QSC CX Series User manual

31
CXSeries
USER MANUAL
▼▼
▼▼
▼ CX4
▼▼
▼▼
▼ CX4T
▼▼
▼▼
▼ CX6
▼▼
▼▼
▼ CX6T
▼▼
▼▼
▼ CX12
▼▼
▼▼
▼ CX12T Rev. B
*TD-000057-00*
*TD-000057-00**TD-000057-00*
*TD-000057-00**TD-000057-00*
*TD-000057-00*

1
TableofContents
PART 1—CX SERIES USER MANUAL
I. Warning Notices ....................................................................................................................................... 2
Speaker Damage............................................................................................................................................3
Speaker Output Shock Hazard.......................................................................................................................3
Rack Mounting Precautions...........................................................................................................................3
II. Overall Description ................................................................................................................................... 4
III. Inputs............................................................................................................................................................ 6
Input Sensitivities.......................................................................................................................................... 6
IV. Outputs ......................................................................................................................................................... 6
V. Controls & Displays................................................................................................................................... 8
VI. Operation ..................................................................................................................................................... 8
AC Power .......................................................................................................................................................8
Operation .......................................................................................................................................................8
Troubleshooting .............................................................................................................................................9
Open Input Architecture™Level I.................................................................................................................10
Parallel, Stereo, or Bridged Operation ....................................................................................................... 11
Maximum Long-Term Output Power ...........................................................................................................13
AC Current Consumption............................................................................................................................. 13
Heat Emissions............................................................................................................................................. 14
Protection Circuits .......................................................................................................................................15
VII. Specifications.......................................................................................................................................... 16
PART 2—CX APPLICATION GUIDE..................................................................................19
VIII.Distributed Lines ..................................................................................................................................... 19
IX. Designing the Distributed Sound System.......................................................................................... 20
Loudspeaker Coverage and Placement....................................................................................................... 20
Determining Power Levels...........................................................................................................................22
Selecting the Amplifier ...............................................................................................................................23
Using Components with Different Voltages...............................................................................................24
X. How Many Speakers? .............................................................................................................................25
XI. Other Design Considerations................................................................................................................ 26
Speaker Transformer Saturation ................................................................................................................26
Connecting Both a Distributed Line and a Direct Loudspeaker on One Channel......................................26
WireLoss .....................................................................................................................................................27
AC Current Consumption............................................................................................................................. 29
Heat Emissions............................................................................................................................................. 29
XII. Address & Telephone Information ...................................................................................................... 30

2
EXPLANATION OF GRAPHICAL
SYMBOLS
The lightning flash with arrowhead
symbol, within an equilateral triangle,
is intended to alert the user to the
presence of uninsulated “dangerous
voltage” within the product’s enclo-
sure that may be of sufficient magni-
tude to constitute a risk of electric
shock to humans.
The exclamation point within an equi-
lateral triangle is intended to alert
the users to the presence of impor-
tant operating and maintenance (ser-
vicing) instructions in the literature
accompanying the product.
CAUTION: To reduce the risk of electric shock, do not
remove the cover. No user-serviceable parts inside.
Refer servicing to qualified service personnel.
WARNING: To prevent fire or electric shock, do not
expose this equipment to rain or moisture.
CAUTION
RISKOFELECTRICSHOCK
DONOTOPEN
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.
AVIS
RISQUEDECHOCÉLECTRIQUE
NEPASOUVRIR
VORSICHT: Um das Risiko eines elektrischen Schlages
zu vermindern, Abdeckung nicht entfernen! Keine
Benutzer Wartungsteile im Innern. Wartung nur durch
qualifiertes Wartungspersonal.
WARNUNG: Zur vermeidung von Feuer oder
elektrischen Schlägen, das Gerät nicht mit Regen
oder Feuchtigkeit in Berührung bringen!
VORSICHT
GEFAHREINESELEKTRISCHEN
SCHLAGES.NICHTÖFFNEN!
SAFEGUARDS
Electrical energy can perform many useful func-
tions. This unit has been engineered and manufac-
tured to assure your personal safety. Improper use
can result in potential electrical shock or fire hazards.
In order not to defeat the safeguards, observe the
following instructions for its installation, use and
servicing.
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 ob-
server les instructions suivantes pour l’installation,
l’utilisation et l’entretien de l’appareil.
EXPLICATION DES
SYMBOLES GRAPHIQUES
Le symbole éclair avec point de flèche
à l’intrérieur d’un triangle équilatéral
est utilisé pour alerter l’utilisateur de
la presence à l’intérieur du coffret de
“voltage dangereux” non isolé
d’ampleur suffisante pour constituer
un risque d’elétrocution.
Le point d’exclamation à l’intérieur
d’un triangle équilatéral est employé
pour alerter les utilisateurs de la
présence d’instructions importantes
pour le fonctionnement et l’entretien
(service) dans le livret d’instruction
accompagnant l’appareil.
ERKLÄRUNG DER GRAPHISCHEN
SYMBOLE
Der Blitz nach unten zeigendem Pfeil in
einem gleichseitigen Dreieck weist den
Benutzer auf das Vorhandensein einer
unisolierten, ”gefährlichen
Spannung“ im Gehäuse hin, die stark
sein kann, einer Person einen
elektrischen Schlag zu versetzen.
Das Ausrufzeichen in einem
gleichseitigen Dreieck weist den
Benutzer auf wichtige Betriebs- und
Wartungs- vorschriften in den
beiliegenden Unterlagen des Gerätes
hin.
DECLARATION OF CONFORMITY
for all CX and CXT models
We declare as our sole responsibility
that this product is in compliance with
the EMC Directive 89/336/EEC and con-
forms to the requirements of the Har-
monized Product Standards EN 55013
(Product Emissions), and EN 55020
(Product Immunity).

