Rev. B
Rev. A
The SEQ-2 is an embedded stereo (dual-channel) five-band graphic equalizer accessory for use with select QSC power
amplifiers. Compatible amplifier models and lines, both current and discontinued, include:
All PLX (original series), two-channel CX, and two-channel DCA models (with a BSC-3 or BSC-5 BusCard installed)
All four-channel CX and DCA models (with a BSC-7 BusCard installed)
PowerLight models PL 1.0, PL 1.0HV, PL 1.4, PL 1.5X, PL 1.6HVX, PL 1.8, and PL 2.0HV (with a BSC-2* or BSC-4 BusCard installed)
PowerLight models PL 3.4, PL 3.8X, and PL 4.0 (with a BSC-6 BusCard* installed)
All MXa models (MX 1000a, MX 1500a, MX 2000a, and MX 3000a; Note: does not include MX 700), which use Level 1 Open
Input Architecture
All EX models (EX 800, EX 1250, EX 2500, and EX 4000), which use Level 2 Open Input Architecture
Legacy CX models CX6, CX6T, CX12, and CX12T, which use Level 1 Open Input Architecture
* When the SEQ-2 and BusCard are installed in an amplifier, access to some or all of the SEQ-2’s trimpots is restricted.
Using the SEQ-2 as a default EQ is ideal for rental sound systems, since it virtually eliminates the possibility of unauthorized
tampering with settings or other such user errors.
Physically, the SEQ-2 is a small circuit card that mounts inside the amplifier. EX, MXa, and legacy CX amplifier models that use
Open Input Architecture have a two-section row of 22 solder holes called a “Mini Slot” on their input boards. This is where
the SEQ-2 is installed. The input board is part of the removeable input module, so the SEQ-2 can be installed without opening
the amplifier chassis or even removing the amplifier from its equipment rack.
Other models such as the PowerLight, PLX, DCA and CX
series require the installation of an appropriate BusCard in
order to provide a slot for the SEQ-2. Depending on the
amplifier model, a BusCard can provide as many as four
slots for accessory cards. Each slot is equivalent to the “Mini
Slot” of the older amplifiers’ Open Input Architecture. For
ease of installation, it is best to mount the SEQ-2 to the
BusCard before installing the BusCard itself inside the
amplifier. NOTE: The PLX2, PowerLight 2, and PowerLight 3
series amplifiers are not compatible with BusCards.
The installation process involves soldering, so only qualified
technical persons should attempt to install the SEQ-2; ideally,
you should enlist QSC’s Technical Services department or an
Figure 1. Boost and cut response curves of the SEQ-2
authorized service center to perform the task. The installation
section of this manual offers more information about installing the SEQ-2.
Both channels feature electronically balanced input circuitry and five bands of fixed-frequency boost/cut filtering. Figure 1
shows the audio spectral characteristics of the filtering circuits. Either channel can be bypassed or engaged by placement of
a jumper on the SEQ-2 card.
The SEQ-2’s standard filter section frequencies are set in two-octave intervals: 40 Hz, 160 Hz, 630 Hz, 2.5 kHz, and 10 kHz;
however, the equalizers can be constructed with custom frequencies. The standard Q (center frequency ÷ bandwidth at ±3
dB points) of each filter section is 0.75, but that figure can also be customized.
Copyright © 2000, 2003, 2010 QSC Audio Products, LLC. All rights reserved.
The SEQ-2 circuit board has two 3-pin headers, and two groups of five trimmer potentiometers, or trimpots (see Figure 2); all
are used for programming the module. The circuitry for the two channels is identical.
Depending on its position on some BusCards, the SEQ-2’s bypass/engage jumpers and headers may not be easily accessible
once the accessory is installed; on such units, configure the jumpers before installing the accessory on the BusCard.
However, the trimpots, which control the amount of boost or cut on each band, can be fully adjusted after installation.
Notes on Stereo, Bridged, or Parallel Operation
The input board or amplifier into which the SEQ-2 is installed typically has a switch for setting the operating mode of the
amplifier—i.e., stereo, parallel mono, or bridged mono. In the signal flow, the Mini Slot or BusCard is located somewhere
after this switch, so you must
configure the channels of the
SEQ-2 according to the oper2
ating mode selected. In ste3
Place jumper across pins 1 and 2 to bypass
Place jumper across pins 1 and 2 to bypass
Place jumper across pins 2 and 3 to engage
Place jumper across pins 2 and 3 to engage
reo or parallel mode, you
J2 J3
must configure or bypass both
Channel 1 engage/bypass Channel 2 engage/bypass
channels. If the amplifier is in
bridged mode, bypass channel 2 and use channel 1’s
input and processing only.
Bypassing the filtering
To completely bypass a
channel’s filtering circuitry,
Figure 2. Engage/bypass headers on the SEQ-2
set the jumper on its header
across pins 1 and 2, which are the upper two pins (see Figure 2). Note: If you neglect to place a jumper on a header, no
signal will pass on that channel.
