essential safety measure for washing machines etc, but not so for a laptop. The only thing that can cause that is the power adapter itself. And with the laptop case being made of plastic there's no danger for you to get electrocuted.

[nix808]

Hey again,
So Bert, you are saying that it's fine to run 2 pins as long as I don't get a short circuit in my adapter, eh. I might try this, but I am a little wary because the techs at the electronics shops I have been calling all say that the earth connection is for power surges. It would be sweet to have no noise what so ever. I kinda pose the same question once again, would this be the same as running my equipment in any 2 pin connection country? Am I more likely to cook my electronics?
Thanks for your help, nix

[BertKoor]

Nope, a power surge is a sudden increase of the volts coming from the mains outlet. Caused by striking lightning or whatever... The ground connection can't help with that, since it solely occurs on the two lines that carry the mains power.

If you cut the ground connection from the power then it's exactly the same as what you describe. Most countries DO have 3-pin power. But weather it's used or not depends on the installation and the devices.

In my house only about 1/3 of the outlets have ground. In new houses that's more close to 100%. Most devices that use less than 100 watts have 2-pin power plugs here (provided they are double-isolated) and they fit in 3-pin outlets.

If your electronics decide to kick the bucket, they'll do that anyway.

[nix808]

Sorry to harp on, but I just want to make this clear before I endanger my lappy. I am not increasing the likelyhood of an electical fault by disconnecting the ground?
Cheers, nix

[BertKoor]

I am not increasing the likelyhood of an electical fault by disconnecting the ground?

Not very likely, no... Just don't put the laptop in your bath tub

I do the mixing / engineering for a live band of some friends regulary. In my gig bag I have a power extension cord without any ground, to connect to my power strips. Especially for cases where I get hum problems, and this is one easy and fairly safe way to cut the ground loop.

I must say that I trust my equipment not to break down. And I don't let anyone hover a glass of beer above the mixing console. Those are my safety measures

[nix808]

Thanks for your help with this Bert ,
I might keep using the ground loop filter, as the hum has gone for intents and purposes. If I'm feeling finicky about my sound quality I'll try disconnecting the ground. I would like to protect my laptop from shorts, as it's integral to my setup.
Sorry to repeat myself, but would disconecting the ground be the same as setting up in the US, say?
And this would mean no more beer and playing in the bath? Damn!
Thanks for your patience, nix