Earth loop with TV and car Stereo

[WotEver]

... I think there might be some interesting earth paths going on

Not with the TV...

 

Tony

[Tony Ross]

Hi All,

 

Thanks for the replies. Certainly provided a good debate! I'll start by making up a cable 3.5mm to 3.5mm and remove the earth shield from one end and then go from there. The existing cable was not a cheap one but as the jack plugs are sealed, I can't get into them to detatch the screen.

 

I'll keep you posted with progress,

 

Many thanks,

 

Tony

[WotEver]

I'll start by making up a cable 3.5mm to 3.5mm and remove the earth shield from one end and then go from there.

Let us know how you get on

 

Tony

[DHutch]

Cant really any anything, other than the fact i get exactly the same when i use my MP3 player with a pair of mains powered while its on charge. Thats of the same outlet of a 300w MSW inverter.

 

Sadly the MP3 player charger is earthed (just looked) but while I dont have the speakers to hand with me (AntecLansing 2100's) im 98% certain they use a two pin european plug with a wrap around adapter plug. Which if the case, would rule out an earth loop, which would fit with the fact that to me it doesnt sound like one either.

 

We also get a simular noise on the car radio (12vdc run of a 24->12 converter) when the batteries are on charge.

 

Daniel

[WotEver]

The smoothing in the PSU of an average run-of-the-mill TV or radio (or PC for that matter) won't have been designed to remove all the nasty harmonics from a MSW inverter.

 

I'm 100% convinced it's not an earth loop.

 

Tony

[dmr]

I have spent quite some time with similar issues and despite my degree in electronics and many years working with audio electronics I still don't fully understand it.

Its most likely not the inverter thats to blame but all the switching that goes on within the mains power supply "brick". This is why its better on battery power

I often see similar issues when working with "real" mains electricity.

Its not a "classic" hum loop but is probably related and depends on a sort of capacitive rather than direct coupling.

Removing the earth from the connecting lead might work, or it might make things worse, or it might take all the low frequencies away.

The answer is the isolation transformer as many posts have suggested, but don't pay £38, have a look on eBay.

The HiFi purists don't like them but for a car radio on a boat it should be fine. My own measurements have not found the loss of low frequency that is often mentioned.

A 12v boat electric system can produce significant volt drops (or rises?) on the negative wire so an isolation transformer is also a good safety measure. I run my PC from a little car adaptor (12v to 19v) and managed to damage the radio due to the non isolated grounds when I connected the computer sound to the radio!!

[Tony Ross]

I have spent quite some time with similar issues and despite my degree in electronics and many years working with audio electronics I still don't fully understand it.

Its most likely not the inverter thats to blame but all the switching that goes on within the mains power supply "brick". This is why its better on battery power

I often see similar issues when working with "real" mains electricity.

Its not a "classic" hum loop but is probably related and depends on a sort of capacitive rather than direct coupling.

Removing the earth from the connecting lead might work, or it might make things worse, or it might take all the low frequencies away.

The answer is the isolation transformer as many posts have suggested, but don't pay £38, have a look on eBay.

The HiFi purists don't like them but for a car radio on a boat it should be fine. My own measurements have not found the loss of low frequency that is often mentioned.

A 12v boat electric system can produce significant volt drops (or rises?) on the negative wire so an isolation transformer is also a good safety measure. I run my PC from a little car adaptor (12v to 19v) and managed to damage the radio due to the non isolated grounds when I connected the computer sound to the radio!!

 

Will be interested to see what happens with the low frequencies as the main reason that I route the audio to the Car Stereo is because that uses a pair of domestic hi-fi (Gale) mini monitors and has an active sub which takes every thing below 125hz! The sound is great when watching movies from a battery powered source but frustratingly buzzy using "The mains".

If there is a significant roll off, it somewhat defeats my original objective.

 

Tony

[WotEver]

The most bizarre case that I can recall was in a major London based recording studio which had just taken delivery of a hugely expensive fully automated AMS Neve sound desk. With all the channels open it made a great radio receiver, picking up Radio 4 perfectly. After MUCH faffing around, experimenting with tin foil shields, flying earth wires and the such it was eventually cured by cutting a metre off the mains lead.

 

Tony

[Tony Ross]

Will be interested to see what happens with the low frequencies as the main reason that I route the audio to the Car Stereo is because that uses a pair of domestic hi-fi (Gale) mini monitors and has an active sub which takes every thing below 125hz! The sound is great when watching movies from a battery powered source but frustratingly buzzy using "The mains".

