Metric Halo Mobile I/O - Manual (Page 336)

Troubleshooting Guide
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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 uses less
power than is supplied by a single circuit from your premises’ wiring (generally 10-15 amps in residential
installations and 20 amps in commercial installations).
It is usually a bad idea to put some devices in your system on a power conditioner and other devices on a
separate strip, socket or conditioner, unless you have a technical ground. The power conditioner can introduce
a ground differential.
The power supply provided with Mac laptops does not have a hard ground. This means that if the laptop
is plugged in, it will dump high frequency buzz into the ground. That ground is shared with the Mobile I/
O FireWire cable. If Mobile I/O will be connected unbalanced to other audio gear, the ground buzz can
contaminate the signal if the Mobile I/O is not hard-grounded to the same ground as your other audio gear.
To hard ground the Mobile I/O you will need to use a 3-pin power cable on the Mobile I/O power supply
and power the Mobile I/O with the power supply. Plug the 3-pin IEC power cable into the same circuit and
same ground as your other gear.
On the other hand, if you are encountering ground loop problems while operating with the Mobile I/O’s power
supply, you may find that lifting the Mobile I/O’s ground resolves the problem. This can be accomplished by
using a 2-Pin IEC cable (without the third ground pin), or by using a ground lift block (generally available in
hardware stores, also known as a 3 pin to 2 pin converter). In general, it is better to resolve the fundamental
grounding problems in your system, but this is a quick fix that may help. There are no hard and fast rules for
solving this type of problem other than fixing the fundamental grounding issues, so if you go this route, you
will have to experiment with lifting various grounds in your system until you find the magic combination. Or
switch to balanced interconnects.