QSC Audio Stereo Amplifier MX2000a User Guide

MXa Series

▲

MX 1000a

MX 1500a

MX 2000a

MX 3000a

*TD-000026-00*

Rev. B

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I. WARNING NOTICES

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

SPEAKER DAMAGE

CAUTION: To reduce the rish of electric shock, do not remove

the cover. No user-serviceable parts inside. Refer servicing to

qualified service personnel.

The MXa Series amplifiers are among the most powerful

professional amplifiers available and is capable of pro-

ducing much more power than many loudspeakers can

handle. It is the user’s responsibility to use suitable

speakers with the amplifier and to use them in a sensible

way that will not cause damage.

WARNING: To prevent fire or electric shock, do not expose this

equipment to rain or moisture.

QSC will not be responsible for blown speakers. Consult

the speaker manufacturer for power-handling recom-

mendations.

AVIS

EitherchanneloftheMX3000aamplifierhasspecialclip-

limitingprotectioncircuitrythatreducesthesignallevelat

the onset of heavy clipping. This not only allows the

amplifiertooperateatahighaveragepowerlevelwithout

audible distortion occurring, but it also prevents the

speakers’ being destroyed by excessive clipping. How-

ever, if the amplifier is operating normally and your

speakers fail anyway, it is virtually certain that they could

not handle the high power, despite the lack of clipping.

RISQUE DE CHOC

ÉLECTRIQUE

NE PAS OUVRIR

ATTENTION: Pour eviter les risques de choc électrique, ne pas

enlever le courvercle. Aucun entretien de pièces intérieures

par l’usager. Confier l’entretien au personnel qualifié.

AVIS: Pour eviter les risques d’incendie ou d’électrocution,

n’exposez pas cet article à la pluie ou a l’humidité.

Even if you reduce the gain using the amplifier’s front

panel attenuator controls, it is still possible to reach full

output power if the input signal level is high enough.

A single high-power crescendo can blow high-frequency

driversalmostinstantaneously,whilelow-frequencydriv-

ers can usually withstand very high, continuous power

levels for a few seconds before they fail. Reduce power

immediately if you hear any speaker “bottoming out”—

harsh pops or cracking distortion that indicate that the

speaker voice coil or diaphragm is striking the magnet

assembly.

VORSICHT

GEFAHR EINES

ELEKTRISCHEN SCHLAGES.

NICHT ÖFFNEN!

VORSICHT: Um das Risiko eines elektrischen Schlages zu

vermindern, Abdeckung nicht entfernen! Keine Benutzer

Wartungsteile im Innern. Wartung nur durch qualifiertes

Wartungspersonal.

QSC recommends that you use amplifiers of this power

range for more headroom (cleaner sound) rather than for

increased volume.

WARNUNG: Zur vermeidung von Feuer oder elektrischen

Schlägen, das Gerät nicht mit Regen oder Feuchtigkeit in

Berührung bringen!

SPEAKER OUTPUT SHOCK HAZARD

An MXa amplifier is capable of producing hazardous

output voltages. To avoid electrical shock, do not touch

any exposed speaker wiring while the amplifier is operat-

ing.

SAFEGUARDS

Electrical energy can perform many useful functions. This unit has

been engineered and manufactured to assure your personal safety.

Improperusecanresultinpotentialelectricalshockorfirehazards.

Inordernottodefeatthesafeguards,observethefollowinginstruc-

tions for its installation, use and servicing.

RACK MOUNTING PRECAUTIONS

In portable racks, to avoid damage to either the amplifier

mountingearsorthemountingrails, supporttheamplifier

at all four corners. Contact the QSC Customer Service

Department to order rear support brackets.

PRECAUTIONS

L’énergie électrique peut remplir de nombreuses fonctions utiles.

Cet appariel a été conçu et réalisé pour assurer une sécurité

personnelle entiére. Une utilisation impropre peut entraîner des

risques d’électrocution ou d’incendie. Dans le but de ne pas rendre

inutiles les mesures de sécurité, bien observer les instructions

suivantes pour l’installation, l’utilisation et l’entretien de l’appareil.

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Theamplifiersrequirearackdepthof18inches(45.7cm)

to clear the rear support ears. Allow some additional

clearance for input and output connectors at the rear

panel, which is 16.9 inches (42.9 cm) behind the plane of

the front mounting rails. The built-in cooling fan draws air

in at the rear of the chassis and exhausts it through vents

in the front panel. The flow-through cooling scheme

allows you to rack-mount the amplifiers one atop the

other, with no clearance necessary in between. This

mounting technique also helps support the weight of the

upper amplifiers.

II. OVERALL DESCRIPTION

The MXa Series from QSC comprises four high-effi-

ciency professional power amplifier models, each with

two independent channels. The MX 1000a, MX 1500a,

and MX 2000a, can deliver, respectively, 275, 400, and

475 watts into 8-ohm loads, and 400, 600, and 725 watts

into 4-ohm loads

Either channel of the MX 3000a is capable of delivering

850 watts into 8-ohm loads, 1300 watts into 4-ohm loads,

or more than 1600 watts into 2 ohms.

