Mackie 408S Owner's Manual download pdf (Page 30)

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TS phone plug. The balanced-to-unbalanced

connection has been anticipated in the wiring

of Mackie jacks. A 1/4" TS plug inserted into a

1/4" TRS balanced input, for example, auto-

matically unbalances the input and makes all

the right connections. Conversely, a 1/4" TRS

plug inserted into a 1/4" unbalanced input

automatically ties the ring (low or cold) to

ground (earth).

Grounding

Grounding exists in your audio system for

two reasons: product safety and noise reduc-

tion. The third wire on the power cord exists

for product safety. It provides a low-resistance

path back to the electrical service to protect

the users of the product from electrical shock.

Hopefully, the resistance to ground through the

safety ground (third wire) is lower than that

through the user/operator to ground. If you re-

move this connection (by breaking or cutting

the pin off, or by using a ‘ground cheater’), this

alternate ground path ceases to exist, which is

a safety hazard.

The metal chassis of the product, the

ground connections provided by the various

connectors, and the shields within your con-

necting cables provide a low-potential point for

noise signals. The goal is to provide a lower im-

pedance path to ground for noise signals than

through the signal wiring. Doing so helps

minimize hum, buzz, and other extraneous

non-audio signals.

Many “authorities” tell you that shields

should be connected only 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. Use balanced lines if at all possible. They

provide better immunity to induced noise

and ground loops. Remember that you can

balance a line by inserting in-line a piece of

equipment that has a balanced output.

2. Avoid using three-phase power lines since

they are usually used for air conditioning

and other heavy power equipment. If using

240VAC single phase with center-ground

power, connect all audio equipment to one

side of the AC power, and all lighting and

other equipment to the other side.

3. Be sure all AC outlet safety grounds are

connected to one common point in a star

ground arrangement. This common ground

point should then tie back to earth ground

at the service entrance by one heavy

stranded wire, #2 gauge or larger.

4. Don’t cut the third pin off the power cord.

Carry some ground-lifter adapters and use

them only if you have to plug into an

ancient two-wire outlet.

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. If you bundle your cables together, don’t

bundle AC wiring and audio wiring to-

gether. Bundle them separately.

7. If your sound system insists on humming,

you may want to teach it the words.

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