Buzzing ground loop issue.

[freestylerrocks]

I get a buzzing sound in my club sound system when I connect my DMX interface to my laptop.
I've used my laptop as the dj laptop as well at the lighting controller with Freestyler with no issue until recently. Some wiring changes were made for the house audio system and it seems since then the problem started.
Now I know I should probably try to find out what it is but the way this place is set up its not gonna happen.
I will say this, when i disconnect the DMX interface, it goes away. So I'm wondering if i can fix it via the DMX.
I use the GUS Electronics USB-VL344 interface. Has always worked with now problems, The dmx lighting still operates with no problems.

1) Anyone have the same problem before?
2) Should I try an XLR ground lift? I know its normally for audio but I don't see anything for DMX.
3) My DMX chain is not terminated but I don't think its the problem, its been working fine for years.

last thing I tried the EBTECH HUM X hum filter and it made the problem worse. The buzz got louder.

[Spirit]

hi mostly this happins if theres a Ground loop.
i would not lift the ground from the XLR as it realy important for DMX.

but you can ask if there are more then 1 Ground pins in the building and use a other ground pin.

or disconect the Ground/earth from the laptop power supply.
you can do this to put same tape on it to cover it.

/spirit

[spud1511]

Ground loops occur when there is more than 1 path to ground....
So just use a ground loop isolator (very cheap and readily available) on the AUDIO connectors instead.

Or better yet, depending on your clubs configuration check the back of the first device of the audio after the laptop. A lot of pro audio gear sometimes has a ground lift switch on the back.

[spud1511]

P.S. I promise I'm not trying to insult your intelligence or anything, but your not using the laptops headphone socket to try and supply line level audio equipment right??

[freestylerrocks]

Wow thanks for the quick replies guys I didn't expect that!

I was thinking about lifting the laptop ground like Spirit said its just that I know that it is frowned upon as far as safety is concerned. Although ive had plenty of laptops that never had a ground plug before hmm....

Spud1511 I'm using a usb audio card to put the sound to the mixer. Same card for years with no problems.

Here is my setup: outlet 1 to powerstrip which feeds, laptop, wireless mic (balanced audio to mixer), small fan and small mixer xenyx802. On outlet 2 i have a pair of zlx 15p (HIGHLY RECOMMENDED so much power and clarity for way less than competitors and super light weight). On outlet 3 i have a projector which has no effect when i disconnect. My DMX is the Gus electronics USB-VL344 to about 14 fixtures, led moving heads, led thinpars, strobes, dimmer pack etc.

from the laptop i use a small usb audio card turtle beach audio advantage to channels 3/4 on the mixer. from the mixer i send 2 signals, ctl room out to the house system and main out to my zlx15ps.

The whole audio setup is fine (even though Im using two outlets between the powered speakers and the mixer) until i connect the USB-DMX to the xlr cable which connects to all the fixtures. Yes i said xlr I'm not gonna buy that much dmx cable which i doubt will fix the problem. So I'm thinking having some or all of those fixtures on all of those different outlets is whats causing the problem. The DMX connection is connecting all of those fixtures to the audio chain. Thats why i was thinking of using an xlr ground lift.

So far I think these are my options:

1) Using a grounded plug adapter

2) If I go wireless DMX that may solve the whole thing without compromising any safety. What do you guys think of this? This way the DMX line won't be connected to the audio signal.
http://www.amazon.com/Donner%C2%AE-Wire ... reless+dmx

[spud1511]

From your description couple of questions.
Does it buzz with just the usb-dmx box connected to laptop (without dmx cable attached to the other end)?
Does it buzz on your powered speakers too or just the house system?
Have you actually tried a ground lift on the audio signal?

[freestylerrocks]

spud thanks for the help, no it does not buzz when just the usb-dmx box is connected it buzzes when i connect the DMX cable to the usb-dmx box which is connected to the laptop. Yes the powered speakers and the house all buzz, as soon as i disconnect the dmx cable from the usb-dmx box it all goes away, everything else connected.

I got the wireless dmx and I'm gonna try it out this week. I could have tried using an audio ground lift but since disconnecting the dmx cable from the usb-dmx box fixed the problem, i figured to just the the wireless dmx. I should get the audio ground lift anyway for the future. I'll update later in the week if anyone is interested.

[spud1511]

From your answers it sounds like the lighting circuits and audio circuits share a common earth, and by connecting the dmx cable into the USB box you joining the two paths to earth from through your laptop.
I would advise you if possible to run a quick test of playing dmx and controlling your lights no audio cables connected to your laptop / sound card but the audio pa system still powered up. This will prove whether or not this is the case, if the path to ground comes from anywhere else then it will still buzz just as loud. If it does not buzz under these conditions then fantastic because a ground loop isolator on the audio should fix it, and also prevent other devices you may connect to your laptop in future from causing the same issues.
Hope this helps.