QSC CMX 300Va 2 Channel Power Amplifier User Manual
- June 4, 2024
- QSC
Table of Contents
QSC CMX 300Va 2 Channel Power Amplifier
EXPLANATION OF SYMBOLS
The term “WARNING!” indicates instructions regarding personal safety. If the
instructions are not followed the result may be bodily injury or death.
The term “CAUTION!” indicates instructions regarding possible damage to
physical equipment. If these instructions are not followed, it may result in
damage to the equipment that may not be covered under the warranty.
The term “IMPORTANT!” indicates instructions or information that are vital to
the successful completion of the procedure.
The term “NOTE” is used to indicate additional useful information.
The intent of the lightning fl ash with an arrowhead symbol in a triangle is to alert the user to the presence of an un-insulated “dangerous” voltage within the product’s enclosure that may be of sufficient magnitude to constitute a risk of electric shock to humans.
The intent of the exclamation point within an equilateral triangle is to alert the user to the presence of important safety, and operating and maintenance instructions in this manual.
IMPORTANT SAFETY INSTRUCTIONS
WARNING!: TO PREVENT FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE.
- Read these instructions
- Keep these instructions.
- Heed all warnings.
- Follow all instructions.
- Do not use this apparatus near water.
- Clean only with a dry cloth.
- Do not block any ventilation opening. Install in accordance with the manufacturer’s instructions.
- Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifi ers) that produce heat.
- Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with one wider than the other. A grounding type plug has two blades and a third grounding prong. The wide blade or the third prong are provided for your safety. If the provided plug does not fi t into your outlet, consult an electrician for replacement of the obsolete outlet.
- Protect the power cord from being walked on or pinched particularly at plugs, convenience receptacles, and the point where they exit from the apparatus.
- Only use attachments/accessories specifi ed by the manufacturer.
- Unplug this apparatus during lightning storms or when unused for long periods of time.
- Refer all servicing to qualifi ed service personnel. Servicing is required when the apparatus has been damaged in any way, such as power-supply cord or plug is damaged, liquid has been spilled or objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture, does not operate normally, or has been dropped.
- The appliance coupler, or the AC Mains plug, is the AC mains disconnect device and shall remain readily operable after installation. On units equipped with powerCon® connectors, the AC Mains disconnect device is the AC Mains plug only; do not use the appliance coupler.
- Adhere to all applicable, local codes.
- Consult a licensed, professional engineer when any doubt or questions arise regarding a physical equipment installation.
RoHS Statement
The CMX 300Va, CMX 500Va, CMX 800Va and CMX 2000Va amplifi ers are in
compliance with European Directive 2002/95/EC – Restriction of Hazardous
Substances (RoHS).
The CMX 300Va, CMX 500Va, CMX 800Va and CMX 2000Va amplifi ers are in
compliance with “China RoHS” directives. The following chart is provided for
product use in China and its territories:
| CMXa
---|---
Part Nam
|
(Toxic or hazardous Substances and Elements )
P
|
(H
|
C
|
Cr(vi
|
PBB
|
PBDE
PCB Assemblie
|
X
|
O
|
X
|
O
|
O
|
O
Chassis Assemblie
|
X
|
O
|
X
|
O
|
O
|
O
O: Indicates that this toxic or hazardous substance contained in all of the homogeneous materials for this part is below the limit requirement in SJ/ T11363-2006.
X: Indicates that this toxic or hazardous substance contained in at least one of the homogeneous materials used for this part is above the limit requirement in SJ/T11363-2006.
FCC 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 with 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 turning 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 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/TV technician for help.
Warranty (USA only; other countries, see your dealer or distributor)
QSC Audio Products 3 Year Limited Warranty
QSC Audio Products, LLC (”QSC”) guarantees its products to be free from
defective material and/or workmanship 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, one of our authorized service stations or an authorized QSC
International Distributor via pre-paid transportation with a copy of proof of
purchase (i.e., sales receipt). This warranty provides that the examination of
the return product must indicate, in our judgment, a manufacturing defect.
