Vasr
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2) If I lift the ground of the wall socket where the TP is plugged in (that is to say, all audio gear), but my DAC is connected to the PC by the USB cable, wouldn't that connection work as a shunt to the grounded wall socket where the pc is connected?
3) In Argentina, all buildings have circuit breakers installed. I'm not an electrician, but in the event of a non-grounded device malfunctioning and letting the current go through the chassis, wouldn't this circuit breaker cut all power?
Typically, you don't want audio signal cables to act as the safety electrical ground (let us call it "earth ground") for the equipment as they tend to be connected to rather sensitive components and even a momentary high-voltage surge through them can damage things or they may melt and leave the equipment ungrounded. The ground loop in the signals we are hearing and trying to fix are in the order of mVs to a volt, not the 110 or 220v electricity supply.
Part of the confusion in this area comes from the use of the "ground" in two different contexts - as the "safety wire" in case of electric shorts of the main power to the equipment chassis which may create a shock hazard ("earth ground") and the "signal ground" which is the reference ground used for the circuitry and the audio connectors (or even in a balanced connector wired incorrectly). In most equipment (but not necessarily), they both happened to be connected to the chassis as a common conductor. Some audio equipment provide a switch to lift the ground of the signals if necessary, which just separates the signal reference ground from the "earth" ground. Some equipment do this all the time. The "earth" grounding for the main supply connected to the chassis remains the same in these and unrelated.
The "earth" ground for the main power is always connected to the chassis (if conducting material) to handle the case if a live main gets shorted to the chassis inside a device and makes the chassis live and a shock hazard. For this to work, the chassis through the third ground pin will have a low resistance path to the electrical circuit. So, if the live electric wire gets shorted to the chassis, it creates a surge within the live wire through the ground pin that will trip circuit breakers and/or blow out fuses as a safety measure. Without it the chassis is not "earthed" to affect the circuit breakers or fuses. So a short of the live wire to the chassis without a ground pin will just make the chassis live without tripping circuit breakers and a shock hazard.
The schuko plug will simply act as a two-pin plug without the ground attached if the ground clip isn't mated to a corresponding receptacle which is likely what is happening in your case. So you would no longer have that ground protection.
The ground loops (at signal level not in the electrical circuit) happen because there may be a small electric potential between the grounds of two equipment connected to their respective "earth" grounds with different impedance paths to the connector shields (signal grounds). So you have ground loop currents flowing through the signal "ground" affecting the sensed signal. This is more of an annoyance than a safety issue.
This can be solved if the signal is sent through a galvanically-isolated connector, or made differential as in a correct balanced connector, or the unbalanced signal ground is disconnected from the "earth" (chassis) ground or the "earth" ground itself is grouped into a single path to eliminate that potential difference in the signal grounds between two devices when they are connected to "earth" ground in multiple devices.
The preference would be to try it in the order above to fix it. None of the fixes involve permanently removing the "earth" ground from any device. The ground shunt as a last resort connects the chassis/"earth ground" of two pieces of equipment together with a low resistance wire strong enough to carry main voltage so you can disconnect the ground from one device and have the ground pin from the other act as the safety ground for both. The surge through it in case of a short will trip circuit breakers. The audio connectors should not serve this purpose via their shields.