QSC Audio CX168 User Manual
CX168
8-Channel Installed Sound
Professional Audio Amplifier
User Manual
*TD-000095-00*
TD-000095-00 rev.A
1
IMPORTANT SAFETY PRECAUTIONS
& EXPLANATION OF SYMBOLS
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
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 enclosure that may be of sufficient
magnitude to constitute a risk of electric shock to humans.
The exclamation point within an equilateral triangle is intended to alert the user to the
presence of important operating and maintenance (servicing) instructions in this manual.
The lightning flashes printed next to the OUTPUT terminals of all ISA amplifiers are intended to alert the user
to the risk of hazardous energy. Output connectors that could pose a risk are marked with the lightning flash.
Do not touch output terminals while amplifier power is on. Make all connections with amplifier turned off.
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK, DO
NOT REMOVE THE COVER. NO USER-SERVICEABLE PARTS
INSIDE. REFER SERVICING TO QUALIFIED PERSONNEL.
WARNING: TO PREVENT FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS
EQUIPMENT TO RAIN OR MOISTURE.
This amplifier has a serial number located on the rear panel.
Please write this and the model number down and keep them for your records.
Model: CX168
Serial Number:______________________________
Date of Purchase:____________________________
Purchased From:_____________________________
FCC INTERFERENCE STATEMENT
NOTE: This equipment has been tested and found to comply with the limits for a class B digital device, pursuant to part
15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interference in a
residential installation. This equipment generates, uses, and can radiate radio frequency energy and if not installed
and used in accordance to the instructions, may cause harmful interference to radio communications. However, there is
no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful
interference to radio or television reception, which can be determined by switching the equipment off and on, the user
is encouraged to try to correct the interference by one or more of the following measures:
- Reorient or relocate the receiving antenna.
- Increase the separation between the equipment and the receiver.
- Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
- Consult the dealer or an experienced radio or TV technician for help.
© Copyright 2001, QSC Audio Products, Inc.
“QSC” and the QSC logo are registered with the U.S. Patent and Trademark Office
2
QSC® is a registered trademark of QSC Audio Products, Inc.
The Audio Precision logo is the property of Audio Precision, Beaverton OR
All trademarks are the property of their respective owners.
TABLE OF CONTENTS
INTRODUCTION:
CX168 Overview .......................................................................................4
Front Panel Illustration .........................................................................................4
Rear Panel Illustration ........................................................................................5
Mounting Dimensions .........................................................................5
INSTALLATION:
What is Included..............................................................................................6
Rack Mounting ....................................................................................6
Supporting the Rear of the Amplifier.....................................................6
Fan Cooling...........................................................................................7
AC Mains (AC Power) Connection..............................................................................7
SETUP:
Setting the Configuration (MODE) Switches....................................................8
Setting Operating Mode (Stereo, Parallel, or Bridge)........................................9
Clip Limiter Setting.............................................................................10
Low Frequency (Subaudio) Filter Settings................................................................10
Low Frequency Filtering Tips and CX168 Frequency Response Curve...................11
CONNECTIONS:
Inputs: Connecting to the Input Terminal Block Inputs ...................................12
Outputs: Connecting the Outputs in Stereo or in Bridge Mode .........................14
OPERATION:
Power Switch ............................................................................................16
LED Indicators .......................................................................................17
Gain Controls ......................................................................................18
DataPort Connector ...................................................................................20
APPLICATIONS:
Four Room, Stereo Feed..............................................................................................22
Tri-Amplified, Stereo Cabinets with Subwoofer..............................................22
APPENDIX:
Detailed Explanation of Stereo, Parallel, and Bridge Operating Modes..........24
Multiple Speaker Loads in Series........................................................26
Multiple Speaker Loads in Parallel........................................................27
Connecting to the DataPort Inputs.......................................................13
How to use the 8-pin Output Connectors................................15
Security Plate for Gain Controls .........................................................19
DataPort Guidelines for the CX168.........................................21
TROUBLESHOOTING ........................................................................................................28
SPECIFICATIONS ......................................................................................................30
WARRANTY INFORMATION .............................................................................................32
HOW TO CONTACT QSC AUDIO PRODUCTS ............................................................................32
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INTRODUCTION
Congratulations on your purchase of the CX168 power
amplifier. To help you obtain the best results from your
purchase, we encourage you to carefully review this manual.
