Internal ground loop in Apollon NCMP6350 (Hypex NC502MP)

[March Audio]

You mean like this?

Whilst the soldering doesnt look good, yes this is correct wiring at the RCA end.

That other coax cable is no good.


I seem to post the following on a daily basis

 

[Absolute]

It can't be stressed enough because we sheeple without understanding of the finer things in life can't make sense of any of this.

 

[audioBliss]

Whilst the soldering doesnt look good, yes this is correct wiring at the RCA end.

That other coax cable is no good.

Well it doesn't work anyway with the nc502mp With my nc400 I have no problems. Also my point anyway was how would I know if the cable is correct before buying? I can't see any information about this type of stuff before buying cables. And as proven even if you have the "correct" cable it's a no go for the nc502mp.

 

[March Audio]

Well it doesn't work anyway with the nc502mp With my nc400 I have no problems. Also my point anyway was how would I know if the cable is correct before buying? I can't see any information about this type of stuff before buying cables. And as proven even if you have the "correct" cable it's a no go for the nc502mp.

Absolutely agree, there is no reason for people to know what a "correctly wired" cable would be. However we do advise customers about this. Its obviously a bigger issue than I ever thought as there are so many threads here that cover it. I think its worth me putting some info on our website and in the manuals about it.

As I have already mentioned its not a fundamental issue with the NC502MP modules. There is something else amiss with your amp if its buzzing with nothing connected.

Im sure Apollon will sort it out, could easily be as simple as a loose wire. Sh**t happens

 

[audioBliss]

f course stuff happens and I have full understanding of that but there are different opinions here on if the buzzing is normal or not. This is what I want to find out.

Did you read Apollons response I posted? I think both Apollon and I thought a wire had come loose or something like that. But according to them, after testing was done, the buzzing is normal and affects all MP modules.

The buzzing should however go away with a balanced connection according to their testing. This I have not personally tested yet.

 

[March Audio]

f course stuff happens and I have full understanding of that but there are different opinions here on if the buzzing is normal or not. This is what I want to find out.

Did you read Apollons response I posted? I think both Apollon and I thought a wire had come loose or something like that. But according to them, after testing was done, the buzzing is normal and affects all MP modules.

The buzzing should however go away with a balanced connection according to their testing. This I have not personally tested yet.

Its *NOT* normal.

Sorry I only read it after posting. I am a little surprised by their response. However I also agree it will probably reduce to inaudible levels once you have terminated the connection and connected the source.

 

[boXem]

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.

For EMC reasons, one like to group all inputs and outputs in the same area. The inputs close to mains is a weakness that has a workaround. Other solution would be speaker outputs at this place, but there would be no workaround.

You mean like this?

Looks like there is no contact between blue/shield of the cable and connector shield. Anyhow, since your amplifier hums when open, I fear that a proper RCA-XLR connector will not solve the issue. I see a problem in the way the module is installed by Apollon.

?

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

If you connect 10 cm of a perfectly shielded/twisted cable on the amplifier module and leave it completely open on the other side, you will get clearly audible hum, especially on channel 1.

f course stuff happens and I have full understanding of that but there are different opinions here on if the buzzing is normal or not. This is what I want to find out.

Did you read Apollons response I posted? I think both Apollon and I thought a wire had come loose or something like that. But according to them, after testing was done, the buzzing is normal and affects all MP modules.

The buzzing should however go away with a balanced connection according to their testing. This I have not personally tested yet.

I have been looking at pictures from the big brother NCMP8350. Build is beautiful, but I wonder how AES48 is handled. Connectors seem to be Neutrik NC3FD-LX series, which do not offer integrated grounding, meaning that pin 1 needs wire connection to the chassis. On the pictures this connection is not visible. The workaround I was talking about does not seem to be applied, explaining the hum when connectors open. Do you have a way to check resistance between pin 1 and case?

 

[March Audio]

If you connect 10 cm of a perfectly shielded/twisted cable on the amplifier module and leave it completely open on the other side, you will get clearly audible hum, especially on channel 1.

?

I can't speak for your experience but I do not see this problem and none of our amps buzz with the inputs open.

