QSC ISA 300T User manual

User Manual
ISA Audio Power Amplifiers
ISA Series
Installed
Sound
Amplifiers
TD-000093-00 rev.C
*TD-000093-00*
nISA 300T
nISA 500T
nISA 800T
nISA 280
nISA 450
nISA 750

CAUTION: TO REDUCE THE RISK OF ELECTRIC
SHOCK, DO NOT REMOVE THE COVER. NO USER-
SERVICEABLE PARTS INSIDE. REFER SERVICING
TO QUALIFIED PERSONNEL.
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.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
© Copyright 2000, QSC Audio Products, Inc.
QSC® is a registered trademark of QSC Audio Products, Inc.
“QSC” and the QSC logo are registered with the U.S. Patent and Trademark Office
The Audio Precision logo is the property of Audio Precision, Beaverton OR
All trademarks are the property of their respective owners.
IMPORTANT SAFETY PRECAUTIONS
& EXPLANATION OF SYMBOLS
WARNING: TO PREVENT FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS
EQUIPMENT TO RAIN OR MOISTURE.
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.
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: ISA ________________________________
Serial Number:______________________________
Date of Purchase:____________________________
Purchased From:_____________________________
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.
2

INTRODUCTION:
ISA Series Overview .......................................................................................4
Front Panel Illustration .........................................................................................4
Rear Panel Illustrations ........................................................................................5
FEATURES & SETUP :
Power Switch ............................................................................................6
Cooling Air Inlet and Exhaust Vents ...............................................................6
LED Indicators ........................................................................................7
Gain Controls ........................................................................................8
Input Jacks ..........................................................................................8
DataPort V2 Connector ...................................................................................9
Daisy Chaining to Other Devices from the DataPort V2 ................................9
Stereo & Parallel Operating Modes ..................................................................10
DIP Switch Settings ...................................................................11
Bridge Mono Operating Mode .......................................................................12
DIP Switch Settings ................................................................12
Low Frequency Filter ..........................................................................13
DIP Switch Settings ..............................................................13
Frequency Response Curves ..................................................................14
Clip Limiter ........................................................................................15
DIP Switch Settings ...............................................................15
INSTALLATION:
Rack Mounting ....................................................................................16
Mounting Dimensions .........................................................................16
Cooling Requirements ........................................................................17
AC Mains (AC Power) ..............................................................................17
CONNECTIONS:
Inputs: XLR and Terminal Block Input Jacks ...............................................18
Inputs: DataPort V2 Connections and Notes ...........................................19
Outputs: Using the Screw Terminal Connections ............................................20
Outputs: Direct Low Impedance (2-16 ohm loads) ................................................21
Outputs: Distributed High Impedance (“T” models only) ..................................22
Power Sharing Between High and Low Impedance Outputs (“T” models only) .......24
Securing Output Wiring to the Chassis .................................................................25
OPERATION:
Gain Controls .........................................................................................................26
AC Power Switch .........................................................................................26
Front Panel LED Indicators ................................................................................26
Normal Operating Levels ......................................................................................26
APPLICATIONS:
General Notes, Distributed Line Principles .....................................................27
Low Frequency Filtering, Distributed Output Examples ........................................28
Multiple Low Impedance Loads in Series or Parallel Connections .........................30
DataPort V2 Application Information ...........................................................................32
TROUBLESHOOTING ........................................................................................................33
SPECIFICATIONS ......................................................................................................35
WARRANTY INFORMATION .............................................................................................39
HOW TO CONTACT QSC AUDIO PRODUCTS ............................................................................39
3
TABLE OF CONTENTS

