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9

CHAPTER3

More than just a self-powered stage monitor, the MJF-212A 
uses sophisticated amplification and protection circuitry 
and an advanced limiting system to produce consistent 
and predictable results in any system design. This chapter 
will help you understand and harness the power of the 
MJF-212A monitor’s amplifier and audio systems.

AUDIO INPUT

The MJF-212A stage monitor presents a 10 kOhm balanced 
input impedance to a three-pin XLR connector with the 
following connections:

 

Pin 1 — 220 kOhm to chassis and earth ground (ESD 
and RF clamped)

 

Pin 2 — Signal ( + )

 

Pin 3 — Signal ( - )

 

Case — Earth (AC) ground and chassis

 

CAUTION: 

Shorting an input connector pin 

to the case can form a ground loop and 

cause hum.

Pins 2 and 3 carry the input as a differential signal; pin 
2 is hot relative to pin 3, resulting in a positive pressure 
wave when a positive signal is applied to pin 2. Pin 1 is 
connected to earth through a 220 kOhm, 1000 pF, 15 V 
clamp network. 

This ingenious circuit provides virtual ground lift at audio 
frequencies, while allowing unwanted signals to bleed to 
ground. Use standard audio cables with XLR connectors 
for balanced signal sources. Make sure that pin 1 (shield) is 
always connected on both ends of the cable. Telescoping 
grounding schemes are not recommended.

 

CAUTION: 

Make sure that all cabling 

carrying signals to MJF-212A monitors in a 

looped system is wired correctly: Pin 1 to Pin 1, Pin 
2 to Pin 2, and so forth, to prevent the polarity from 
being reversed. 

TIP: 

If abnormal noises such as hissing and 

popping are produced by the loudspeaker, 

disconnect the audio cable from the loudspeaker. If 
the noise stops, most likely the problem is not with 
the loudspeaker. Check the audio cable, source, and 
AC power to pinpoint the problem.

Audio signals can be daisy-chained using the Loop output 
connector on the user panel of the MJF-212A stage monitor 
(Figure 3.1). A single source can drive multiple MJF-212A 
monitors with a paralleled input loop, creating an unbuffered 
hard-wired loop connection.

Figure 3.1. 

Side panel audio input connectors 

When driving multiple MJF-212A loudspeakers in a system, 
make certain that the source device can drive the total load 
impedance required by the paralleled input circuit. The 
source device must be capable of producing 20 dBV (10 
volts rms into 600 ohms) in order to produce the maximum 
peak SPL over the operating bandwidth of the loudspeaker.

To avoid distortion, make sure the source device provides 
an adequate drive circuit design for the total paralleled load 
impedance of the system. 

         

NOTE: 

Meyer Sound’s Galileo™ loudspeaker 

management system is highly recommended. 

In addition to maintaining signal integrity for long 
cable paths, it offers independent outputs and filters 
to help you optimize performance. 

         

NOTE: 

For details on the MJF-212A 

monitor’s audio input characteristics and 

amplification, see Appendix B.

AmPlIfICATION AND PROTECTION CIRCUITRy

The MJF-212A is powered by Meyer Sound MJF amplifier 
modules in a three-channel amplifier configuration with 
a total power of 1275 watts (2550 watts peak). The MJF 
amplifier utilizes complementary-power MOSFET output 
stages (class AB/H). The specific functions for the MJF-212A 
stage monitor such as crossover point, frequency and 
phase response, and driver protection are determined by the 
control card installed in one of the MJF amplifier modules.

CHAPTER 3: AmPlIfICATION AND AUDIO

Содержание MJF-212A

Страница 1: ...OPERATING INSTRUCTIONS ULTRAseries MJF 212A High Power Stage Monitor Keep these important operating instructions Check www meyersound com for updates...

Страница 2: ...to 4600 m 15 000ft Non operating altitude to 6300 m 25 000ft Shock 30 g 11 msec half sine on each of 6 sides Vibration 10 Hz to 55 Hz 0 010 peak to peak excursion 2007 Meyer Sound All rights reserved...

Страница 3: ...d by Meyer Sound or sold with the loudspeaker Handles are for carrying only 13 Unplug this loudspeaker during lightning storms or when unused for long periods of time 14 Refer all servicing to qualifi...