 

[audioBliss]

I actually looked exactly for this connection to the chassi and I did not find it either. The amp is still at Apollon, I'm not sure if they have shipped it yet or not. When I get it back I can check the resistance.
Btw that connector seems to have this option but I don't really know what that means or looks like in the chassi https://www.neutrik.com/en/product/nc3fd-lx :
Optional connection to easily join pin1 to chassis ground

 

[boXem]

I do not.

I do
Before we enter in an endless loop, my youngest son is two, and he is my fourth child. My resistance to the "no" is at it's highest level and I am ready for the Olympics of the affirmation .
Edit

I can't speak for your experience but I do not see this problem and none of our amps buzz with the inputs open.

Glad to see you still have this charming habit to modify your posts after people replied to them.
At which point did anybody suggest that your amplifiers would be buzzing? Why being so defensive?
Your amplifiers do not buzz, good for you and your customers. My amplifiers do not buzz either, even without fancy wiring.

 

[March Audio]

I do
Before we enter in an endless loop, my youngest son is two, and he is my fourth child. My resistance to the "no" is at it's highest level and I am ready for the Olympics of the affirmation .
Edit

Glad to see you still have this charming habit to modify your posts after people replied to them.
At which point did anybody suggest that your amplifiers would be buzzing? Why being so defensive?
Your amplifiers do not buzz, good for you and your customers. My amplifiers do not buzz either, even without fancy wiring.

Fred its not being defensive. I have been simply answering some misconceptions and inaccurate descriptions of the behaviour of the Hypex modules.

If you are having problems with these amp modules buzzing there is something amiss in your set up. I have tested countless of them and they simply dont behave as you describe. A differential input with good CMR shouldnt do so unless there is some "inbalance" in the wiring.

Here is a video to demonstrate with a NC502MP module quickly lashed up on the bench.

With the input connector open there is no buzz.

When I plug in an open balanced cable there is no buzz. I can of course provoke buzz (mains pick) up if I touch either hot or cold leg. I did this just to prove the amp is actually on and connected to the speaker

 

[boXem]

Fred its not being defensive. I have been simply answering some misconceptions and inaccurate descriptions of the behaviour of the Hypex modules.

If you are having problems with these amp modules buzzing there is something amiss in your set up. I have tested countless of them and they simply dont behave as you describe. A differential input with good CMR shouldnt do so unless there is some "inbalance" in the wiring.

Here is a video to demonstrate with a NC502MP module quickly lashed up on the bench.

With the input connector open there is no buzz.

When I plug in an open balanced cable there is no buzz. I can of course provoke buzz (mains pick) up if I touch either hot or cold leg. I did this just to prove the amp is actually on and connected to the speaker

Thanks for the video.
OP has the problem.
I have the problem with the exact same setup as yours (I watched the video 3 times). I need to do extra wiring to remove the buzz.
Only reason I see is that both the OP and myself are too far away from south pole...
Or that Hypex made changes since I made my tests.

 

[March Audio]

Thanks for the video.
OP has the problem.
I have the problem with the exact same setup as yours (I watched the video 3 times). I need to do extra wiring to remove the buzz.
Only reason I see is that both the OP and myself are too far away from south pole...
Or that Hypex made changes since I made my tests.

I have been using these modules for about 3 years and not seen the problem so I dont think there have been any relevant board revisions from Hypex.

 

[boXem]

I have been using these modules for about 3 years and not seen the problem so I dont think there have been any relevant board revisions from Hypex.

Then that's the south pole proximity.

 

[Apollon Audio]

I would fully agree with @Fred Jacquot 's statement.

"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. "

Let me be clear. In my reply I haven't said that this is normal. I mentioned that when we tested all MP stereo modules, all had the same "issue" if I can call it this way. We experienced this only with the first channel which is very near to the smps. The input cables like mentioned by @Fred Jacquot when not connected to a source act as antennas. The buzz is hardly audible even when listening up close. Nothing like a ground loop or touching the wires like @March Audio demonstrated in his video. In our tests the buzz was only audible when putting the ear right next to the tweeter. My opinion is that this is not an issue or a problem at all. Probably no one is using an amplifier without any input signals connected. When a source is connected (xlr balanced or rca unballanced) the quiet buzz goes away. For RCA ubalanced the right adapter cables are needed. OP had very bad unshielded coaxial cables like I can see from the pictures. I believe that this was the main reason for the problem that he experienced when connecting an unbalanced source to the amplifier.