FRONT PANEL
(all models)
Thank you for the purchase of your new ISA amplifier. To get
the most out of your amplifier, review this manual carefully. The
installation, connection and operation sections provide useful
guidelines to get you up and running quickly and correctly.
The QSC shipping box should contain:
1- The amplifier
2- This user manual
3- #14AWG AC line cord with IEC connector
After you have removed the amplifier from the box, make sure
you save the box and packing material for safely storing or
shipping the amplifier in the future.
The ISA Series amplifiers offer professional-quality perfor-
mance at an affordable price. Three power-points are offered in
both directly-coupled and autotransformer-coupled output.
Output power at 2 ohms ranges from 430 to 1200 watts per
channel.
The ISA amplifier was designed to fit your installed sound
requirements. The detented gain controls, located on the rear
panel, provide accurate, repeatable adjustments. Each channel
has defeatable clip limiting and selectable-response low
frequency filters. QSC’s rear-to-front airflow cooling helps to
keep other system components in the equipment rack cooler,
enhancing overall system reliability.
For those systems with QSC DataPort accessories (DSP,
crossovers & filters, remote cinema monitoring) a DataPort V2
(version 2) is included on all ISA models. Consult your QSC
representative for accessory compatibility information.
The ISA amplifiers are easy to use. All operating mode
switches are grouped together on the rear panel. A mode
switch configuration chart is printed directly on the rear panel for
easy, accurate reference. This helps to avoid configuration
problems. On the autotransformer-coupled “T” models, separate
screw-terminal output connections are provided for both low
impedance loads and high impedance (25/70/100 volt) loads.
The “connectability” of the “T” models makes them simple to
use in almost any installed sound application.
The ISA amplifiers are built for long service life. XLR and
terminal block input connectors provide tight, noise-free
connections. The chassis design incorporates robust output
cable dressing tie-down points to keep stress off the connec-
tions, making them more reliable. All signal processing is done in
side loops and then returned to the main signal path. This
maintains high signal fidelity and provides a more robust system.
Your new ISA amplifier will give you many years of great
sound. It is the best value in installed sound amplification with
legendary QSC durability and performance.
INTRODUCTION- INTRODUCTION AND FRONT PANEL ILLUSTRATION
4. Cooling air exhaust vents
5. Mounting holes for optional handles
6. Mounting holes for rack mounting
1. Power indicator LED
2. Power switch
3. Clip and Signal indicator LEDs
4

1. Gain Controls
2. Terminal Block Inputs
3. DataPort V2 Connector
4. XLR Inputs
INTRODUCTION- REAR PANEL ILLUSTRATIONS
9. Serial Number Label
10. Circuit Breaker for AC Power
11. Tabs for Securing Output Wires
12. AC Power Connector, IEC type
REAR PANEL
ISA 280
ISA 450
ISA 750
5. Mode Switches
6. Mode Switch Configuration Charts
7. Cooling Air Inlet Vent
8. Output Connections, Low Impedance
REAR PANEL
ISA 300T
ISA 500T
ISA 800T
1. Gain Controls
2. Terminal Block Inputs
3. DataPort V2 Connector
4. XLR Inputs
5. Mode Switches
6. Mode Switch Configuration Charts
7. Cooling Air Inlet Vent
8. Output Connections, Low Impedance
9. Serial Number Label
10. Output Connections, Distributed (high impedance)
11. Circuit Breaker for AC Power
12. Tabs for Securing Output Wires
13. AC Power Connector, IEC type
5
NOTE! Output connection terminals shown without protective cover in place for clarity (rear panel, above & below).

The front panel of ISA series amplifiers is tailored for installed
sound. The power switch is the only front panel control; gain
controls are located on the rear panel to minimize control
tampering. LED indicators are provided for power, input signal
and to warn of clipping.
If the POWER LED fails to illuminate when the switch is in the ON position:
The power switch is a rocker-type switch. To turn the amplifier
on, push in on the top portion of the switch. To turn the amplifier
off, push in on the bottom portion of the switch.
The green power LED should light up when the switch is in the
on position.
When the power is switched off, the LED may takes several
seconds to go out; this is normal.
FEATURES & SETUP- POWER SWITCH, COOLING AIR VENTS
Rear panel circuit breaker:
Tripped or open position;
press to reset.
Rear panel circuit breaker:
Normal operating position
If the circuit breaker opens repeatedly with nothing
connected to the amplifier and it is connected to the
proper AC source as labeled on the rear panel serial
number label, then the amplifier requires servicing
.
Keep the inlet and exhaust air vents clear of any obstructions. Insure
that the air exhausted from the vents has an exit from the equipment
enclosure.
Equipment enclosures with insufficient air flow will cause amplifier
overheating. Enclosures must allow fresh air to enter and hot air to
exit.
If dust builds up, clogging the vents, use a soft brush and a vacuum
cleaner to remove the dust. Use the brush to loosen the dust while the
vacuum is used to pull the dust away from the amplifier.
1- Check the AC cord and insure that both ends are fully inserted into their receptacles. If the power LED
still fails to illuminate,
2- Check the AC outlet for voltage with a circuit tester or known good device (lamp, etc.).
3- Check the AC circuit breaker on the rear panel of the amplifier. The illustration at the right shows the
circuit breaker in its normal (operating) position and its tripped position (amplifier AC power turned off by
protective circuit breaker).
COOLING AIR INLET AND EXHAUST VENTS-
NOTE! It is normal for the circuit breaker to open if the
amplifier is operated continuously at output levels at or
exceeding specified power levels.
POWER SWITCH-
6

