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Author Topic: Ground Hum driving me nuts....  (Read 2935 times)

Barkley McKay

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Ground Hum driving me nuts....
« on: April 07, 2006, 01:39:59 PM »

Hi All,

Hope I have found the right community for this!

I am trying to eliminate the source of hum in my home studio and it refuses to go.

I have stripped the equipment back to basics and slowly built it back up. All the mains plugs for each unit go back to the same single outlet in a star earth congig ( I'm UK. 240 volt 50Hz). All balanced to unbalanced have had the cold/ring/pin 3 wired to the screen at the unbalanced end (as the A&H is unbalanced)

this is the order:

1. Allen & Heath GS3 console + Genelec 1030 - All fine at full control room volume

2 MOTU 828 mk1 added, slight hum but not annoying

3. Behringer ADA8000 converter added,bigger hum when all faders set to unity, but turn down one set or the other ( ie leave 828 up and 8000 down, vice versa) the hum is enormous. Both appear to have good earths on the mains. it alsmost seems as if the hum goes out of phase and cancels when they are at the same level. I have checked the signal phase ( to check I had not revesed the wiring) by playing identical sound files through both and it seems to be fine in that regard.

I cannot see how I can do anything else with these. If I turn off the ADA8000 the hum diminishes, but disappears from the console altogether if I disconnect its mains plug ( whilst the 828 is still up in the mix). The ADA 8000 is totally silent when the MOTU 828 is off.

The transformer in the MOTU 828 is quite audible acoustically from the unit itself and sounds to be at the same pitch, Could this be the culprit?

any help would be appreciated.

thanks

Barkley

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jtsoundtech

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Re: Ground Hum driving me nuts....
« Reply #1 on: April 10, 2006, 11:14:36 AM »

I think the 828's transformer is a likely culprit based on the evidence you disceibe.  However, there's also the possibility of some other noise from your household appliances getting into your audio system.  You may want to investigate isolating your ground for the outlets that feed your equipment.  This means running a separate grounding rod into the earth than the one that is currently in place downstream from the circuit breaker pannel.  Then, I believe, you could somehow link the ground side of your "audio " outlets to it.  I'm not sure of the steps involved with this, it's been a while since my teachers explained this to me, but hopefully, I've given you the right idea.  Please check with someone more knowledgable than I before trying this at home!!  Good luck.  
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Regards,

Jessica
Graduate of Full Sail Real World Education
http://profile.myspace.com/index.cfm?fuseaction=user.viewpro file&friendID=33304014

Barkley McKay

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Re: Ground Hum driving me nuts....
« Reply #2 on: April 11, 2006, 09:09:41 AM »

Thanks.
I've since discovered that the room has a ring main setup with all the cabling buried under concrete, so basically I'm within a big 50Hz loop!
I found a temporary fix by putting a small connecting wire between the (unused) word clock BNC connector outer lug on the ADA8000 and onto a metal sleeved jack on the 828. It is acceptable now.

Time to get in the electrician!

Barks
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Teddy G.

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Re: Ground Hum driving me nuts....
« Reply #3 on: April 12, 2006, 02:53:06 PM »

A new wall-wart would seem to be in order, but, have you tried a computer-type UPS, on your stuff? They make 'em big enough to do entire factories! Though, maybe just one from the Office Store could be tried?

Works for me!


TG
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