Balanced interconnection and ground

[Davide]

Thank you all for the replies.
Everything seems clear to me now.
I only have one doubt left. In this case, with Hypex module, is it better to have the source (DAC) with floating or grounded power supply? (whatever it makes difference)
The fact of creating a loop should it always be prevented or if properly managed is it fine anyway?

 

[antcollinet]

Thank you all for the replies.
Everything seems clear to me now.
I only have one doubt left. In this case (with Hypex module) is it better to have source (DAC) with floating or grounded power supply? (whatever it makes difference)

I don't think it is possible to be definitive. It depends so much on the system, and the specific design of individual components.

However, since you have balanced connections from DAC to amp, you don't really have to worry so much about ground noise being an issue.

 

[Geert]

is it better to have the source (DAC) with floating or grounded power supply? (whatever it makes difference)

There's always the option of connecting it to ground with a small capacitor (say 4,7nF). It provides a path for noise without the risk of introducing ground loops.

 

[Sokel]

Doesn't Nc5xxx grounds itself thought it's heatshink and the mounting screws to the chassis?
Heatshinks are always tied to ground.
Why would it need the separate j4.3 to the chassis?

 

[mcdn]

Doesn't Nc5xxx grounds itself thought it's heatshink and the mounting screws to the chassis?
Heatshinks are always tied to ground.
Why would it need the separate j4.3 to the chassis?

Not according to the datasheet - the mounting screws have no electrical connection that I can see.

J4.3 is the shield connection for the input signal, not a safety earth, and not a return path for the audio signal. The assumption is the shield is connected to the chassis at the input point (pin 1), and that J4.3 is connected to the shield of the internal cabling.

 

[Sokel]

Not according to the datasheet - the mounting screws have no electrical connection that I can see.

J4.3 is the shield connection for the input signal, not a safety earth, and not a return path for the audio signal. The assumption is the shield is connected to the chassis at the input point (pin 1), and that J4.3 is connected to the shield of the internal cabling.

Then it must be a special scheme,cause traditionally all heatshinks must be tied to ground.
About j4.3,we're saying the same,it doesn't need to separately connect to chassis,it will eventually do through the shielding of the cable on the connector.

 

[Geert]

Then it must be a special scheme,cause traditionally all heatshinks must be tied to ground.

There still is a ground connection on J6, where the main power supply connects to.

 

[somebodyelse]

It looks to me like Hypex have already got an RC connection to some of the mounting posts and expect the heat spreader to be connected to chassis.

 

[Sokel]

It looks to me like Hypex have already got an RC connection to some of the mounting posts and expect the heat spreader to be connected to chassis.

Icepower does it the same way too:



(Scheme includes a front end too,don't confuse it with the amp)

 

[GXAlan]

However, since you have balanced connections from DAC to amp, you don't really have to worry so much about ground noise being an issue.

My Yamaha CX-A5100 (two prong power) via XLR to my Meyer Sound Amie (three prong power) generates a ground loop that’s audible and annoying even though it’s a presumably a proper balanced connection as both companies make PA gear.

I can remove the hum by taking the phono lug of the Yamaha to the ground lug of my line conditioner. The ground lug of my line conditioner is attached to earth safety ground.

Ideas? I have tried a few XLR cables. It’s not a big deal to use the grounding wire, but I am curious. Panamax, Belkin, Monster Power all have ground lugs on their power conditioners (with Panamax being the only one still making power conditioners)

 

[antcollinet]

My Yamaha CX-A5100 (two prong power) via XLR to my Meyer Sound Amie (three prong power) generates a ground loop that’s audible and annoying even though it’s a presumably a proper balanced connection as both companies make PA gear.

I can remove the hum by taking the phono lug of the Yamaha to the ground lug of my line conditioner. The ground lug of my line conditioner is attached to earth safety ground.

Ideas? I have tried a few XLR cables. It’s not a big deal to use the grounding wire, but I am curious. Panamax, Belkin, Monster Power all have ground lugs on their power conditioners (with Panamax being the only one still making power conditioners)

What is the source into the Yamaha? I'm wondering if the noise is on the signal before it is sent over XLR to the speaker. Or given that the Yamaha is not grounded when you are getting the noise, in order for it to be a ground loop there must be some other kit that is grounded connected to the AVR.

 

[GXAlan]

What is the source into the Yamaha? I'm wondering if the noise is on the signal before it is sent over XLR to the speaker. Or given that the Yamaha is not grounded when you are getting the noise, in order for it to be a ground loop there must be some other kit that is grounded connected to the AVR.

During my troubleshooting, I could have it occur with nothing plugged in and no source playing. The grounded product connected to the AVR is the active speaker!

 

[Geert]

My Yamaha CX-A5100 (two prong power) via XLR to my Meyer Sound Amie (three prong power) generates a ground loop that’s audible and annoying even though it’s a presumably a proper balanced connection as both companies make PA gear. I can remove the hum by taking the phono lug of the Yamaha to the ground lug of my line conditioner.

It's unlikely that there is a ground group, without there being a physical ground loop ... (ground connected at 2 different locations). Looks like it's actually the other way around; the Yamaha relying on the ground of the receiving end. That would work for the unbalanced connections, but not necessarily for the balanced outputs.