FEATURES & SETUP- LED INDICATORS
CLIP : red LED that illuminates when the amplifier
clips.
Normal indication: illumination briefly at extreme
output power peaks. Occasional clipping (once briefly
every few seconds) when operation at high power
levels is normal. At power-on, the clip LEDs may briefly
flash; this is normal.
Continuous operation at high power may trigger the
thermal protection circuitry, shutting down the amplifier
and fully illuminating the clip LED. Operation will
resume after the amplifier has cooled down sufficiently.
SIGNAL:green LED that lights up when the input
signal is strong enough to drive the output to about -40
dB from rated 8-ohm power.
Normal indication: varying brightness corresponding
to strength of input signal.
POWER:green LED that illuminates when the power
switch is set to the on position and AC power is present
at the IEC cord receptacle.
Normal indication: at power-on the LED will illumi-
nate at half-brightness for 2-3 seconds, then it illumi-
nates to full-brightness.
If no indication: check gain settings, input cables,
connections and audio source. If audio source is
extremely low signal strength, signal LED may not
illuminate; this is normal but indicates that the input
signal strength should be increased.
Occasional illumination: normal for weak input
signal strength.
Illuminated dimly all the time with brighter
flashing: normal for “average”input signal strength.
Fully illuminated (on): normal for “pushing”the
amplifier hard. Also, the clip indicator will probably
flash dimly with the beat of the program material and
brightly during extreme peaks in the material.
If no indication: see previous page for suggested
items to check.
When power is switched off: the LED may take
several seconds to extinguish (go out); this is normal.
If no indication: normal if the amplifier is operated at
very low output levels.
Occasional illumination: Occasional clipping (once
briefly every few seconds) when operation at high
power levels is normal. Continuous operation at high
power may trigger the thermal protection circuitry,
shutting down the amplifier and fully illuminating the
clip LED.
Illuminated most of the time: Not normal; reduce the
output of the amplifier and/or input signal to avoid
thermal shutdown of the amplifier and possible speaker
damage.
Fully illuminated (on): Amplifier is in thermal shut
down. Reduce gain settings or input signal and allow
the amp to cool down. Leave the power on so that the
fan continues to run; operation will automatically
resume after the amplifier has cooled sufficiently.
7

FEATURES & SETUP- GAIN CONTROLS & INPUT JACKS
GAIN CONTROLS-
The Gain controls are located on the rear panel to minimize
control tampering after installation. When viewing the amplifier
from the rear, they are on the left end, top and bottom, as shown
in the illustration to the right.
The Gain controls are detented (11 steps) for repeatable
adjustment. Surrounding the Gain control, the power attenua-
tion level is shown in dB. To operate the Gain control, rotate the
control’s knob so that the desired level is achieved. There is a
detent in the knob to indicate its position.
Maximum gain depends on the model, see chart, below.
MAXIMUM VOLTAGE GAIN BY MODEL
ISA 280, 300T 30.5 dB
ISA 450, 500T 33.0 dB
ISA 750, 800T 35.0 dB
The attenuation level markings around the Gain controls are
power levels, not voltage. To have an idea of the approximate
output power, the table (at left) provides the output power by
model as a function of the Gain setting. The data provided is per
channel power for an 8 ohm load, input fully driven.
INPUTS-
The ISA series of amplifiers are equipped with XLR and terminal
block connectors. Input impedance is 20k ohm balanced, 10k
ohm unbalanced. The proper termination and connection
information is provided in the CONNECTIONS section of this
manual. Unused input connections may be used to daisy chain
the input to additional amplifiers.
Additionally, a DataPort V2 connector is provided for users of
QSC DataPort products. The DataPort V2 can be used to provide
input signals to the amplifier and to monitor the amplifier with
the appropriate QSC DataPort product. See the following section
for DataPort V2 information.
TERMINAL BLOCK
CONNECTORS
XLR CONNECTORS
8
WHERE THEY ARE-
WHERE THEY ARE-

