A flowing through the building's ground system G to the neutral wire at the utility ground bonding point at the service panel. The ground loop between components C1 and C2 creates a second parallel path for the current. The current divides, with some passing through component C1, the signal cable S ground conductor, C2 and back through the outlet into the ground system G. The AC voltage drop across the cable's ground conductor from this current introduces hum or interference into component C2. Solutions The solution to ground loop noise is to break the ground loop, or otherwise prevent the current from flowing. Several approaches are available. Group the cables involved in the ground loop into a bundle or snake. The ground loop still exists, but the two sides of the loop are close together, so stray magnetic fields induce equal currents in both sides, which cancel out. Create a break in the signal cable shield conductor. The break should be at the load end. This is often called ground lifting. It is the simplest solution; it leaves the ground currents to flow through the other arm of the loop. Some sound system components have ground lifting switches at inputs, which disconnect the ground. One problem with this solution is if the other ground path to the component is removed, it will leave the component ungrounded and stray leakage currents may cause a very loud hum in the output, possibly damaging speakers. Put a small resistor of about 10Ω in the cable shield conductor, at the load end. This is large enough to reduce magnetic-field-induced currents but small enough to keep the component grounded if the other ground path is removed. In high-frequency systems this solution leads to impedance mismatch and leakage of the signal onto the shield, where it can radiate to create RFI, or, symmetrically through the same mechanism, external signals or noise can be received by the shield and mixed into the desired signal. Use a ground loop isolation transformer in the cable. This is considered the best solution, as it breaks the DC connection between components while passing the differential signal on the line. Even if one or both components are ungrounded, no noise will be introduced. The better isolation transformers have grounded shields between the two sets of windings. A transformer generally introduces some distortion in frequency response. A transformer designed specifically for the relevant