TheMXaSeriesderivesmuchofitsdesignfromourhigh-

end EX Series amplifiers. They are engineered for stabil-

ity and exceptional reliability, with protection for open or

short circuits and mismatched loads. To protect your

loudspeakers, the outputs mute during turn-on and turn-

off, and also in the event of a DC fault. All protection

circuitry automatically resets to normal when conditions

assure safe operation.

Each channel has its own transformer secondary (MX

1000a and MX 1500a) or power transformer (MX 2000a

and MX 3000a) and bipolar multi-rail power supply. The

power transformers are mounted in the front of the

amplifier chassis, as close to the front mounting rails as

possible; this keeps the unit’s center of gravity forward to

minimize the twisting force on the front mounting ears.

Still, the amplifier should be supported at all four corners,

especially if it is in a portable rack such as in touring or

mobile applications.

The amplifiers feature thermal protection. The MX 3000a

features a variable-speed fan, which responds continu-

ously to the cooling needs to minimize noise and dust

build-up, and a thermal limiter that reduces gain up to 15

dB if the amplifier overheats above 80˚ C. The other

models have a two-speed fan. If an MXa amplifier over-

heats to 85˚ C or higher, a protection circuit mutes the

output.

The MX 1000a and MX 1500a are both two rack spaces

high and weigh 19 kg (42 lb). The MX 2000a and MX

3000a occupy three rack spaces. The MX 2000a weighs

24.5 kg (54 lb), and the MX 3000a weighs 31 kg (69 lb).

GAIN 1

GAIN 2

PROT CLIP

SIG PWR

PWR SIG

CLIP PROT

OFF

MX 1500a

Professional Stereo Amplifier

- dB

Figure 1: QSC MX 1500a Front Panel (identical to the MX 1000a)

GAIN 1

GAIN 2

PROT CLIP

SIG PWR

PWR SIG

CLIP PROT

OFF

MX 2000a

Dual Monaural Amplifier

- dB

Figure 2: QSC MX 2000a Front Panel (identical to the MX 3000a)

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MX 1500a INPUTS

III. INPUTS

The amplifier’s input sensitivity is 1.07 volt rms; at this

signal level and any attenuators set for full gain, the

amplifier will produce full rated power—350 watts, 20Hz-

20kHz,0.1%THD—intoan8-ohmload.Theinputimped-

ance is 20 kilohm balanced and 10 kilohm unbalanced,

typical of QSC amplifiers.

An MXa amplifier features balanced inputs, connected

via barrier strip terminals or 1/4” (6.3 mm) tip/ring/sleeve

phone jacks. The tip of the input jack is wired for “nega-

tive’orinvertedpolarity,whiletheringisthenon-inverting

input. Thus, ifthevoltageatthetipispositivewithrespect

to that at the ring, the amplifier channel will produce a

negative voltage at its output.

For use with unbalanced signals, connect the unused

terminal to ground to avoid a reduction in gain caused by

a floating input; use a two-conductor (tip/sleeve) plug, or

connect a jumper between the inverting input terminals

on the barrier strip and their adjacent ground terminal.

MX 2000a INPUTS

The amplifier’s input sensitivity is 1.05 volt rms; at this

signal level and any attenuators set for full gain, the

amplifier will produce full rated power—450 watts, 20Hz-

20kHz,0.1%THD—intoan8-ohmload.Theinputimped-

ance is 20 kilohm balanced and 10 kilohm unbalanced,

typical of QSC amplifiers.

MX 1000a INPUTS

The amplifier’s input sensitivity is 1.1 volt rms; at this

signal level and input attenuators set for full gain, the

amplifier will produce full rated power—250 watts, 20Hz-

20kHz,0.1%THD—intoan8-ohmload.Theinputimped-

ance is 20 kilohm balanced and 10 kilohm unbalanced,

typical of QSC amplifiers.

MX 3000a INPUTS

The amplifier’s input sensitivity is 1 volt rms; at this signal

levelandanyattenuatorssetforfullgain,theamplifierwill

produce full rated power—800 watts, 20Hz-20kHz, 0.1%

THD—into an 8-ohm load. The input impedance is 20

kilohm balanced and 10 kilohm unbalanced, typical of

QSC amplifiers.

An MXa Series amplifier features a Level I Open Input

Architecture slot. See Section 2 for more information

about Open Input Architecture.

–

BRIDGED MONO

WARNING:TO REDUCE THE RISK OF FIRE

OR ELECTRIC SHOCK, DO NOT EXPOSE THIS

EQUIPMENT TO RAIN OR MOSTURE.

CHANNEL 2

CHANNEL 1

AVIS

RISQUE DE CHOC ELECTRIQUE

NE PAS OUVRIR

–

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

TIP NEG RING POS

SLEEVE GND

TIP NEG RING POS

SLEEVE GND

CLASS 2 WIRING

STEREO 4 OHM MIN/CH.

CH 2 INPUT CH 1

BRIDGED MONO 8 OHM MIN. CLASS 1 WIRING MUST BE USED

BRIDGED MONO OPERATION: PLACE BRIDGING SWITCH ON INPUT PANEL

TO BRIDGED POSITION. CONNECT INPUT SIGNAL TO CH 1 ONLY.