DATAPORT V2-
What It Is- The DataPort V2 is used for connection to optional
QSC DataPort accessories. DataPort accessory devices can
provide remote cinema monitoring, DSP, filter and crossover
functions.
The “V2”DataPort connection is a “version-2”of QSC’s original
DataPort. It has a reduced feature set from the original, while
maintaining essential amplifier monitoring capability. It does not
supply +15 VDC power required by some DataPort accessories.
FEATURES & SETUP- DATAPORT V2
Where It Is- The DataPort V2 connector is
on the rear panel, left side and center.
Using the DataPort V2- Some DataPort accessories plug
directly in to the DataPort while others use an interconnect-
ing QSC Dataport cable. Consult the accessory’s
documentation for recommended mounting and interconnect
information.
Do not use the XLR or terminal block connections for inputs
when the DataPort V2 is used as the input signal source. If
you do, the signals from the DataPort V2 and regular inputs
will be mixed, possibly with unexpected results.
What Can I Connect to the DataPort V2?
Consult your QSC representative for up-to-date
accessory compatibility. QSC has several DataPort-
based accessories available like the:
DSP-3 Digital Signal Processing Module
XC-3 Crossover
SF-3 Subwoofer Filter
LF-3 Low Frequency Filter
DCM Crossovers & Monitors
(page 32 has additional information)
9
Daisy Chaining to Other Amplifiers
While Using the DataPort V2 for
Input Signals- If the incoming audio
input signal is through the DataPort V2,
the XLR and terminal block connectors can
be used to daisy chain the input signal to
other equipment. The signal at these
connectors will be about 10 dB lower (in
voltage) than the incoming DataPort V2
signal. The illustration to the right shows
the basic daisy chain hookup. Note that
the XLR connections may also be used for
daisy chaining the audio to other devices.
Daisy chaining may not be possible with
accessories that cover the XLR and/or
terminal block connectors.
Daisy chaining the DataPort V2 input to other devices using the terminal block connectors.
NOTE! The DataPort V2 can only supply a maximum
current of 40 mA. Some accessories, such as the
DSP-3, require more than 40 mA to operate. Use an
external power supply with such accessories.

FEATURES & SETUP- STEREO & PARALLEL OPERATING MODES
PARALLEL:
The channel 1 and channel 2 inputs are connected together,
applying a single input signal to both channels of the amplifier. A
signal into any input jack will drive both channels. Each
channel's low frequency filtering, clip limiting, and gain control
still function independently. Each channel drives its own speaker
load.
You can patch the input signal on to additional amplifiers (daisy
chain) by using any of the remaining input jacks. This feature
eliminates the need for “Y”cables.
When to use PARALLEL input configuration: Use parallel
mode when you need one signal to drive both channels; each
channel having its own control (gain, clip limiter, low-frequency
filter).
How to use PARALLEL mode:
1- Set the DIP switches for PARALLEL mode (see facing page).
2- Connect the one input signal to any one input connector.
3- Connect the two speakers: one to CH1’s output terminals, one
to CH2’s output terminals.
STEREO:
Each input signal is sent to its respective channel. Each channel
has independent low-frequency (subaudio) filtering, clip limiting,
gain control, and output connection.
When to use STEREO input configuration: Use stereo mode
for stereo sources (L-R inputs) and any other situation that
requires each channel to be completely separate from the other.
How to use STEREO mode:
1- Set the DIP switches for stereo mode operation (see facing
page).
2- Connect the two input signals; one to CH1 and one to CH2
(XLR or terminal blocks)
3- Connect the two speakers; one to CH1’s output terminals, one
to CH2’s output terminals.
NOTE: Ensure that the MODE SWITCHES are set
to STEREO when feeding two separate signals to
the two channels.
STEREO MODE OPERATION
PARALLEL MODE OPERATION
10

