Mackie 408M Owner's Manual - Page 29

6. Write the RA number in BIG PRINT on top of the box. 7. Ship the powered mixer to us. We suggest insurance for all forms of cartage. Ship to this address: Mackie Designs SERVICE DEPARTMENT 16140 Wood-Red Rd. NE, Ste. 5 Woodinville, WA 98072 8. We'll try to fix the mixer within three business days. Ask Tech Support for current turn-around times when you call for your RA number. We normally send everything back prepaid using UPS Orange (three-day air). However, if you rush your powered mixer to us by next-day air, we'll treat it in kind by shipping it back the same way in which it was received. This paragraph does not necessarily apply to non-warranty service. APPENDIX B: Some Arcane Mysteries Illuminated Balanced Lines Unbalancing a Line Balanced lines offer increased immunity to external noise (specifically, hum and buzz). Because a balanced system is able to minimize noise, it is the preferred interconnect method, especially in cases where very long lengths of cable are being used. A long unbalanced cable carries with it more opportunity for noise to get into a system - having balanced inputs means very little noise will enter the system via snakes and other cables that typically must run a long length. A balanced line is a three-wire system where two wires carry the signal and the third is a ground wire that shields the inner conductors from EMI. The two inner conductors carry the same signal, but with opposite polarity. The balanced input amplifies only the difference between the two conductors. But a signal that is common to both conductors, and in phase, is rejected (canceled out) at the balanced input. This includes hum from AC lines or other EMI induced noise. An unbalanced line does not have this noise-rejecting capability because it has only two conductors. One conductor carries the signal and the other is a ground wire that shields the inner conductor. Any hum or EMI noise that gets through the shield is added to the signal and amplified at the unbalanced input. Often the hum can be louder than the signal itself! 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 will also be connected to the ground 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 and the ground connections of the balanced input. If there are ground-loop problems, try connecting the unbalanced ground connection only to the input low connection, and leaving the input ground 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" 29