[SOLVED] Ground loop between grounded Hypex NC400 DIY amp and ungrounded Denon 3700X

[anphex]

Hi guys!
(@mods please move this thread of seciton is wrong).
When running my new Denon AVR 3700X with my Hypex NC400 DIY amps I have to use an RCA-XLR cable, this one to be specific: https://www.cordial-cables.com/de/produkte/cfu-mc

Now I have some ground hiss the whole time in all speakers, even in the surround speakers that are plugged into the internal amps of the Denon X3700. It gets really bad when I run a game that hits 120 fps. Not only does the hiss become some real audible full spectrum noise, it becomes so loud it's audible besides the game sound.

The Denon gets its video and audio signal via a 2.1 HDMI fiber cable, so we probably can cross it out as culprit since there shouldn't be any metal contact.
When I unplug the NC400 from the RCA pre outs of the Denon and use its internal amps instead for all speakers everything is absolutely fine. No noise whatsover.
Now of course I want to use my NC400 amps and enable the internal amps of the Denon only when I need surround sound.

Can you recommend me a good cable for this purpose that eliminates this ground issue? Or is there some other way?

 

[DonH56]

It will probably take more than a cable. You could try isolating the (-) XLR input with a resistor, but instead I would look at a ground isolation device. There are line-level devices (transformers) you plug between the Denon and XLR cables, and power (wall) devices. The only experiences I have with power-line isolation are a somewhat pricey but effective Hum-X adaptor, and much more expensive commercial units. And I do not know what sort of wall power you have (where are you located? Guessing not U.S.A.)

There are many solutions for line-level isolation so I suggest you try them first. Here are a bunch from Amazon: https://smile.amazon.com/s?k=rca+ground+loop+isolator&crid=3LL9XQUGROHCE&sprefix=rca+groun,aps,203&ref=nb_sb_ss_ts-doa-p_1_9 There are also more expensive solutions ranging from Jensen transformers to active (DI) boxes.

HTH - Don

 

[beren777]

• The HDMI "fiber" cable is converting from light to electrical before passing off to the AVR, so it's getting power somewhere. And where there is power there is the potential for a loop. What is the make and model of the cable? Some use external power adapters and some use HDMI Cable Power. (I see some models that can run off the existing 5V from an HDMI port, too.)
• What is your game source? A PC or console? I had a very bad problem with game noise (Nvidia 3080 -> Denon 3700H) that would vary by GPU load. To my shock and surprise, running DDU and then an offline reinstall of the drivers cleaned it up significantly.
• Do you still hear the noise if you connect the game source to the AVR via a passive HDMI 2.1 cable that is 6ft or less in length?

 

[pma]

If the RCA==>XLR cable is to be effective, it needs insertion of a resistor into -IN wire with value same as is output impedance of the sound source.

 

[audio2design]

I have noted some HDMI fiber cables are not exclusively fiber and have additional copper conductors.

 

[anphex]

• The HDMI "fiber" cable is converting from light to electrical before passing off to the AVR, so it's getting power somewhere. And where there is power there is the potential for a loop. What is the make and model of the cable? Some use external power adapters and some use HDMI Cable Power. (I see some models that can run off the existing 5V from an HDMI port, too.)
• What is your game source? A PC or console? I had a very bad problem with game noise (Nvidia 3080 -> Denon 3700H) that would vary by GPU load. To my shock and surprise, running DDU and then an offline reinstall of the drivers cleaned it up significantly.
• Do you still hear the noise if you connect the game source to the AVR via a passive HDMI 2.1 cable that is 6ft or less in length?

1. This one: https://www.amazon.de/HDMI-Glasfaser-Kabel-unterstützt-4K60/dp/B08LYQN5YX/ref=sr_1_21?keywords=glasfaser+hdmi&qid=1637567301&sr=8-21&th=1 . Note that I didn't have any problems on any device. I am using this cable on my bed room tv too to connect it to my computer. I never had any issues until I started using the Denon + Hypex.
Edit. Now after reading the description again this is a hybrid cable with copper and fiber.
2. An EVGA 3090, and as you already confirmed it varies with load/framerate. I will try a driver reinstall later!
3. I can't try this since my PC and AVR are about 10 meters apart. That's why I needed the fiber cable in the first place (or I could have bought a very expensive cable instead).