FEATURES & SETUP- STEREO & PARALLEL MODE DIP SWITCH SETTINGS
ISA 280, ISA 450, ISA 750:
Refer to the switch setting keys for each mode, to the right.
These keys are printed on the amplifier’s rear panel for easy
reference when you are behind the equipment rack.
SETTING THE DIP SWITCHES FOR STEREO OR PARALLEL MODE- “T” models
ISA 300T, ISA 500T and ISA 800T:
Refer to the switch setting keys for each mode, at the right.
These keys are printed on the amplifier’s rear panel for easy
reference when you are behind the equipment rack.
ISA 280, ISA 450 and ISA 750 mode switches.
ISA 300T, ISA 500T and ISA 800T mode switches.
STEREO Mode- Set switch #4, 5, 6 and #7 to the
left.
PARALLEL Mode- Set switch #4 and #5 to the
right; set switch #6 and #7 to the left.
STEREO Mode- Set switch #3, 4, 5, 6, 7 and #8 to
the left.
PARALLEL Mode- Set switch #3, 4 and #5 to the
right. Set switch #6, 7 and #8 to the left.
11
SETTING THE DIP SWITCHES FOR STEREO OR PARALLEL MODE- “non-T” models

FEATURES & SETUP- BRIDGE OPERATING MODE & DIP SWITCH SETTINGS
BRIDGE MODE OPERATION-
Note that speaker connection for bridge mono mode is
different than other modes. See section on Connections:
Outputs for proper bridge mode output connections.
SETTING THE DIP SWITCHES FOR BRIDGE MODE-
Bridge mode combines both output channels into one output.
This mode is for driving a single, high-power-rated load with
twice the “normal”voltage swing. This results in about 4 times
the peak power and about three times the sustained power of a
single channel. It is also common to call this bridge mono mode.
When to use BRIDGE mode: Use BRIDGE mode when you
need to deliver the power of two channels to a single 8 or 4 ohm
load, such as a subwoofer. Do not use less than 4 ohm loads in
bridge mode. Refer to the CONNECTIONS section of this manual
for details.
Constant voltage drivers rated at 140 volts or 200 volts can be
accommodated by bridging the high impedance output terminals
of the ISA 300T, ISA 500T or ISA 800T. Refer to the CONNEC-
TIONS section of this manual for details
How to use BRIDGE mode:
1- Set the DIP switches for bridge mode (see below).
2- Connect the one input signal to CH1’s input (XLR or terminal-
block).
3- Connect the one speaker load to the bridge output terminals
4- Use channel 1’s gain control, clip limiter and filter.
ISA 300T, ISA 500T and ISA 800T models: switches #3, 4, 5, 6, 7 and #8
must all be set to the right-side position. Switch #10 should be set to its
left-side position. See chart, above.
ISA 280, ISA 450 and ISA 750 models: switches #4, 5, 6, 7 and #8 must all
be set to the right-side position. Switch #10 should be set to its left-side
position. See chart, above.
ISA 280, ISA 450 and ISA 750:
1- Switch #4, 5, 6 and #7 must all be switched to the
right.
2- Switch #8 must be switched to the right to disable
channel 2’s low-frequency filter.
3- Switch #10 should be switched to the left so that
channel 2’s clip limiter is off. Channel 1’s clip limiter
controls both channels in bridge mode.
4- Set switch #1, 2 and #3 as required. Channel 1’s
settings determine the bridge mode clip limiting and low-
frequency filtering.
ISA 300T, ISA 500T and ISA 800T:
1- Switch #3, 4, 5, 6, 7 and #8 must all be switched to
the right to operate in bridge mode.
2- Switch #10 should be switched to the left so that
channel 2’s clip limiter is off. Channel 1’s clip limiter
controls both channels in bridge mode.
12

