Example systems with and without ground loop problems

Examples of hum-free systems without ground connection

Typical home stereo system where all components have ungrounded (two pin) mains connectors. If the system has radio it uses the built-in antenna or short piece of wire as antenna.

Typical home stereo system where all components have ungrounded (two pin) mains connectors. The radio receiver is connected to the antenna connector in the wall.
Typical home stereo system where all components have ungrounded (two pin) mains connectors. The stereo system is connected to PC soundcard (PC has grounded powwr connector).
Typical home theatre system where all components have ungrounded (two pin) mains connector. The ground ground connection is formed through TV and VCR which are connected cable TV feed.
Stereo system is mostly built using components which have ungrounded power connectors. One system component has grounded power connector.

Small home studio system which consists of grounded and ungrounded equipments which are located near each other. All equipments are powered from one power outlet using multiple output grounded exptension power cord. The system has lots og ground loops but they are very small and they don't have any current flowing in them unless there is strong changung magnetic field near the system.
Typical home theatre system with TV, VCR and radio reciever all connected to the mains antenna outlet. The system components have all ungrounded (2 pin) power connectors. The ground loop is formed through antenna wires but the loop is small and there is normally nor current flowing in those wires so no humming problems are expected unless there is strong magnetic fields nearby. If there is magnetic fields nearby then the problems can be reduced by keeping antenna and audio cables near each other.

Typical home stereo system where all components have ungrounded (two pin) mains connectors. The stereo system is connected to PC soundcard (PC has grounded powwr connector) and the receiver is connected to the wall antenna connector. Problematic ground loop is formed by the connection between the ground pin in PC mains connector and the antenna connector shield in the wall.
Typical home theatre system where all components have ungrounded (two pin) mains connector. The ground ground connection is formed through TV and VCR which are connected cable TV feed.
Typical home theatre system where all components have ungrounded (two pin) mains connector. The ground ground connection is formed through TV and VCR which are connected cable TV feed and through PC connected to system.
The audio system has two or more equipments which have grounded power connector and which are connected to different power outlets.