With information including connections, configuration and
operation, it offers many useful guidelines.
The CX168 provides a high level of channel density in a small,
lightweight form factor ideal for multi-zone audio systems.
Representing the culmination of QSC’s extensive experience
in power amplifier development, the CX168 is a highly
versatile, reliable, and user-friendly tool that will likely remain
a central component of your system for years to come.
Like the entire CX Series, the CX168 is equipped with QSC’s
exclusive PowerWaveTM switching power supply technology
to virtually eliminate noise and hum while reducing the unit’s
overall weight. Comprehensive protection circuitry includes
DC, infrasonic, thermal overload and short circuit protection.
The CX168 includes 4 HD15 DataPorts (one per channel pair)
for remote management or DSP. These ports allow each
channel pair to be governed by QSControl, QSC’s audio
networking system—enabling the system operator to control
amplifier gain levels, check the unit’s clipping and thermal
status, plus monitor numerous additional system parameters.
Alternatively, these DataPorts facilitate connection of signal
processing equipment, such as QSC’s DSP-3, which offers two
channels of independent digital signal processing - including
crossover filters, shelf filters, signal delay, compression, peak
limiting, and parametric filters.
As individual channel pairs may be bridged, the CX168 is
configurable as a 4-, 5-, 6-, 7-, or 8-channel unit. Further, the
CX168 features detachable Phoenix-style input and output
connectors—enabling the audio system to be wired with
greater ease. Other features include 1-dB recessed and
detented gain controls and a security cover for tamper-proof
installations.
The CX168 is easy to use. All operating mode switches are
grouped together on the rear panel, with one switchblock per
channel pair. These switches enable clip limiter on/off, LF
filter on/off, LF filter select and operation modes. The
amplifier’s front panel includes corresponding LEDs to indicate
Bridged or Parallel modes in addition to Signal and Clip
status.
Your CX168 power amplifier was designed to provide many
years of trouble-free, great-sounding operation. We hope you
enjoy your new CX168.
FRONT PANEL
FRONT PANEL WITH
SECURITY PLATE
4
INTRODUCTION
REAR PANEL
DIMENSIONS
AND MOUNTING
POINTS
5
INSTALLATION: UNPACKING & RACK MOUNTING
What is Included
Your CX168 shipping container, as shipped from the factory,
includes:
- CX168 eight channel audio power amplifier
- this user’s manual
- security cover (plate) for gain controls
- self-adhesive rubber feet (use for non-rack mount applications)
- eight 3-pin terminal block input connectors
- two 8-pin terminal block output connectors
- #14AWG IEC-type detachable power cord
Rack Mounting
Use four screws and washers to secure the amplifier to the
equipment rack rails. Support the weight of the amplifier
while securing it to the rails to avoid bending or distorting
the mounting ears. The amplifier may be used in an
equipment rack or as a stand-alone unit. Rack mounting is
optional. Self-adhesive rubber feet are provided for non-rack
mount applications.
Supporting the Rear of the Amplifier
Unless the amplifier is being installed in its final, fixed
location, we strongly recommend supporting the rear of the
amplifier.
Save the container and packing material
so the amplifier may be shipped without
damage if service is ever required. If the
original container is not available, be
sure to use a strong shipping container with enough
packing material to prevent the amplifier from being
damaged in transit.
Supporting the rear of the amplifier is required for mobile
and portable use. If the amplifier is to be transported in any
way, install the optional rear rack mounting ear kit to
support the rear of the amplifier. During transport, the shock
loads encountered on the chassis and rack can easily
damage an unsupported amplifier and the rack rails. With
proper support, reliability is enhanced.
Rear rack mounting ear kits are an accessory item and are
available from QSC’s Technical Services Department or from
your dealer or distributor. Refer to the literature included
with the rack mounting ear kit for installation instructions.
Two methods of rear rack mounting ear attachment are
possible; use the method that best suits you application.
Optional rear rack mounting ear attachment methodsrefer to the rear rack mounting ear kit’s documentation
for details
6
INSTALLATION: COOLING & AC MAINS REQUIREMENTS
Fan Cooling
The CX168 amplifier draws cool air into the rear of the
amplifier and exhausts hot air from the front. This is done so
the equipment in the rack stays as cool as possible. This
method of cooling gives the operator “direct” air temperature feedback at the front of the rack, where it is the most
convenient. The front panel’s temperature indicates “how
hard” the amplifier is working.
