From the information I have found, a ground loop is basically two possible paths back to the ground with varied resistance.

Let me explain what I have figured out about my system.

First path of ground from laptop:
Laptop -> 3-prong AC ground (Surge Protected)

Second path (This is the complicated part):
Laptop -> Stereo audio connection (Red and White) -> Receiver -> 25 ft. HDMI -> Projector -> 3-prong AC ground (Different outlet on same circuit, I believe)(Different Surge Protector)

I am 99% sure that the second path of ground is correct and obviously, this is the one I wish to remove or somehow get rid of the hum coming from the Receiver.

Right now there is no possible way to get the laptop or projector onto another circuit, unless I used a big extension cable to reach another circuit. Of course, this would not be practical for long term use.

Note: The only to components within my home theater that have a ground are my laptop and projector.

Any suggestions or solutions (preferably free) would be great! Thank you in advance.

If anyone needs more information I will be happy to offer it.

Laptops are often not grounded, they 'float'. The 3 prong power supply converts AC to DC, then the DC output is just + and - without a ground lug.

Grounding is typically used as a protective feature against shock hazard in AC supplies and in many laptop power supplies only works on the AC side. It is often there to reduce high frequency noise coming from the power supply oscillator by grounding the metal shielding, and at times a ferrite core maybe at the DC output plug to help quell that interference too that propagate to the DC side.

You could try this, but generally data lines, like Ethernet and modem, also float and are connected to ground by MOV or avalanche diodes that work only in overvoltage conditions.

http://digital.ni.com/public.nsf/allkb/3C6360322410D7A786256E1D0070C375

Laptops are often not grounded, they 'float'. The 3 prong power supply converts AC to DC, then the DC output is just + and - without a ground lug.

Grounding is typically used as a protective feature against shock hazard in AC supplies and in many laptop power supplies only works on the AC side. It is often there to reduce high frequency noise coming from the power supply oscillator by grounding the metal shielding, and at times a ferrite core maybe at the DC output plug to help quell that interference too that propagate to the DC side.

You could try this, but generally data lines, like Ethernet and modem, also float and are connected to ground by MOV or avalanche diodes that work only in overvoltage conditions.

http://digital.ni.com/public.nsf/allkb/3C6360322410D7A786256E1D0070C375

Sorta true, but often these supplies (as well as the data lines) still have capacitors to ground... discovered that the hard way a few weeks ago when I blew up a laptop here in the lab at work...
These capacitors are specifically designed to pass HF noise, so the potential for the loop is there...

So, does the hum go away when you unplug the laptop's power supply and run off battery?

[QUOTE=Smallfry7;15835387]From the information I have found, a ground loop is basically two possible paths back to the ground with varied resistance.
[QUOTE]

Let's cut to the chase. The following device will proably give you considerable relief, and not hurt sound quality:

http://www.radioshack.com/product/index.jsp?productId=2062214

[quote=Smallfry7;15835387]From the information I have found, a ground loop is basically two possible paths back to the ground with varied resistance.
[quote]

Let's cut to the chase. The following device will proably give you considerable relief, and not hurt sound quality:

http://www.radioshack.com/product/index.jsp?productId=2062214

Thanks! I didn't know they made an isolation device and called it simply for what is should do.

Laptops are often not grounded, they 'float'. The 3 prong power supply converts AC to DC, then the DC output is just + and - without a ground lug.

Grounding is typically used as a protective feature against shock hazard in AC supplies and in many laptop power supplies only works on the AC side. It is often there to reduce high frequency noise coming from the power supply oscillator by grounding the metal shielding, and at times a ferrite core maybe at the DC output plug to help quell that interference too that propagate to the DC side.

You could try this, but generally data lines, like Ethernet and modem, also float and are connected to ground by MOV or avalanche diodes that work only in overvoltage conditions.

Thank you for all the replies. First, I cannot figure out what 'float' means, unless it means "not grounded." I couldn't find a ferrite core lying around. I know I have one somewhere.;)

Second, the noise changed from a hum to a popping noise. Don't ask me why, but I think it started when I unplugged a surge protector from upstairs (which had nothing to do with my home theater.)

Third, I plugged in an analog VGA cable to my projector from my laptop and the noise disappeared. :eek:
EDIT::: THE NOISE IS NOT REMOVED, just significantly reduced.

Sorta true, but often these supplies (as well as the data lines) still have capacitors to ground... discovered that the hard way a few weeks ago when I blew up a laptop here in the lab at work...
These capacitors are specifically designed to pass HF noise, so the potential for the loop is there...

So, does the hum go away when you unplug the laptop's power supply and run off battery?

Yes, the hum is completely gone when on battery and the hum goes away also when I sever any part of the connection on the second 'accidental' ground.

Another thing I notice is that the speakers will pick up CPU usage (when the laptop is either plugged in /or not) and play it back as sound. This also happens when I move the mouse.

Hopefully I can find the reason for all this noise. :rolleyes:

http://upload.wikimedia.org/wikipedia/commons/archive/1/12/20050803190506%21Ferrite_core.jpg

Sorry SF, on the pic above the cylindrical shaped thing just before the jack is a ferrite core. Float yes, means not grounded.

http://zone.ni.com/devzone/cda/tut/p/id/3394





Thank you for all the replies. First, I cannot figure out what 'float' means, unless it means "not grounded." I couldn't find a ferrite core lying around. I know I have one somewhere.;)

Second, the noise changed from a hum to a popping noise. Don't ask me why, but I think it started when I unplugged a surge protector from upstairs (which had nothing to do with my home theater.)

Third, I plugged in an analog VGA cable to my projector from my laptop and the noise disappeared. :eek:
EDIT::: THE NOISE IS NOT REMOVED, just significantly reduced.



Yes, the hum is completely gone when on battery and the hum goes away also when I sever any part of the connection on the second 'accidental' ground.

Another thing I notice is that the speakers will pick up CPU usage (when the laptop is either plugged in /or not) and play it back as sound. This also happens when I move the mouse.

Hopefully I can find the reason for all this noise. :rolleyes:

Does anyone know why the analog VGA connection to projector would semi-stabilize ground (Or what ever the problem is)? And on that note, is this even a ground loop problem?:confused: Or is my electricity polluted somehow and I need one of those Monster Power Filtering things?

Does anyone know why the analog VGA connection to projector would semi-stabilize ground (Or what ever the problem is)? And on that note, is this even a ground loop problem?:confused: Or is my electricity polluted somehow and I need one of those Monster Power Filtering things?


Was it the VGA instead of the digital, or along with?

Does anyone know why the analog VGA connection to projector would semi-stabilize ground (Or what ever the problem is)? And on that note, is this even a ground loop problem?:confused: Or is my electricity polluted somehow and I need one of those Monster Power Filtering things?

Your AC is not polluted. Do not fall for that crap. Laptops into sound systems have issues. That is why in the Pro world we use a Direct Box to hook them up. Whirlwind makes a box called the PCDI. This is all simple its not voodoo.