Mackie SR408 / SR568 Owner's Manual - Page 78

the cable pick up hum more efficiently.

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Many "authorities" tell you that shields should only be connected at one end. Sometimes this can be true, but for most (99%) audio systems, it is unnecessary. If you do everything else correctly, you should be able to connect every component of your audio system using standard, off-the-shelf connecting cables that are available at any music store. Here are some guidelines: 1. All return lines to the stage should be balanced. At a minimum, they should be impedance balanced. Remember that you can balance a line by inserting a piece of equipment in-line that has a balanced output. 2. Run your own AC power wiring from the stage for the mixer and related equipment. Don't use the "conveniently located" receptacle thoughtfully provided by the management for your use. You have no idea how it's wired or grounded. 3. Carry an outlet tester, available at any wellstocked hardware store. Use it to tell you if the outlet you're about to plug into is wired correctly. Consider it cheap insurance. 4. If you carry enough equipment that you need to wire directly into the electrical service, then use a voltmeter to ensure that the line voltage is correct, then use the outlet tester mentioned in #3, above. Do this before you connect any of your audio equipment. Chances are that your 120V gear won't be too happy if it sees 220V for any length of time. 5. Cables that are too long are less likely to pick up hum if you uncoil them in their entirety, and then find a place to stow the excess. Leaving the excess coiled only helps the cable pick up hum more efficiently. 6. Don't run unbalanced lines to or from the stage. It's not the impedance, it's the fact that they're unbalanced. It's a good idea to use a direct box to make the unbalanced source look like a microphone. 7. For really extreme cases, you may need to insert 1:1 or isolation transformers into each return line from the front-of-house location to your amp racks. 8. Don't cut the third pin off of the power cord. Carry some ground-lifter adapters and use them only when you have to plug into an ancient two-wire outlet. 9. If you bundle your cables together, don't bundle AC wiring and audio wiring together. Bundle them separately. 10.If your sound system insists on humming, you may need to teach it the words. 78

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78
Many “authorities” tell you that shields
should only be connected at one end. Some-
times this can be true, but for most (99%)
audio systems, it is unnecessary. If you do ev-
erything else correctly, you should be able to
connect every component of your audio system
using standard, off-the-shelf connecting cables
that are available at any music store.
Here are some guidelines:
1.
All return lines to the stage should be
balanced. At a minimum, they should be
impedance balanced. Remember that you can
balance a line by inserting a piece of equip-
ment in-line that has a balanced output.
2.
Run your own AC power wiring from the
stage for the mixer and related equipment.
Don’t use the “conveniently located”
receptacle thoughtfully provided by the
management for your use. You have no idea
how it’s wired or grounded.
3.
Carry an outlet tester, available at any well-
stocked hardware store. Use it to tell you if
the outlet you’re about to plug into is wired
correctly. Consider it cheap insurance.
4.
If you carry enough equipment that you
need to wire directly into the electrical
service, then use a voltmeter to ensure that
the line voltage is correct, then use the
outlet tester mentioned in #3, above. Do
this before you connect any of your audio
equipment. Chances are that your 120V
gear won’t be too happy if it sees 220V for
any length of time.
5.
Cables that are too long are less likely to
pick up hum if you uncoil them in their
entirety, and then find a place to stow the
excess. Leaving the excess coiled only helps
the cable pick up hum more efficiently.
6.
Don’t run unbalanced lines to or from the
stage. It’s not the impedance, it’s the fact
that they’re unbalanced. It’s a good idea to
use a direct box to make the unbalanced
source look like a microphone.
7.
For really extreme cases, you may need to
insert 1:1 or isolation transformers into
each return line from the front-of-house
location to your amp racks.
8.
Don’t cut the third pin off of the power
cord. Carry some ground-lifter adapters
and use them only when you have to plug
into an ancient two-wire outlet.
9.
If you bundle your cables together, don’t
bundle AC wiring and audio wiring to-
gether. Bundle them separately.
10.
If your sound system insists on humming,
you may need to teach it the words.