This warranty does not extend to any product which has been subjected to
misuse, neglect, accident, improper installation, or where the
date code has been removed or defaced. QSC shall not be liable for incidental
and/or consequential damages. This warranty gives you specifi c legal rights.
This limited warranty is freely transferable during the term of the warranty
period. The warranty on QSC products is NOT VALID if the products have been
purchased from an unauthorized dealer/online e-tailer, or if the original
factory serial number has been removed, defaced, or replaced in any way.
Damage to, or loss of any software or data residing on the product is not
covered. When providing repair or replacement service, QSC will use reasonable
efforts to reinstall the product’s original software confi guration and
subsequent update releases, but will not provide any recovery or transfer of
software or data contained on the serviced unit not originally included in the
product.
Customers may have additional rights, which vary from state to state or from country to country. In the event that a provision of this limited warranty is void, prohibited or superseded by local laws, the remaining provisions shall remain in effect.
The QSC limited warranty is valid for a period of three (3) years from date of
purchase in the United States and many (but not all)
other countries.
For QSC warranty information in countries other than the United States,
contact your authorized QSC international distributor. A list of QSC
International distributors is available at www.qsc.com.
To register your QSC product online, go to www.qsc.com and select ”Product Registration”. Other questions regarding this warranty can be answered by calling, e-mailing or contacting your authorized QSC distributor.
Phone: 1-800-854-4079 within US and Canada, +1-714-754-6175 international, Email: warranty@qsc.com, Website: www.qsc.com.
Introduction
These rugged, fan-cooled, 2-channel, 2RU/3RU amplifi ers provide high-value performance and power in a strong, compact chassis. The series comprises four models: the CMX 300Va, CMX 500Va, CMX 800Va and CMX 2000Va.
Features
- Independent, user-defeatable clip limiters
- Fully selectable low-frequency fi ltering; choice of 30 or 50 Hz roll-off
- Stereo (dual-channel), parallel-input, or Bridge Mono operating modes
- Balanced inputs — XLR, ¼” (6.3 mm) TRS, and barrier strip
- Pluggable terminal block and NL4 outputs
- 21 detent gain knobs
- Front panel LED indicators for signal and clip and power
- Attenuation control security plate
Front Panel
- Power switch
- Power indicator LED
- Cooling vents
- Clip and Signal indicator LEDs, (Channel 1)
- Attenuation controls (Channel 1)
- Clip and Signal indicator LEDs, (Channel 2)
- Attenuation control (Channel 2)
- Lockout plate retention screw
Back Panel
- Barrier strip input
- XLR inputs, Channels 1 and 2
- TRS inputs, Channels 1 & 2
- Confi guration dip switches
- Fan
- NL4 output, Channel 1 and 2
- Terminal block connector outputs, Channels 1 and 2
- Circuit Breaker
- Serial number label
- Confi guration switch chart
- IEC power inlet (power cord connector)
Features and Setup
Attenuation Control Security Plate
The Attenuation control security plate (— Figure 4) provides protection
against accidently adjusting the Attenuation controls on the amplifi er face.
Attach the plate, after making fi nal adjustments to the Attenuation controls,
by sliding the tabs into the installation slots. Secure in place with the
attachment screw.
Setting the Mode Switches
The CMXa has mode switches for STEREO, PARALLEL INPUTS, or BRIDGE MONO modes.
Each channel has independent clip limiting and low frequency fi ltering.
Clip Limiter
What it is
When the audio signal drives the amplifi er’s output circuit beyond its power
capability, it clips, flattening the peaks of the waveform. The clip limiter
detects this and reduces the gain to minimize the amount of overdrive. To
preserve as much of the program dynamics as possible, limiting reduces the
average program level until peaks barely clip.
Each channel has its own clip limiter, and you can switch it on or off
independently, as shown in — Figure 5.
When to use it (or not)
When driving full-range speakers, clip limiting reduces high-frequency
distortion caused by bass overloads. It also protects higher frequency drivers
from excess overdrive and harsh clipping harmonics.