3
I.WarningNotices
SPEAKER DAMAGE
The CX Series amplifiers are among the most powerful professional amplifiers available and are capable of
producing 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.
QSC will not be responsible for blown speakers. Consult the speaker manufacturer for power-handling
recommendations.
Even if you reduce the gain using the amplifier’s rear 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 speaker drivers almost instantaneously, while low-
frequency drivers can usually withstand very high, continuous power levels for a few seconds before they too
die.Reduce power immediately if you hear anyspeaker “bottoming out”-harsh pops or cracking distortionthat
indicate that the speaker voice coil or diaphragm is striking the magnet assembly.
QSC recommends that you use amplifiers of this power range for more headroom (cleaner sound) rather than
for increased volume.
SPEAKER OUTPUT SHOCK HAZARD
ACXamplifieriscapableofproducinghazardousoutputvoltages.Toavoidelectricalshock,makesurethecover
isinplaceovertheoutputterminals,anddonottouchanyexposedspeakerwiringwhiletheamplifierisoperating.
RACK MOUNTING PRECAUTIONS
Tominimize twistingstress on the front mounting ears, the amplifier’s internally mounted outputtransformers
are located close to the front panel. Nevertheless, when rack mounting any CX amplifier, make sure it is well
supportedatallfourcornerstoavoiddamagetoeither the amplifier mounting ears or themountingrails.
Contact the QSC Technical Services Department to order rear support brackets.
LIFTINGPRECAUTIONS
In order to safely move or install the amplifier, it is recom-
mended that two persons share the weight when lifting and
positioningtheunit.
SICHERHEITSVORSCHRIFTENBEIMHOCHHEBEN
Um den Verstärker sicher zu verschieben oder einzubauen,
wirdempfohlen,dasGewichtdesVerstärkersbeimHochheben
undVerschiebengleichmäßigaufzweiPersonenzuverteilen.
Optional rear rack
mounting ears.

4
II.OverallDescription
The CX Series from QSC comprises six high-efficiency professional power amplifier models, each with two
independent channels. The table below lists the range’s audio power ratings.
Each channel has its own power transformer secondary. The CX4, CX4T, CX6 and CX6T utilize complementary
Class AB linear output circuitry. For improved efficiency, the CX12 and CX12T utilize Class H step linear
complementaryoutput circuitry andhave bipolar multi-rail power supplies.The power transformers,as arethe
output transformers, are mounted in the front of the amplifier chassis, as close to the front mounting rails as
possible;thiskeepstheunit’scenterofgravityforwardtominimizethetwistingforceonthefront
mounting ears. Still, the amplifier should be supported at all four corners, especially if it is in a
portable rack.
TheCX4andCX4Taretworackspaceshigh;theCX6,CX6T,CX12,andCX12Tarethreerackspaces
high. The adjacent table lists the amplifiers’ weights by model.
The amplifiers require a rack depth of 18 inches (45.7 cm) to clear the rear support ears. Allow
someadditionalclearanceforinputandoutputconnectorsattherearpanel,whichis16.9inches
(42.9 cm) behind the plane of the frount mounting rails. The built-in cooling fan draws air in at
therearofthechassisand exhausts itthroughventsinthefrontpanel.Theflow-throughcooling
schemeallowsyoutorack-mounttheamplifiersoneatoptheother,withnoclearancenecessary
in between. This mounting technique also helps support the weight of the upper amplifiers.
TheCX Series derives much of its design from our award-winning MXa Series amplifiers. Theyare engineered
forstabilityandexceptionalreliability,withprotectionforopenorshortcircuitsandmismatchedloads.Toprotect
your loudspeakers, the outputs mute during turn-on and turn-off, and also in the event of a DC fault. The CX4
and CX4T are AC coupled and cannot pass DC to the load. Therefore, the DC fault muting is not required. All
protection circuitry automatically resets to normal when conditions assure safe operation.
Every CX amplifier features thermal management and protection in the form of a two-speed fan and extruded
aluminumheatsinkswithdirect-mountedoutputdevices.Ifaheatsinkoverheatsto85½Corhigher,aprotection
circuit mutes the amplifier channel output.
MODEL NET WEIGHT
CX4 13.6 kg; 27 lb
CX4T 18.2 kg; 37 lb
CX6 20 kg; 42 lb
CX6T 25 kg; 55 lb
CX12 22.7 kg; 50 lb
MODEL 8ΩΩ
ΩΩ
Ω14ΩΩ
ΩΩ
Ω12ΩΩ
ΩΩ
Ω225 volts370 volts1100 volts1
CX4 150 watts 225 watts 350 watts
CX4T 150 watts 225 watts 350 watts 150 watts4175 watts4175 watts4
CX6 200 watts 300 watts 450 watts
CX6T 200 watts 300 watts 450 watts 200 watts3250 watts3250 watts3
CX12 425 watts 600 watts 900 watts
CX12T 425 watts 600 watts 900 watts 400 watts3500 watts3500 watts3
1: FTC watts per channel, 20 Hz–20 kHz, 0.1% THD
2: EIAwatts perchannel, 1 kHz,1% THD
3: Watts per channel, 45 Hz-15 kHz, 0.25% THD
4: Watts per channel, 50 Hz-15 kHz, 0.25% THD

