Video Ground Loop Isolator Schematic
Car Audio Ground Loop Isolator Schematic
Ground Loop Isolator Schematic

A little bit of knowledge is a dangerous thing -- that's what your old Grandpa used to say. Car audio systems seem like about the simplest proposition in the world; use your brain, follow the cables, and connect stuff where it's supposed to go. What's hard about that? But audio systems are just like any other electrical system, and a lot can go wrong in the details. Once of them is the nefarious 'ground loop,' which is a phenomena that induces a maddening hum in the speakers. A 'ground loop isolator' is a good temporary fix, but this might be a good time to talk to a pro about finding a more permanent solution.

Step 1

Turn the system off. Open the trunk or hatch and locate the amplifier, or locate the amp and its RCA jacks wherever they are in the car.

Step 2

Unplug the RCA cables from the amplifier. Plug the red and white RCA connectors into their respective -- usually color-coded -- jacks on the ground loop isolator.

A ground loop isolator prevents interference in a ground loop circuit. A ground loop circuit is one in which two or more circuits are connected to the same ground wire. Ideally, all circuits in a ground loop circuit have the same voltage potential. The circuit diagram illustrates a simple ground loop. Two circuits share a common path to ground. This path has a resistance of.Ideally, the ground conductor would have no resistance (=), yielding no voltage drop across it, =, keeping the connection point between the circuits at a constant ground potential.In that case, the output of circuit 2 is simply =.

Step 3

Plug the red and white RCA cables extending from the ground loop isolator into the amplifier.

Ground the ground loop isolator by screwing the terminal into a bare metal spot of the car or by plugging it in to the negative terminal of the amp. Some ground loop isolators are self-grounded while others require this step. If the ground loop isolator has additional wires -- beside the RCA cables-- they are for grounding.

Tip

Ground loop isolators are considered a band-aid, as they suppress a problem that was created during installation. The only true way to fix the problem is to find the cause of the noise and eliminate it. Sometimes running the power wire down one side of the car and the RCA cables down the other will fix the problem. One common cause is using power wire that is too small for the audio system. Both induce a magnetic field in the signal wire, which is likely the cause of your noise.

Photo Credits

rca cables isolated image by JoLin from Fotolia.com

In an electrical system, a ground loop or earth loop occurs when two points of a circuit both intended to be at ground reference potential have a potential between them.^[1] This can be caused, for example, in a signal circuit referenced to ground, if enough current is flowing in the ground to cause two points to be at different potentials.

Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. The use of differential connections can provide rejections of ground-induced interference. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide.

Ground loop at 50 Hz captured with audio equipment.
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3Common ground loops
5In low frequency audio and instrumentation systems

Description[edit]

A ground loop is caused by the interconnection of electrical equipment that results in there being multiple paths to ground, so a closed conductive loop is formed. A common example is two pieces of electrical equipment, A and B, each connected to a utility outlet by a 3 conductor cable and plug, containing a protective ground conductor, in accordance with normal safety regulations and practice. This only becomes a problem when one or more signal cables are then connected between A and B, to pass data or audio signals from one to the other. The shield (screen) of the data cable is typically connected to the grounded equipment chassis of both A and B, forming a closed loop with the ground conductors of the power cords, which are connected through the building utility ground wire. This is the ground loop.

In the vicinity of electric power wiring there will always be stray magnetic fields oscillating at the utility frequency, 50 or 60 hertz. These ambient magnetic fields passing through the ground loop will induce a current in the loop by electromagnetic induction. In effect, the ground loop acts as a single-turn secondary winding of a transformer, the primary being the summation of all current carrying conductors nearby. The amount of current induced will depend on the magnitude of nearby utility currents and their proximity. The presence of high power equipment such as industrial motors or transformers can increase the interference. Since the wire ground loop usually has very low resistance, often below one ohm, even weak magnetic fields can induce significant currents.

Since the ground conductor of the signal cable linking the two pieces of equipment A and B is part of the signal path of the cable, the alternating ground current flowing through the cable can introduce electrical interference in the signal. The induced alternating current flowing through the resistance of the cable ground conductor will cause a small AC voltage drop across the cable ground. This is added to the signal applied to the input of the next stage. In audio equipment such as sound systems, the 50 or 60 Hz interference may be heard as a hum in the speakers. In a video system it may cause onscreen 'snow' noise, or syncing problems. In computer cables it can cause slowdowns or failures of data transfer.

Representative circuit[edit]

Simplified circuit illustrating a ground loop.

The circuit diagram illustrates a simple ground loop. Two circuits share a common path to ground. This path has a resistance of ${displaystyle scriptstyle R_{G}}$ . Ideally, the ground conductor would have no resistance ( ${displaystyle scriptstyle R_{G};=;0}$ ), yielding no voltage drop across it, ${displaystyle scriptstyle V_{G}=0}$ , keeping the connection point between the circuits at a constant ground potential. In that case, the output of circuit 2 is simply ${displaystyle scriptstyle V_{text{out}}=V_{2}}$ .

However, if ${displaystyle scriptstyle R_{G}neq 0}$ , it and ${displaystyle scriptstyle R_{1}}$ together form a voltage di

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Description[edit]

Representative circuit[edit]

Ground Loop Isolator Schematic