Programming the equalizer
To use the equalizer on a
channel of the SEQ-2, set the
jumper across pins 2 and 3
on that channel’s header. Figure 3 shows the trimpots and
the frequencies they control.
Figure 4 shows the effect of
a trimpot on boost and cut.
Channel 2
10 kHz
2.5 kHz 630 Hz
Channel 1
160 Hz
40 Hz
10 kHz
2.5 kHz 630 Hz
160 Hz
40 Hz
Figure 3. The SEQ-2’s ten trimpots, by channel and frequency band
-12 dB
-2 0 +2
+12 dB
Figure 4. Details of trimpot adjustment
Installating the SEQ-2 requires PC board soldering skills, so only qualified service technicians should attempt it. Any
authorized QSC service center—or, for an additional installation fee, the QSC Technical Services department—can perform
the installation.
When installed, the SEQ-2 settings and adjustments are not externally adjustable; this can prevent tampering by
unauthorized users.
Installing the SEQ-2
Tools and materials you will need:
Soldering iron
Desoldering iron or other suitable desoldering equipment
Phillips screwdriver
Wire cutters
Rosin-core electronic solder
Non-conductive alignment tool (slot type), for adjusting trimpots
The SEQ-2 contains active components which can be damaged by electrostatic discharge (ESD). Be sure to practice standard
ESD precautions and always ground yourself and your workstation before handling exposed circuit cards.
EX, MXa, or legacy CX models
The SEQ-2 installs on the input PC board of a QSC EX, MXa, or legacy CX (except the CX4 and CX4T) Series amplifier. Some
older EX or MXa amplifiers may require an upgrade to replace the original input board; for these amplifiers, contact the QSC
Technical Services department for details on compatibility.
Preparing the input board (MXa, EX, and legacy CX models only)
If installing in a PowerLight, PLX, DCA, or current CX amplifier, skip ahead to the BusCard preparation procedure.
Input card
12 10 8
-dB 0
12 10 8
0 70 100 ISOL.OUTPUT
70V 25V
0 70 100 ISOL.OUTPUT
-dB 0
70V 25V
Figure 5. Location of the input card (legacy CX model shown). MXa and EX
amplifiers are similar.
Do not use desoldering braid, because it may damage the solder pads on the input board or BusCard, and it also might not
adequately remove solder.
CAUTION: On MXa, EX, and legacy CX amplifiers, preparing the input board for installation of the SEQ-2 involves removing
solder from feed-through holes on a two-sided circuit card. Excessive heat can easily damage the solder pads you will be
working on. Proper equipment and experience with desoldering delicate PC board circuitry is essential to successfully
perform the following procedure. Please contact the QSC Technical Services department if you feel you might not be
qualified to perform the installation yourself. One last warning: damage caused by an improper installation will void the
Before you start any work, turn off the amplifier power switch and disconnect the AC power cord from the AC source.
Disconnect all cables from the amplifier’s input panel.
Position the amplifier so the rear of the chassis is facing you. The input panel is located on the left side of the rear panel. See
Figure 5.
Begin the installation by locating and removing the screws securing both the upper blank and lower input panels to the
rear side of the chassis (two screws on each mini panel). See Figure 5. The upper blank panel will simply drop off when
its screws are removed.
Gently pull the lower input panel out from the amplifier. Once it is removed, you will notice a ribbon cable connecting
the input PC board to the amplifier. Disengage the locking wing clamps on the ribbon header and carefully remove the
ribbon head from the socket on the board. Now the input panel assembly is completely free from the amplifier.
“Mini Slot”
Figure 7. Input card of an EX Series amplifier. MXa Series input
cards are fairly similar.
Figure 6. Input card of a legacy CX Series amplifier
Next, unsolder and remove the wire jumper pairs (W305/W306 and W405/W406 on EX Series amplifiers; W303/W304
and W403/W404 on MXa and legacy CX Series amplifiers). Under or next to where the jumpers were is arow of solder
holes, with one section of 10 holes and another with 12. This is the Mini Slot in which the SEQ-2 will be installed. See
Figures 6 and 7.
Continue preparing the PC board by removing solder from all 22 in-line socket holes. Once this is done, you are ready
to install the SEQ-2. Proceed to the section below on mounting the SEQ-2 to the input card.
PowerLight (original series), PLX (original series), CX, and DCA models
These models require an appropriate BusCard. The SEQ-2 should be installed on the BusCard before the BusCard itself is
installed in the amplifier. If the SEQ-2 is to be installed on a BusCard that is already installed in the amplifier, temporarily remove
the BusCard for the installation procedure. NOTE: The PLX2, PowerLight 2, and PowerLight 3 series amplifiers are not
compatible with BusCards.
Preparing the BusCard (PowerLight, PLX, DCA, and current CX models only)
Some BusCard models accommodate more than one accessory card. If you are installing more than one accessory, you
should decide on the proper order of signal flow through them. For example, if one of the accessories is an SPL-1 Stereo
Power Limiter, it should generally go last. A UF-2 or UF-3 Universal Filter would usually work best if it is first in the signal
flow, especially if it is used as a crossover.