 

[beren777]

1. This one: https://www.amazon.de/HDMI-Glasfaser-Kabel-unterstützt-4K60/dp/B08LYQN5YX/ref=sr_1_21?keywords=glasfaser+hdmi&qid=1637567301&sr=8-21&th=1 . Note that I didn't have any problems on any device. I am using this cable on my bed room tv too to connect it to my computer. I never had any issues until I started using the Denon + Hypex.
Edit. Now after reading the description again this is a hybrid cable with copper and fiber.
2. An EVGA 3090, and as you already confirmed it varies with load/framerate. I will try a driver reinstall later!
3. I can't try this since my PC and AVR are about 10 meters apart. That's why I needed the fiber cable in the first place (or I could have bought a very expensive cable instead).

Thanks for the reply. I had a similar issue with a Zotac 3080. Key point is to run DDU and then the driver reinstall offline. Disconnect your network before you start. Run DDU. Reboot. Install Nvidia drivers (latest version). Reboot. Connect network.

If you can temporarily move the PC for testing purposes, it would be informative to know if the issue persists using a 6ft passive HDMI 2.1 cable.

Do you have a voltmeter you can use to test to see if the cable has electrical continuity from end to end? Some of these "optical" cables may grab power from one end or the other, and then have a copper interconnect to pass power to the remote end. It's also possible the noise is being picked up and encoded by the source end along with the signal.

Please also test with ONLY the core items connected: PC, remote TV, hypex amp. Nothing else should be connected to the PC except video to remote TV, power cable, keyboard/mouse. Nothing else but the PC HDMI input and Hypex amp should be connected to the AVR. Nothing else connected to the remote TV except HDMI from the AVR.

I think EMI is being generated by either the graphics card or PC power supply. For me, it happened even if I went into the graphic card settings and disabled the audio output.

 

[anphex]

Thanks for the reply. I had a similar issue with a Zotac 3080. Key point is to run DDU and then the driver reinstall offline. Disconnect your network before you start. Run DDU. Reboot. Install Nvidia drivers (latest version). Reboot. Connect network.

If you can temporarily move the PC for testing purposes, it would be informative to know if the issue persists using a 6ft passive HDMI 2.1 cable.

Do you have a voltmeter you can use to test to see if the cable has electrical continuity from end to end? Some of these "optical" cables may grab power from one end or the other, and then have a copper interconnect to pass power to the remote end. It's also possible the noise is being picked up and encoded by the source end along with the signal.

Please also test with ONLY the core items connected: PC, remote TV, hypex amp. Nothing else should be connected to the PC except video to remote TV, power cable, keyboard/mouse. Nothing else but the PC HDMI input and Hypex amp should be connected to the AVR. Nothing else connected to the remote TV except HDMI from the AVR.

I think EMI is being generated by either the graphics card or PC power supply. For me, it happened even if I went into the graphic card settings and disabled the audio output.

I narrowed it down to the GPU. I did a full DDU and clean reinstall but no improvement. Instead I noticed that when I am close to my computer I can hear almost the same sound coming from the GPU(?) that's coming from my speakers, kind of like a coil whine. When I unplug the culprit HDMI cable the noise also vanishes from the GPU! My guess or rather hope is that I just have a weird contact between motherboard or PC case. Luckily I am going to upgrade to Z690 and 12700KF tomorrow and I will check everything for clean connections. If it doesn't improve it seems that the cable or finally the GPU itself is the problem. .... Then again it's weird that the problem only apprears when connecting the Hypex Amps. Should't the Denon amps have the same issue? Or doesn't the Denon just care because it has an ungrounded topology and only by connecting the Hypex amps it "passes" the bad current to the whole system?

 

[Lambda]

GPUs pull hundreds of amps internally.
Are you sure your GPU is properly Grounded to the case with low impedance?
is the metal part connected to the case or is the case some how non conductive or painted?

This discussion here is relevant for your problem:

Ferrite bead

Hi everyone, Got these cables as a gift. They come with ferrite bead. What's its use? Does it improve quality of sound? Is it there to only lower the electronic noise? Can anyone explain? Thanks

www.audiosciencereview.com

RCA cable Magnetic interference measurement and comparison

Cables are cables and there is no difference?! I designed a test to see if they perform significantly different in therms of "magnetic shielding" or Leakage inductance. This test dose not test for ground loop currents but interference from close by magnetic in homogeneous magnetic files. The...

www.audiosciencereview.com

Also used this kind of cable

 

[anphex]

GPUs pull hundreds of amps internally.
Are you sure your GPU is properly Grounded to the case with low impedance?
is the metal part connected to the case or is the case some how non conductive or painted?