When driving subwoofers, some users let the amplifi er clip without limiting
because it gives extra “punch” to kick drums and similar sounds.
CAUTION: In bi-amp systems, excessive limiting will affect the frequency
balance.
Input Low-Frequency Filter
What it is
The low-frequency (LF) filter rolls off signals below either 30 Hz or 50 Hz (—
Figure 8 and — Figure 9). This improves bass performance by limiting sub-audio
cone motion, making more power available for the speakers’ rated frequency
range.
The filter settings for each channel are controlled individually through the
DIP switch settings shown in — Figure 6. When the filter is turned off (—
Figure 7), a 5 Hz roll-off protects against DC or deep sub-audio inputs.
When to use it (or not)
As a rule, your speakers will sound better with proper filtering. Unless you
already have fi altering in a preceding device, match the setting to the low-
frequency rating of your speakers. Vented (bass refl ex, ported, etc.) speakers
are especially sensitive to cone over-excursion at frequencies below their
rated limit.
The 50 Hz fi lter works well with most compact full-range speakers, and has a slight boost at 100 Hz for greater fullness. The 30 Hz fi lter is intended for subwoofers and large full-range cabinets. The “off” position should be used only for applications such as studio playback monitoring, where you need to know if there are unwanted sub-audio signals present in your mix.
Parallel Input Mode
What it is
The Parallel Input switches let you operate the amplifi er in Parallel mode,
delivering the same signal to both channels without using a Y cable. Each
channel drives its own speaker load, with independent gain, fi ltering, and
clip limiting.
Set switch positions 4 and 5 to “PARALLEL INPUTS” to couple the inputs
together (— Figure 10). Turn the switches to “STEREO” for stereo, bi-amping,
or other 2-channel modes.
With the inputs in parallel, you can use the other set of input connectors to
carry the signal to other amps (— Figure 11). This is often called a “daisy-
chain.”
When to use it
Use the Parallel mode when driving two speakers with one input signal
(Parallel mode) while keeping separate control of both channels’ gain,
filtering, and limiting. Use Parallel mode and Bridge Mono mode to patch the
signal to additional amplifi ers through the extra input jacks.
NOTE: If you’re using a balanced signal, use only balanced patch cables;
even one unbalanced cable will unbalance the entire signal chain, possibly
causing a hum.
NOTE: Turn off the “Parallel Inputs” switches when feeding the amp two separate signals.
Bridge Mono Mode
What it is
Bridge Mono mode combines the power of both amp channels into one speaker,
resulting in twice the voltage swing, four times the peak power, and
approximately three times the sustained power of a single channel. This mode
uses Channel 1’s input, attenuation control, input filter, and clip limiter;
Channel 2’s dip switch settings should be in the OFF position, and the
attenuation control should be at maximum attenuation (— Figure 12 and — Figure
13).
When to use it (or not)
Use Bridge Mono mode to deliver the power of both channels to a single 8 or 4
load. Set switch positions 6 and 7 to BRIDGE MONO ON (— Figure 12). Use
Channel 1’s inputs, and connect the loudspeaker as shown in — Figure 14 or —
Figure 15).
Bridge Mono Precautions
This mode puts a high demand on the amplifi er and speaker, Excessive clipping
may cause protective muting or speaker damage. Be sure the speaker has a suffi
cient power rating.
WARNING!: Output voltages greater than 100 volts RMS are available between the bridged terminals of the CMXa. CLASS 3 wiring methods (NEC 1999), as specifi ed in accordance with national and local codes, must be used to connect the speaker.
The Difference Between Modes
Stereo Mode
Stereo mode is the typical way of using the amplifi er. Each channel is fully
independent. Separate signals connect at the inputs, the attenuation knobs
control their respective channels, and separate speakers connect to each
output. The dip switches are set as shown in — Figure 16, a schematic
illustration in — Figure 17.
Examples:
- Two-channel (stereo) playback.
- Two independent mono signals, such as main and monitor mixes.
- Bi-amped operation, with the low frequencies in Channel 1 and the highs in Channel 2.
