MACKIE SRM350 2-WAY - Manual (Page 15)

15
Bad sound!
• Is it loud and distorted? Follow the
procedures described in the “Quick
Start” section to verify that the levels
are set properly.
• Is the input connector plugged com-
pletely into the jack? Be sure all
connections are secure. It’s a good idea
to periodically clean all electrical
connections with a non-lubricating
electrical contact cleaner.
Noise
• Make sure all connections to the active
speakers are good.
• Make sure none of the signal cables are
routed near AC cables, power trans-
formers, or other EMI-inducing devices.
• Is there a light dimmer or other SCR-
based device on the same AC circuit as
the SRM350? Use an AC line filter or
plug the SRM350 into a different AC
circuit.
Hum
• Turn the LEVEL control all the way
down. If the noise disappears, it’s
coming from the signal source. If not,
try disconnecting the cable connected to
the INPUT jack. If the noise disappears,
it could be a “ground loop,” rather than
a problem with the SRM350. Try some
of the following troubleshooting ideas:
• Use balanced connections throughout
your system for the best noise rejection.
• Whenever possible, plug all the audio
equipment’s linecords into outlets which
share a common ground (see the dia-
gram on page 13). The distance between
the outlets and the common ground
should be as short as possible.
Never remove the ground
pin on the power cord of
the SRM350 or any other
component. This is very
dangerous.
• The hum may appear when using an
unbalanced source (consumer preamp,
CD player, VCR, etc.). This is caused by
the unbalanced-to-balanced interface
between the devices (and exacerbated
by the fact that most consumer audio
equipment have a two-wire linecord,
without the third-pin safety ground).
shield
1 2
3
XLR RCA
3-Conductor Cable
Use an interconnect cable wired as
shown below. The important point is
that the shield and the wire from the
XLR pin 3 are joined at the RCA
(source) end.
• Disconnect any cables which come in
from outside, such as cable TV, satellite
TV or roof top antennas. They must be
disconnected from every part of your
system, such as the TV, VCR and
preamp. If the hum goes away, you can
add a “ground loop isolator” in your
cable line. This is an inexpensive device
available from video or TV dealers, or
you can make your own from two TV
baluns (standard TV 75/300 ohm
adaptors):
The baluns are threaded at one end
(75 ohm) to fit TV coax cable and have
two wires at the other end (300 ohm).
They will not affect the video quality.
• If the hum persists, try removing compo-
nents one at a time from the back of the
mixer or preamplifier, and check for hum
each time (turn off your equipment
before you undo any connections). It is
fairly common to find more than one
problem.
• If your preamp or mixer are the only
things connected to the SRM350s and
the hum is still there, try different
connection cables, or move the preamp/
mixer to another location.
join (+insulate) Balun Balun