If there is a significant roll off, it somewhat defeats my original objective.

 

Tony

 

Is this the type of isolation transformer to consider? I'm always suspicious if something appears too cheap.

 

Tony

 

My link

[WotEver]

Is this the type of isolation transformer to consider? I'm always suspicious if something appears too cheap.

 

Tony

 

My link

I have absolutely no idea what that is. Perhaps someone else will know.

 

Tony

 

These are what I used to use.

 

Tony

 

Here's one from Farnell.

[Pretty Funked Up]

Will be interested to see what happens with the low frequencies as the main reason that I route the audio to the Car Stereo is because that uses a pair of domestic hi-fi (Gale) mini monitors and has an active sub which takes every thing below 125hz! The sound is great when watching movies from a battery powered source but frustratingly buzzy using "The mains".

If there is a significant roll off, it somewhat defeats my original objective.

 

Tony

 

125Hz is barely bass - more like mid/bass.

In my world below 50-60Hz is where the bass is.

 

Most people would be happy or simply not notice the loss in bass frequecies with an isolator.

Rather than call it an earth loop call it a ground loop.

It occurs whenever the source and the amp are connected to the same power source (and each other).

GL

Edited September 23, 2011 by Pretty Funked Up

[Tony Ross]

125Hz is barely bass - more like mid/bass.

In my world below 50-60Hz is where the bass is.

 

Most people would be happy or simply not notice the loss in bass frequecies with an isolator.

Rather than call it an earth loop call it a ground loop.

It occurs whenever the source and the amp are connected to the same power source (and each other).

GL

 

No disagreement about 125hz being "barely bass". The mini monitors roll off significantly below about 100hz and therefore the cut off options on the car stereo being 125hz and 70hz, 125hz was the better one to go with without causing a hole. Fortunately, being on the confines of a boat the lower frequencies aren't obviously directional and as such that figure works well.

 

If an isolator proves to be an option, at what level should I expect so see the bass roll off at?

 

Tony

[Tony Ross]

I have absolutely no idea what that is. Perhaps someone else will know.

 

Tony

 

These are what I used to use.

 

Tony

 

Here's one from Farnell.

 

Hi Tony,

 

Thanks for the links. The farnell one looks like it could be mounted in a box without having to put a pcb together. What would the circuit diagram look like as this would presumably need to go on the stereo "audio in" line between the source and the car stereo aux in? I've looked on their tech specs but that didn't seem to help.

 

Tony

[Pretty Funked Up]

If an isolator proves to be an option, at what level should I expect so see the bass roll off at?

 

Tony

 

Oooo tricky one, can only guess at that. The maplins one i used to use prolly put out nothing lower than about 45Hz but where it starts the roll off i dont know, 80-90hz

completely guessing!!

 

try a tune with it in and repeat the tune with it out

[WotEver]

What would the circuit diagram look like...

Hiya,

 

For a simple unbalanced connection:

From the TV, connect screen to black, signal to red, put insulation tape over blue. To the amp, connect screen to yellow, and signal to white.

 

To make a balanced connection you'd need two transformers:

From the TV, connect screen to yellow, and signal to white. To the amp, using balanced cable (twisted pair signal and screen)connect screen to blue, red to red, and black to black. At the other end, connect your balanced cable to the other transformer the same way (screen to blue, red to red, and black to black) and your unbalanced 3.5mm jack to the amp as screen to yellow, and signal to white.

 

Tony

[Tony Ross]

Hi All,

 

At last got back to the boat last weekend to look at this issue again.

 

I think I can safely say it is the inverter and not an earth loop as I originally suspected as the buzzing is not present when connected to the 240v shorepower. Thanks for all of the suggestions but I now need to come up with a cunning plan. Am thinking of one of the Sterling 400w pure sinewave low noise inverters just to provide for the TV/Audio as this should hopefully be buzz free.

 

regards,

 

Tony

[Pretty Funked Up]

I would ask around to borrow an inverter to test. Earth loop is a problem when your using the same power source, being on shore power would break the loop and kill the hummmmmm.

 

Just to be sure before spending money, i ask around and borrow to test.

 

Another way to test it would be to use a totally seperate battery to run your inverter off for a test. If the hum stays then its not an earth loop.

Edited November 1, 2011 by Pretty Funked Up

[WotEver]

Like I said several weeks ago...

I'm 100% convinced it's not an earth loop.

 

Tony

[Tony Ross]

Like I said several weeks ago...

 

 

Tony

 

And quite right you were too.

 

Many thanks,

 

Tony