Parallel Input Mode
This mode is similar to the Stereo mode, except that the inputs for Channel 1
and Channel 2 are internally connected together. A signal into Channel 1 jack
drives both channels directly (— Figure 18). Use Channel 1 Input, do not
connect different sources to both channels. Each channel’s attenuation control
still functions as usual, and each channel feeds its own speaker load. The dip
switches are set as shown in — Figure 19.
In Parallel mode, you can patch the input signal on to additional amplifi ers
by using any of the remaining input jacks. See Ch. 2 in — Figure 18.
Example:
One mono signal driving both channels, with independent attenuation control
for each speaker system.
Bridge Mono Mode
This mode combines the full power capabilities of both channels into a single
speaker system. The amplifi er internally re-confi gures so that both channels
operate as a unit. This delivers double the output voltage, resulting in four
times the peak power and three times the sustained power into a single 8 or 4
speaker load. The Bridge Mono mode section on page 10 describes the special
loudspeaker connection used.
Examples:
- Driving a single 8 speaker with the combined 4 power of both channels.
- Driving a single 4 speaker with the combined 2 power of both channels.
Precautions:
- Bridge Mono mode makes it possible to drive thousands of watts into a single speaker. AC current consumption will usually be higher. Avoid excessive signal level, and make sure the wiring and speaker can handle the power.
- If the load is 4 or less and prolonged overloads occur, the amplifi er will probably mute for several seconds during peaks, and the circuit breaker may trip.
- Do not use 2 loads.
- Ensure Channel 2 dip switches are set to off (— Figure 20), and Channel 2 attenuation control is set to maximum attenuation.
NOTE: See the additional Bridge Mono precautions on page 10.
Distributed Constant Voltage Outputs
Please refer to the above section on Bridge Mono mode for proper setup confi guration.
70/100 Volt Operation:
- The CMX 300Va and 500Va must be confi gured for Bridge Mono mode for 70 Volt operation.
- The CMX 800Va and CMX 2000Va can operate in 70 Volt operation in Stereo mode or Bridge Mono mode.
- The CMX 500Va and CMX 800Va must be confi gured for Bridge Mono mode for 100 Volt operation. Please refer to the Bridge Mono mode section for proper setup confi guration.
The CMX 2000Va can operate in 70 Volt or 100 Volt operation in STEREO mode or BRIDGE MONO mode.
Installation
Rack mounting of the amplifi er is optional.
Use four screws and washers when mounting the amplifi er to the front rack
rails.
Support the amp at the rear also, especially in mobile and touring use; rear
rack mounting ear kits are available from QSC’s technical services department
or by special order from your dealer or distributor. Use the dimensions in —
Figure 23 and — Figure 24 for planning.
Connections
Inputs
Each channel has active balanced XLR and ¼” (6.3 mm) inputs wired in parallel
(— Figure 25). The input impedance is 20 k balanced, 10 k unbalanced.
Balanced signals are less prone to AC hum, but unbalanced signals can be
suitable for short cable runs. The signal source’s output impedance should be
less than 600 to avoid high-frequency loss in long cables.
Balanced Inputs
Use the XLR or ¼” (6.3 mm) TRS input jacks, or the barrier strip (— Figure 26
through — Figure 28).
Unbalanced Inputs
- Connect the unused side (Pin 3) of the balanced input to ground (Pin 1), as shown in — Figure 26.
- A tip-sleeve ¼” (6.3 mm) connector will correctly terminate the unused side of the input as shown in — Figure 27.
- For Stereo operation, use the inputs for both Channel 1 and Channel 2. For Parallel or Bridge Mono operation, use the Channel 1 input.
- See the section on operating modes for more information. To patch the audio signal to other amps (Parallel and Bridge Mono modes only), see the instructions for using Parallel Inputs on page 9.
Outputs
NL4 Outputs
CMXa amplifi ers offer a choice of output connections, with two NL4 jacks and a
Terminal Block connector.
