Okay, so I'm stumped. The setup is a DVX100a, firewire out to an Inspiron 9300 for use with DV Rack. For sound, a Behringer sound board with XLRs to the camera. When I run the laptop on battery power, no problem. But the minute I plug into AC, I get a distinct buzz when monitoring sound from the camera. Take out the AC and go to battery, buzz is gone. This occurs even when the Behringer board is turned off and unplugged, but still have XLR connected to camera. I have replaced the board, and the AC adaptor for the laptop. The buzz is unique in that it appears as if I'm listening to the innards of the computer. When I move the mouse I can hear it in the headphones. I can hear a ticking like the internal clock of the computer or something. If I open a program, the buzz shifts tone and other little clicks and buzzes start up. Anybody have any thoughts on this. Is it a ground issue? Do laptops have ground issues? I immediately suspected the board, but after replacing it and still with the same problem, it keeps coming back to the laptop. Any help would be appreciated. I can go quite a bit on the two batteries I have for the laptop, but it sure would be nice to go on AC for long shoots.
Bad buzz
- Thread starter dodger
- Start date
smithy
Well-known member
dodger said:
Have you tried it without the behinger board? Meaning mic straight to camera? Behringer are known to be noisy in it's circuitry. Laptops do tend to be noisy but not to the point that you will hear it in your output on your headphones. Try updating your bios and drivers then see if that helps. It could be your soundcard or firewire port that is making the noise. You may consider getting a separate PCMCIA firewire card so that it doesn't share the same port as the one connected to you motherboard. In addition don't share any other peripherals on the same firewire port that is connected to the DVX. If no avail it may be the laptop itself has grounding issues in which you may need to get it repaired or replaced.
Basically, as Wabbit hinted, sounds like you have a ground loop. And a problem with the Behringer adding noise into the mix. If you do a search for Behringer, you can read about my experience with my Behringer mixer.
If you're using a Behringer 1002, you can run it on batteries to try to eliminate some of the noise.
Phil
If you're using a Behringer 1002, you can run it on batteries to try to eliminate some of the noise.
Phil
I have tried the setup without the board - mic straight to camera - and no problem. That's why I originally thought it was the board, and promptly had it replaced. However, if it's the board, why is there no problem at all when the board is used (plugged into AC) and the laptop is on battery? Meaning, if it was the board wouldn't it be causing a problem regardless of how the laptop is being powered. I definitely think it's some kind of ground loop as it only occurs when the laptop is on AC. Or, as Smithy says, it may be a ground issue with the laptop itself, but again only when on AC. And if it's the firewire port why would it be absolutely quiet when on battery power. I have no other peripherals connected to the port with the DVX. But I will try using a card, just to see. Right now I'm using the firewire port that is on the computer, and a card for the external hard drive. But the hard drive is not an issue, because the symptoms occur whether or not the hard drive is connected. Anyway, I will try all the suggestions from everyone and let you know. Thanks.
smithy
Well-known member
I have my dvx setup into my 6pin pcmcia firewire card and have the 4pin firewire out from my laptop going to my external hard drive when I'm using DVrack. I used a name brand 6pin to 6pin firewire cord and not a generic brand. Maybe because it is 6pin cord..there is a ground built into the cord for the extra pin. I know it has the capability to power peripheral phantomly using 6pin cords and not available on 4pin cables.
wabbit
Evil has Ears
From the above link:
"Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.
When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other. "
To isolate one side you can use the second link posted above (Hum-X if the link is not working).
As for the ticking and hearing mouse move, is this all the time or just when you are running on AC. Never heard of that before. :undecided It would be great if you could post up an MP3 of that noise.
Cheers
"Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.
When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other. "
To isolate one side you can use the second link posted above (Hum-X if the link is not working).
As for the ticking and hearing mouse move, is this all the time or just when you are running on AC. Never heard of that before. :undecided It would be great if you could post up an MP3 of that noise.
Cheers
smithy
Well-known member
I meant six to four to camera via pcmcia card not four to four and four to six to enternal HD. Belkin Firewire 25ft. Firewire is used to camera. Another thing is that I use a surge suppressor strip to wall outlet then connect laptop to the surge suppressor and a tripplite Line conditioner to the camera power adaptor. Just in case there are electrical dropoffs in the area. Especially when your in congested urban areas where power fluctuations occur frequently. Another option might be to get a 12v invertor and run you equipment off of a car battery so there won't be a ground loop and still give you ample power for many hours until a recharge is necessary.
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Hey, thanks to Wabbit and Smithy for all the help. I think the Hum-X may be the solution. Karl Soule over on the Serious Magic forum suggested a three prong to two prong adaptor and lo and behold if I put it on either the sound board or the laptop the bad buzz disappears. So, it's definitely a ground issue and though the 3 to 2 adaptor works, I suppose it is better to go with the Hum-X which still maintains a ground but claims to eliminate the problem. Nevertheless, for the weekend's upcoming shoot in Reno, this will work. Thanks again for all the enlightenment regarding ground loops. Before I hit the air, maybe a good buzz is in order.