Does a mini class-D amp benefit from electrical grounding?

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#21
You don't understand what he writes. He leaves audio GND floating. He does use PE for the casing!!!

- Keep in mind that metal casing should always be connected to PE in a rigid way. This is for safety. Every country has rules/regulations how to do this. Probably 2.5 mm yellow/green stranded wire with rings, bolt and nut.

- Keep in mind that audio GND is a different item and that many do not connect GND to PE directly.

- If the PSU or SMPS has a PE connector it MUST be connected to PE for correct and safe working. If not it will not be safe and it will pollute your mains voltage as filtering in those only works when PE is connected.

- In audio GND is not PE! Except in many anglosaxon countries where GND is connected with PE and people suffer to solve hum problems and ground loops. Do a search on this forum to read the joys of this. In many languages there exist 2 different words for safety ground and audio ground. In dutch we call PE "safety earth/randaarde" and audio ground "mass/massa". It makes matters more easy. We also draw these with different symbols. If both items are called ground then things go wrong rapidly.
 
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#25
I think you are trolling. If not please use the term "safety earth" and use all you internet browsing capabilities to find out what it is and what it does.

AFAIK there exist no electronic circuits without GND. GND does not come from the wall outlet. The wall outlet has L, N and PE (the latter sometimes missing in older houses).

GND is most often the 0V point in the PSU AFTER transformation so in general the low voltage side. Can not make it more clear and will not make it more clear.
 
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#27
I'm not trolling. I am just confused a lot. Imagine that you were learning this from scratch again. I also understand that you cannot explain everything here in this thread.
If the wall outlet comes with PE, do I just need to make sure that the amp is connected to a power supply connected to PE or a sound source connected to PE?
 
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#31
Let's make it simpler.

As far as I know, the amp connects its RCA jacks to the amp's metal chassis.
My computer's power supply is connected to the wall outlet's PE. The amp's power supply is not.
RCA cables connect the amp to the computer.

Is this a safe setup?

In my direct experiences, if either the computer power supply or the amp power supply is connected to PE, my fingers do not feel electricity on the amp's metal chassis. If neither is connected to PE, my fingers feel electricity on the amp's metal chassis.
 
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#32
jean-paul said:
GND is most often the 0V point in the PSU AFTER transformation so in general the low voltage side. Can not make it more clear and will not make it more clear.
Click to expand...

Fully agree J-P. The audio ground is simply the reference for all signals in the system. If you measure supply voltage, or signal level, you measure against a common reference that usually is called 'ground' or '0V'. But it has nothing to do with the ground outside your house or anything earth-like.

PE is the actual connection to the 'ground' on which you stand and which you touch. By connecting an enclosure to this PE ground, you make sure that there is no voltage between that case and the rest of your world, so it is completely safe to touch that enclosure.

Now, that said, there is always a little leakage through things like a power transformer so the 'ground' (the reference) of your audio system may accumulate some voltage, and when you touch things like the RCA connector shell, you may feel a tingle. It can be suppressed by connecting the audio ground to PE but that may in turn cause ground loops and hum in your system. That is why often this connection between audio ground and PE is made (as J-P mentioned) with a resistance, low enough to drain the leaked charge, but large enough not to cause ground loop hum.. Yes, it's a bit of black magic ;-)

Jan
 
#33
I think I figured it out.

* If either the amp's power supply or the sound source's power supply is connected to PE, the amp is safe to touch because its RCA jacks are connected to the amp's metal enclosure.
* If neither is connected to PE, just find a convenient electrical line to directly connect the amp's metal chassis to the wall outlet's PE.
* If both is connected to PE, there is a ground loop.
* GND is just an internal reference point of the amp. It's like GND GPIO pin of Raspberry Pi. You are not supposed to connect Raspberry Pi's GND GPIO pin directly to PE.

I just need to figure out how to securely connect the metal amp enclosure to the wall outlet's PE.
 
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#34
jan.didden said:
Now, that said, there is always a little leakage through things like a power transformer so the 'ground' (the reference) of your audio system may accumulate some voltage, and when you touch things like the RCA connector shell, you may feel a tingle. It can be suppressed by connecting the audio ground to PE but that may in turn cause ground loops and hum in your system. That is why often this connection between audio ground and PE is made (as J-P mentioned) with a resistance, low enough to drain the leaked charge, but large enough not to cause ground loop hum.. Yes, it's a bit of black magic ;-)

Jan
Click to expand...

Right. What also often happens is connecting PE devices to non-PE outlets. The built-in mains filter capacitors in SMPS from L and N to PE will then form a voltage divider where half the mains voltage will occur. As the casing is connected to the PE pin of the inlet this causes the metal casing to carry half the mains voltage. Your feet will be the connection to the floor which is PE in a way. Touching the casing will then also cause a nasty tingle. For some this is difficult to understand but if you draw the situation it is self explanatory.

Stuff that has a PE connector should therefor always be connected to PE wall outlets.
 
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#37
CowCat said:
Do you just let your amp completely float without any grounding or earthing?
That's good to know.
I hope there is no stray live wire nearby.
Click to expand...

Let me start with a similarity that may be easier to understand. You stand in front of a tower and the guy next to you ask you how tall the tower is? You reply “I cannot tell because I do not know what is the sea level compared to here”. A useful reply? No, because a normal understanding in this case would be measured from the surrounding ground and up. This was probably what the guy meant. Say the tower measures 50m from the surrounding ground and to the top, it will also be 50 meter high if put on the top of Mount Blanc or on a flat Dutch polder. For many things we measure we use a reference which we use as basis for our measurements. A ground wire is the reference we use when we measure signals inside an audio unit. We even connect ground wires from the MP3 player to the pre-amplifier ground and to the power amplifier ground so we have the same reference for signals in that signal chain. Nobody cares if the static potential (no current ability) to for instance safety earth is 20V or 50V. The signal levels are measured from the relevant reference and we do not in that moment care about what would be the signal level compared to something else that is not our present concern. Similarly to that nobody cares about the sea level when they have to tell the height of a tower in-land.

“stray live wire nearby” - sounds really dangerous!
 
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#38
FauxFrench, A few hours ago, I understood the meaning of ground and protective earth. I remembered that raspberry pi's GND GPIO pin is connected to other devices' grounds, not PE.

scottjoplin, Is it normal for a good class 2 insulation to leak a little bit of electricity to the metal enclosrue that my fingers can feel?
 
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