mains hum/earth loop

supapete

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Hello all,
I've put a search in and got nowhere. Sorry if this subject has whiskers on. Sorry if I'm in the wrong department.

I have a pretty standard project studio revolving around a couple of mixers. All of my gear, which is varied, laces up in any configuration I wish- silently.

Occasionally, I would like to input audio from my digibox. When I do, I get a big-time mains hum. If I input audio similarly from my televes RSD 7254, not a hint of noise.

I've exchanged digiboxes making no difference. All's o.k until I plug the dish in.

I have a quad lnb and I have to say that none of the receivers run absolutely silently through their respective tv's/dvd recorders. However the noise is over taken by the signal.

I can work round this, but it would be convenient to leave a permanent input from the digibox into my mixer.

Any suggestions, please ?

best regards


P.S:)
 

mhku

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Have you tried one of the Maplin ground loop isolators?

_http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&&source=14&doy=31m3
 

supapete

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mhku said:
Have you tried one of the Maplin ground loop isolators?

_http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&&source=14&doy=31m3

I've just had a look at this. I've never come across these things in spite of earth loops and mains hums being a constant bugbear in my line. I've always remedied them in the "old fashioned methods" which all failed hitherto except disconnecting earth leads all over the place.................:-rofl2 only joking. Just sent off for a couple of gl isolators. Let you know and thanks for the prompt response. I'll prees the "thanks" button.:) regards P.S
 

mhku

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There's a bit more detail here:

_http://www.epanorama.net/documents/groundloop/
_http://www.channld.com/hum.html

The second most common source of hum and buzz is the voltage difference between two safety grounds separated by a large distance or the voltage difference between a safety ground and an "Earth" ground (such as a grounded satellite dish or cable TV source). This problem is usually called "ground loop". This is the most common one in severe humming problems.

That Maplins device was suggested to me when I had a bad hum on a pre-amp/ power amp hifi; I didn't try it as I sold them both and bought something else.
 

mhku

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SoundOnSound also suggest using resistors to remove ground loop hum:

_http://www.soundonsound.com/sos/1994_articles/aug94/groundloops.html

In a typical audio system, a resistor of around 100 ohms will be high enough to significantly reduce any induced hum currents, while still being low enough not to affect the level of the signal passing through the cable.
 

supapete

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Yep, familiar with those principles. My studio is at a pro level and devoid of any sort of hum or noise. It's only when I connect the digibox into the gubbins that I get a hum. The hum is the worst I've ever heard regardless of gain/level settings on the mixers. Hence the reasons I've asked you guys. Thanks for the responses, I'm awaiting the ground loop isolator.

Whilst I've got your attention, I wonder if you could comment on a scrolling ghost-like horizontal line on my tv's. It's the same on all. It's more apparent at switch-on in the mornings. The present receivers from the quad lnb are panasonic 31 &50 and a thomsonD/3. I've substituted grundig and pace receivers. It seems to disappear as the day goes on.

regards P.S
 

Llew

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Souds like the classic 100Hz hum bar. Probably injected through that earth loop problem you have.

Llew
 

supapete

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Thankyou, again. The common denominators are the mains supply-a rural type earth=double up on neutral and the quad lnb. Do these quad lnb's cause problems ? I ask as there's no earth connection involved with the receivers and my televes which is on its own lnb introduces no noise at all, again no earth connection. regards all. P.S
 

supapete

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If I may, I'd like to persue this matter a little further. I've disconnected the coax from the quad lnb and connected the receiver up to a single lnb. No noise.

Are there any proceedures I must follow as regards grounding when installing quad lnb's connecting to multi receivers ?

Is this noise thing an inherent quality with quad lnb's ?

Could it be symptomatic of a duff quad lnb ?

Are there good and bad lnb's? If so can anyone recommend a known quality component?

Signal strength and quality are all good on all 4 receivers by the way.

Assistance would be much appreciated. Thanks and regards. P.S
 

supapete

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O.K, men. Sent off for ground loop isolators abovementioned. Blow me down, they've got rid of the clag ! Thanks again. I've also sent off for a thomson quad lnb for belt and braces as the ghost line is still there but barely moving so I hope it's a matter of a damp/duff lnb or connectors. At least I can leave everything laced up, now.:-worship
 

mhku

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You're probably better off starting a new thread about quad LNBs in the appropriate section.

Good to hear you got the hum sorted (if that's what clag is?). :)
 

supapete

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:)Right, I guessed there'd be an overlap of forums for my post. Thanks everyone for contributuins.:)

What I ommitted to say was that each digibox was connected to the tv scart s via a packard bell easy hdd recorder. 2 into one tv and 1 into another. The fourth is simply used as dab radio in the kitchen. :-doh2

This morning, before I turned into my squirrel mode up and down the cat ladder to change the lnb I thought I'd make sure nothing was affecting the lnb. I unlaced absolutely everything and restored factory presets to everything and plugged the receivers directly into the tv's.......perfect, and no clag either.:eek:

So my ghost scrolling and mains hum has been brought about by something other than the receivers/lnb. Here I go again:-doh2

But thanks again. I'll report back just for interest.

best regards


P.S
 

supapete

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anglesey
This is the epilogue of this thread, now.U-zzz Sorry if it's been a sleeping tablet.

All of the dvd recorders I have attached to each digibox via standard SCART connectors were purchased from a supplier of "guarenteed refurbished returns". Each unit is identical. Someone, however, had earthed the chassis of the power supply of one of the units. I dismantled each one to ensure there were no discrepencies in manufacture and there wasn't.

The remedy, therefore, was obvious.:)

The end.

regards all. P.S
 

mhku

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All of the dvd recorders I have attached to each digibox

Buy a bank of Dreamboxes wiht built-in HDD :D
 
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