5
2 4112
Front
features of
CX6, CX6T,
CX12 or
CX12T
amplifier
2345
112
109
7 78 14
6 11
10 11
13
109
7 78
6
14
13
Front
features of
CX4 or CX4T
amplifier
1—Power Switch
2—Power Indicators (Ch1, Ch2)
3—Signal Indicators (Ch1, Ch2)
4—Clip Indicators (Ch1, Ch2)
5—Protect Indicators (Ch1, Ch2)
6—Accessory Slot Cover
7—Gain Control
8—Detachable Input Header
9—Cooling Fan
10 —Shrouded Output Connector
(Direct Outputs)
11 —Shrouded Output Connector
(Isolated Outputs)
12 —Mounting Holes for
Optional Handles
13 —Rear Support Ear
14 —Parallel/Stereo/Bridge
Switch
Rear
features of
CX4
amplifier
Rear features
of CX4T
amplifier
109
7 78
13
109
7 78
11 10 11
13
Rear features
of CX6T or
CX12T
amplifier
Rear
features of
CX6 or CX12
amplifier

6
Channel 2+
Channel 2-
Ground
Ground
Ground
Channel 1-
Channel 1+
Loosen screw,
insert wire here,
then tighten screw.
III.Inputs
CX amplifiers feature balanced inputs, connected via a Euro-style 7-terminal
detachable header. Attach input signal wires as shown. If you are connecting an
unbalanced signal to an input, use the non-inverting (+) input and the ground
terminalsof the header,and also connecta wirejumper between theinverting (-)
input and the ground terminal. The wire jumper will prevent a reduction in gain
caused by a floating input.
Ifyou needXLR or 1/4”RTS inputs on your CX6, CX6T, CX12,CX12T, use the optional MX-1
input expander (available through QSC’s Technical Services Department).
TypicalofQSCamplifiers,theinputimpedanceofaCXSeriesamplifieris20kilohmsbalanced
and 10 kilohms unbalanced.
EachCX Series(except CX4, CX4T) amplifier features a Level I OpenInput Architecture slot.
See the Operation Chapter for more information about Open Input Architecture.
INPUT SENSITIVITIES
Audio signals of these levels will produce full rated output power at 8 ohms.
CX4,CX4T 0.98 volt (+2.0 dBu)
CX6,CX6T 1.02 volt (+2.4 dBu)
CX12,CX12T 1.00 volt (+2.2 dBu)
IV.Outputs
Covered barrier strips located on the rear panel allow speaker cable connections to the amplifier
outputs.See thediagrams fordetails onconnecting speakersand/or distributed (25-, 70-, or 100-
volt)lines.Forattachingwires,werecommendusinginsulatedconnectorsofthetypeshown.Always
make sure the amplifier is turned off before you change any output connections or lift the safety
shroud.
Ifyouareoperatingtheamplifierinbridgedmonomodetoachievehigheroutputvoltages,neither
speakerwire isgrounded. Therefore, use the same precautions inhandling anddressing the wire
that you would for the normal “hot”outputs. See the section on bridged mono operation for
additional important instructions.
If you are driving a distributed line, make sure the sum of all the power demands of the speakers
doesnotexceedtheamplifier’spowerrating.Infact,itisgoodpracticetoallowabouta25%safety
margin.Forexample,iftheloadonthedistributedlineis400watts,useanamplifierwithapower
rating of 500 watts. See the Application Notes in the back of this manual for more details on distributed lines.
Lift safety shroud.
Loosen screw
terminals.
Insert wire connectors
under screws.
Tighten screw
terminals.
Lower safety shroud.
Balanced input
connections
Shield
Signal conductor
Wire jumper
between
input and
ground
Unbalanced input
connections

7
Output connections for CXT, bridged
mono mode, 200 volt line.
Output connections for CXT,
bridged mono mode, 140 volt
line.
If your application calls for connecting an 8-ohm speaker and a distributed line to the same amplifier channel,
theCX4T,CX6TandCX12Tcandothat.However,sincemostoftheaudiopowerisdrawnbythedirect-connected
speaker,youmustderatethedistributedline;thedistributedlineshouldhaveatotalpowerloadofnomorethan
one-fourth the amplifier’s normal distributed line power rating. Make sure the direct-connected speaker can
handle the 8-ohm power rating of the amplifier. See Applications Notes section for more details.
Output connections for CXT,
25 volt line. Output connections for
CXT, 100 volt line.
Output connections for
CXT, 70 volt line.
Output connections for CXT, direct low
impedance
Output connections for CXT, bridged mono mode.
Output connections for CX, parallel or stereo mode.Output connections for CX, bridged mono mode.

8
V.Controls&Displays
CX4 AND CX4T
The channel attenuator controls, labeled in dB of attenuation , are located on the rear panel. They have 11
detents, adjustable from 0 dB (full gain) to ×(full attenuation). The LED displays for each channel function
as shown at right.
CX6, CX6T, CX12, AND CX12T
The channel attenuator controls, labeled in dB of attenuation , are located on the rear panel. They have 11
detents, adjustable from 0 dB (full gain) to ×(full attenuation). The LED displays for each channel function
as shown at right.
VI.Operation
AC POWER
The amplifier is available for 100, 120, or 220-240 VAC, 50 or 60 Hz operation. Unless it is specially ordered
otherwise, each amplifier is configured for the line voltage in the market it is sold in. For example, those sold
in Japan are 100 VAC; for North and Central America, 120 VAC; for Europe and most of Asia, 220-240 VAC.
ThepowercordhasaplugforconnectingtoastandardACsource.For120-voltoperation,theplugisastandard
15-ampere grounded NEMA fitting; it meets safety agency requirements for current consumption of less than
12 amperes during “normal”operation, but peak current draw under heavy usage can be higher.
Modelsbuiltfor220to240-voltusehaveastandardSchuko(continentalEurope)connectoronthepowercable.
OPERATION
CX4 and CX4T
When first powering up, start with the gain controls off until proper operation is verified (upon turning on
theACswitch,the“POWER”LEDshouldcomeon,andafterthreeseconds,themutingwillstopandsound
can be heard). The amp should now be working.
Gainshouldbekeptintheupperhalfofitsrangeforfullperformance.“POWER”LEDindicatorsareprovided
to monitor the operation of each channel. Each channel has a red “CLIP”indicator that will show any
distortion in the amplifier. The mute circuit should cut the sound off as soon as you turn off the amp, and
mute for three seconds before restoring power to the speakers. This blocks turn-on and turn-off thumps.
LED Display for CX4 and
CX4T:
LED Display for CX6, CX6T,
CX12, and CX12T:

9
CX6, CX6T, CX12 and CX12T
When the amplifier is first turned on, the red “PROTECT”LED on each channel will light for about two or
threeseconds,duringwhichtheoutputrelayswillstayopentomutethespeakers.Aftertheturn-onmuting
interval,the“PROTECT”LEDsturnoff,thegreen“POWER”LEDslight,andtheoutputrelaysclosetoenable
the speaker outputs. Even during the muting interval, the yellow “SIGNAL”and red “CLIP”LEDs operate
normallyifthere is asignal present. Ifthe “CLIP”LED ison while theamplifier is muted,cut the gainback
immediately to avoid a full-power blast of sound when the output relays close. If a channel stays muted
with“PROTECT”lit,orifits“SIGNAL”or“CLIP”indicatorslightupwhenthegainisturnedallthewaydown,
it may be defective; see the troubleshooting segment for more information.
The“SIGNAL”LEDindicatessignal levelsthatare-30dB(referencedtofullrated outputpower)orhigher.
Whe the amplifier is shut off, the amplifier should mute both channels virtually instantaneously, with the
“PROTECT”indicators lit until the power supplies are discharged.
TROUBLESHOOTING
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).
•Ifreducingthegainreleasesthemuting,raisethegainbackupslowlywhileyouwatchthe“SIGNAL”
and “CLIP”indicators; the problem may be an abnormal signal (with excessive ultrasonic energy, for
example) that could otherwise damage your speakers.
PROBLEM: No sound (CX6/CX12)
•Is the channel muted? (If the “PROTECT”indicator is lit, the channel is muted; see below.)
•Isthe“SIGNAL”LED litorflashing?(Ifso,the speakerisopenorblown,thereisanopencircuitinthe
speaker wiring, or there is an open circuit in the internal output wiring of the amplifier.)
•Ifthe“SIGNAL”indicator is dark, thereis probably not enoughsignal,or even noneatall. Try turning
up the rear panel attenuators or boosting the signal level at the input.
•Ifthe“SIGNAL”indicatorshowslittleornoactivitybutthe“CLIP”LEDislitorflashing,thereisprobably
a short circuit in the speaker wiring, especially if the “PROTECT”indicator starts flashing. It is also
possible,but less likely,that the channel’s output relayis defective and will notopen, thereby short-
circuiting the channel output and producing the same symptoms.
PROBLEM: Channel goes into muting, with “PROTECT”LED on (CX6/CX12)
•If the fan is running full speed, the channel probably suffers from severe overheating. Unless there
isablockageintheflowofcoolingair,thechannelshouldreturntonormalwithinaminuteorso(see
“Overheating,”below).

10
•Ifthefanisnotrunningatfullspeed,orthechanneldoesnotresettonormalafteracool-downperiod,
themutingisprobablybecauseofaDCfaultorotheramplifierfailure,especiallyifthe“SIGNAL”or
“CLIP”indicators are lit even with the attenuator turned all the way down.
PROBLEM: Overheating
•Thethermal management system on a CX Series amplifier featuresa two-speed fan that
modulatesthecoolingairflow over the heatsinks inresponsetothecooling needs.
If the air flow is blocked, however, or if the amplifier is overdriven into very low
impedanceloads,theamplifiercouldoverheateventhoughthefanisrunningatfull
speed.
CX4 & CX4T
•At85½Cbothchannelswillmute.The“POWER”LEDwillremainlit,althoughthe“CLIP”indicatorwill
be dark. The amplifier will remain this way until the temperature drops to a safe level.
CX6, CX6T, CX12 & CX12T
•At 85½C, the channel’s output relay will mute the output. The channel will remain muted until the
temperaturedropstoasafelevel.Evenwhilethechannelismuted,the“SIGNAL”and“CLIP”indicators
willfunctionnormally.Ifthe “CLIP”indicator is flashing orcontinuouslylit,reducethe gain to hasten
the cool-down and prevent repeated thermal shutdowns.
PROBLEM: Hum in the audio
•Becauseofitsgrounded-collectoroutputtransistorconfiguration,whichmaximizesthermalefficiency,
thesignalgroundonaCXamplifiercannotbelifted.Theamplifier’sbalancedinputsaremeanttoreject
hum,butifhumremainsaproblem,checkthetightnessofthetwomountingscrewsontheinputpanel
(except CX4 and CX4T); if they are loose, the panel itself might not be well grounded to the chassis.
Ifyouhaveanyproblemswiththesescrews,contacttheQSCTechnicalServicesDepartment.Insome
cases,suchaswhentheaudiosignalcablesareroutednearlightingdimmersthatusetriacs,youmay
need to use input isolation transformers because of the extremely high noise field produced by the
dimmer circuitry. See the paragraphs on Open Input Architecture for further information on input
transformers.
OPEN INPUT ARCHITECTURE™LEVEL I (CX6, CX6T, CX12 and CX12T only)
OntherearofaCXamplifierareanupperandalowerinputpanel;bothareeasilyremoveableforfutureupgrades.
This is the concept of Open Input Architecture, and the opening in which the panels mount is called the “slot.”
Asinstalledatthefactory,theloweristheCXstandardinputpanelandtheupperoneisablank.Aribboncable
connects the “slot”panels to the rest of the amplifier. It carries input signals, speaker output monitor signals,
mutingstatus,andclipactivity;theseareforsupportingfutureaccessoriesandremotecontrolsystems.Although
thephysical dimensions ofthe CX, MXa,and EXpanels are thesame, their internalcabling isdifferent and the
CX platform supports most (but not all) of the MXa functions but doesn’t support all of the EX functions. The
CX and MXa Open Input Architecture slot thus is designated as “Level I”and the EX as “Level II.”
Tightening input panel
mounting screws

11
ThestandardinputpanelinstalledontheCXSeriesamplifierhasbalancedEuro-styledetachableheaderinputs,
gaincontrols, and theParallel-Stereo-Bridge switch. Thepanel’s circuitboard has solderfootprints for passive
roll-off circuit components, input isolation transformers, and other special customizations.
TheMX-1InputExpanderpanelmaybeinstalledintheupperpanelposition.ItfeaturesXLRinputsand1/4"RTS
inputs. Installation instructions are included with the expansion kit.
Otheravailableaccessoriesincludeauniversalfilterandastereopowerlimiter;moreareindevelopment.Contact
QSC for more details before using accessories with CX amplifiers. See the CX Application Notes also.
PARALLEL, STEREO, OR BRIDGED OPERATION (CX6, CX6T, CX12 and CX12T only)
The Parallel-Stereo-Bridge switch is located on the input panel. Always turn off the amplifier before
changing the position of this switch.
Themostcommonlyusedoperatingmodeforapoweramplifieris“Stereo,”inwhichthetwochannels
are independent and separate all the way from input to output. Set the switch in the center position
for stereo operation.
“Parallel”tiesthetwochannel inputs together sothatboth will be drivenbythe same signal, without
theneedforexternaljumpersorwiring.Aftertheinputsbothchannelsoperateindependently;though
theycarrythesamesignal,theirgaincontrolsaffectonlytheirrespectivechannels,andtheymustuse
separate speakers. Never parallel the speaker outputs!
The “Bridge”position uses both channels to provide about three times the power to a single speaker
loadthatasinglechanneldoes.Inthisposition,theswitchfeedschannel2withaninvertedsignalfrom
channel 1. Thus, when one channel “pushes,”the other “pulls,”providing twice the voltage swing of
a single channel.

12
Instructions for bridged operation
CX4 and CX4T
1. Toengagethebridgedmonomode,jumperthebarrierstripinputsontherear,inaccordancewiththe
diagramprintedunderthebarrierstrip inputs. Connect the amplifierinputtochannel1only, with the
jumpers as shown to channel 2. Channel 1 and channel 2 gains must be matched. A 4, 8, or 16 ohm
speaker load can be connected across the two red speaker terminals, using the red binding post of
channel 1 for “+”or “hot.”
CX6, CX6T, CX12 and CX12T
1. Set the switch to the “Bridge”position.
2. Connect the signal to channel 1’s input only. Do not connect an input signal to channel 2. However,
as a convenience for routing the same signal to multiple amplifiers without using Y connectors, the
modeswitchconnectsthechannel1andchannel2inputsinparallel.Therefore,youcanusechannel
2’s input terminals to pass the audio signal on to other amplifiers.
3. Useonlychannel1’sgaincontroltosetthelevel.Bothchannels’“SIGNAL”and“CLIP”indicatorsshould
flash identically when the amplifier is operating.
4. Connectthe single speaker load acrossthe + amplifieroutputs as shownin the Outputs chapter. The
positive speaker wire goes to channel 1, and the negative to channel 2.
MODE BRIDGÉMONO:
ATTENTION
TOUT LES MODÈLES—
Des tensions de sorties
aussi élevée que 160
volts rms sont
disponible aux bornes
du amplificateur CX en
mode bridgémono (200
volts aux sorties
isolés).
CX4T, CX6T ET CX12T
(opération 140V et
200V)—On doit utiliser
du câblage entièrement
isoléde CLASSE 1 pour
relier l’amplificateur
aux haut-parleurs.
VORSICHTBEIMONO-
BRÜCKENBETRIEB:
ALLE TYPEN—Zwischen
den Ausgangsklemmen
derCX-Verstärker
können Ausgangs-
spannungen bis 160 Volt
RMS anliegen (200 Volt
bei isolierten
Ausgänge).
CX4T,CX6T UND CX12T
(140V- u. 200V-
Betrieb)—Der Anschluß
mußvom Verstärker bis
zum Lautsprecher mit
vollisoliertem Kabel
erfolgen.
PRECAUCIÓNPARAEL
MODO MONO PUENTE
TODOLOSMODELOS—
Voltajes de salida de
hasta 160 VRMS existen
entre los terminales de
puente del amplificador
CX (200 voltios a las
salidas aisladas).
CX4T,CX6TYCX12T
(operación 140V y
200V)—Utilice
cableado de CLASE
UNO totalmente aislado
para conectar las
altoparlantes.
BRIDGED-MONOMODE
CAUTION:
ALL MODELS—Output
voltages as high as 160
voltsrmsareavailablebe-
tween the CX amplifier’s
bridged terminals (200
volts at isolated outputs).
CX4T, CX6T and CX12T
(140V and 200V opera-
tion)—Fully insulated
CLASS ONE wiring must
be used to connect the
amplifier to the loud-
speakers

13
MAXIMUM LONG-TERM OUTPUT POWER
Inaproperlydesignedsoundsystem,youcanobtainthedesiredsoundlevelwithoutusingthefulloutputpower
of the amplifier; if the “CLIP”indicators flash once in a while, that is perfectly normal.
If the amplifier is operated at extremely high power levels, it may overheat or may even damage the speakers.
Theamountofstressontheamplifierdependslargelyontheloadandhowhardtheamplifierdrivesit.Ingeneral,
the lower the load impedance, the more stressful the load is.
8-Ohm Loads and Lightly Loaded 25V, 70V, or 100V Lines
Theamplifiercanoperateatpracticallyanypowerlevelwithoutriskofoverheating.However,ifitispushedhard
enoughtocontinuallylightthe“CLIP”indicator,theamplifier’saverageoutputpowercanreach110to475watts
(depending on the model), which is more than many speakers can handle.
4-Ohm Loads and Heavily Loaded 25V, 70V, or 100V Lines
Ifthe“CLIP”indicatorflashesoccasionally,theamplifierisapproachingitsmaximumlong-termpowercapacity.
Ifitislitabouthalfthetime,theamplifierchannelwillprobablygointothermalprotectionwithinafewminutes.
2-Ohm Loads
Except for an occasional flash, keep the “CLIP”indicator dark to avoid overheating the amplifier channel.
AC CURRENT CONSUMPTION
A major objective in the design of the CX Series amplifiers-even the higher-powered models-is to permit their
operation from readily available, standard AC power sources.
“Normalconditions”inpoweramplifierratingmeansoperatingwitharandomprogramsource(pinknoise),using
pinknoiseasa source,atanaveragepowerlevelequaltoone-eighthofmaximumpower.Thisisrecognized by
most of the world’s safety agencies as the loudest you can play music through an amplifier and still keep the
incidenceofclippingtoareasonableminimum.Anamplifier’speakcurrentdrawatfulloutputpowerinto2ohms
is several times what the “normal”draw is, but its various protection circuits will prevent this condition from
lasting more than a minute or two.
Whenyouplan the ACpower hookups foryour amplifiers, usethe table intheSpecifications section topredict
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.

14
HEAT EMISSIONS
Essentially, a power amplifier draws electrical energy from the AC mains, converts it to DC, and then converts
itagainintoananalogoftheinputsignaltosendouttotheloudspeakers.AnyACpowerthatenterstheamplifier
throughthepowercordanddoesnotexitthroughthespeakeroutputsturnsintoheat,whichtheamplifiermust
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 the table below to predict the heat that will be emitted by your amplifier.
Full Power 1/3 Power 1/8 Power Idle
Model Channel Load BTU/hr kcal/hr BTU/hr kcal/hr BTU/hr kcal/hr BTU/hr kcal/hr
CX4,CX4T 8ΩΩ
ΩΩ
Ω+ 8ΩΩ
ΩΩ
Ω645 163 615 155 510 128 85 22
4ΩΩ
ΩΩ
Ω+ 4ΩΩ
ΩΩ
Ω1265 318 1060 267 830 210 85 22
2ΩΩ
ΩΩ
Ω+ 2ΩΩ
ΩΩ
Ω2340 590 1700 429 1295 326 85 22
70V + 70V 1365 344 1050 264 800 202 85 22
CX6,CX6T 8ΩΩ
ΩΩ
Ω+ 8ΩΩ
ΩΩ
Ω1406 354 1020 257 604 152 229 58
4ΩΩ
ΩΩ
Ω+ 4ΩΩ
ΩΩ
Ω2525 637 1617 408 921 232 229 58
2ΩΩ
ΩΩ
Ω+ 2ΩΩ
ΩΩ
Ω4658 1174 2532 638 1290 325 229 58
70V + 70V 2010 507 1503 379 1141 288 229 58
CX12,CX12T 8ΩΩ
ΩΩ
Ω+ 8ΩΩ
ΩΩ
Ω1791 452 1239 312 805 203 297 75
4ΩΩ
ΩΩ
Ω+ 4ΩΩ
ΩΩ
Ω3330 840 2081 525 1222 308 297 75
2ΩΩ
ΩΩ
Ω+ 2ΩΩ
ΩΩ
Ω5698 1437 3146 793 1611 406 297 75
70V + 70V 3772 951 2338 589 1280 323 297 75
Heat emissions of CX
amplifiers under various
conditions

