Need Help - Computer Audio Noise Problem

[v-four]

Hi all,

I'm new to this site and have come hat in hand to get help with my computer audio problem. My problem is a follows:

 

With the stereo ON and the PC OFF, I get a constant stream of static through the speakers. Once I turn the PC on the static stops.

I have tried two different usb cables and there is no change to what I have described. If I change the input on the stereo and/or the DAC the static remains, the only way I can get the static to stop is, turning ON the PC or the DAC.

 

The problem started since installing the SOTM PCI-e usb card. I have sent the card back to SOTM to get checked and have been told it is working perfectly. Reinstalled it and the problem remains.

 

My current configuration is:

Custom build fanless PC design with power delivered through an APC H15 Power Conditioner:

· Perfect Home Theater FLM-7 chassis

· Gigabyte H97 GA-H97N-WIFI motherboard, Latest Bios version - F8

· i7 4790S CPU

· 16gb ram

· 256gb SSD for the OS

· 1tb SSD for music storage

· 50” plasma TV as the monitor

· Windows 10 Pro

· J River 21

· 160w pico power supply

 

SOTM USB card connected via USB to my Cambridge Audio DacMagic Plus which is connected via unbalanced IC’s to my stereo. The SOTM card also has the rear faceplate power switch in the off position.

The static has to be coming through the signal side of the USB cable, as the power is turned off at the card & the power side of the USB cable is disabled.

 

Any help is greatly appreciated.

 

v-four

[AlainGr]

Hi v-four,

 

It may not be an accurate diagnostic, but have you tried to check if it does the same:

- With the PC unplugged

- With the USB cable unplugged between your PC and Dac Magic

- With the Dac Magic unplugged from the AC while the USB cable is plugged between the PC and DAC

?

 

It does not cure the problem, but it may help identify what is causing this anomaly.

 

Remember that each time you are doing this, turn all your components OFF... I was negligent in the past, looking for a ground loop and I forgot once to "mute" or turn OFF the volume and I almost blew my speakers...

 

Like I say, it may not solve the problem, but at least it may help you identify where it starts...

 

I suggest that for the sake of your investigation, you could unplug all the other components not related to your stereo system (TV + all not directly related to your PC > dac > stereo sytem - even unplugging the interconnects with those (TV + all)...

 

Regards,

[One and a half]

Does the static sound like aliens invading, chatter at varying frequencies, or white noise like FM off station, motor boating, or a steady hum?

 

If there's a TV involved, there's usually the possibility of a cable service connection that adds a ground loop in the system.

 

As AlainGr suggested, unplug with the power off is a good start, and first thing to try is to disconnect the Antenna feed in from a cable service or even the Antenna from the TV. This happened to me, it was the last thing I checked, and then no more noise. Added a filter in and never had a problem since. Try the Jensen transformers, they work very well. Next to try the TV HDMI cable to the PC.

 

What you've got is a complex path where noise is shunted the wrong way and it's audible. If you disconnect the USB cable and the problem goes away, you could break the return path for something different completely.

 

From what I can remember of the PCIe bus is that it's still on even though all the lights are out. When changing RAM, it was advised (to me ) to remove the AC power or the battery from a notebook to do so. The SOTM is most likely off, but the 0V and the shield of the USB cable are still very much part of a return path.

 

Ensure all your gear is plugged into the one APC unit including the wall warts.

 

Be prepared for a long diagnosis and lots of questions.

[AlainGr]

Does the static sound like aliens invading, chatter at varying frequencies, or white noise like FM off station, motor boating, or a steady hum?

 

If there's a TV involved, there's usually the possibility of a cable service connection that adds a ground loop in the system.

 

As AlainGr suggested, unplug with the power off is a good start, and first thing to try is to disconnect the Antenna feed in from a cable service or even the Antenna from the TV. This happened to me, it was the last thing I checked, and then no more noise. Added a filter in and never had a problem since. Try the Jensen transformers, they work very well. Next to try the TV HDMI cable to the PC.

 

What you've got is a complex path where noise is shunted the wrong way and it's audible. If you disconnect the USB cable and the problem goes away, you could break the return path for something different completely.

 

From what I can remember of the PCIe bus is that it's still on even though all the lights are out. When changing RAM, it was advised (to me ) to remove the AC power or the battery from a notebook to do so. The SOTM is most likely off, but the 0V and the shield of the USB cable are still very much part of a return path.

 

Ensure all your gear is plugged into the one APC unit including the wall warts.

 

Be prepared for a long diagnosis and lots of questions.

 

 

+1

[AudioDoctor]

Ensure all your gear is plugged into the one APC unit including the wall warts.

 

+1 to this. IMO having a common ground is essential to stereos.

[v-four]

Thanks AlainGr and One and a half for the info, I tried the following:

PC unplugged and stereo on = problem remains

With the PC off, USB cable unplgged, and stereo on= problem resolved

With the PC off & plugged in, DAC magic off & plugged in, and stereo on = problem resolved

 

With the Dacmagic off the problem is gone, so it is the interaction between the SOTM card & the dac that is causing the issue. When using a Toslink connection between the PC & dac there is no problem but the sound is better when using the SOTM card.

The PC & Dac are both plugged into the APC H15. I do have a filter on the main shaw cable line coming to the router.

OK now what does all this mean??

This the first SOTM has heard of a problem like this.

[AlainGr]

I am reluctant to suggest this, but I had a ground loop a few years ago and the only way I was able to circumvent the situation was to add a cheater plug like this one to lift the earth for a component. This is not recommended, since in the event that a short circuit happen in the said component, there is a danger of electrocution (or fire). In my case, after many hours of trying different approaches, that was the only solution that I could come with. This model can work in Canada (the NEMA type)... This image is an example of a 3 prong type turned into a 2 prong (lifting the earth) for a component.

 

In my case it was the power amp that had its earth lifted. As you can see, this one comes with a little ring, where one can decide to "ground" it again, by attaching the screw that holds the plastic plaque (wall plaque) to the metal casing.

 

[One and a half]

What does the DACMagic power supply look like...3 prongs or two?

 

See on the back of the DacMagicPlus the Ground lift switch? Switch to off and report.