CONNECT SPKR (+) TO CH 1 (+) OUTPUT. CONNECT SPEAKER (–) TO

CH 2 (+) OUTPUT. SET CH 2 GAIN FULLY CLOCKWISE AND REGULATE

LEVEL WITH CH 1 GAIN CONTROL.

STEREO

PARALLEL

BRIDGE

CH 2

CH 1

–

GND

–

Figure 3: QSC MX 1500a Back Panel (identical to the MX 1000a)

–

BRIDGED MONO

WARNING:TO REDUCE THE RISK OF FIRE

OR ELECTRIC SHOCK, DO NOT EXPOSE THIS

EQUIPMENT TO RAIN OR MOSTURE.

CHANNEL 2

CHANNEL 1

–

TIP NEG RING POS

SLEEVE GND

TIP NEG RING POS

SLEEVE GND

CH 2 INPUT CH 1

CLASS 2 WIRING

STEREO 4 OHM MIN/CH.

STEREO

BRIDGED MONO 8 OHM MIN. CLASS 1 WIRING MUST BE USED

BRIDGED MONO OPERATION: PLACE BRIDGING SWITCH ON INPUT PANEL

TO BRIDGED POSITION. CONNECT INPUT SIGNAL TO CH 1 ONLY.

CONNECT SPKR (+) TO CH 1 (+) OUTPUT. CONNECT SPEAKER (–) TO

CH 2 (+) OUTPUT. SET CH 2 GAIN FULLY CLOCKWISE AND REGULATE

LEVEL WITH CH 1 GAIN CONTROL.

PARALLEL

BRIDGE

CH 2

CH 1

–

GND

–

AVIS

RISQUE DE CHOC ELECTRIQUE

NE PAS OUVRIR

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

Figure 4: QSC MX 2000a Back Panel (identical to the MX 3000a)

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IV. OUTPUTS

V. OPERATIONS

When the amplifier is first turned on, the red “PROT” LED

on each channel will light for about three seconds, during

which the output relays will stay open to mute the speak-

ers. After the turn-on muting interval, the “PROT” LEDs

turn off, the green “PWR” LEDs light, and the output

relays close to enable the speaker outputs. Even during

themutinginterval, theyellow“SIG” andred“CLIP” LEDs

operate normally if there is a signal present. If the “CLIP”

LED is on while the amplifier is muted, cut the gain back

immediatelytoavoidafull-powerblastofsoundwhenthe

output relays close. (Whenever it is practical, at turn-on

youshouldhavetheattenuatorsallthewaydowntoavoid

this situation.) If a channel stays muted with “PROT” lit,

or if its “SIG” or “CLIP” indicators light up when the gain

is turned all the way down, it may be defective; see the

troubleshooting segment for more information.

Four “touch-proof” binding posts—one pair per chan-

nel—on the rear panel allow speaker cable connections

to the amplifier outputs. The special design allows con-

nection of large diameter speaker cable while reducing

shock hazard due to the high output power of MXa

amplifiers.The“hot”terminalofeachoutputpairisthered

one; the black one is signal ground.

If you are operating the amplifier in “bridged” mode,

connect the speaker load across the red terminals only;

the red terminal of Channel 1 then is “hot” or “in-phase.”

The red terminal of Channel 2 is not grounded, however,

so use the same precautions in handling and dressing

the wire that you would for the normal “hot” outputs.

CONTROLS AND DISPLAYS

The “SIG” LED indicates signal levels that are -30 dB

The front panel-mounted attenuator controls are labeled

indBofattenuationandarecontinuouslyadjustablefrom

0 dB (full gain) to ∞ (full kill).

(referenced to full output power) or higher.

When the amplifier is shut off, the amplifier should mute

both channels virtually instantaneously, with the “PROT”

indicators lit until the power supplies are discharged.

The LED displays for each channel function as follows:

ON/OFF MUTING

The “PROT” indicator lights

whenever the output is muted. At

turn-on, the amplifier mutes for a

few seconds; at turn-off, it mutes

immediately and remains muted

until the power supplies have

drained.

PWR SIG

CLIP PROT

LED

COLOR

PWR

SIG

Green

Yellow

Red

Main power supply active on this channel.

Shows signal is present

NO SIGNAL

PWR SIG

CLIP

Shows output capability is being

exceeded, with clipping distortion

Only the “PWR” LED is lit. This is

normal.

CLIP PROT

PROT

Red

Shows when the output is muted by

protection circuitry.

Table 1: LED Display Operation

NORMAL SIGNAL

The “PWR” LED is lit, and the

“SIG” LED is lit or flashing. This

is normal.

CLIP PROT

PWR SIG

AC POWER

Any MXa Series amplifier can be wired for 100, 120, or

220–240 VAC, 50 or 60 Hz operation. Unless it is spe-

cially ordered, each amplifier is configured for the line

voltage in the market for which it is intended. For ex-

ample, those intended for Japan are 100 VAC; for North

and Central America, 120 VAC; for Europe and most of

Asia, 220–240 VAC.

OCCASIONAL CLIPPING

The “PWR” and “SIG” LEDs are lit,

and the “CLIP” LED flashes on

occasional peaks. This is normal.

