Internal ground loop in Apollon NCMP6350 (Hypex NC502MP)

[audioBliss]

Aha, so I finally found the person who could explain this to me. Well that explains perfectly the situation with the input differences and all! Thank you for this, I love getting to the bottom of things.

Anyways the amp should have been shipped today so looking forward to plugging it in and this time with a balanced connection

Edit: btw what is this secret sauce? shielding that input? just using balanced connection?

 

[Matias]

...and before people start masturbating with quality of cables...

Awww I was just about to roll mu-metal sheets around the inner cables.
https://www.ebay.com/c/1045144994

 

[Panelhead]

Sorry for not carefully reading your first post and asking stupid questions.
In fact, there was at least someone on the internet knowing about this issue, me .
The "problem" affects all NCxxxMP. The issue is that a few SMPS components are radiating 50 Hz and harmonics really close to the inputs. As you can see below, input 1 is more subject to the issue than input 2 since it's closer from these components. As soon as the impedance between the two input wires becomes high (no input cable plugged in example), the two wires become nice antennas, catch the 50 Hz and harmonics, that you can hear in your speakers.
View attachment 85352

There is a secret sauce to avoid this, and before people start masturbating with quality of cables, I use ribbon cable and reach hum levels far below audibility with no input cable plugged.

Is the amplified “silent” with a balanced source connected?

 

[boXem]

Is the amplified “silent” with a balanced source connected?

Depends the source impedance. In example, with a motu m2 powered, silent, unpowered, hum.

 

[Chromatischism]

and no one on basically the whole internet has heard about this.

How many people run their amp with no input cables connected?

If I got a bad noise out of mine when I connected/disconnected something incorrectly, I would assume that's an invalid configuration and I'm doing something wrong - not think it's defective and send it back. My 2 cents I guess. At least you achieved some peace of mind that it's ok.

 

[Panelhead]

Same with unpowered source. I think most input channels are mouser when connected to a source that Is not powered.
Powered is maybe a couple hundred ohms. Unpowered may be open at DC.

 

[audioBliss]

How many people run their amp with no input cables connected?

If I got a bad noise out of mine when I connected/disconnected something incorrectly, I would assume that's an invalid configuration and I'm doing something wrong - not think it's defective and send it back. My 2 cents I guess. At least you achieved some peace of mind that it's ok.

No one seems to be reading what I'm writing in the thread? First of all, I had the hum issue even when input sources connected on said channels. Second of all I was asked by the manufacturer to disconnect everything and listen if I had a ground loop to try and pin point the problem. And I replied that I did and that it was even louder. Apollon said that this was not normal and suggested I send the amp back! I could then not get a definitive answer to as if a balanced pre-amp would help. Even Apollon was surprised when testing it that all MP modules have this characteristic like I said! It was even kind of funny that the exact channels I said I hear a hum when inputs connected were the ones that were then shown to be extremely close to a noise source on the board!

I will see what is what when I have the amp back and of course if a balanced connection solves the issue I will probably even order another one because it sounds great but I do not want to have something that I don't know if it is defective or not. I also have to be able to explain this if I ever sell it to anyone later down the road.

What it comes down to is that most likely you must have a balanced AV processor with the MP modules which is fine or you need to take great care when selecting cables but who knows I have tested several from reputable brands like Hosa with no luck. With all other ncore amps like nc400, nc500, nc1200 it is no problem using any rca-xlr cable or any unbalanced pre-amp they will work regardless if you have special cables or whatever with absolute dead silence in the speaker at all times. Do you see the difference?

To be clear Apollon built a very solid amplifier that was very well packaged and they have provided great support!

 

[Chromatischism]

Noted.

I will add I'm using an NC252MP without humming issues and that's just with RCA preouts from my Denon X4500H. So I do not believe balanced connections are required. The cables I have used are KabelDirekt and a custom one from Ghent using Star Quad.

Now, if I go up and put my ear to the speakers there is some low level noise, but I'm not concerned about something I can't hear from my seat.