FEATURES & SETUP- LOW FREQUENCY FILTER & DIP SWITCH SETTINGS
SETTING THE FILTER DIP SWITCHES-
1- Set switch #3 and #8 to the on or off position as desired.
2- Select the desired roll-off frequency at switch #2 and #9.
3- If filter off is selected, the frequency selection has no effect.
If operating in BRIDGE MODE-
1- When in bridge mode, channel 2’s low frequency filter and
clip limiter should be switched off.
2- Channel 1’s filter settings (and clip limiter) determine amplifier
behavior. Set channel 1’s low frequency filter on-off switch,
frequency selection switch and clip limiter as desired.
ISA 280, ISA 450 and ISA 750 models: frequency selection is
30 and 70 hertz. Low frequency filter can be switched on or off
with switches #3 and #8.
Generally, match the frequency selection to your speaker’s low frequency capability. This improves speaker performance by limiting
subaudio cone movement, making more power available for the speaker’s rated frequency range. Unless you already have filtering in
the signal path preceeding the amplifier, use the low frequency filter to protect your speakers from cone over-excursion caused by
frequencies below the speaker’s limits. The speaker’s documentation will specify the low frequency limit.
ISA 280, ISA 450 and ISA 750‘s have defeatable low frequency
filters with selectable roll-off frequencies of 30 and 70 hertz.
Each channel has its own low frequency filter which can be
enabled or defeated using the filter on-off switch. The frequency
is determined by the frequency selection DIP switch. There is a
5 hertz roll-off in the filter off position to protect the speaker
loads from sub-audio or DC signals. The off position should be
used only for subwoofer systems with rated frequency response
below 30 hertz or if low frequency filtering is provided by other
devices.
ISA 300T, ISA 500T and ISA 800T’s have selectable roll-off
frequencies of 50 and 75 hertz. The frequency is determined by
the frequency selection DIP switch.
The low frequency filter
is always active and is not defeatable.
This is required by
the presence of magnetic devices (coupling transformers) in
constant voltage distributed audio systems. The low impedance
outputs of these models have the same low frequency roll-off as
the autotransformer coupled high impedance outputs.
ISA 300T, ISA 500T and ISA 800T:
If operating in STEREO or PARALLEL MODE-
1- Select the desired roll-off frequency (50 or 75 hertz) at switch
#2 and #9. Each channel can be set independently.
If operating in BRIDGE MODE-
1- Select the desired roll-off frequency at switch #2. Setting of
switch #9 is ignored.
To Prevent Output Transformer Saturation-
The 50 Hz filter setting prevents transformer saturation for
normal, unclipped program levels. If heavy clipping is possible,
use the 75 Hz setting for extra protection. See “Low Frequency
Filtering for 70-100V Systems”, page 28.
Differences Between “T” & “non-T” Models:
ISA 300T, ISA 500T and ISA 800T models: frequency selection
is 50 and 75 hertz. Low frequency filter is always active and
can not be defeated (turned off).
ISA 280, ISA 450 and ISA 750:
If operating in STEREO or PARALLEL MODE-
13

FEATURES & SETUP- FREQUENCY RESPONSE CURVES
Frequency response curve for: ISA 300T
ISA 500T
ISA 800T
Note! There is no “Filter OFF”
selection on “T” models.
Frequency response curve for: ISA 280
ISA 450
ISA 750
50 hertz selection
75 hertz selection
Filter ON
70 hertz selection
Filter ON
30 hertz selection
Filter OFF
14