CLIP PROT

PWR SIG

STEADY CLIPPING

The“PWR”,“SIG”,and“CLIP”LEDs

are lit continuously. The channel is

in hard clipping, and you should

reduce power immediately to avoid

speaker damage.

CLIP PROT

PWR SIG

The power cord has a plug for connecting to a standard

AC source. For 120-volt operation, the plug is a standard

15-amperegroundedNEMAfitting;itmeetssafetyagency

requirements for current consumption of less than 12

amperes during “normal” operation, but peak current

draw under heavy usage can be much higher.

THERMAL MUTING

PWR SIG

The “SIG” LED is flashing, and the

“PROT” LED is lit; this indicates

that the protection circuitry is mut-

ing the output. The condition will

reset itself when conditions allow.

CLIP PROT

KEY

Not Illuminated

Flashing

Full Brightness

Figure 5: LED displays further explained.

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PROBLEM: Hum in the audio

Because of its grounded-collector output

TROUBLESHOOTING

•

transistor configuration, which maximizes

thermal efficiency, the signal ground on an

MXaamplifiercannotbelifted.Theamplifier’s

balancedinputsaremeanttorejecthum,but

if hum remains a problem, check the tight-

ness of the two mounting screws on the

standard input panel; if they are loose, the

panelitselfmightnotbewellgroundedtothe

chassis.Ifyouhaveanyproblemswiththese

screws, contact the QSC Customer Service

Department. In some cases, such as when

the audio signal cables are routed near

lighting dimmers that use triacs, you may

need to use input isolation transformers be-

cause of the extremely high noise field pro-

duced by the dimmer circuitry. See the para-

graphs on Open Input Architecture for fur-

ther information on input transformers.

PROBLEM: Channel will not come out of muting

•

If reducing the gain control to ∞ attenuation

does not release muting, the channel is

defective or overheated (see“Overheating,”

below).

•

If reducing the gain releases the muting,

raise the gain back up slowly while you

watch the “SIG” and “CLIP” indicators; the

problem may be an abnormal signal (with

excessive ultrasonic energy, for example)

that could otherwise damage your speak-

ers.

PROBLEM: No sound

•

Is the channel muted? (If the “PROT” indica-

tor is lit, the channel is muted; see below.)

In addition, be sure to check wiring to assure

that shields are properly terminated and no

ground loops have been created.

•

Is the “SIG” LED lit or flashing? (If so, the

speaker is open or blown, there is an open

circuit in the speaker wiring, or there is an

open circuit in the internal output wiring of

the amplifier.)

PROBLEM: Overheating

•

If the “SIG” indicator is dark, there is prob-

ably not enough signal, or even none at all.

Try turning up the front panel attenuators or

boosting the signal level at the input.

•

The thermal management system on an

MXa Series amplifier features either a two-

speed fan (MX 1000a, MX 1500a, and MX

2000a) or a variable-speed fan (MX 3000a)

that modulates the cooling air flow over the

heatsinks in response to the cooling needs.

If the air flow is blocked, however, or if the

amplifier is overdriven into very low imped-

ance loads, the amplifier could overheat

even though the fan is running at full speed.

Ifthe“SIG”indicatorshowslittleornoactivity

but the “CLIP” LED is lit or flashing, there is

probablyashortcircuitinthespeakerwiring.

It is also possible, but less likely, that the

channel’s output relay is defective and will

not open, thereby short-circuiting the chan-

nel output and producing the same symp-

toms.

•

At approximately 55°C, the fan runs at high

speed.

At approximately 80˚ C, the thermal limiter

on the MX 3000a will start to reduce gain, up

to 15 dB as needed, to reduce the amount of

heat produced.

PROBLEM: Channel goes into muting, with “PROT”

LED on

•

If the fan is running full speed, the channel

probably suffers from severe overheating.

Unless there is a blockage in the flow of

cooling air, the channel should return to

normalwithinaminuteorso(see“Overheat-

ing,” below).

•

Atapproximately85˚C,thechannel’soutput

relay will mute the output. The channel will

remain muted until the temperature drops to

asafelevel.Evenwhilethechannelismuted,

the “SIG” and “CLIP” indicators will function

normally. If the “CLIP” indicator is flashing or

continuously lit, reduce the gain to hasten

the cool-down and prevent repeated ther-

mal shutdowns.

•

If the fan is not running at full speed, or the

channel does not reset to normal after a

cool-down period, the muting is probably

because of a DC fault or other amplifier

failure, especially if the “SIG” or “CLIP” indi-

cators are lit even with the attenuator turned

all the way down.

