SLEEVE TIP SLEEVE TIP
Figure D: RCA Plug

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 insert 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 center post and the ground (earth) or shield to the surrounding “basket.”

UNBALANCING A LINE

In most studio, stage and sound reinforcement situations, there is a combination of balanced and unbalanced inputs and outputs on the various pieces of equipment. This usually 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

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 special adapters to interconnect your equipment. For example, you may need a balanced XLR female 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 balanced 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 return from the unit to the mixer is on the ring.

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