AC Line hum problem??
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AC Line hum problem??
I hope someone can help me out with this problem or point me in the right direction. We are removing cassette machines from 2 churches who
do weekly shows and replacing them with laptops. The laptops are connected to the line out on the mixers. We get good clean audio using
the battery packs in the laptops ---- but when the power supplies are
connected there is a bad hum. Is this AC line hum?? What ever it is -
any ideas how to get rid of it?
Thanks
do weekly shows and replacing them with laptops. The laptops are connected to the line out on the mixers. We get good clean audio using
the battery packs in the laptops ---- but when the power supplies are
connected there is a bad hum. Is this AC line hum?? What ever it is -
any ideas how to get rid of it?
Thanks
- Lester
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I had this problem before we went to using Circuitwerkes and DTMF to fire the underwriting spots in our sports feeds. We were using a laptop and feeding them down the phone line. Plugging the laptop into my sports mix was causing a hum when the power supply was plugged in.
I fixed it by using a ground loop isolator like this one:
Rat Shack car audio ground loop isolator
This might also work:
http://www.jkaudio.com/pureformer.htm
I fixed it by using a ground loop isolator like this one:
Rat Shack car audio ground loop isolator
This might also work:
http://www.jkaudio.com/pureformer.htm
- The-Hammer
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Also check the laptop power bricks. I've heard of others having problems when the cord from the wall to the brick is 2-wire instead of a 3-wire connection. A switch to a generic power brick with a 3-wire cord solved the problem.
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"Any technology, no matter how primitive, is magic to those who don't understand it" - Ambrose's Corollary to Clarke's Third Law.
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Sounds like some isolation transformers are needed.
These damn laptops... ( and desktops too ) do funny things with grounds.
Don't depend on the chassis actually being true ground.
Desktop PC's don't usually have a power transformer in the power supply.
From the line cord right to the switching supply input. ( how they are made cheep)
Take a DVM and measure for volts (and current too) from the chassis ground,
or the common return on your sound card, between your computer of choice
and the ground and/or audio return of the sound system.
You may find a suprise....... ( can we say "ground loop"???)
....... a lot of open discussion now begins.......
These damn laptops... ( and desktops too ) do funny things with grounds.
Don't depend on the chassis actually being true ground.
Desktop PC's don't usually have a power transformer in the power supply.
From the line cord right to the switching supply input. ( how they are made cheep)
Take a DVM and measure for volts (and current too) from the chassis ground,
or the common return on your sound card, between your computer of choice
and the ground and/or audio return of the sound system.
You may find a suprise....... ( can we say "ground loop"???)
....... a lot of open discussion now begins.......
"..... If you are not part of the solution,
then you are part of the problem........
then you are part of the problem........
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Thanks!
The Ground Loop Isolator took care of the problem. I had one on the rack, but don't know why! Lester, your idea of going to another outlet, one the mixer isn't connected to, helps alot. But we couldn't have an
extension cord draped across the alter - so that wasn't an option.
And ---- the problem is with Dell. The IBM laptop works fine.
The Ground Loop Isolator took care of the problem. I had one on the rack, but don't know why! Lester, your idea of going to another outlet, one the mixer isn't connected to, helps alot. But we couldn't have an
extension cord draped across the alter - so that wasn't an option.
And ---- the problem is with Dell. The IBM laptop works fine.
- Lester
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