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SPECIFICATIONS

FTC Watts Per Channel 20Hz-20kHz, 0.1% THD EIA Watts Per Channel 1kHz, 1% THD

MODEL

8Ω Load

4Ω Load

8Ω Load

4Ω Load

2Ω Load*

MX 1000a

MX 1500a

MX 2000a

MX 3000a

250

350

450

800

350

500

650

1200

275

400

475

850

400

600

725

1300

500

750

1000

1600

*typical

Bridged Mono 20Hz-20kHz, 0.1% THD

Bridged Mono 1kHz, 1% THD

MODEL

16Ω Load

8Ω Load

4Ω Load*

MX 1000a

MX 1500a

MX 2000a

MX 3000a

500

700

900

1600

700

1000

1500

2000

3200

1000

1300

2400

*typical

MX 1000a

MX 1500a

MX 2000a

MX 3000a

DYNAMIC HEADROOM

8 ohms

2.0

2.3

2.0

2.5

2.0

2.5

1.9

2.9

4 ohms

DISTORTION

SMPTE-IM

Less than 0.05%

FREQUENCY RESPONSE

20 Hz to 20 kHz, ±0.15 dB

8 Hz to 100 kHz, +0, -3 dB

DAMPING FACTOR

NOISE (A-weighted)

VOLTAGE GAIN, dB

Greater than 200

100 dB below rated output (20 Hz to 20 kHz)

40 (32 dB)

1.1

50 (34 dB)

1.07

56 (35 dB)

1.05

80 (38 dB)

1.0

SENSITIVITY, V RMS

(for rated power, 8-ohms)

INPUT IMPEDANCE

CONTROLS

10K unbalanced

20K balanced

Front: AC Switch, Ch. 1 and Ch. 2 Attenuator Knobs

Rear: Parallel/Stereo/Bridge Switch

INDICATORS (per channel)

PWR:

SIG:

CLIP:

PROT:

Green LED

Yellow LED

Red LED

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MX 1000a

MX 1500a

MX 2000a

MX 3000a

CONNECTORS (each channel)

COOLING

Input:

Output:

Barrier strip and 1/4” RTS phone jack

“Touch-Proof” binding posts

MX 1000a, MX 1500a, MX 2000a: 2-speed fan with back-to-front air flow

MX 3000a: Continuously variable speed fan, with back-to-front air flow

AMPLIFIER PROTECTION

Output Averaging^™short-circuit protection, open circuit, ultrasonic, RF, thermal

muting (thermal limiting also on MX 3000a). Stable into reactive or mismatched

loads.

LOAD PROTECTION

Turn-on/turn-off muting, clip limiting (MX 3000a only), DC-fault load grounding

relay with internal fault fuses.

OUTPUT CIRCUIT TYPE

MX 1000a, MX 1500a, MX 2000a: Complementary linear stage with

2-step high-efficiency circuit

MX 3000a: Complementary linear stage 3-step high-efficiency circuit

POWER REQUIREMENTS

100, 120, 220-240 VAC, 50/60 Hz

POWER CONSUMPTION

Normal operation: 1/8 power @ 4Ω per channel

Maximum: full power @ 2Ω per channel

Divide current by 2 for 220-240 VAC operation

Normal Operation @ 120 VAC

Maximum @ 120 VAC

22A

5.5A

29A

7.5A

38A

<12A

58A

DIMENSIONS

Faceplate Width

Chassis Depth

Standard 19" (48.3 cm) Rack Mounting

17.9” (45.5 cm) deep (to support rear ears)

Faceplate Height (2 rack spaces)

Faceplate Height (3 rack spaces)

3.5” (8.9 cm)

5.25” (13.3 cm)

WEIGHT

Shipping, Lbs

Net, Lbs

49 lbs/22.2 kg

42 lbs/19 kg

49 lbs/22.2 kg

42 lbs/19 kg

62 lbs/28 kg

54 lbs/24.5 kg

74 lbs/33.8 kg

69 lbs/31 kg

OPEN INPUT ARCHITECTURE^™LEVEL I

On the rear of an MXa or EX amplifier are an upper and

a lower input panel; both are easily removable for future

upgrades. ThisistheconceptofOpenInputArchitecture,

and the opening in which the panels mount is called the

“slot”. As installed at the factory, the lower is the MXa or

EX standard input panel and the upper one is a blank. A

ribbon cable connects the “slot” panels to the rest of the

amplifier. It carries input signals, speaker output monitor

signals, muting status, and clip activity; these are for

supporting future accessories and remote control sys-

tems. Although the physical dimensions of the MXa and

EX panels are the same, their internal cabling is different

and the MXa platform does not support all the EX

functions. The MXa Open Input Architecture slot thus is

designated as “Level I” and the EX as “Level II.”

The MX-1 Input Expander panel may be installed in the

upper panel position. It features XLR inputs and addi-

tional 1/4” RTS inputs. Installation instructions are in-

cluded with the expansion kit.

Other accessories include a stereo precision attenuator

(for the lower panel position) and a cinema crossover (for

the upper panel position). More are in development.

The standard input panel shipped with each MXa Series

amplifier has balanced 1/4” (6.3 mm) RTS phone jacks

and barrier strip inputs and the Parallel-Stereo-Bridge

switch. The panel’s circuit board has solder footprints for

passive roll-off circuit components, input isolation trans-

formers, and other special customizations.

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INSTRUCTIONS FOR BRIDGED

OPERATION

PARALLEL, STEREO, OR BRIDGED

OPERATION

1. Set the switch to the “Bridge” position.

The Parallel-Stereo-Bridge switch is located on the input

panel, next to the input jack for channel 1).

2. Connect the signal to channel 1’s input only.

Do not connect anything to the input of

channel 2.

