Originally Posted by peniku8
you should basically only lose the 6db gain, which increases S/N.
Originally Posted by Trimlock
that happens because most consumer brands attach the signal wire to the ground wire.
That happens because devices leak current onto the ground line (including audio devices.)
Audio devices use the ground line as 0V reference for signal return current; and often amplify the differential.
If they floated the reference or used floated balanced split-phase (like real XLR does), then it won't be a problem since the nasty currents isn't contaminating the signal-path (in that case).
What really makes it worse is that the leakage current is often 60hz (i.e. mains AC), so you get a hum.
Also MOVs can dump surges and spikes onto the ground line from H-G and N-G, giving you noise;
so can power supplies...
So can stray electromagnetic and electrostatic fields too!
Grounding is required to save your life in case of a device fault where it energizes a shield or chassis to mains-voltage, the current can return to the pole transformer tripping the circuit breaker / fuses.
GFCI's take that a step further and detect current loss through any other path than the neutral return, interrupting the mains-voltage and thus: potentially saving your life.
Unfortunately all of those paths are giant loops, coupling all devices together.
If an audio device couples the shield and ground together at both ends, that too doesn't help any.
Hum eliminators work by optical or galvanic decoupling, the noise on either side, stays on that side.
There is a cost that you pay for doing that: bandwidth limiting and reduced S/N, being the two main ones.
In commercial installations (such as radio stations and studios) they often float the audio rack with rubber mats so that it doesn't touch the ground, and they use series-grounding via a single ground conductor rather than star grounding via multiple parallel ground conductors; forcing the electrons down a single path.
The ground wire at your service panel isn't the same as the ground wire at your wallsockets. That wire exists only to short lightning (and any other high-voltage nasties) to dirt, rather than letting it find ground via you or your electronics. It never carries mains-current (or at least: should-never); where as the ground wires in the walls can/might carry full mains-current. This is why sub-panel neutrals aren't re-bonded to panel ground (the dirt should NEVER be used as a mains-current carrier! That's what neutrals and dedicated ["ground"] return-conductors are for!)
Consider yourself edumacated