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

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anphex

anphex

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The Hypex only have XLR input and I am using a regular consumer adapter or a cable with direct RCA-XLR soldered plugs. Both have the same result. I am not savyy enough in electronic engineering for figuring this out with resistors, bridging, floating without the worry of frying myself or my house.

I ordered this thing and I hope it will do some magic and fix this problem:

Edit: Regarding the PC connection: the hum gets severly worse when running games at 120fps that cause a high GPU load. So yes, the GPU is also involved but I can't fix anything there.
 
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anphex

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Yes, both monoblocks have the grounding cable connected to the case. The were both build exactly by following the DIY manual.

Okay, new input: I checked the cables I used and found this wiring:

1638276797259.png



In another thread regarding the same wiring issue I found the recommendation for monoprice cables that have this wiring:
1638276834687.png


Would that solve my issue?
 
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Lambda

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I had different association or definition with "DIY"

The were both build exactly by following the DIY manual.
Is there A "the manual" if i search for DIY Hypex NC400 i find lots of different looking and differently build versions.
So you assembled this?
https://www.diyclassd.com/product/nc400-mono-kit/24
in the video They solder the XLR plug but in the PDF it shows a plug...
but ok this narrowed it down.

look what kind of cable they uses in the manual:
1638277191452.png

not the same as the cabel you uses:
1638277239719.png


by connecting this adapter
you basically build this
1638277358928.png

See how connecting bin 3 and 1 makes you end up with this configuration?

Now the manual says this Only ok if "Use class II construction and use a 2-prong mains inlet"

 
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anphex

anphex

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First of all thank you for trying to help me out, I really really appreciate it.
The Hypex were built with the latest "plug only no soldering" kit. I'll check if I can find the manual later but there wasn't anything about the wiring because it was all plugs with a fixed configuration, namely XLR balanced.

Your point made me see how my setup is wrong, nice! I want to keep the XLR though since everything else would be tinkering by an amateur (me) and I don't want to break things or degrade the performance of the Hypex any further than neccesary. Also it may be that I will be using XLR pretty soon again.

What do you say about the monoprice cable? It looks like the grounding issue connecting grounded and ungrounded devices was adressed. Would they work?
 

Lambda

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What do you say about the monoprice cable? It looks like the grounding issue connecting grounded and ungrounded devices was adressed. Would they work?
According to the manual is is not recommend to connect ground to signal - if you have a Cassy that is connected to earth.
But for safety and probably leagal reasons it is.
I would not recommend to change this!

but to uses the workaround shown in the Manual on site 19:
https://www.boomaudio.de/media/pdf/f5/26/90/NC400_04xx59gpdrooxikWq.pdf

1638278682321.png


You do not have to do this Inside the amplifier!
You can build the equivalent circuit outside the amp in the cable.

What they showing in this schematic is Signal- shall only be connected to Ground over 100ohm and 100nF
Signal- on the XLR plug is Pin3 and Ground is pin 1.

So on the XLR side pin1 and 3 shuld be connected over a resistor.
Or not at all:
commongroundfilter.jpg


Source: https://cdn.shopify.com/s/files/1/0247/3799/files/preventing_hum_and_rfi.pdf
See also: https://www.ranecommercial.com/kb_article.php?article=2107 (search for "hybrid shield termination")

So far I have only seen this schematic applied to the cable shield of fully balanced circuits where the twisted pair is used for the transmission of the hot and cold signal. Now, let's say we have an unbalanced source like the RCA out of a HiFi DAC and want to feed it into a balanced XLR circuit ...

unbal_out_to_bal_in.jpg

Basically this shuld do the trick.
ideally you would then add an abput 100Ohm resistor...

"XLR ground lift" is also of cause commercially available
 
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anphex

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I just remembered that from a time I wanted to get into microelectronics I have lots of basic components lying around in a box. I am 100 % sure that there are some 100 Ohm resistors and nF capacitors, even a soldering iron and some tin.
Well if I have no other option I will try out doing this to the cables!

Thank you! I will report back in a few!
 

Lambda

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I ordered this thing and I hope it will do some magic and fix this problem:
if you want to order something like this make sure to uses on with XLR out and a "ground lift" switch

kcEdCM-5t_Ul7U8bVzFBQtwYfSJ6aHNa7WazTciJn_JCL6bHbX4fnMpTHPXKPAHqi8rMzRUhBIZyxwn8GNjbZK6uASkvARf7Xohyh_wP



I just remembered that from a time I wanted to get into microelectronics I have lots of basic components lying around in a box. I am 100 % sure that there are some 100 Ohm resistors and nF capacitors, even a soldering iron and some tin.
Not relay that critical! 50-2000Ohms will do and it shuld even work without the resistor.
the capacitor is only for EMI and not strictly necessary.