The most commonly used operating mode for a power

amplifier is “Stereo,” in which the two channels are

independent and separate all the way from input to

output. Set the switch in the center position for stereo

operation.

3. Turn up the gain on channel 2 all the way.

Use channel 1’s gain control to set the level.

Both channels’ “SIG” and “CLIP” indicators

should flash identically. (If you have used

other amplifiers, this step may be different.

But it is correct; in the bridged mode, chan-

nel 2 receives its feed from a sample of

channel 1’s output. The sample is calibrated

such that channel 2, at full gain, will produce

a voltage equal in magnitude but opposite in

polarity to channel 1’s.

“Parallel”tiesthetwochannelinputstogethersothatboth

will be driven by the same signal, without the need for

externaljumpersorwiring. Aftertheinputsbothchannels

operate independently; though they carry the same sig-

nal, their gain controls affect only their respective chan-

nels, and they must use separate speakers. Never par-

allel the speaker outputs!

The “Bridge” position uses both channels to provide

about three times the power to a single speaker load that

a single channel does. In this position the switch feeds

channel 2 with an inverted signal from channel 1. Thus,

when one channel “pushes,” the other “pulls,” providing

twice the voltage swing of a single channel.

4. Connect the single speaker load across the

red binding posts of the amplifier outputs as

shown in Figure 2-2. The positive speaker

wire goes to channel 1, and the negative to

channel 2.

BRIDGED-MONO MODE CAUTION:

TIP NEG RING POS

SLEEVE GND

The voltage across the outputterminals ofa bridgedMXa

amplifier may equal or exceed 100 volts rms and may be

as high as 170 volts (MX 3000a), 130 volts (MX 2000a), or

120 volts (MX 1500a). Use fully insulated CLASS ONE

wiring, andthe loadmustbe ratedforupto2400watts (@

8 ohms) for the MX 3000a, 1300 watts (@ 8 ohms) for the

MX 2000a, 1000 watts (@ 8 ohms) for the MX 1500a, and

700 watts (@ 8 ohms) for the MX 1000a.

STEREO

PARALLEL

BRIDGE

CH 1

Figure 6: Parallel-Stereo-Bridge switch shown in the

normal (Stereo) mode position.

VORSICHT BEIM ÜBERBRÜCKTEN

MONO-MODUS:

STEREO

Switch on Input Panel

(Left side of rear panel)

PARALLEL

BRIDGE

Zwischen den überbrückten Terminals eines MXa-

Verstärkers besteht eine Ausgangsspannung mit einem

quadratischen Mittelwert von mehr als 100 Volt und

vielleicht von bis zu 170 Volt (MX 3000a), 130 Volt (MX

2000a), oder 120 Volt (MX1500a). Zu verwenden ist voll

isolierte Verdrahtung der US-Klasse Eins, und die

angeschlossene Belastung muß für bis zu 2400 Watt (8

Ohm) beim MX 3000a, 1300 Watt (8 Ohm) beim MX 2000a,

1000 Watt (8 Ohm) beim MX 1500a, und 700 Watt (8 Ohm)

beim MX 1000a ausgelegt sein.

–

BRIDGED MONO

–

CHANNEL 2

CHANNEL 1

–

CLASS 2 WIRING

STEREO 4 OHM MIN/CH.

BRIDGED MONO 8 OHM MIN. CLASS 1 WIRING MUST BE USED

BRIDGED MONO OPERATION: PLACE BRIDGING SWITCH ON INPUT PANEL

TO BRIDGED POSITION. CONNECT INPUT SIGNAL TO CH 1 ONLY.

CONNECT SPKR (+) TO CH 1 (+) OUTPUT. CONNECT SPEAKER (–) TO

CH 2 (+) OUTPUT. SET CH 2 GAIN FULLY CLOCKWISE AND REGULATE

LEVEL WITH CH 1 GAIN CONTROL.

CONNECT ONE SPEAKER LOAD ONLY.

Figure 7: For Bridge mode, use CH 1 input only, and set

Input switch and connect load as shown.

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AC CURRENT CONSUMPTION

VI. LONG-TERM OUTPUT

POWER

A major objective in the design of the MXa Series

amplifiers—even the highest-powered models—is to

permit their operation from readily available, standard

ACpowersources.TheMX3000acandeliver1600watts

per channel into 2-ohm loads—a total of 3200 watts—yet

its rated current draw under “normal conditions” is less

than 12 amperes at 120 volts AC, which is 1440 watts.

In a properly designed sound system, you can usually

obtain the desired sound level without using the full

outputpoweroftheamplifier;ifthe“CLIP”indicatorsflash

once in a while, that is perfectly normal.

Iftheamplifierisoperatedatextremelyhighpowerlevels,

it may overheat or may even damage the speakers. The

amount of stress on the amplifier depends largely on the

load and how hard the amplifier drives it. In general, the

lower the load impedance, the more stressful the load is.

How is this possible? First, “normal conditions” in power

amplifier rating means operation, using pink noise as a

source, at an average power level equal to one-eighth of

maximum power. This is recognized by most of the

world’s safety agencies as the loudest you can play

music through an amplifier and still keep the incidence of

clipping to a reasonable minimum. An amplifier’s peak

current draw at full output power into 2 ohms is several

times what the “normal” draw is, but its various protection

circuits will prevent this condition’s lasting more than a

minute or two.