Mounting the SEQ-2 to the input card or BusCard
Carefully insert the header pins of the SEQ-2 accessory card fully into the socket holes of the input card or BusCard. Make
sure the accessory is correctly oriented and inserted into the correct side of the input card or BusCard. Turn the assembly
over and solder the SEQ-2 in place. Make sure all the header pins are well soldered. Visually inspect for cold solder joints.
Verify that you have sufficient clearance to re-install any ribbon connectors onto the assembly. Finish by trimming the
SEQ-2 header pins as required.
EX, MXa, or legacy CX models only: Reconnect the ribbon cable to the input board connector. Press the locking clamp
wings of the connector closed. You will feel them snap onto place.
PowerLight, PLX, DCA, or current CX models only: On PowerLight PL 3.4, PL 3.8X, and PL 4.0 models, as well as 2 RU
PowerLight models using the BSC-2 BusCard, adjust the SEQ-2 trimpots as needed before you finish mounting the
BusCard; the trimpots will be difficult to reach and adjust afterward.
Connect the appropriate ribbon cables to the BusCard and mount it inside the amplifier, as described in the BusCard
Setting up the SEQ-2
The SEQ-2’s equalization settings may be adjusted only while the amplifier chassis is open (on BusCard-equipped models) or
while the input card is removed (on models using Open Input Architecture), because the trimpots are inaccessible once the
amplifier chassis is closed.
CAUTION: Sometimes it may be necessary to adjust the SEQ-2 while the amplifier is running.
Because of the risk of exposure to high voltages inside the amplifier, such adjustments must be
made only by a qualified technician.
CAUTION: Use only non-conductive tools to adjust an SEQ-2 that is installed in an amplifier.
Equalization adjustments
Figure 3 shows the SEQ-2’s ten trimpots and their respective center frequencies. Figure 4 shows the adjustment range for each
trimpot. Note that the rate of change in boost or cut varies over the trimpot’s rotation; the adjustment is finer toward the middle
and more dramatic at the extremes.
Closing up the amplifier
EX, MXa, or legacy CX models only: Carefully reposition the input board/SEQ-2 assembly into the amplifier chassis and
secure it by fastening the two mounting screws. Make sure the screws are tightened snugly, but do not over-torque them.
Re-install the upper blank panel.
PowerLight, PLX, DCA, or current CX models only: re-install the chassis cover and secure it by fastening all the screws.
Make sure they are tightened snugly, but do not over-torque them.
Installation of the SEQ-2 is now complete, and the amplifier is now ready to be re-installed into the system.
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 SEQ-2.
Product Warranty
QSC Audio Products, Inc. guarantees the SEQ-2 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.
Only a qualified technician should service your QSC product. There are no user serviceable components inside the unit and
the risk of electric shock exists. Also, some components in your unit may require specific QSC replacements.
Technical Assistance
If you suspect that your SEQ-2 is defective, check your system configuration and SEQ-2 settings to determine the origin of
the problem. Incorrect audio interfacing, poor cabling, or other system-level defects are the most frequent causes of
problems in audio systems. For technical assistance beyond the scope of this manual, contact QSC Technical Services. We
also offer comprehensive service manuals for many QSC models; contact us for details.
Factory Service
If your SEQ-2 does need factory service, contact QSC Technical Services for return instructions. We will issue you a Return
Authorization (RA) number for each unit . QSC cannot be responsible for products that are returned without an RA number.
Product Return Guidelines
Pack the product well for protection during shipment. Upon request, QSC will provide a factory shipping carton and
packaging free of charge.
Include a copy of the sales receipt, your name, return address, and phone number with your return correspondence.
Please include a reasonably detailed description of the defect.
Call QSC Technical Services for a Return Authorization number.
Mark the Return Authorization number on the outside of the packaging.
Ship the product prepaid to QSC Technical Services at the address listed below. We recommend United Parcel Service
QSC Technical Services
1665 MacArthur Blvd.
Costa Mesa, CA 92626
(800) 772-2834 (USA only)
+1 (714) 957-7150
+1 (714) 754-6175
+1 (714) 754-6173
Qualified Service Centers
For your convenience, QSC maintains a network of qualified service centers. If you wish to take your QSC product to a local
service center, you may call QSC Technical Services for a referral for one near you. However, accessories, input modules, and
other peripheral QSC products must be returned to the QSC factory for service.
International Servicing
For service on QSC products purchased outside of the United States, contact the distributor or dealer in the country where
the product was originally purchased. In many countries, the distributor or dealer may also refer you to a qualified service
centers. QSC Technical Services can help you contact the distributor in your country.
Rev. B
“QSC” is a registered trademark of QSC Audio Products, LLC 1665 MacArthur Blvd. Costa Mesa, CA 92626 (714) 754-6175 FAX (714) 754-6174