If you have a Soldering iron and a spare XLR cable you can try to disconnect pin1 and see if it works.

If you don’t uses any resistor at all make sure the Receiver is some how connected to ground. and not completely "floating"
 
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anphex

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Well cutting off pin 1 sure is the easiest way right now. I will try it out later today, the cable is useless anyway if I don't get to fix this buzz issue.
 

peng

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What do you say about the monoprice cable? It looks like the grounding issue connecting grounded and ungrounded devices was adressed. Would they work?

The Monoprice RCA to XLR cable works great when I tried it with the HA-1 and Hypex amp. I have not tried it with a Denon AVR yet, will so later now that you got me curious. My bet is it will work because the Monoprice cable is wired correctly.
 
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anphex

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The Monoprice RCA to XLR cable works great when I tried it with the HA-1 and Hypex amp. I have not tried it with a Denon AVR yet, will so later now that you got me curious. My bet is it will work because the Monoprice cable is wired correctly.

Looks to me like the HA-1 (this one?) has also a grounded plug. So there shouldn't be any issue no matter the cable.
 
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anphex

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if you want to order something like this make sure to uses on with XLR out and a "ground lift" switch

kcEdCM-5t_Ul7U8bVzFBQtwYfSJ6aHNa7WazTciJn_JCL6bHbX4fnMpTHPXKPAHqi8rMzRUhBIZyxwn8GNjbZK6uASkvARf7Xohyh_wP




Not relay that critical! 50-2000Ohms will do and it shuld even work without the resistor.
the capacitor is only for EMI and not strictly necessary.

If you have a Soldering iron and a spare XLR cable you can try to disconnect pin1 and see if it works.

If you don’t uses any resistor at all make sure the Receiver is some how connected to ground. and not completely "floating"
I absolutely love you right now. Cutting pin1 completely resolved the issue. You can't imagine how happy and relieved I am. Please PN me your Paypal adress so I can tip you something. You probably saved me hours of meddling and sending back and forth equipment.
 

peng

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Looks to me like the HA-1 (this one?) has also a grounded plug. So there shouldn't be any issue no matter the cable.

No, mine is the Oppo HA-1 but if I remember right it has the grounded pin too.
 

Lambda

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Cutting pin1 completely resolved the issue. You can't imagine how happy and relieved I am.
I’m happy i could help locate the problem!
I was worried you would blame me for cutting your XLR cable if this would not have fixed it :p

Completely removing pin1 ground connection might result in some problems in terms of higher Sensitivity to other EMI.
Maybe it is all fine forever.

If so adding an Resistor and Capacitor will help with this.
100Ohm might be a starting point to Low and the noise will come back to high and it won't help.
With the capacitor its the opposite higher is better but to high and the noise will come back.

it is also good practice to add Ferrite clamps. to both sides of the cable.
F1232485-01

They help almost only with high frequency noises and RF but they are cheap and they have completely no negative effect on the sound.
Class D, SMPS, And Computer/GPUs are notorious for having emitting some HF/RF noises over long cables.

And what PMA says is also true:
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.

rca-xlr_corr.png
Adding an extra resistor same as output impedance in series with the Signal - wire might also lower noises.

Please PN me your Paypal adress so I can tip you something.
Not to worry! i’m happy i could help
 

Webninja

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I too have issues with ground loops on my x3700h. I’m using Buckeye amps and Dylan has been very helpful.

I’m using the Monoprice RCA to XLR, and the noise went from audible from a few feet away to only if you put your ear near the speakers.

Biggest improvement was plugging projector into the same outlet as the Denon.

Still would like to go to zero sound from the ground loop. I’ll try a few things mentioned in this thread.
 
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anphex

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Update after three days:
The AVR or maybe the Hypex amps are rather poppy since I removed the PIN 1 connection. It's barely noticable but happens about 1-3 times in a song of 4 minutes. Mostly when I am on Windows desktop listenting to spotify at a rather high volume. When I have no music running, there is also no popping.

I vaguely remember when I was still using the Gustard X16 with balanced connections this also happened but way less frequently.
Any explanations?

