Mackie SR244 / SR324 Owner's Manual - Page 53

NOTE: All the 1⁄4" inputs on the SR24•4 are designed to accept both balanced and unbalanced sources. Note: All the 1⁄4" TRS outputs on the SR24•4 implement "impedance balancing". The tip carries the signal while the ring is tied to ground through a resistor whose value mimics the output impedance of the tip circuit. When you plug a balanced cord into one of these outputs, both the tip and ring conductors have equal impedance, significantly improving the common mode characteristics. 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. The Mackie SR24•4 uses switches in the channel insert and bus insert jacks, input jacks and AUX returns. See Special Mackie Connections farther on. 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. Once again, 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 electrically SLEEVE TIP SLEEVE TIP identical to a 1⁄4" TS phone Figure D: RCA plug plug or jack. Connect the signal to the center post and the ground (earth) or shield to the surrounding "basket." There are Tape In and Tape Out RCA jacks on the Mackie SR24•4. 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 hum or radio frequency 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 the Mackie SR24•4 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 connections. 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 The insert jacks on the SR24•4's input channels 1-20 (1-28 on the SR32•4), the SUBS and MAIN MIX L/R are the threeconductor, TRS type 1⁄4" phone. They are Appendices 51