Wednesday, June 26, 2013
More on Ground Loops
If you read this blog, you may have noticed many articles on the potential sources for ground loops. IMHO, proper grounding is one of the biggest causes of signal degradation, especially in audio systems. Proper electrical grounding at all points in your home entertainment system improves audio quality by lowering crosstalk (muted levels of nearby signals), lowering RFI and EMI effects (sporadic oscillations or hum), and literally cleaning up the grunge at very low audio levels such as when reverberations decay into the silence (smearing of clarity near the “noise floor”). Even if you have taken great pains to minimize the influences of such effects by installing quality line filters and assuring yourself of running all of your gear on the same electrical phase, grounding issues still creep into your system through other connected components.
The average home theater system today has numerous connections to it above and beyond the realm of RCA or balanced patch cords. Ethernet connections, antenna feeds, HDMI cables, and separate ground wires (such as from a turntable) all may be potential sources for grounding issues. Keeping everything straight is not that difficult IF you consider their influences as part of the entire system. Say for example you started with a stereo that grew to a surround sound system that grew to a cable television connection that then added a media streamer. Each time you added something to your system, did you just hook it up from the instructions or did you consider proper grounding? I suspect that the answer to this is the former since the emotion of the moment, the excitement to hear or see this new piece of gear in action, is what controlled your installation efforts.
And once you turned on your system, did you notice anything that wasn’t there before? Did the system perform admirably or was there a compromise noticed after time that made the sound change? If the sound adversely changed, it is almost certain that what you just added made this change. And it is almost certain that this change is due to how the new grounds within that new addition impacted the overall grounding scheme of the combined systems.
If you have ever been to an outdoor concert and heard hum coming from the PA system, you know how annoying major grounding issues can be. But in your home theater hopefully these types of major grounding issues are already resolved. If not, the easiest way to isolate the source of a grounding issue is to disconnect each piece one at a time from your system. When the problem goes away, you have identified the source. But then what? You know what is wrong but how do you know what to do about it?
Tracking down the source of the problem within the individual piece or added system takes time and thought, and a clear understanding of what a ground loop is. Basically, a ground loop is a path that electricity takes when there are multiple paths from which to choose. Like a lightning strike that has one main bolt and several branches like an inverted tree, electricity will always flow at the path of least resistance (the main bolt in a lightning flash or here the primary ground wire) but will also flow at any other possible path (the branches of a lightning flash or here the ground loop). You can also visually see this effect of you pour water into a bucket with one big hole and a much, much smaller hole. Not only will the water rush out the big hole but it will also trickle out the little hole and it is the little hole that provides a visual representation of the effects of a ground loop.
Lightning Takes Many Paths to Ground
So let’s get back to the effects of ground loops in the home theater. Below is a grounding diagram provided by TYCO Electronics to help computer network installers properly ground the newer CAT6a shielded network cables (using shielded twisted pairs or type STP). There are several sources of ground loops built into this wiring diagram, each detrimental to the overall noise in that system. See if you can tell where they are.
The most obvious ground loop is through the power plugs of the workstation and the equipment in the network equipment rack through the new shielded CAT6a cable. If the ground of the CAT6a female jack on the workstation is connected to the same point as the ground in the power plug (and it most certainly will be), this is where the source of the problem occurs. Lifting the ground of the network equipment or workstation (such as by using a “cheater” plug that converts a 3-pin power connection to a 2-pin connection) will eliminate the ground loop but in doing so it will raise the risk of electrical shock or worse electrocution and is therefore not advised.
The most effective way to ground a shield is to ground it at the source and not the destination. Polarized RCA patch cords in audio systems already use this grounding method to help reduce ground loop effects introduced from the shields and the ground wires inside of the patch cords. The arrows on these cables indicate which end is connected to the destination (arrow points at the destination). In reality, this arrow tells you which end of the cable the shield is NOT connected to ground (shield is not connected to the outer case on this end).
Polarized RCA Interconnect Cables
This same practice would be beneficial with shielded network cables. Somewhere along this path, the ground must be lifted and the best place to do so is at the workstation CAT6a female jack (the destination). Doing so will retain the noise immunity provided by the use of a shielded network cable and eliminate the ground loop. Can this be done easily? Yes. Here, the shield-to-ground path must be literally disconnected but can you think of a way to do this? Here is the answer: use an unshielded CAT6a cable from the wall jack to the workstation.
If the new system you are connecting to your already quiet home entertainment system suddenly becomes noisy, it is easy to see that the source of the noise may not be a simple thing to eliminate although through elimination you have identified the source of that noise. Connecting any new component to your existing system can introduce ground loops and increase this undesired noise. My eBooks on getting more sound from your home entertainment system (see the Extreme Audio series below) discuss where to look for such potential sources for grounding issues at every point along the way in your home entertainment system. Using these eBooks, you may be able to identify where the three remaining sources of potential grounding issues are in the above TECO grounding diagram (yes, there are three other sources for potential problems).
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