Edit: Oh I found exactly what causes the pops! When I change a browsertab or do anything the causes a rather large change in the displayed content of my TV. Not always, but some when it happens it's with this context. What could it be?
 
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ronnzi

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So I had this same issue and solved it. I posted about it in another forum, so I’ll just copy and paste my response from there here:

Just wanted to chime in to say I had this same issue with my RTX 3090 HTPC. With just the AVR it was fine, but when I introduced an external amplifier into my setup via RCA preouts, there was tons of electrical hum that would only go away if I unplugged the HDMI cord from the 3090. It didn’t even have to be a direct connection - if an hdmi cable was plugged in from my computer to the tv, and my tv to the AVR via a separate cable, the noise still came through! And it definitely wasn’t something that could be ignored - it was very audible.

First, I tried a high end power conditioner/filter and it did nothing. I ran across the Hum-X product listed above that I would have had to theoretically connect my computer to in order to fix the problem. This sort of sounded like the ideal solution, since it wouldn’t directly impact the audio chain and would still provide a safety measure for the grounding of my PC. Unfortunately, my PC power supply is 1000watts, and the Hum-X explicitly states not to use it for anything over 6 amps (720watts). My computer actually pulls a lot of power, so this was a no go.

Ultimately, it looked like RCA isolators were the only things that were likely to work, but given that I am using external amplification for the purpose of getting as good sound as possible, I didn’t want to go with a cheap approach that would potentially degrade the sound quality.

After lots of research, I ended up buying Jensen RCA isolation transformers that have been proven to measure basically no audible different in sound quality.

Here is a link:

https://www.parts-express.com/Jense...O_uY52H5GoKgK5RuJ654PigzZAuL1yrAaAnjyEALw_wcB
.

I’m super happy with the results. The buzzing is completely gone, my computer is still hooked up and being supplied with normal power, and though I didn’t take personal measurements, Audio Science Review has examined Jensen transformers and found them to be the way to go in these types of unsolvable ground loop situations (see this link: Jensen ISO-Max CI-1RR Review (Isolation Transformer)).

Might have been more expensive than necessary for most people (I had to get 3 of the dual RCA transformer to cover all my channels ). Given how many things I already have in the sound chain, like multiple MiniDSP products now, I wanted to go with as good an option as possible to not detract further from the signal quality. The system sounds great, and I have no regrets.

It’s possible that running a fully balanced AVR and amplifier setup over XLR cables would avoid these ground loop issues created by the GPU altogether, though I don’t know for certain since I never tested it. For me though, I was happy with my setup and my AVR only has RCA preouts, so I decided to go this route than trying to see if that would’ve worked better.
 
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anphex

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For trying out sake I connected the signal ground of the Denon with a screw on the case of one of my Hypex amps. Still, the pops remain.
They are very rare and mostly quiet, but when listening to a calm song they are noticable.

1638808563951.png


Edit: Dunno if I just have good-ears-day or the grounding slightly improved the sound. Could this happen? If I'd let my fantasy run wild I could imagine the noise I had before and that was gone after removing Pin 1 was now floating between the + and - of the audio cables and modulating the sound?
 
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anphex

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Okay, the new thing is the popping and clicking that even persists when disconnecting the hypex completely. I tried about everything: BIOS settings, energy management adjustments, latency analysis...

I will try out some different HDMI cables and ports tomorrow and try out toslink for my TV. Since the pop almost always occurs when moving a window or switching a tab on PC I guess it's either something TV, GPU oder CPU related. I'd love to increase sample size of HDMI audio but I can't find some settings to adjust this like with an USB driver of an interface.
Funnily enough the panning of the click sound is completely random. Sometimes left, center, right or something in between.
 
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anphex

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I am at my wits end. I tried about everything:

  • tried Hypex and internal amps
  • tried disconnecting everything except the PC HDMI on the AVR
  • with and without signal ground
  • disabled about any possible power saving settings +
  • reset BIOS to stock values
  • adjusted sample rate
  • tried out ASIO with increased buffer sice
  • checked latency monitor (everything is as green as it could get)
  • disconnecting TV yields no difference
  • reinstalled driver
  • used the additional usb-energy supply for the fiber HDMI cable
  • used another power cable
The popping sounds stick around! Reminder: they happen when playing as song, they increase in intensity and frequency when I do some desktop work meanwhile. I am getting desperate.
 
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