We have more than 100 brand new MP series modules here. I have unpacked many of them, connected the power, speakers and xlr input signal direct to the board. There is no scientific knowledge needed to connect a MP series module. No other additioanl electornics were involved. My findings were that all modules behaved the same.

My suggestion is that you do not frustrate yourselves over this. Connected to a source this amplifer performs and measures per specifications.

 

[Apollon Audio]

For EMC reasons, one like to group all inputs and outputs in the same area. The inputs close to mains is a weakness that has a workaround. Other solution would be speaker outputs at this place, but there would be no workaround.

Looks like there is no contact between blue/shield of the cable and connector shield. Anyhow, since your amplifier hums when open, I fear that a proper RCA-XLR connector will not solve the issue. I see a problem in the way the module is installed by Apollon.

If you connect 10 cm of a perfectly shielded/twisted cable on the amplifier module and leave it completely open on the other side, you will get clearly audible hum, especially on channel 1.

I have been looking at pictures from the big brother NCMP8350. Build is beautiful, but I wonder how AES48 is handled. Connectors seem to be Neutrik NC3FD-LX series, which do not offer integrated grounding, meaning that pin 1 needs wire connection to the chassis. On the pictures this connection is not visible. The workaround I was talking about does not seem to be applied, explaining the hum when connectors open. Do you have a way to check resistance between pin 1 and case?

There are no issues when the right rca-xlr adapter cable is used. We tested this with ordinary Neutrik xlr-rca adapters, our custom adapter cables made after RANE (https://www.ranecommercial.com/kb_article.php?article=2107) or our custom adapter cables made like Bruno Putzeys suggest (https://www.hypex.nl/img/upload/doc/an_wp/AN_Legacy_pin_1_problems.pdf)
. The almost inaudible buzz goes away immediatelly when the source is connected whether it is a balanced source or unbalanced. Our placement of modules in our multichannel amps has nothing to do with the buzz.

The Neutrik connectors that we use have a extra pin which you can solder to the pin1. When soldering this extra pin to pin1 you connect the shell and case to pin1.

The resistance between pin1 and case is 0.52 Ohms.

 

[audioBliss]

To be honest I don't know what to make of it all but if I don't have any buzz when I connect the amp to my balanced pre-amp with these cables https://shop.sommercable.com/en/Cab...l-Stage-22-Highflex-SG0Q.html#tab_description then I basically don't care about the other scenarios at this point. Are these also bad cables? I mean I just don't know. Please recommend cables that are compatible if the linked cables are not good - it would not surprise me if even pure XLR cables can be made incorrectly at this point.

One use case that would be good though is if I could have some of the channels unplugged and that not affecting the other channels that are plugged in. I guess I will just have to wait and see. And just to make it more clear I have 21 speakers in my room and some speakers have high sensitivity and I sit quite close to some of them so when stuff starts buzzing it's kind of annoying.

Thank you.

 

[Apollon Audio]

To be honest I don't know what to make of it all but if I don't have any buzz when I connect the amp to my balanced pre-amp with these cables https://shop.sommercable.com/en/Cab...l-Stage-22-Highflex-SG0Q.html#tab_description then I basically don't care about the other scenarios at this point. Are these also bad cables? I mean I just don't know. Please recommend cables that are compatible if the linked cables are not good - it would not surprise me if even pure XLR cables can be made incorrectly at this point.

One use case that would be good though is if I could have some of the channels unplugged and that not affecting the other channels that are plugged in. I guess I will just have to wait and see. And just to make it more clear I have 21 speakers in my room and some speakers have high sensitivity and I sit quite close to some of them so when stuff starts buzzing it's kind of annoying.

Thank you.

These xlr Sommer cables are great.

 

[restorer-john]

And just to make it more clear I have 21 speakers in my room

I see your 21 speakers and raise you to 36 speakers (18 pairs), 6 unused powered subwoofers and one centre speaker. And then there's some electronics...

 

[audioBliss]

I see your 21 speakers and raise you to 36 speakers (18 pairs), 6 unused powered subwoofers and one centre speaker. And then there's some electronics...

Hehe when you’ve been in the hobby long enough you usually end up with some stuff.