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 Forum index » Instruments and Equipment » General Discussion
Laptop PSU and humming?
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DumbStruck



Joined: Jun 11, 2007
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PostPosted: Tue Oct 23, 2007 8:06 am    Post subject:  Laptop PSU and humming?
Subject description: When I use my external sound card with my laptop power supply I get a hum
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Anyone had this problem? or know of a device I can buy to stop it happening I have tried obvious things like taking the battery out etc.

I never had this problem with my old laptop, and consequently it has restricted my live set to 1:30 h.

Any ideas ? ? ?
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Kassen
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PostPosted: Tue Oct 23, 2007 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Use it without the adapter's ground.
use a external power adapter for your soundcard if possible.

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Mohoyoho



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PostPosted: Tue Oct 23, 2007 9:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Agreed. I had the same problem with mine. After I put a two prong adaptor, my sound cleaned up beautifully. In the 5 years I've owned the laptop, I have never been shocked or have had my computer fried.
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elektro80
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PostPosted: Tue Oct 23, 2007 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Some external interfaces should only be powered with the bundled power supply if the computer won´t supply power over USB/Firewire. Double powered is not recommended.
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Grizzle



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PostPosted: Tue Oct 23, 2007 11:42 am    Post subject: Reply with quote  Mark this post and the followings unread

That happens to me as well... When I play live I have to plug out my laptop and run on batteries or the ground hum goes over the P.A. It doesn't happen at home only when going out into a P.A. I thought it used to be just DELL laptops.... they had a problem with interference from the screen coming up on the soundcard output... but no it seems like a lot of laptops have the problem.

I have seen people play until their batteries runs out. It can be a pretty cool way to end a set.... bang it out for x lenght of time and then 'tpsffhh' the power goes... everyone looks up at you and you point to the darkend screen on the laptop... kinda punk... Not ideal for every situation but I have seen it work.

Taking out the earth... hmmm - I'd imagine that to be a risky enough procedure given some of the shady set-ups I've played on. Homemade doesn't describe some of them Smile

Another idea... I might be wrong and I have little knowledge to back it up but... another idea might be to buy a few RF rejectors. You know the little things you usually see on monitor cables to prevent RF and EM interference. You can buy them and just click a load of them onto the cable between your soundcard and computer. I know that the MBOX USB cable has one on it... so I'm guessing if you had more of them it might help. I'm not a tech so I'm not sure maybe somebody else here might know if that works.

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blue hell
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PostPosted: Tue Oct 23, 2007 12:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grizzle wrote:
I thought it used to be just DELL laptops....


No it's just an ordinary ground loop throught the laptop's power supply usually. Laptops used to have no safety ground but nowadays most seem to have it.

RF rejection ferrites are not likely to help, ground lifting usually does.

And just in case .. be sure to have ALL wireless stuff (like network and blue tooth) switched OFF.

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also .. could someone please turn down the thermostat a bit.
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Grizzle



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PostPosted: Tue Oct 23, 2007 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

maybe this will help:

http://pages.prodigy.net/jforgione/FT_HUM.html

a page about elimination of ground loop hum.

You can get a box called EBTECH Hum Eliminator for $59 HERE

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Fozzie



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PostPosted: Thu Oct 25, 2007 2:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

strange though it is, I have an external soundcard that hums terribly when the psu is connected, unless it is grounded. In my home, most power sockets are not grounded in the living room, which makes this rather annoying when it use it there occasionally.

However, I don't understand how this can happen. The situation in which ground lifting helps to solve a groundloop is easy enough to understand, but I don't get what induces the hum in this case.

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