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In Reply to: Chassis ground vs. source signal ground? posted by A.A. on April 25, 2007 at 18:54:27:
Could there be issues with ground loopsYes, there could be and unforunately a lot of people do have problems with ground loops like this.
As you can see from the reactions to your post, this is a subject that causes a lot of confusion. Grounding (and shielding) seems simple but is in fact a complicated subject. I will not pretend that I understand it myself, but I'm willing to give it a try.
Let's stick to the same terminology and use 'signal ground' as the chosen zero-potential (e.g. 0V) and 'wall socket ground' as the grounding pin (europe) or neutral (US?) of the wall socket which should ultimately be really 'ground'.
If the signal ground is connected to wall socket ground inside the amplifier, regardless of it being connected to the chassis or not, and the same is happening in the CD player, then we can easily see a loop formed by the ground wire in the AC power lines and the interconnect.
This loop really has nothing to do with grounding, it's just a loop formed by these wires. Unfortunately these loops more often than not have a rather large area and this is the source of the problem. You can look at it as a very large one-turn coil and part of this coil is the interconnect. We all know what happens if you present an alternating magnetic field in a coil; it induces current.
So now we have a current flowing in the interconnect ground wire caused by stray alternating magnetic fields.
Not good.
As you said, some equipment do not have the signal ground connected to wall socket ground. Then, obviously, there is no loop. Balanced connections are less prone to ground loops. An output or intput transformer also breaks any ground loops.About grounding the chassis: safety regulations allow for a metal chassis to not be grounded if double insulation is applied, and many modern audio equipment do indeed not have the chassis grounded. In europe much of the audio equipment does not even have a wall connector that uses the ground wire! In these cases, the metal chassis is often connected to signal ground.
Related to this is the problem that may occur when you use different wall sockets to power your audio gear. Or connecting the ground to a water pipe like someone mentioned. This will make things worse as you are now greatly enlarging the loop and bypassing the safety guards which may render them useless. Always get the power for your equipment from the same point.
I want to repeat, this has nothing to do with grounding perse. It is just a loop of wires.
I agree with Ron that the naming is unfortunate. There really is no such thing as 'signal ground' and I much prefer the designation 'circuit common'. The aparatus will function perfectly without a wall socket ground wire (dismissing safety). In fact, for normal operation I would expect there to be no audio currents running through the AC wall socket ground wire at all.
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Follow Ups
- Re: Chassis ground vs. source signal ground? - arend-jan 04:04:53 04/28/07 (0)
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