Metric Halo 2882 operating guide - Manual (Page 97)

Mobile I/O User’s Guide
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It is usually a bad idea to put some devices in your system on a power con-
ditioner 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 fun-
damental grounding issues, so if you go this route, you will have to experi-
ment with lifting various grounds in your system until you find the magic
combination. Or switch to balanced interconnects.
Finally, the Apple Cinema Display has a known issue with its backlight dim-
mer. If you run the Apple Cinema Display with its backlight at anything other
than full brightness, the backlight dimmer will introduce a midrange buzz
into the system ground which will appear in unbalanced interconnects
(input and output) with Mobile I/O. This issue affects other devices that con-
nect to the computer’s system ground. The work around is to run the display
at full brightness, or use balanced interconnects.