Troubleshooting Guide
498
Ground Loops
The
MHLink Gigabit Ethernet backplane
is immune to ground loops between 3d boxes plugged
in at remote locations. This is because all Ethernet connections are transformer-coupled at both
ends, providing galvanic isolation from the grounding issues normally caused by connecting
devices running on different AC power circuits.
In turn, the "twist" of the Ethernet cable Unshielded Twisted Pair (UTP) wiring provides rejection
of RF noise interference over long (and short) cable runs.
Please remember however, that local ground loops are still possible any time you connect ana-
log or digital hardware devices.
Audio systems, in general, are susceptible to ground loop problems. Digital Audio Interfaces for comput-
ers are even more susceptible to grounding issues since they must interface with the computer’s system
ground, which tends to be much more dirty than the ground used by audio gear. By taking care when you
connect the various components of your audio system you can avoid the hums, buzzes, and noises that
characterize ground loops and other grounding problems.
First of all, most grounding issues go away if you utilize balanced interconnects between your audio gear.
Balanced interconnects inherently reject ground differentials and common mode interference introduced
by grounding problems. Balanced connections are not much more expensive than unbalanced connections
and solve so many problems that if both ends of the connection support balanced interconnect, you should
not even consider using unbalanced cables.
You may get the idea that we hate unbalanced connections. You’re right. We do. You should too.
If you have to use unbalanced connections, or if any ground-related problems remain, you will find that
the key to the issue is ensuring that you have a common hard ground between all the gear that you are
interfacing. This is commonly referred to as a technical ground. A technical ground is characterized by a
consistent low impedance path between each device and a common reference ground, ideally connected
directly to earth ground. The above is sometimes difficult due to electrical wiring problems in the house,
studio, or stage you are using. In the extreme case, you may need to hire a qualified electrician to untangle
and correct electrical service problems in your working environment.
Unbalanced connections are a fact of life when interfacing with guitar amps, and, paradoxically, guitar amps
are extremely sensitive to grounding issues since they use so much gain to achieve the effect of a “Guitar
Amp”. If you will be interfacing with guitars and guitar amps, you need to be very careful about grounding.
Common electrical wiring approaches to residential installations, and sub-par studio and stage installations
use daisy-chained grounds for ease of installation and economy. Unfortunately, daisy-chained grounds can
introduce significant ground differentials between sockets, and these differentials can vary depending on
other loads (like refrigerators, TV’s and other household appliances) on the circuit.
Other problems with electrical service installations are improper wiring of power phases to the three-phase
service and improper connections between the safety ground and hot legs of the three-phase service.
These types of problems tend to be characterized by loud 60Hz hums in the audio system. Unfortunately,
these types of problems extend well beyond noise in your audio system to genuine safety hazards. If you
determine that your electrical wiring has problems beyond a simple daisy-chained ground, you should
consult a licensed electrician immediately, as ignoring these problems can damage either you or your gear.
If you do not have a well implemented technical ground, you will want to ensure that all of the devices
in your audio system are plugged into the same phase and same ground. You can generally accomplish
this by running all your gear off of the same socket (using a power strip or power conditioner) if your gear