The NL4 connector is designed specially for high-power speaker connections. It
locks in place, prevents shock hazard, and assures the correct polarity.
The upper NL4 jack has both Channel 1 and Channel 2 outputs, so it is
especially useful for Parallel, bi-amp, or Bridge Mono mode operation (see
Bridge Mono mode operating precautions on page 10). The other NL4 carries only
the output from Channel 2.
For easier insertion, use the NL4FC connectors with quick-lock thumb latches
(Not shown).
Speaker Cabling
Larger wire sizes and shorter lengths minimize both loss of power and
degradation of damping factor. Do not place speaker cables next to input
wiring.
WARNING!: To prevent electric shock, do not operate the amplifi er with any of the conductor portion of the speaker wire exposed.
Terminal Block Connector
The terminal block connector requires the following assembly.
- Strip the wires to 7 ~ 8 mm.
- Insert the wires into the male part of the connector according to the Mode you are using. See below.
- Use a fl at-tip screwdriver to secure the wires. Tighten the screws to 6 in.-lbs.
- Insert the plug into the receptacle on the amplifi er.
- Use a fl at-tip screwdriver to secure the connector. Tighten the screws to 6 in.-lbs.
Stereo and Parallel Mode : Connect the wires as shown in — Figure 30, or
as shown by the solid wires in — Figure 32.
Bridge Mode: Connect the wires as shown in — Figure 31, or as shown by
the dashed wires in — Figure 32.
| Terminal Block Connector | Wiring | UL | IEC |
|---|---|---|---|
| Wire range | – | 6 mm2 | |
| Solid wire (AWG) | 28 – 10 | – | |
| Stranded wire (AWG/mm2 ) | 28 – 10 | – | |
| Torque (lb.-in.) | 6 | – | |
| Wire strip length |
— Table 3 —
| 7 – 8 mm| –
Operation
AC Power Switch (AC Mains)
Make sure you connect the amplifi er to the correct AC line voltage, as shown
on the serial number label. Connecting to the wrong line voltage is dangerous
and may damage the amplifi er (— Figure 33).
Before applying power, check all connections and turn the attenuation controls
fully counterclockwise to maximum attenuation.
One second of muting is normal when the amp is turned on or off (— Figure 34).
Attenuation Controls
The controls are marked with a scale indicating attenuation. Maximum
attenuation is fully counterclockwise, minimum attenuation is fully clockwise.
he Attenuation controls are marked in numeric increments from ∞ to 0
(clockwise) indicating the amount of attenuation. Settings should normally be
made within the lower attenuation range. The range above 14 on the attenuation
scale should not be used for normal program levels, as the input headroom
could be exceeded, but can be used for testing at reduced gain levels. At the
maximum attenuation setting (∞), the signal is completely cut off(— Figure
35).
LED Indicators
The green SIGNAL LED indicators light at approximately 0.1% of full power.
The red CLIP LED indicator fl ashes during overload (clipping). If the amplifi
er’s protection circuitry triggers protective muting, the signal and clip LEDs
will not light.
If this occurs during use, see the Troubleshooting section on page 17.
Fan Cooling
The fan speed varies automatically to maintain safe internal temperatures.
Keep the front and rear vents clear to allow full air fl ow. Hot air exhausts
out the front of the amp so it does not heat the interior of the rack. Make
sure that plenty of cool air can enter the rack, especially if there are other
units that exhaust hot air into it.
Safe Operating Levels
The amp’s protective muting system guards against excessive internal
temperatures. With normal ventilation and 4 – to 8 loads, the amplifi er will
handle any signal level
including overdrive-but make sure that the speakers can handle the full power!
However, lower load impedances and higher signal levels produce more internal
heating. Into 2 loads, frequent or prolonged clipping (indicated by constant fl
ashing of the red CLIP LED) may trigger protective muting. Bridged mono mode
doubles the output impedance of the amp; 4 is the minimum load impedance.
Heavy clipping may cause muting. If this happens, see the Troubleshooting
section on page 17.
Troubleshooting
Problem: No Sound
Indication: POWER indicator not lit
Check the AC plug. Also check the circuit breaker on the rear panel.