15
PROTECTION CIRCUITS
Thedesigngoalinhigh-efficiencyamplifierssuchastheCXSeriesistoincreasetheamplifier’sabilitytodeliver
peak power without increasing its size, weight, and cost. However, the higher power flow through the output
components makes effective, responsive protection circuitry absolutely vital. To this end, the design of the CX
series takes a comprehensive approach to protection.
As in all QSC amplifiers, the inputs are resistively buffered for overload and RF protection. Chassis bypass
capacitors at inputs and outputs further improve RF rejection.
CX amplifiers use the proven Ouput 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.
Turn-on/turn-off muting keeps transients-both from the amplifier itself and from upstream equipment-from
reachingthe speakers whenthe amplifier isturned on or off. Theturn-on delay isapproximately 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.
Inside a CX6, CX6T, CX12, or CX12T amplifier, an NTC (negative temperature coefficient) thermistor in series
withthepowerswitchandtransformerprimarylimitsinrushcurrent.Thethermistorinitiallyhasahighresistance,
which then diminishes rapidly as it warms, to avoid power loss. Typically, the inrush current of an CX Series
amplifier thus is equal to that of another amplifier of about 1/3 to 1/2 its power rating. The low inrush of the
smaller CX4 and CX4T does not require an NTC thermistor.
WhentheDCfaultprotectioncircuitryofaCX6,CX6T,CX12,orCX12TsensesaDCvoltageonachanneloutput,
it actuates a relay which shorts the output and load to ground. The amplifier’s Output Averaging protection
circuitry will limit current to further protect the output devices. If the DC problem persists, that channel will go
into thermal protection mode and should be serviced by a qualified technician.
The output stage of a CX4 or CX4T channel has AC coupling to prevent it from passing DC.
Temperaturesensorsonthechannelheatsinksandthepowertransformersarepartofthethermalmanagement
circuitry. The temperature sensors govern whether the dual-speed fan should run at low or high speed. Below
55½C,thefan runs atlow speed; above,it runs athigh speed. Ator above 85½C,the channel mutestogo into
thermal protection.
Built-insecond-order50Hz(CX4T)andthird-order45Hz(CX6TandCX12T)Butterworthhigh-passfilteringhelps
prevent saturation in speaker transformers on distributed lines by sharply reducing the amount of ultra-low
frequency energy the amplifier puts out. However, some lower-quality speaker transformers have rated low-
frequencyresponsesthatdonotevenextendaslowasthesefilters;ifyouhaveanyoftheseinyourdistributed
line system you should insert corresponding high-pass filtering in the audio path before the amplifier.

16
VII.Specifications
CX4 CX4T CX6 CX6T CX12 CX12T
POWER OUTPUT
Directoutput,wattsperchannel,
bothchannelsdriven
8Ω, 20 Hz–20 kHz, 0.1% THD 150 200 400
8Ω, 45 Hz–20 kHz, 0.1% THD** 150 200 400
8Ω, 1 kHz, 1% THD 170 170 220 220 475 475
4Ω, 20 Hz–20 kHz, 0.1% THD 225 300 600
4Ω, 45 Hz–20 kHz, 0.1% THD** 225 300 600
4Ω, 1 kHz, 1% THD 270 270 350 350 700 700
2Ω, 1 kHz, 1% THD* 350 350 450 450 900 900
Isolatedoutputs,wattsperchannel,
bothchannelsdriven
70Vor100V,45 Hz–16 kHz, 0.25% THD** 175 250 500
25V, 45 Hz–16 kHz, 0.25% THD** 150 200 400
DirectOutputs,bridgedmono
8Ω20 Hz–20 kHz, 0.1% THD 450 600 1200
8Ω, 45 Hz–20 kHz, 0.1% THD** 450 600 1200
4Ω, 1 kHz, 1% THD* 700 700 900 900 1800 1800
Isolatedoutputs,bridgedmono
50V, 45 Hz–16 kHz, 0.25% THD** 300 400 800
140V, 45 Hz–16 kHz, 0.25% THD** 350 500 1000
200V, 45 Hz–16 kHz, 0.25% THD** 350 500 1000
*typical
DISTORTION
SMPTE-IM,lessthan0.05%
FREQUENCY RESPONSE**
CX4, CX6, CX12: 20 Hz–20 kHz, ± 0.2 dB
CX4Tdirectoutputs: -3 dB @ 50 Hz, -0.2 dB @ 20 kHz
CX4Tisolatedoutputs: 50 Hz–16 kHz, +0, -3 dB
CX6T,CX12Tdirectoutputs: -3 dB @ 45 Hz, -0.2 dB @ 20 kHz
CX6T,CX12Tisolatedoutputs: 45 Hz–16 kHz, +0, -3 dB
**Lowfrequency responseon “T”versionsislimitedby18 dB/octave45-Hz high-passfilter. Lowfrequencyresponse
on CX4T versions is limited by 12 dB/octave 50-Hz high-pass filter.
DAMPINGFACTOR
200(@directoutputs)
OUTPUTREGULATION
100V 1.0dB 1.0dB 1.1 dB
70V 1.1dB 1.1dB 1.2 dB
25V 2.0dB 2.0dB 2.0 dB
NOISE
100dB belowratedoutput(20Hzto20kHz)