 

[antcollinet]

It's unlikely that there is a ground group, without there being a physical ground loop ... (ground connected at 2 different locations). Looks like it's actually the other way around; the Yamaha relying on the ground of the receiving end. That would work for the unbalanced connections, but not necessarily for the balanced outputs.

i'm suspecting common mode mains nose coupling to the ground somehow and going down the XLR cable to the speaker ground. I"m struggling to see though how that can result in differential noise on the hot/cold xlr audio connection. It is precisely this type of case that balanced connections are intended to mitigate.

My next step would be to measure the output of the amp directly on the XLR output with the speakers disconnected, to see if the noise is somehow coupling onto the analogue signal internally to the amp

I'd also be checking if the pin 1 and/or screen of the XLR is connected to ground at both ends.

 

[GXAlan]

It's unlikely that there is a ground group, without there being a physical ground loop ... (ground connected at 2 different locations). Looks like it's actually the other way around; the Yamaha relying on the ground of the receiving end. That would work for the unbalanced connections, but not necessarily for the balanced outputs.

That makes sense actually.

“Yamaha's proprietary power supply ground configuration, called DAC on Pure Ground, ensures that the power supply will never negatively affect sound quality.”

And

“Even the RCA unbalanced connection uses a ground sensing transmission method that achieves simple balanced transmission”

And in Crutchfield Q&A
HOW CAN THIS UNIT USE A TWO PRONG AC POWER WITH A BALANCED THREE PIN XLR? DOESN'T THERE HAVE TO BE A GROUND SOMEWHERE?
Trey Feb 20, 2018
1 ANSWER
A
The XLR is two pins (for balanced signal) and shield which is tied to ground on the receiver. There is a separate grounding point on the back of the CX-A5100 if you want to bond that to safety ground, though typically it's only needed for phono cartridges. It might be grounded by the amplifier, but note then that this potentially will create a "ground loop" which would add noise if both the receiver is tied to safety ground as well as the amplifier unless the resistance between them is very low. As it is, shield is connected to the CX-A5100 chassis which integrates the shield with the faraday cage around the preamp, which floats from neutral. Up to you on how to ground it, but I suspect this approach means you have the choice rather than introducing a potential ground loop if your amp ties shield to safety ground.

My next step would be to measure the output of the amp directly on the XLR output with the speakers disconnected, to see if the noise is somehow coupling onto the analogue signal internally to the amp

I have measured the CX-A5100 with my E1DA Cosmos ADC and never saw anything unusual but that was in a different part of the home when I did the measurements.

Next few weeks are busy but I am very curious to figure this out.

I'd also be checking if the pin 1 and/or screen of the XLR is connected to ground at both ends.

I had both generic Monoprice star quad and Neutrik/Canare star quad cables do the same. About 6-10 ft run.

 

[antcollinet]

I had both generic Monoprice star quad and Neutrik/Canare star quad cables do the same. About 6-10 ft run.

Im thinking of checking the actual components - eg the speakers. Do they ground the shield and pin 1 internally.

 

[Geert]

i'm suspecting common mode mains nose coupling to the ground somehow and going down the XLR cable to the speaker ground. I"m struggling to see though how that can result in differential noise on the hot/cold xlr audio connection. It is precisely this type of case that balanced connections are intended to mitigate.

If it's noise induced in the circuit before the Yamaha's differential output stage, due to to a missing path to ground, then it is a common mode signal which will make it to the receiving end. Hard to say.

If you look at the diagram on the Amie's plate amp you see pin 1 has no hard connection to ground, so shielding of the connection might be insufficient with a floating source like the Yamaha. The Q&A text @GXAlan quoted seems to confirm they are aware of potential compatibility issues.

In this case it maybe makes sense to connect pin 1 in the XLR connector to the connectors housing at the side of the Amie.

 

[sergeauckland]

If it's noise induced in the circuit before the Yamaha's differential output stage, due to to a missing path to ground, then it is a common mode signal which will make it to the receiving end. Hard to say.

If you look at the diagram on the Amie's plate amp you see pin 1 has no hard connection to ground, so shielding of the connection might be insufficient with a floating source like the Yamaha. The Q&A text @GXAlan quoted seems to confirm they are aware of potential compatibility issues.

View attachment 343511

In this case it maybe makes sense to connect pin 1 in the XLR connector to the connectors housing at the side of the Amie.

That is SO wrong! Pin1 should go to ground immediately, and it's the audio ground only that should go through the 1k resistor/capacitor/diode ground-lift components, ideally with a switch to bypass them.

S.

 

[Speedskater]

That is SO wrong! Pin1 should go to ground immediately, and it's the audio ground only that should go through the 1k resistor/capacitor/diode ground-lift components, ideally with a switch to bypass them.

S.

Yep, Audio Engineering Society Standard, AES48 requires the XLR pin1 to be directly attached to the metal chassis at the connector.

In the June 1995 AES Journal, John Windt has a paper on the 'Hummer Tester".
This is a bit about the tester from Bill Whitlock:

 

[GXAlan]

If it's noise induced in the circuit before the Yamaha's differential output stage, due to to a missing path to ground, then it is a common mode signal which will make it to the receiving end. Hard to say.

If you look at the diagram on the Amie's plate amp you see pin 1 has no hard connection to ground, so shielding of the connection might be insufficient with a floating source like the Yamaha.

Looking at the Meyer Sound Amie manual: