Meyer Sound MJF-212ATM CHAPTER 3: AmPlIfICATION AND AUDIO

CHAPTER 3

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