Confi rm that the AC outlet works by plugging in another device. If too many
amplifi ers are used on one outlet, the building’s circuit breaker may trip and
shut off power.
An overload in Bridged Mono mode may cause the amplifi er to click off for several seconds. Check the load impedance (4 minimum), or reduce signal level.
An amplifi er that keeps shutting off may have a serious internal fault. Turn
it off, remove AC power, and have the amplifi er serviced by a qualifi ed
technician.
Indication: SIGNAL LED responding to signal level
If the green SIGNAL indicators are lighting normally, the fault is somewhere
between the amp and the speaker. Check the speaker wiring for breaks. Try
another speaker and cable.
Indication: SIGNAL LED not lit
If the green POWER indicator LED is lit and the fan is running, yet the signal
LEDs indicate no signal, check the input. Make sure the signal source is
operating and try another input cable. Connect the source to another channel
or amplifi er to confi rm its operation.
Indication: CLIP LED fl ashing
If the red CLIP indicator fl ashes when signal is applied, the amplifi er output
may be shorted. Check the speaker wiring for stray strands or breaks in the
insulation.
Indication: CLIP LEDs bright and steady
The amplifi er is in protective muting.
One second of muting is normal when the amp is turned on or off.
Overheating will cause protective muting. The fan will be running at full speed and the chassis will be hot to the touch; sound should resume within a minute as the amplifi er cools to a safe operating temperature. Check for proper ventilation. If the fan isn’t running at all, the amplifi er requires servicing.
Problem: Distorted Sound
Indication: CLIP LED fl ashing
If the red CLIP indicator fl ashes before the signal indicator does, the load
impedance is abnormally low or shorted. Unplug each speaker one by one at the
amplifi er. If the CLIP LED goes out when you disconnect a cable, that cable or
speaker is shorted. Try another cable and speaker to locate the fault.
Indication: CLIP LED not fl ashing
This could be caused by a faulty speaker or loose connection. Check the wiring
and try another speaker.
The signal source may be clipping. Keep the amplifi er attenuation controls at
mid-point so that the source does not have to be overdriven.
Problem: No channel separation
Check the switch settings on the back of the amplifi er. Make sure the
“Parallel Input” and “Bridge Mode” switches are OFF in dual-channel, bi-amp,
or stereo use where different signals go to each channel.
Make sure other equipment in the signal path, such as mixers, preamps, etc.,
are set for stereo, not mono.
Problem: Hum
Move cabling and signal sources to identify “hot spots” in the system. Cables
with faulty shielding are a frequent entry point for hum.
Problem: Hiss
Unplug the amplifi er input to confi rm that the hiss is coming from the source
or a device upstream; erratic or popping noises indicate an electronic fault
in the offending unit.
To keep the normal noise floor low, operate the primary signal source at full
level, without clipping, and avoid boosting the signal further between the
source and the amplifi er.
Problem: Squeals and feedback
Microphone feedback should be controlled with mixer controls. If noise
continues to build up with zero mic gain, there is a serious fault in the
signal processors or cables. Working in succession from the signal source
towards the amplifier, check each device in the signal path by reducing its
gain or unplugging it.
Specifications
Mailing Address:
QSC Audio Products, LLC
1675 MacArthur Boulevard
Costa Mesa, CA 92626-1468 USA
Telephone Numbers:
Main Number: 714-754-6175
Sales & Marketing: 714-957-7100 or toll
free (USA only) 800-854-4079
Customer Service: 714-957-7150 or toll
free (USA only) 800-772-2834
Facsimile Numbers:
Sales & Marketing FAX: 714-754-6174
Customer Service FAX: 714-754-6173
World Wide Web:
www.qsc.com
E-mail:
info@qsc.com
service@qsc.com
© 2013 QSC Audio Products, LLC. All rights reserved. QSC™ and the QSC logo are
registered trademarks of QSC Audio Products, LLC.
All other trademarks are the property of their respective owners. Patents
pending.
References
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