 

[March Audio]

What it comes down to is that most likely you must have a balanced AV processor with the MP modules which is fine or you need to take great care when selecting cables but who knows I have tested several from reputable brands like Hosa with no luck. With all other ncore amps like nc400, nc500, nc1200 it is no problem using any rca-xlr cable or any unbalanced pre-amp they will work regardless if you have special cables or whatever with absolute dead silence in the speaker at all times. Do you see the difference?

!

Sorry but this is not correct.

We have plenty of customers using single ended RCA sources and not had one single complaint about hum or noise with NC122MP. NC252MP or NC502MP based amps.

You do require a correctly wired RCA to XLR cable, but this is applicable to *all* balanced input amps including theNC400, NC500 and NC1200 and those from other manufacturers.

 

[restorer-john]

At the end of the day, placing the input differential header (with likely 9mm unshielded pins) immediately adjacent to the AC mains and input filtering is just a totally bone-headed design from Hypex.

But in the interests of getting it all on a super compact PCB, stuff like that happens all too often these days. An unterminated input on a powered up amplifier should be silent. Not as silent as a shorted input or a low R source, but there should be no audible hums or buzzes.

 

[March Audio]

At the end of the day, placing the input differential header (with likely 9mm unshielded pins) immediately adjacent to the AC mains and input filtering is just a totally bone-headed design from Hypex.

But in the interests of getting it all on a super compact PCB, stuff like that happens all too often these days. An unterminated input on a powered up amplifier should be silent. Not as silent as a shorted input or a low R source, but there should be no audible hums or buzzes.

These modules are audibly silent unterminated.

 

[audioBliss]

Sorry but this is not correct.

We have plenty of customers using single ended RCA sources and not had one single complaint about hum or noise with NC122MP. NC252MP or NC502MP based amps.

You do require a correctly wired RCA to XLR cable, but this is applicable to *all* balanced input amps including theNC400, NC500 and NC1200 and those from other manufacturers.

I have two different RCA to XLR cables. Both work flawlessly with my nc400 amps with any preamp, dead silent every time. Exact same cables reveal the issue at hand with the NC502MP. Do I have correct cables or not? How would one know?

 

[boXem]

These modules are audibly silent unterminated.

The modules, yes. But as soon as some unterminated wiring is plugged on them it's no more the case.
They need some care during integration, simply following AES48 is not enough.

 

[boXem]

I have two different RCA to XLR cables. Both work flawlessly with my nc400 amps with any preamp, dead silent every time. Exact same cables reveal the issue at hand with the NC502MP. Do I have correct cables or not? How would one know?

Open the RCA side and take a picture.

 

[March Audio]

The modules, yes. But as soon as some unterminated wiring is plugged on them it's no more the case.
They need some care during integration, simply following AES48 is not enough.

Nope.

Our amplifiers are silent when nothing is plugged in the XLR connectors.

Yes it does need care, but if you are picking up hum it implies that one leg on the internal link cable is "seeing" more noise than the other leg. Shouldnt really be the case (well not in a significant way) on a few cms of twisted shielded cable.

 

[audioBliss]

Open the RCA side and take a picture.

Here you can have both sides

 

[boXem]

Here you can have both sides
View attachment 85494

No good, they use coax cable and slap an XLR plug on it. What's needed is pair + shield, as on the drawing Apollon sent you. The Cordial I linked makes it for 12 EUR a pair, VAT included.

 

[boXem]

Nope.

Our amplifiers are silent when nothing is plugged in the XLR connectors.

Yes it does need care, but if you are picking up hum it implies that one leg on the internal link cable is "seeing" more noise than the other leg. Shouldnt really be the case (well not in a significant way) on a few cms of twisted shielded cable.

Nope what?

 

[audioBliss]

You mean like this?

 

[March Audio]

Nope what?

?

Your implication was that as soon as you connect internal wiring they hum. This is not the case.