Emu XL-7 & MP-7 User's Group

Before this gets too out of hand, I figured I'd offer some insights
into what causes hum.  The answer?  Just about everything.  =)  See the
last paragraph for an issue specific to the XL-7.

As with all gear, ground loops can be a problem.  If two devices are
plugged in to each other via audio cables and have different ground
references (i.e. plugged into different AC circuits), some of the AC
power "leaks" through the audio cables, causing 60 cycle (and possibly
harmonics) hum.  To solve this problem, search around the web for tips
on reducing ground loops.  I'm sure there are many more comprehensive
sites out there than what I can offer.

Second, most analog gear (especially mixers) is sensitive to
electromagnetic interference.  Particularly nasty culprits are computer
monitors, halogen lamps, computer cases, refrigerators, etc.  The only
solution here is to try and physically rearrange the interfering
devices.

Finally, the XL-7 has a requirement that the front panel be grounded to
the main chassis.  The symptom of this is buzzing from the HEADPHONE
JACK ONLY.  If you also have hum out of the mains or subs, go back and
reread the previous two paragraphs, because this is not your issue.  If
you must open up your unit (eeek, that didn't sound good) make sure to
check that all ribbon cables are snug, as they have a tendency to come
loose when you pull the two pieces apart.  Also, make sure to put all
the screws back in when you put it together again.  This should ensure
that grounding comes from the chassis rather than the headphone ribbon
cable (the littlest one).

Hope this helps,
  -Aaron

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