45
balanced ground (earth) will also be
connected to the ground (earth) at the
unbalanced input. If there are ground-loop
problems, this connection may be left
disconnected at the balanced end.
• When connecting an unbalanced output to a
balanced input, be sure that the signal high
(hot) connections are wired to each other.
The unbalanced ground (earth) connection
should be wired to the low (cold) and the
ground (earth) connections of the balanced
input. If there are ground-loop problems, try
connecting the unbalanced ground (earth)
connection only to the input low (cold)
connection, and leaving the input ground
(earth) connection disconnected.
In some cases, you will have to make up spe-
cial adapters to interconnect your equipment.
For example, you may need a balanced XLR fe-
male connected to an unbalanced
1
⁄
4
" TS
phone plug.
SPECIAL MACKIE CONNECTIONS
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 bal-
anced input, for example, will automatically
unbalance the input and make all the right con-
nections. Conversely, a
1
⁄
4
" TRS plug inserted
into a
1
⁄
4
" unbalanced input will automatically
tie the ring (low or cold) to ground (earth).
TRS Send/Receive Insert Jacks
Mackie’s single-jack inserts are the three-
conductor, TRS-type
1
⁄
4
" phone. They are
unbalanced, but have both the mixer output
(send) and the mixer input (return) signals in
one connector (See Figure F).
The sleeve is the common ground (earth) for
both signals. The send from the mixer to the
external unit is carried on the tip, and the re-
turn from the unit to the mixer is on the ring.
SWITCHED
1
⁄
4
" PHONE JACKS
Switches can be incorporated into
1
⁄
4
"
phone jacks, which are activated by inserting
the plug. These switches may open an insert
loop in a circuit, change the input routing of
the signal or serve other functions. Mackie
uses switches in the channel insert and bus in-
sert jacks, input jacks and AUX returns. We
also use these switches to ground the line-level
inputs when nothing is plugged into them.
In most cases, the plug must be inserted
fully to activate the switch. Mackie takes
advantage of this in some circuits, specifying
circumstances where you are to insert the plug
only partially. See
Special Mackie
Connections
, later in this section.
RCA PLUGS AND JACKS
RCA-type plugs (also known as phono
plugs) and jacks are often used in home stereo
and video equipment and in many other appli-
cations
(Figure D).
They are
unbalanced
and electri-
cally identical to a
1
⁄
4
" TS phone plug or jack
(See Figure C). Connect the signal to the cen-
ter post and the ground (earth) or shield to
the surrounding “basket.”
UNBALANCING A LINE
In most studio, stage and sound reinforce-
ment situations, there is a combination of
balanced and unbalanced inputs and outputs
on the various pieces of equipment. This usu-
ally will not be a problem in making
connections.
• When connecting a balanced output to an
unbalanced input, be sure the signal high
(hot) connections are wired to each other,
and that the balanced signal low (cold)
goes to the ground (earth) connection at
the unbalanced input. In most cases, the
TIP
SLEEVE
TIP
SLEEVE
Figure D: RCA Plug
