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Earthing Problem? Dynamics Plugins
Old 16th December 2010
  #1
Gear Nut
 
luca1's Avatar
 

Earthing Problem?

Hi, really not sure if this the place to be but dunno where else it would go.

I bought a power adapter to convert my australian plug to a UK plug (now livin in UK). I have monitor speakers, laptop and soundcard all powered off same board.

I recently changed adapter for laptop power from big ass international one to a smaller single adapter I bought off Amazon.

The second I plugged my laptop into the board an ugly hybrid hiss/hum noise started comming through my speakers. Then I changed back to the old adapter and it went away.

The new cheap adapter has
"does not earth with side contact earth plugs"
written on it and a 13A fuse in it.

Any ideas what causing the hum, as far as I'm aware this is a ground loop problem, though I know FA about electrics as such.

Thanks :D
:Luca
Old 16th December 2010
  #2


Obviously that power supply for the laprock is kicking all kinds of noise out. Since the currents have a path to ground through some of the audio gear, you hear it in your speakers....

Can you run balanced connectors between your "soundcard" and monitors?



-tINY

Old 16th December 2010
  #3
Lives for gear
 
jhbrandt's Avatar
Luca,

I have seen this many times with laptops that have a grounded power connection.

The problem is that sometimes the manufacturers connect the 'common' wire on the DC side of the supply to the ground. - This is can be one of the + or - connections in that laptop and not necessarily the chassis ground. This will present a different reference within the laptop compared to any outboard gear that is also grounded - causing the buzz.

Your best bet is to use an ungrounded power connection and use a chassis ground connection for that reference. Attach a ground wire to the aux VGA connector or any type connector on the lappie that you can get a small screw into to connect to the chassis ground. Use a lift on the lappie power supply. - either that, or buy a laptop power supply that is 'isolated' but grounded for safety.

Cheers,
John
Old 20th December 2010
  #4
Gear Nut
 
luca1's Avatar
 

Hey thanks for the replies, I really know little about grounding and that so this is really good info for me

I had the laptop made by ADK pro audio and the power supply sent through them. I know I don't really know what I'm talking about but I reckon they wouldn't have sent a dud wiring job.

Also what makes me say this is, when I use the universal travel adaptor (still using the same power suply, just with different connector to fit in wall socket) that has no fuse in it I get absolutely no noise, but then when I plug in the one I got from Amazon.co.uk which has a fuse in it and is marked 'fused' thats when the hum shows up.

So i really think its the little wall socket adapter not the power supply.

So bearing in mind I have been using the same power supply unit but with different adapters on the end to fit into the wall sockets in different countries,
I guess my question now would be, could the adapter with the fuse cause the hum, whereas a 'unfused' adapter (such is the one I usually use) would not?..

:Luca
Old 20th December 2010
  #5
Lives for gear
 
jhbrandt's Avatar
Quote:
Originally Posted by luca1 View Post
So bearing in mind I have been using the same power supply unit but with different adapters on the end to fit into the wall sockets in different countries,
I guess my question now would be, could the adapter with the fuse cause the hum, whereas a 'unfused' adapter (such is the one I usually use) would not?..
Luca,

It is very possible. It could be that the adapter that is giving you fits is earthing something that it's not suppose to.
-- Like the doctor on the old 'Hee Haw' show would always say when his patient asked him, "Hay doc! whenever I do this... My arm really hurts!" Doc's reply, "Well, Don't do that!"

Like I always say sometimes... If it's not broke, don't fix it. (Get rid of the adapter that gives you problems)

Cheers,
John
Old 24th December 2010
  #6
Gear Nut
 
luca1's Avatar
 

Quote:
Originally Posted by jhbrandt View Post
Luca,

Like I always say sometimes... If it's not broke, don't fix it. (Get rid of the adapter that gives you problems)

Cheers,
John
Bwa ha yeah makes sense! :D

I'm just trying to figure it out for the next time I buy a little travel adapter cause I need a couple of them to plug in my other gear. At the moment I only have enough for my laptop (that doesn't hum) but need to plug in my Kaoss pad and other things.

Then when I go to Europe to play I will need adapters there, just don't want to get caught out.

The adapter that makes no hum says it has a fuse and has 'T2.5AH' written on it, is this a 2.5 amp fuse? Where as the dodgy plug says it has a 13 amp fuse in it.. hmmm. Maybe I should just buy another adapter from somewhere else and see how I go..
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