8-Ohm Loads

The amplifier can operate at practically any power level

without risk of overheating. However, if it is pushed hard

enough to continually light the “CLIP” indicator, the

amplifier’s average output power can reach 250 to 800

watts (depending on the model), which is more than

many speakers can handle.

When you plan the AC power hookups for your amplifi-

ers, use Table 2 to predict the current requirements per

amplifier. You can use the one-eighth power figures to

predict the normal continuous current draw, then add a

safety margin to allow for occasional crescendos.

4-Ohm Loads

If the “CLIP” indicator flashes occasionally, the amplifier

is approaching its maximum long-term power capacity. If

it is lit about half the time, the amplifier channel will

probably go into thermal protection within a few minutes.

2-Ohm Loads

Except for an occasional flash, keep the “CLIP” indicator

dark to avoid overheating the amplifier channel.

Table 2: Current requirements, in amperes, at 120 VAC under various conditions (divide by 2 for 220–240 VAC operation):

Output

AC Current

MODEL Load power

@ Full power @ 1/3 power @ 1/8 power @ Idle

MX 1000a

MX 1500a

MX 2000a

MX 3000a

8+8

4+4

2+2

275 x 2

400 x 2

500 x 2

5.5

7.5

8+8

4+4

2+2

400 x 2

600 x 2

750 x 2

5.5

6.5

8+8

4+4

2+2

475 x 2

725 x 2

1000 x 2

9.5

7.5

8+8

4+4

2+2

850 x 2

9.5

1300 x 2

1600 x 2

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HEAT EMISSIONS

Essentially, a power amplifier draws electrical energy

from the AC mains, converts it to DC, and then converts

itagainintoananalogoftheinputsignaltosendouttothe

loudspeakers. Any AC power that enters the amplifier

through the power cord and does not exit through the

speaker outputs turns into heat, which the amplifier must

rid itself of by exhausting it to the outside. In indoor use

this may present a sizeable challenge to a building’s air

conditioning system. Use Table 3 to predict the heat that

will be emitted by your amplifier.

Table 3: Heat emissions of MXa amplifiers under various conditions:

Load 1/3 Power, both channels 1/8 Power, both channels Idle, both channels

MODEL

MX 1000a

BTU/hr

1035

kcal/hr

BTU/hr

580

kcal/hr

150

BTU/hr

kcal/hr

8Ω

4Ω

2Ω

265

365

545

1430

2140

270

305

915

1035

MX 1500a

MX 2000a

MX 3000a

8Ω

4Ω

2Ω

1165

1875

2770

295

475

700

770

1010

1415

195

255

360

110

8Ω

4Ω

2Ω

1850

3100

4730

470

785

1080

1755

2760

275

445

700

145

1195

8Ω

4Ω

2Ω

2980

7100

755

1795

2600

2015

3600

5040

510

910

200

10280

1275

PROTECTION CIRCUITS

The design goal in high-efficiency, lighter-weight ampli-

fierssuchastheMXaSeriesistocontrolmorepowerwith

fewer or smaller load-bearing components, e.g., resis-

tors, transistors, transformers, etc. However, the higher

power flow through these components makes effective,

responsive protection circuitry absolutely vital. To this

end,thedesignoftheMXaseriestakesacomprehensive

approach to protection.

ing the speakers when the amplifier is turned on or off.

The turn-on delay is approximately three seconds to

allow the power supplies and circuitry to stabilize. Turn-

off muting occurs almost immediately after power is shut

off. Muting occurs whether power is turned on and off

using the front panel power switch or externally at the AC

source.

An NTC (negative temperature coefficient) thermistor in

series with the power switch and transformer primary

limits inrush current. The thermistor initially has a high

resistance, which then diminishes rapidly as it warms, to

avoid power loss. Typically, the inrush current of an MXa

Series amplifier thus is equal to that of another amplifier

of about 1/3 to 1/2 its power rating.

As in all QSC amplifiers, the inputs are resistively buff-

ered for overload and RF protection. Chassis bypass

capacitors at inputs and outputs further improve RF

rejection.

MXa amplifiers use the proven Output Averaging™ short

circuit protection system. This circuit permits full output

current even into resistive or reactive 2-ohm loads, but

reduces the current safely by about 75% if the output is

shorted.

When the DC fault protection circuitry senses a DC

voltage on the amplifier output, it activates a relay which

shorts the output and load to ground. If the DC is due to

a fault in the amplifier channel’s output circuitry, it will

probably produce enough current flow to blow the fault

fuseinserieswiththeoutput.Thiswilldisablethechannel

Turn-on/turn-off muting keeps transients—both from the

amplifieritselfandfromupstreamequipment—fromreach-

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output until it can be repaired, at which time the fuse

should be replaced also.

VIII. TECHNICAL ASSISTANCE

& SERVICE

Temperature sensors on the channel heatsinks and the

power transformers are part of the thermal management

circuitry. On the MX 1000a, MX 1500a, and MX 2000a,

the temperature sensors govern whether the dual-speed

fan should run at low or high speed. Below 55˚ C, the fan

runs at low speed; above, it runs at high speed. At or

above 85˚ C, the channel mutes to go into thermal

protection.

