Buzz from laptop chord???

[meeks]

Went with guitar rig tonight through the PA, for the first time, but was getting a buzz from the laptop chord through PA ???

Any way to stop this, don't have enough battery power to make it through a show and that buzzing needs to stop

[UltraJv]

Its a ground loop. Disconnect the ground from the laptop PSU. You can do this in one of two ways, either remove the grounding wire in the mains cable to the plug or get a ground lift box to do it.

[meeks]

So, clip the ground off the cable...or get a "ground lift box"...what is that?

[UltraJv]

So, clip the ground off the cable...or get a "ground lift box"...what is that?

Its an adaptor that you can buy which allows you to do this nondestructively.

[meeks]

Is it just one of those (:o) ----> (: ) litle grey thingies that were used in the seventies and eighties to plug three prongs into two prong house outlets, the ones that most everyone has?

[nix808]

Yeah, you can do that, but the sparkies I talked to when I had this problem didn't recomend taking the ground away, for you are not protected from surges. You can also get ground loop filters, which are just a small device in you line out, cheaper than DI boxes with ground lift. The electricians thought that was the best solution.
Cheers, nix

[meeks]

Still need some clarification:

My problem is definently in the power supply. I'm not seeing how DI boxes or ground lift filters in the audio chain would help. Problem I'm still having is avoiding the two prong converter.
http://www.audioholics.com/tweaks/conne ... -and-buzz/

I asked the little techies about this at fry's but they, like I still, have no idea of what a AC ground lift is? I've googled but still can not get a hit on a ground lift box/filter other than for a cable TV cord and stereo I/O boxes used for surround sound. In short nothing seems to be pointing me in the AC power cord direction (when the laptop is on batteries its fine)...I think I'm being daft so help clarify. Thanks again.

Ground Lift - A process used to eliminate ground loops (usually present in the form of hum) in systems whereby one or more of the grounds in the system is disconnected ("lifted"). The process can be executed via an in-line adaptor which disconnects pin one of the XLR connector, or via a switch found on many pieces of audio equipment, which disconnects the audio signal ground from the chassis ground. The highly unsafe and heartily not recommended method to lift a ground is by cutting or otherwise disabling the grounding pin on the AC cord. This is a highly dangerous way to eliminate ground loops. Avoid it at all costs.

Ground Loop - A state of a video, audio, or other system, in which too many grounds of different pieces of equipment are connected at too many different points. Variances in ground potential between different pieces of equipment create a voltage difference running along the grounds of the equipment which results in a mains frequency hum in the system. This hum will manifest itself at 60 Hz (in the US; 50 Hz in Europe) and its various harmonics.The easiest way to alleviate potential (ha ha) ground loop problems is by ensuring that all audio equipment (including electronic musical instruments, video equipment, and intercom) are connected to ground at one point, using a centralized power distribution source. Audio ground-lifting, often an option on direct boxes and some mixing desk input channels, is also a popular method to disconnect the audio shield between pieces of equipment. AC ground lifts, which remove the third grounding pin from the AC connection, should be avoided whenever possible; disabling the grounding pin from the AC connection can result in a potentially hazardous situation. Don't do it whenever possible.

[C00kie]

Still need some clarification:

My problem is definently in the power supply. I'm not seeing how DI boxes or ground lift filters in the audio chain would help. Problem I'm still having is avoiding the two prong converter.

So let's have a look at a random setup with a ground loop:


The ground loop exists because the shielding of the audio wire is connected to the chassis of both devices at either end, which in turn are interconnected by means of the ground of the mains power.

So there are two points at which you can break the loop:
1) At mains power. Either with an adapter or simply put some isolation tape on the ground pin. In my gig bag I have a special power strip with disconnected ground for such situations. There's hardly any risk involved, really...

2) In the audio line. Either with a DI (which should be employed anyway when connecting it over more than 10 meters) or using a ground isolator. Even Radio Shack has a simple one for audio:
http://www.radioshack.com/product/index ... Id=2062214
Both a DI and ground isolator contain a small transformer which allows alternating currents to pass but doesn't conduct directly. Look up "galvanic isolation"... The DI also converts the signal to mic level and makes it balanced. That travels better over large distances.

[Chuck E. Jesus]

not sure if this applies, but my digi camera came with a coil thing you wrap the power supply (charger) cord around, said to eliminate ac line noise...

[darrenn]

Google this, and then buy one - then say goodbye to all your strange noises:
ART DTI DUAL TRANSFORMER / ISOLATOR
Do not remove the earth pin or anything silly or you could do yourself some damage if your transformer goes.
Darren

[botkiller]

A power conditioner would help you at some point too:

http://www.furmansound.com/

They eliminate a good chunk of hum and also keep your gear from getting zapped out when plugging into sub par electrics at bars &c.

[meeks]

I get it, I was being daft. and thanks to all. Also it was plugged into a power conditioner if that makes any difference.

Will this work?
http://www.guitarcenter.com/shop/docume ... 99&index=0

It comes in active or passive, any difference on that?

[thecontrolcentre]

Will this work?
http://www.guitarcenter.com/shop/docume ... 99&index=0

It comes in active or passive, any difference on that?

looks like it's mono to me ... you'd probably want a stereo input for a laptop.

[meeks]

just for future reference:


http://www.native-instruments.com/knowl ... tions/269/

[Øyvind]

Yes