Xonar essence ground loop

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Got severe ground loop issues with this card running into my luxman amp. It also causes mains hum through the amp when off. Disconnecting the signal cables stops it as does unplugging the power from the pc. Removing the earth pin on the amp also solves it, but obviously isn't safe.

I've got an old Jensen transformer with octal socket somewhere. Would this be ideal to solve the problem?
 
If that solves the problem, do it.
Amp Ground pin is there just for removing the ground loop problems.

no, the amp ground pin is a path for currents that might otherwise electrocute you to take to ground....

i'm assuming you are talking about your safety ground connection Kei?

tamphist, probably best to get a good idea about exactly what we are dealing with, before making potentially deadly recommendations..... dont you think?
 
We're talking the earth connection in the plug.

The noise problems only started when I added the sound card iirc. (Swapped from a creative x-fi with drive bay) I only have the xonar card and h6 daughter board with my graphics card connected. The only other peripherals are hard drives and a DVD drive.

Using onboard audio or audio out of hdmi on the graphics card are noise free. Using the other pcb slot does not change things.
 
Even with the card out of the motherboard and just plugged into the psu, there is continuity between the signal ground at the phono and the chassis and other objects grounded in the case. The case is fully coated in paint/powder coat which insulates it anyway.
 
Can you connect the audio cable without the ground connect on one end of the cable?
This would eliminate your ground loop and the cable will still be shielded as it will be still connected to ground on one end.

Connecting the two chassis together won't change things as the loop is formed from the two chassis and the signal cable and they are connected just the same through the power plug.

If this ground pin you talk about is built in to the amplifier for this purpose then use it, as what it is doing is just separating the audio ground from the earth ground and the power supply is still connected to the earth ground.

I learned this the hard way on my Mackie 32-8 mixer as there are two ground systems in it.
One that goes to the earth ground for the chassis's and a separate one for the audio signals.

Ground loops are a PIA and just moving around cables and re-situating the power source cables can solve it too.

I had this same issue a while back and redid every thing and now I have no noise with the same machines, same cables and same computers and sound cards.

Make sure that all of the power for the devices are coming from the same source and daisy chained off of the same source and not from a different plug even though it is the same circuit.
The reason is that if the other plug has a longer run of cable it will cause a mismatch of resistance on the line compared to the other units and cause an imbalance and therefore induce a small amount of AC on the ground side.

After I had done this I did not have to lift any of the ground's on any of my equipment and it is now absolutely dead quiet even with every gain and slider turned to its maximum settings (including the amps) and no noise what so ever.
No mods and all I did was re situate the wiring.
I lucked out as sometimes it is not this easy.

Good Luck !!!

jer :)

P.S. My imbalance was so bad that just connecting the two chassis together with a wire resulted in some sparking as I tried to connect a wire from the mixer to the computer and it does not do this now even with a rather long run of audio cable!
FWIW
 
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I'd already tried linking the two chassis together to no avail and they have always run from the same extension chord. (cable lengths are pretty similar too) The ground loop is sufficiently troublesome, that using a coax digital connection to my marantz AV receiver and then using the marantz as a pre-amp doesn't stop it. (switching to optical should stop it) What is peculiar is that there is no mains hum present whilst the pc is on, just a high pitch whine and various buzzes etc in time with various on screen activity. Mains hum only occurs when the pc is switched off, even if the psu switch is off.

Not sure on lifting the signal ground as i use BNC terminated coax to link them. I could make up an adaptor that lifts it.
Rack9_zps89c85b72.jpg
 
Firstly I would draw out a schematic of what is connected and how, it will be easier to pass comment then based on such a diagram.
Then you can trace the current flow, remembering that low frequency signals, may take a different path from the high frequency signals.
What worries me more is that when you mremoved the protective earth connection made things feal furry!!! I would suspect some other problem, that connection should only carru current in a fault situation.
 
I've just tried disconnecting the signal ground and the noise got slightly worse. Also, just to cover all bases, I have also tried enabling/disabling the various options in the bios for noise reduction. (spread spectrum and disabling cool 'n' quiet etc)

Not sure what the VA rating is for the isolation transformer that i have. The pc runs off a 650W psu, what size transformer would i need
 
From what i can find out, the mains isolation transformer that i have (somewhere) is 500VA.

The small octal socket transformer that i have spare is a Gardners AF matching transformer MU7523. (Pri. 75/500Ω Sec. 500Ω) I've attached an image of it.
 

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Depending on what's actually in your PC, that isolation xmfr may still do fine - one likes to stay a factor of 2 away from the power rating. With a fancy graphics card or two, a fast-clocking quadcore and a big monitor, it might break into sweat under heavy load. Do give it a shot when you come across it.

I'm not really sure what the old AF matching transformer would be good for. If I had to guess, I'd say it may have been used to provide line and headphone outputs on a communications receiver way back when.
 
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