The fan varies speed automatically to maintain safe internal
temperatures and minimize noise. Keep the front and rear
vents clear to allow full air flow.
Air flow in QSC amplifiers
Do not obstruct the front or rear air vents! Make sure that plenty of cool air can enter
the rack, especially if there are other units which exhaust hot air into it.
AC Mains Connection
The correct AC line voltage is shown on
the serial number label. Make sure the AC
mains is the correct voltage. Connecting to the
wrong line voltage is dangerous and may
damage the amplifier.
Connect the AC line cord by orienting the
IEC plug correctly and pushing the plug firmly
into the IEC receptacle. It should seat tightly. It
can only be inserted when it is properly
oriented.
Use the cord supplied with the amplifier, or an
equivalent. Insure that the wire gauge of the
cord is #14AWG. Use of #16 or #18 AWG can
be dangerous and is not recommended.
Use the best possible connection to the
AC power source. Avoid extension cords as
they will cause some voltage drop between
the AC source and you amplifier. If the use of
an extension cord is required, ensure that it is
the shortest length possible and is at least
#14 AWG. Ensure that all grounding connections are maintained.
NOTE: Excessive length or inadequate gauge
may result in short muting episodes if all
channels are driven to full power.
The correct AC line voltage is shown on the
serial number label.
Connecting to the wrong line voltage is
dangerous and may damage the amplifier or
constitute the risk of electric shock. Verify the
correct AC line voltage by checking the
specification printed on the serial number
label on the rear panel.
7
SETUP: SETTING THE MODE CONFIGURATION DIP SWITCHES
Setup
By using the mode switches and connecting to the amplifier
properly, the CX168 amplifier can be configured as a 1 to 8
channel amplifier. This flexibility enables the CX168 to be
used for most any multichannel application.
The CX168 can be thought of as four separate 2-channel
amplifiers on one chassis. Each of the four amplifier
sections may be operated in Stereo, Parallel, or Bridge mode
independently of the others. For example, channels 1 & 2
could be set for stereo operation while channels 3 & 4 are
set for parallel operation; all while channels 5 & 6 and
channels 7 & 8 are set for bridge mode.
The channels are grouped as follows:
Channels 1 and 2
Channels 3 and 4
Channels 5 and 6
Channels 7 and 8
You can set the operating mode for each group by setting
that group’s configuration DIP switches in the desired
positions. It is NOT POSSIBLE to group the channels
differently. For instance, you can not bridge channels 3 & 5
because they are not in the same channel group.
Before setting the configuration DIP switches, you must first
decide how the amplifier will connect to the speaker
system.
“MODE” configuration DIP switches are located on
the rear panel and look like the illustration above.
Switch positions shown are for example only. Set
switches as required for your application.
“MODE” switch settings and speaker connection diagrams are printed on a rear panel label, as shown, above.
8
SETUP: SETTING THE MODE: STEREO, PARALLEL, OR BRIDGE
Modes
The following descriptions apply to a channel pair (such as Ch. 1 & 2 or Ch. 7 & 8). It is possible to set each channel pair’s mode
differently and customize the system configuration. All possible combinations will not be shown. The following describes the
behavior of one channel pair in the three modes of operation and the
Stereo- Stereo mode supports two completely
separate audio channels, usually referred to as ‘left’
and ‘right’. Stereo configurations have two separate
input signals and two separate output signals.
Parallel- Parallel mode applies one input signal to
both channels. Both inputs of a channel pair are
connected in parallel when the mode switch is set
for parallel, therefore, connect only one input per
channel pair when in parallel mode. The outputs are
connected the same as stereo mode. Each speaker
will be supplied the same signal, which is still
controlled by that channel’s gain control.
BRDG
and
PAR
LED’s:
Mode switch settings and LED indication for stereo mode operation.
BRDG and PAR indicators should not be illuminated when in stereo mode.
Bridge- Bridge mode combines the two channels of
a pair (such as Ch. 3 & Ch. 4) into one higherpowered channel. Like parallel mode, both inputs of
a channel pair are connected in parallel when the
mode switch is set for parallel, therefore, connect
only one input per channel pair when in bridge
mode. There are 4 possible channel pairs that can
be bridged on the CX168. They are Ch.1-2 Bridge,
Ch. 3-4 Bridge, Ch. 5-6 Bridge, and Ch. 7-8 Bridge.
