Behringer MX9000 user manual Start-Up, Channel setting up procedure

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Well, all other things being equal, the amount of mains hum picked up by a cable is independent of the signal level. Speaker lines run 50 or more volts, enough to diminish the effect of mains radiation to vanishingly small even with no screen. (In fact, at these voltages another effect comes into play: capacitive resistance. It is positively undesirable to use screened cable to wire an amp to a speaker. Speaker leads should be as thick and short as possible, with XLR or wound post terminals.) Line-level signals can usually be run unbalanced over short or moderate distances (rack to desk etc.), but NOT from the back of the hall to the stage, always provided that there are no earth loops (see section 8.3 “Looming Problems” A loop acts as an ariel, positively inviting electromagnetic radiation to flow around the system). Microphone lines, however, are another story altogether.

Most microphones generate not volts, but millivolts. Protecting such a low level signal requires a more sophisticated solution. Hence, all mic networks run along balanced lines. It works like this. The mic diaphragm moves forwards and backwards according to the air pressure increases and decreases that constitute sound waves. Diaphragm movement generates a corresponding electrical signal, which is either positive or negative depending on the direction of travel. The +ve and -ve signals are mirror images of each other: if you shorted

+and - you’d end up with nothing: one would cancel out the other. In fact this cancelling effect is what makes the balanced line work. Instead of simply shorting the negative line to earth, as would be the case in an unbalanced system (losing half the signal, or 6 dB, in the process), the two lines are kept apart until they reach an electronic (or transformer) balanced input.

Here something exquisitely simple happens:

You may not know this, but whenever a signal is amplified, its polarity is reversed. By inverting the negative side and adding it 1:1 to an unchanged positive, a balanced input wastes none of the available signal energy. In doing so, it also subtracts all the radiation picked up along the line. Random noise is unaffected, but you’ll hear no hum, and much reduced thyristor noise (from poorly-screened lighting dimmers). Live, you could not run a rig without balanced mic lines, and although in the studio cable runs are shorter, the recorded medium’s demand on signal to noise is far greater.

When patching a balanced input/output to an unbalanced one, simply short the -ve and screen together at the unbalanced input or output.

Fig. 12.1: A balanced microphone line

13. START-UP

13.1 A-channel setting up procedure

13.1.1Selecting inputs

 

MICROPHONE:

MIC/LINE switch (S1) UP,PAD switch (S1a) UP,

FLIP switch (S3) UP

LINE:

MIC/LINE switch DOWN,

FLIP switch UP

TAPE:

 

FLIP switch DOWN

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Contents Eurodesk MX9000 Safety Instructions Detailed Safety InstructionsForeword Table of Content Track Recording with 2 Samplers Manual Eurodesk OverviewPSU Power Supply Unit MeteringInput switching INPUT/OUTPUT ChannelChannel strip Input gain setting Channel input switching architectureMain equalizer Aux sendsRouting and muting Aux sendsChannel RoutingInserts B-channelSubgroup and Direct Outputs SubgroupsStereo subgroup channel schematic Master Panel Direct outputsAux masters Aux sends Stereo aux returns MIX-B master Mix-BMonitoring MonitoringHeadphones PhonesPFL/SOLO TalkbackConnections Rear panelPower supply unit connector Subgroup inserts Main balanced outputs 10 MIX-B operating level switch and phantom power switch Plug soldering guide Page Patchfield Normalized bayPatchfield Example of patchbay configurations Looming problems Wiring for bay 8 for advanced wiring scheme refer to sectionEqualization Gain Optimization Impedances and Tuning Unbalanced LinesChannel setting up procedure START-UPDesk/tape setting up procedures Track Midi SUITE/DANCE Production Studio Auxless headphones mix SendsSlightly more complicated auxless headphones mix ReturnsTrack Recording with 2 Samplers Lining up record/sample inputsMixdown RecordingHeadphones Professional 24-TRACK StudioTab .1 Channel assignment Very tricky headphones Live P.A. with 2-TRACK RecordingWet monitoring Tab .1 Channel assignments 2-track Live Concert with 24-TRACK Recording Tab .2 Front/rear/stage monitors routing Expanding the Eurodesk MX9000 TimecodeConnections AlignmentBouncing Sequencing LiveINPUT/OUTPUT Configuration ModificationsAux sends post EQ MIX-B source post faderLED meters pre fader Specifications DBr ref. +4 dBu, 24 chs. assigned input B & set @ unity gain Warranty § 1 Warranty CARD/ONLINE RegistrationPage
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