17
VII.Specifications(cont.)
CX4 CX4T CX6 CX6T CX12 CX12T
VOLTAGEGAIN
@directoutputs: 35×(31dB) 35×(31dB) 40×(32dB) 40×(32dB) 56.5×(35dB) 56.5×(35dB)
INPUT SENSITIVITY, VRMS
forratedpower,8ohms 0.98 0.98 1.03 1.03 1.043 1.043
INPUTIMPEDANCE
10Kunbalanced,20Kbalanced
CONTROLS
Front: AC Switch
Rear:Parallel/Stereo/BridgeSwitch(exceptCX4,CX4T)
Ch.1and Ch.2AttenuatorKnobs(11detents:0,-2,-4,-6,-8, -10,-12, -14,-18, -24,off)
FRONTPANEL/INDICATORS(perchannel)
PROTECT: Red LED (except CX4, CX4T)
CLIP: Red LED
SIGNAL: Yellow LED (except CX4, CX4T)
POWER: GreenLED
REAR PANEL/CONNECTORS (each channel)
Input: Euro-styledetachableheader
Output: Coveredbarrierstrips
COOLING
2-speedfan,withback-to-frontairflow
AMPLIFIERPROTECTION
OutputAveraging™short circuitprotection,opencircuit,ultrasonic,RF,thermalmuting.
Stableintoreactive ormismatchedloads.
LOADPROTECTION
Turn-on/turn-offmuting,DC-faultloadgroundingrelaywithinternalfaultfuses.
OUTPUT CIRCUIT TYPE
CX4, CX4T, CX6, CX6T: ClassAB complementarylinear stage
CX12,CX12T: ClassH complementary linearstage, with 2-stephigh-efficiencycircuit
POWER REQUIREMENTS:
100,120,220-240VAC,50/60Hz

18
VII.Specifications(cont.)
POWER CONSUMPTION (see chart on page 13)
Normaloperation:1/8power@4Ωperchannel
Worstcasecontinuousprogram:1/3power@2Ωperchannel
Maximum:fullpower @2Ωperchannel
Multiplycurrenttimes0.5for220-240VACoperation
Model Channel Load AC Current, Full Power AC Current, 1/3 Power AC Current, 1/8 Power AC Current, Idle
CX4, CX4T 8Ω+8Ω5.7 A 3.4 A 2.3 A 0.4A
4Ω+4Ω9.2A 5.2 A 3.5 A 0.4A
2Ω+2Ω13.3 A 7.4 A 4.9A 0.4 A
25V, 70V, 100V 8.7A 5.0 A 3.3 A 0.4A
CX6, CX6T 8Ω+8Ω7.7 A 4.9 A 3.3 A 0.6A
4Ω+4Ω12.5 A 7.4 A 4.8A 0.6 A
2Ω+2Ω18.8 A 11.0 A 7.2 A 0.6A
25V, 70V, 100V 11.2 A 6.7A 4.5A 0.6 A
CX12, CX12T 8Ω+8Ω14.7 A 8.4 A 4.5A 0.8 A
4Ω+4Ω23 A 12.4 A 6.1 A 0.8 A
2Ω+2Ω33 A 16.5 A 8.0 A 0.8 A
25V, 70V, 100V 21 A 10.9 A 5.7 A 0.8A
DIMENSIONS
FaceplateWidth Standard19"(48.3cm)RackMounting
Chassis Depth 17.9"(45.5 cm)deep(to rearsupportears)
FaceplateHeight CX4 & CX4T: 3.5" (13.3 cm)
CX6 & CX6T; CX12 & CX12T: 5.25" (13.3 cm)
WEIGHT CX4 CX4T CX6 CX6T CX12 CX12T
Shipping 33 lb; 16.4 kg 42 lb; 21 kg 49 lb; 24 kg 62 lb; 28 kg 58 lb; 26.3 kg 75 lb; 34 kg
Net 27 lb; 13.6 kg 37 lb; 18.2 kg 42 lb; 20 kg 55 lb; 25 kg 50 lb; 22.7 kg 67 lb; 30.4 kg

19
Part2—CXSeriesApplicationGuide
Withthe helpful advice and input from contractors and consultants around the world, engineersat
QSC designed the CX Series amplifiers to be a versatile and reliable foundation for
high-quality installed sound systems.
ThisapplicationsguidewillhelpyoudesignyoursoundsystemproperlyandutilizeyourCXamplifier(s)effectively.
VIII.Distributedlines
The best way to distribute audio power from a common amplifier among numerous relatively low-powered
loudspeakersistouseadistributedline,whetheralltheloudspeakersaremeanttoreceivethesameordifferent
power levels.
Adistributedlineisusuallyreferredtobyitsmaximumvoltage-
25-,70-,100-,or140-voltlinesaremostcommon.Anamplifier’s
power rating is determined by how much current it can put out
at a standard voltage level; a low-power 70-volt amp has less
currentcapabilitythanahigh-powered70-voltamp,eventhough
theycanbothputoutthesamevoltage.Thehigh-poweredamp
can drive more speakers and at higher power levels than the
lower-powered one can. This is somewhat analogous to AC
electrical distribution, where you might have circuits rated for
15A,20A,30A,etc.,at120or240VAC,andyoucanconnectany
number of appliances to them as long as you don’t exceed the circuit’s current capacity.
Loudspeakers on a distributed line use tapped
transformers to match their power requirements
to the line. A loudspeaker with a 70-volt trans-
former tapped at 2 watts, for example, will
receivethatamountofpowerwhentheamplifier
puts out 70 volts on the distributed line. Trans-
formertapsare usually setat 3 dBintervals, i.e.,
eachsuccessivetapistwicethepowerlevelofits
predecessor.Anexamplewouldbeatransformer
tapped at 0.5, 1, 2, and 4 watts. This allows you
to select a power level that is most appropriate
forthesituationwhilestillretainingtheversatil-
ityofconfiguringotherloudspeakersonthesame
line for different power levels.
8 COM
4
8
16
COM
10W
5W
2.5W
1.2W
70V
4.5V
8
88
Amplifier 70V
0
COM
SPKR
2W
1W
0.5W COM
4
8
16
COM
10W
5W
2.5W
1.2W
COM
4
8
16
COM
10W
5W
2.5W
1.2W
A
B
C
Example of a 70 volt
distributed line
Example of a loadspeaker connected to a
distributed line through a transformer