Any pair or number of pairs can be independently
configured in bridge mode. Use the first channel’s
input and gain control when in bridge mode. The
second channel’s gain control is non-operative and
should be turned all the way down.
Note! Do not connect more than one input per channel pair when operating in parallel or bridge mode. However,
in parallel or bridge mode, the unused input terminals may be used for daisy-chaining the input signal to other
channels of the CX168 or to other amplifiers.
For pictorial description of operating modes, see Appendix.
Mode switch settings and LED indication for parallel mode operation.
PAR indicator should be illuminated and BRDG indicator should not be
illuminated when in parallel mode.
Mode switch settings and LED indication for parallel mode operation.
BRDG indicator and PAR indicator should be illuminated when in bridge
mode.
9
SETUP: MODE SWITCHES: CLIP LIMITER AND LOW FREQUENCY FILTERS
Clip Limiter
The CX168 amplifier has separate clip limiters for each of
the 8 channels. These clip limiters respond only to actual
amplifier clipping. Amplifier clipping generates internal error
signals which cause the clip limiter to quickly reduce gain
and minimize the overdrive. To preserve as much of the
program dynamics as possible, limiting occurs only during
actual clipping. Each channel’s clip limiter can be switched
on or off individually.
The clip limiter is internally set to respond as fast as
possible after clipping is detected. For program material that
is primarily “full-range”, the effect on the overall audio
quality should be imperceptible. We recommend using the
clip limiters for almost all applications, especially full-range
audio applications. Clipping can cause high-frequency
artifacts to be output to the speakers, potentially damaging
fragile high-frequency drivers.
For program material that is primarily low-frequency in
nature (low-frequency or subwoofer drive) this may be
perceived as a “rubbery” effect on the audio. If this is the
case, it may be preferable to turn the clip limiters off and let
the amplifier clip occasionally. With robust, low-frequency
drivers, the occasional clipping should cause no problems.
CAUTION! Clip limiting reduces extreme
overdrive peaks, allowing a higher average
signal level without distortion. Increasing the
gain with the clip limiter engaged until
clipping is again audible, can double the
average output power. Be careful not to
exceed the power rating of the speakers!
Low Frequency Filter
When driving speakers with limited low frequency
response, it is important to limit the low frequency
response of the amplifier. Doing so can result in more
usable bass response since the speaker is not being
overloaded by very low frequencies it can’t handle.
Explanation-
more speaker cone motion to produce the same apparent
loudness as higher frequencies. Properly designed speaker
enclosures help the speaker to move more air with less
motion using techniques like porting. Such enclosures only
benefit from porting down to a certain frequency. Below
this frequency, the speaker is “unloaded” and is basically
free to move around uncontrollably without producing much
bass. Limiting the frequency range of the low frequency
content enables the speaker to behave the way it was
designed to. If frequencies lower than designed are
supplied to the speaker, performance will degrade.
All low frequency filters will change the character of low
frequency transients. For best results, the cabinet design,
speaker capabilities, and program material must be taken
into account when configuring low frequency filtering.
Low frequency sound waves require much
10
SETUP: MODE SWITCHES: CLIP LIMITER AND LOW FREQUENCY FILTERS
Low Frequency Filtering Tips:
The OFF position should be used only for subwoofer systems with rated frequency response below 33 Hz. or if low frequency
filtering is provided by other devices.
Know the specification of the speaker cabinet you are driving. Match the low frequency roll off setting to the specified low
frequency capability of the speaker cabinet. Do not drive the speaker with frequencies below its rating.
Unless you have low frequency filtering before the amplifier, use the low frequency filter to protect your loudspeakers from
cone over-excursion caused by frequencies below the speaker’s limits.
The 33 Hz. rolloff is a good “all purpose” setting. Turn the filter on by setting the appropriate DIP switch to ON position and
select 33 Hz. using its 33/70 Hz. DIP switch. This setting is a good starting point for most large, full-range cabinets.
The 70 Hz. rolloff is a good setting to use with smaller, compact speaker cabinets having limited bass capability. Turn the
filter ON and select the 70 Hz. setting when using smaller cabinets.
The frequency selection ( 33 or 70 Hertz) has no effect unless the filter is set to the ON position.
Frequency Response Curves
Filter off
Filter ON, 70 Hz.
Filter ON, 33 Hz.
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