Страница 4: ...ages auf ein Minimum zu reduzieren den Lautsprecher vom Stromnetz trennen bevor ggf ein Audio Schnittstellensign alkabel angeschlossen wird Das Netzkabel erst nach Herstellung aller Signalverbindungen...

Страница 5: ...Electrical Safety Issues 8 CHAPTER 3 Amplification and Audio 9 Audio Input 9 Amplification and Protection Circuitry 9 MJF 212A Interconnections 10 Cabling 10 The Limiting System 10 Low Frequency Limi...

Страница 6: ...vi...

Страница 7: ...tory installed VEAM Connector Appendix B Specifications and Dimensional Drawings provides detailed acoustic and electrical specifications for the MJF 212A monitor along with detailed dimensional drawi...

Страница 8: ...INTRODUCTION...

Страница 9: ...m concerts as well as corporate AV applications and clubs The MJF 212A produces a peak output of 139 dB SPL with exceptionally flat phase and frequency response The cabinet is constructed from premium...

Страница 10: ...sing package also incorporates Meyer Sound s Intelligent AC power supply which automatically adjusts for common line voltage worldwide and provides both soft turn on and transient protection The MJF 2...

Страница 11: ...distribution system with the load between loudspeakers distributed among the three phases and all of the loudspeakers connected to common neutral and earth ground points Figure 2 1 A sample AC power...

Страница 12: ...For units shipped with the VEAM all in one multipin connector please refer to Appendix A for AC Power pin out Caution When creating AC cables and distribution systems it is important to preserve AC l...

Страница 13: ...o either low or high voltage its power supply automatically turns on again after three seconds if the voltage has returned to either normal operating window If the MJF 212A stage monitor does not turn...

Страница 14: ...hat the circuit breakers on the monitor s user panel trip the white center buttons pop out disconnect the AC power cable Do not reset the breakers with the AC connected Contact Meyer Sound for repair...

Страница 15: ...loudspeaker If the noise stops most likely the problem is not with the loudspeaker Check the audio cable source and AC power to pinpoint the problem Audio signals can be daisy chained using the Loop o...

Страница 16: ...or s left and right 12 inch cone drivers are powered by separate amplifier channels each with a detector but routed to one limiter The lower limit LED on the user panel indicates limiting activity for...

Страница 17: ...he temperature of the heatsink reaches 75 C 167 F the On Temp LED on the rear panel turns from green On to red Temp The unit continues to operate normally even if the On Temp LED is red but this is an...

Страница 18: ...12 CHAPTER 3...

Страница 19: ...his information is permanently retained on each RMS communication board and in the computer RMS database until you modify it Loudspeaker View labels can be modified at any time allowing you to customi...

Страница 20: ...e Service Button the card will be decommissioned from the network and the red Service LED will blink Activity LED Green When the loudspeaker has been commissioned the Activity LED will flash continuou...

Страница 21: ...neutral blue Figure A 1 VEAM multipin connector power pin out For complete wiring conventions and pin outs for AC audio and RMS connections please refer to the Meyer Sound document VEAM Cable Wiring...

Страница 22: ...16 APPENDIX A...

Страница 23: ...00 Hz Note At this frequency the transducers produce equal sound pressure levels TRANSDUCERS Low low mid frequency Two high power 12 cone drivers with neodymium magnets Nominal impedance 2 Voice coil...

Страница 24: ...W 1 x 275 W 2550 W peak Note Amplifier wattage rating based on the maximum unclipped burst sine wave rms voltage that the amplifier will produce for at least 0 5 seconds into the nominal load impedan...

Страница 25: ...23mm 40 13 70 348mm 23 00 584mm 40 PHYSICAL Enclosure Premium birch plywood Finish Black textured Protective grille Powder coated hex stamped steel black mesh Dimensions 27 07 w x 16 11 h x 23 00 d 68...

Страница 26: ...20 APPENDIX B...

Страница 27: ......

Страница 28: ...2007 Meyer Sound Laboratories Inc 05 157 005 02 A Meyer Sound Laboratories Inc 2832 San Pablo Avenue Berkeley CA 94702 www meyersound com T 1 510 486 1166 F 1 510 486 8356...

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