This discussion here is relevant for your problem:

Ferrite bead

Hi everyone, Got these cables as a gift. They come with ferrite bead. What's its use? Does it improve quality of sound? Is it there to only lower the electronic noise? Can anyone explain? Thanks

www.audiosciencereview.com

RCA cable Magnetic interference measurement and comparison

Cables are cables and there is no difference?! I designed a test to see if they perform significantly different in therms of "magnetic shielding" or Leakage inductance. This test dose not test for ground loop currents but interference from close by magnetic in homogeneous magnetic files. The...

www.audiosciencereview.com

Also used this kind of cable

The GPU is firmly mounted in the PCIe socket and screwed to the output slots and also fixed with a metal GPU holder. Thank you for sharing those links. I will check those tomorrow and get to the bottom of it. Right now I just remembered that my previous amp had a ground lift switch that eliminated all noise issues. The first thought would be just removing the grounding cable but from all the warnings I've read this seems to be a very bad idea.

 

[Lambda]

The back plate is painted black on this GPU? you sure it makes good electrical contact to case as well as to the HDMI connector?
Dose your cable have this?

Ferrite bead - Wikipedia

en.wikipedia.org

 

[anphex]

The back plate is painted black on this GPU? you sure it makes good electrical contact to case as well as to the HDMI connector?
Dose your cable have this?

Ferrite bead - Wikipedia

en.wikipedia.org

No, it doesn't have this. It's a unusual cable to begin with (fiber-metal-hybrid). I will check tomorrow when I will reassemble my PC anyway!

 

[beren777]

I narrowed it down to the GPU. I did a full DDU and clean reinstall but no improvement. Instead I noticed that when I am close to my computer I can hear almost the same sound coming from the GPU(?) that's coming from my speakers, kind of like a coil whine. When I unplug the culprit HDMI cable the noise also vanishes from the GPU! My guess or rather hope is that I just have a weird contact between motherboard or PC case. Luckily I am going to upgrade to Z690 and 12700KF tomorrow and I will check everything for clean connections. If it doesn't improve it seems that the cable or finally the GPU itself is the problem. .... Then again it's weird that the problem only apprears when connecting the Hypex Amps. Should't the Denon amps have the same issue? Or doesn't the Denon just care because it has an ungrounded topology and only by connecting the Hypex amps it "passes" the bad current to the whole system?

Sorry that didn't work for you. I don't game often on the TV right now so it's possible I just got lucky that day.

 

[AnalogSteph]

No, it doesn't have this. It's a unusual cable to begin with (fiber-metal-hybrid). I will check tomorrow when I will reassemble my PC anyway!

I hope you have a moldymeter, which would make it easy enough to check for continuity between the shields at both ends.

 

[anphex]

Small feedback. After rebuilding my PC and looking for potential issues, sadly I didn't find anything. The issue is about the same.
I now ordered a passive gadget for galvanic separation that arrives tomorrow. I'll see if it improves anything.

 

[Lambda]

Hm, i thought you have identified the noise source to be your graphics card and the noises comes over the HDMI cable?

 

[anphex]

Oh no. The noise starts as soon as I just even connect the RCA-XLR cable between the Denon and the Hypex amps. The Hypex don't even need to be turned on. I tried several cables and adapters with the same result.

 

[Lambda]

how is the Hypex Wired?

https://www.boomaudio.de/media/pdf/f5/26/90/NC400_04xx59gpdrooxikWq.pdf

So without the PC connected you have nois from the AVR as son as the AVR is connected to the Hypex amp?

 

[anphex]

I never said the Hypex are weird. My guess is just that the grounded Hypex und the ungrounded Denon don't go well together based off my observations.

Even if I run all my speakers on the internal Denon amps once I connect just the RCA pre outs Front L and R to the Hypex amps I get a ground buzz/hiss on all speakers. The issue basically only appears when there is a wire between Denon and one of the two Hypex amps.

 

[Lambda]

I never said the Hypex are weird. My guess is just that the grounded Hypex

sorry "Wired"
So how is the RCA in the Hypex connected? is it connected to ground?

Even if I run all my speakers on the internal Denon amps once I connect just the RCA pre outs Front L and R to the Hypex amps I get a ground buzz/hiss on all speakers. The issue basically only appears when there is a wire between Denon and one of the two Hypex amps.

So Denon only connected to speakers (and not to the PC) but as soon as it gets connected to the Hypex there is hum?