# Phillips LCD HD, HTS 5.1, Sky HD Box and Xbox360 digital sound problem



## nacho66 (Jul 14, 2010)

Hi guys

I bought Phillips 42pfl(xxxx) hd tv and 5.1 hts cinema system over a year ago. Few months ago I got Sky HD box. To connect 5.1 to Sky I got coaxial cable and connected Sky box digital output with hts digital input. Generally it worked fine, however sometimes I could hear sound is slightly delayed to picture (I could fix that by switching channels or pausing-playing a movie). 

Few days ago I got XBOX and only when connecting it to TV with HDMI I realized, that TV has it's own digital output too. So I removed coaxial cable from Sky box and connected it to TV. So now the set up is:

XBOX -> TV HDMI
SKY -> TV HDMI
TV DIGITAL OUTPUT -> HTS DIGITAL INPUT

I now get a problem with the sound. When watching Sky I can hear a slight hum in the background and the whole thing produces a loud bang-crack-snap sound every few minutes.
It's even worse when I switch to XBOX... The sounds becomes discontinous and it simply breaks

I don't know what's going on. All HDMI cables are fine as the image is good and the sound coming from TV is ok too. The sound was also good when it went from Sky Box to HTS directly, via coaxial lead. But from some reason it's causing all sort of trouble when transferred via TV's digital output

Does anyone have experience with similar problem? Any suggestions what's going on and how to fix this?


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## Done_Fishin (Oct 10, 2006)

I suspect that you may have a/some earth loop(s) within your cabling .. you only need to supply an earth link at the common end of the cabling .. if you have more than one then you "might" get that hum and other weird effects


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## ebackhus (Apr 21, 2005)

Agreed. While there is some delay in signal processing at times it may just be better to route through the HTS instead.


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## nacho66 (Jul 14, 2010)

Thanks guys for the answers but I have only limited knowledge on what you're saying. I understand the idea of earth loop but what exactly should I check if it comes to cabling? I'll sketch you a quick map of all the connections - there aren't to many of them actually

All equipment is connected to two four sockets power boards. Apart from TV, SkyBox, Xbox and HTS there's also my ntl modem and a router connected to that board

All connections
SkyBox HDMI -> TV
XBOX HDMI -> TV
HTS HDMI -> TV

TV DIGITAL AUDIO OUTPUT (coaxial) -> HTS DIGITAL AUDIO INPUT

router <-> XBOX ethernet socket

That's all cabling in the set up. Of course there are also cables connecting hts base with all 5 speakers, but that should hardly have anything in common 

The only loop of any kind I see here is sending sound from HTS to TV via HDMI and then sending it back from TV to HTS via coaxial. However, I tried disconnecting that HDMI cable from hts, and it wouldn't make sound any better.
At the moment I have no idea what should I look after. Can you help further with this?

Note that HTS has only one HDMI output and no HDMI inputs so I cannot route all HD signals through it


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## Done_Fishin (Oct 10, 2006)

Earth looping is caused when units are individually earthed and then another cable introduces a new earth connection which "bridges" two or more existing earth connections. This results in a possible loop condition that sets the hum "singing"/

ways of removing these loops are to ensure that the earth is continued in a star fashion ie all units are earthed at a central point and any earth in audio cables is connected only at one end. There are many ways of doing this and fault finding is particularly annoying. Start with a simple system, add your cabling and extra units slowly, wherever your earth loop is being introduced will show as you "test the system" as you expand.


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## nacho66 (Jul 14, 2010)

I have still problems understanding the whole thing. I could never really catch anything in electricity subject. 
If each cable has it's own earthing and I'm using only sockets that factory produced, how can one create an earth-loop. It's just a set of connections - socket - cable - socket

Nevertheless, I tried to strip all connections down and built it from scratch. Tho I didn't have really much options to do it. The only way to determine if it's working on not is to:
- connect XBOX to TV via HDMI
- connect TV to HTS via coaxial

So it's minimum of two connections that I have to start with. And with those two connections the sound is already broken

What should be my next step? Keep in mind that 'hum' sound was only appearing when watching SkyHD signal (coming via coaxial from TV). For XBOX sound, there's no 'hum' - the sound is discontinuous and breaks every fraction of a second


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## Done_Fishin (Oct 10, 2006)

the problem comes when a cable is earthed at both ends.

the cable extends the earth wire from a source through to another unit. 

that unit may already be getting an earth via it's own power socket or another cable that is also earthed at both ends.

it is a bit mind boggling trying to understand at first 

here is an article with some examples of how it might happen. There are of course infinite variations of the same theme and it may only be on cable that is causing you problems. It's just wise to start with as few connections as possible then proceed to add more. Your problem appeared to start with the latest changes in system wiring you made. Start there.

http://www.jaycar.com.au/images_uploaded/humloop.pdf

I'll be back later to discuss the full content of your post.


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## Done_Fishin (Oct 10, 2006)

I would suggest treating these two problems as two problems 

try tackling each type of problem individually.

first the aerial problem .. can you NOT go via HDMI and get good sound ?

if yes then we need to find a way to connect the HDMI in such a way that we connect up slowly, lead by lead, possibly with some sort of adapter


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