Servicing your unit requires a trained technician capable

of performing the type of service you need. There are no

user serviceable components inside your unit and the

danger of electric shock exists. Additionally, some of the

components in your unit has QSC specific parts that

require QSC replacements. Comprehensive service

manuals for some models are available at QSC.

On the MX 3000a, the thermal management circuitry

controls the variable-speed fan according to how much

cooling air flow is required. At and above 80˚ C, the

thermal limiting circuit reduces the audio signal by up to

15 dB. At 85˚ C, the channel mutes to go into thermal

protection.

TECHNICAL ASSISTANCE

If you suspect that your [product] is defective, check your

system configuration and [product] settings to determine

the origin of the problem. In many cases, incorrect audio

interfacing, poor cabling, or other system level impair-

ments are the cause of problems in audio systems. For

technical assistance beyond the information given in this

manual, QSC Technical Services may be contacted.

VII. WARRANTY AND

DISCLAIMERS

FACTORY SERVICE

DISCLAIMER

Intheeventthatyour[product]doesneedfactoryservice,

you may reach QSC Technical Services for return in-

structions. A Return Authorization (RA) number must be

obtained from QSC Technical Services. QSC may not

account for products that are returned without a Return

Authorization number.

QSC Audio Products, Inc. is not liable for any damage to

speakers, amplifiers, or any other equipment that is

caused by negligence or improper installation and/or use

of the SPL-1.

PRODUCT WARRANTY

QSC Audio Products, Inc. guarantees the SPL-1 to be

free from defective material and/or workmanship for a

period of three years from date of sale, and will replace

defective parts and repair malfunctioning products under

this warranty when the defect occurs under normal

installation and use—provided the unit is returned to our

factory via prepaid transportation with proof of purchase

(sales receipt). This warranty provides that examination

of the returned product must disclose, in our judgment, a

manufacturing defect. This warranty does not extend to

any product which has been subject to misuse, neglect,

accident, improper installation, or where the date code

has been removed or defaced.

Product Return Guidelines

1. Pack the product well for protection during ship-

ment. QSC will provide the factory packaging free

of charge upon request.

2. Include a copy of the sales receipt, your name,

return address, phone number, and defect de-

scription with your return correspondence.

3. Call QSC Technical Services for a Return Autho-

rization number.

4. Mark the Return Authorization number on the

outside of the packaging.

5. Ship the product prepaid to QSC Audio Products.

We recommend United Parcel Service (UPS).

QSC TECHNICAL SERVICES

1675 MacArthur Blvd

Costa Mesa, CA 92626

Telephone: (800) 772-2834

(714) 957-7150

(714) 754-6175

Fax: (714) 754-6173

Bulletin Board: (714) 668-7567

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File Library

QSControl Hardware Support

QUALIFIED SERVICE CENTERS

QSC maintains a service center network for your conve-

nience. If you choose to return your product to a local

service center, you may call QSC Technical Services for

a referral. Accessories, input modules and other periph-

eral QSC products must be returned to the factory for

service.

QSControl Software Support

EX, MXa, VS, USA, and Series One

Slot Accessories

General Notes

File Types

Graphics

Mechanical drawings

Specifications

Application notes

INTERNATIONAL SERVICING

Field service notes

Service bulletins

For QSC products that are purchased outside of the

United States, service must be referred to the distributor

or dealer from where the product was purchased. There

are numerous service centers in many countries. The

service centers in your country may be located by your

dealer, distributor, or by contacting QSC Technical Ser-

vices.

Schematics

Pin-outs

Owners manual text segments

Environment files

Computer utilities and drivers

Service manual text segments

Computer configuration tips

Block diagrams

These are primarily text, graphics, utility, and program files.

IX. QSC ONLINE

Security Levels

New User

Full User

QSC User

Sysop

Cursory access, for review

Customer access

Full access

If you have a computer with a modem you can take

advantage of QSC’s convenient technical support bulle-

tin board system, QSC OnLine. Download software

updates, messages, or hardware application notes; up-

load questions, comments, and useful tips, and more.

This service is available free of charge, around the clock,

Supervisory access

User Privileges and Security

New User

Full User

QSC User

30 minutes per day

No uploads

No downloads

365 days a year (366 days in leap years).

Standard messages access

Bulletin access

As of March 18, 1994—

90 minutes per day

5 uploads per day

BBS Hours:

24 hours a day

BBS Telephone Number:

(714) 668-7567

5 downloads per day

Standard messages access

Bulletin access

General

Automatic system maintenance hours:

Unlimited time per day

10 uploads per day

1:00 a.m.–2:00 a.m. Pacific Time

(no log-ons during this hour)

10 downloads per day

Unlimited messages access

All menu and system access

System type:

Host location:

Open (no subscription fee)

QSC Customer Service Department

Costa Mesa, California

*Uploads and messages subject to verification and editing by the sysop.

Support Areas

Communications Settings

Bulletins

14400 bps (also supports 1200, 2400, and 9600 bps)