Soundcraft notepad 124

[a917917]

Hi guys,

 

We've got a brand new soundcraft 124 and have a problem where we receive a hum that is like mains hum but isnt.

We've tried switching boards and the problem goes away. The strange thing is that it only happens with laptops.

It's not the laptops as we have several and the laptops aren't plugged into the mains during the presentations.

The cable is a 15 minijack to dual phono cable.

Has any one has this problem or knows how to fix it?

 

Many thanks,

Alex

[DrV]

during the presentations.

 

Do you mean you also have the laptop plugged into a data projector? Could be a hum loop being created by having logic ground earthed at the projector and again at the desk. If so an audio isolation transformer in line with your laptop audio wold probably cure it.

 

Dave

[TimmyP1955]

This problem is common with computer power supplies (desktop and laptop). A computer power supply is the one and only piece of gear on which I will allow the AC ground to be floated. An alternative is to use an transformer to isolate the computer ground from the mixer ground, such as http://www.audiopile.net/products/DI_Boxes..._cutsheet.shtml and http://www.radialeng.com/re-proav2.htm

[RoyS]

If you're short on funds I'd recommend one of these: http://www.behringer.com/EN/Products/DI20.aspx

 

About £22 from these folks: http://www.bluearan.co.uk/index.php?id=BEHDI20

 

You can also pickup any appropriate leadage/bodge from them too..

[Sound Man]

If you're short on funds I'd recommend one of these: http://www.behringer.com/EN/Products/DI20.aspx

 

NO!

 

Not those horrible things.

 

You'l find plenty of advice here.

 

David

[a917917]

hi guys,

we already float the earth on the laptop power feed, we have a special socket only for tht in our venue.

the problem was the earth through the mixer and the projector, bought two audio isolation devices from cpc and built our own unit which is now in use.

 

Thanks for your help.

 

Alex