FEATURES & SETUP- CLIP LIMITER & DIP SWITCH SETTINGS
CAUTION: Clip limiting reduces extreme overdrive peaks, allowing a higher average signal level without audible
distortion. However, 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 your speakers.
How to use it:
When to use it:
When the audio input signal drives the amplifier’s output circuit
beyond its power capability, the amplifier clips and flattens the
peaks of the waveform. This flattening is what we hear as
distortion during the clipping “event”.
Clipping for short periods can be harmless. Clipping for extended
periods can easily damage high frequency drivers (tweeters,
horns) . Low frequency drivers can tolerate all but severe
clipping; severe clipping can damage any of the systems power
components and should be avoided entirely.
The clip limiter detects clipping (even short events) and quickly
reduces the gain to minimize the amount of overdrive. To
preserve as much of the program dynamics as possible, the ISA
amplifier has limiters which respond only to amplifier clipping.
There is a switchable clip limiter provided for each channel.
CLIP LIMITER selection switches, all models.
Note! In BRIDGE mode, channel 2’s CLIP LIMITER must
be placed in the OFF position for proper operation.
In BRIDGE mode, Channel 2’s clip limiter must be set to the off position to avoid any interaction.
We recommend using the clip limiters in all applications.
When driving full-range speakers, clip limiting reduces high frequency distortion caused
by bass overload. It also protects high frequency drivers from excess overdrive and harsh
clipping harmonics.
When using 70V or 100V transformers, clip limiting prevents excessive overdrive which
could saturate the coupling transformers. See “Low Frequency Filtering For 70-100V
Systems”, page 28.
If operating in stereo or parallel mode, the two limiters are completely independent
of one another.
1- Set each channel’s clip limiter selection switch on or off as desired.
Switch #1 sets channel 1’s limiter. Switch #10 sets channel 2’s limiter.
If operating in bridge mode, channel 1’s clip limiter switch is used to engage or disable
the clip limiter; channel 2’s clip limiter must be switched off.
1- Set channel 2’s clip limiter switch to the off position. This is switch #10.
2- Set channel 1’s clip limiter switch on or off as desired. This is switch #1.
15

INSTALLATION: RACK MOUNTING AND MOUNTING DIMENSIONS
Securing the Front Ears to the Rack Rails
Use four screws and washers when mounting the
ISA amplifier to the front rails. Support the weight
of the amplifier while securing it to the rails to
avoid bending or distorting the front rack mount
ears.
ISA Rack Mounting
Method 2- The amplifier is first
installed from the front of the
rack. Then, the accessory rear
ears are positioned on the rear
rack rails and secured. The pin
installation position can now be
selected. Install the pin so that it
fits well into the slot provided on
the amplifier's rear mounting
tab.
Method 1- The amplifier is first
installed from the front of the
rack and then the ears are
secured directly to the amplifier
with two machine screws as
shown, left. Then the ears are
secured to the rails using
ordinary rail hardware.
Supporting the Rear of the Amplifier
Supporting the amplifier at the rear is extremely
important, especially for mobile and portable use.
Equipment is often installed in racks at a remote
location, then later transported to the installation
site. During transport, the shock loads encoun-
tered on the chassis and rack can easily damage
an unsupported amplifier and the rack rails.
Unless the amplifier is being installed in its final,
fixed location, we strongly recommend supporting
the rear of the amplifier.
Rear rack mounting ear kits are an accessory item
and are available from QSC’s Technical Services
Department or from your dealer or distributor.
The rear rack mounting ear kit may be installed in
two different ways. Refer to the literature
included with the rack mounting ear kit for up-to-
date information. The basic information is
supplied here to give you an idea of how the
accessory rack mounting ears are used.
Amplifiers are inherently heavy. It is
highly recommended that you have an
assistant support the amplifier during
rack installation to avoid injury.
16
NOTE: Rack mounting of amplifier is optional.

INSTALLATION: COOLING REQUIREMENTS & AC MAINS
FAN COOLING-
Keep the front and rear vents clear to allow full air flow. Make sure that plenty of cool
air can enter the rack, especially if there are other units which exhaust hot air into it.
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 sticker on the rear panel.
OPERATING VOLTAGE (AC mains)-
Air flow in QSC amplifiers
All QSC amplifiers draw cool air into the rear of the amplifier and
exhaust the hot air from the front. This is done so that the
equipment in the rack stays as cool as possible. This method of
cooling also gives the technician “direct”air temperature
feedback at the front of the rack, where it is the most conve-
nient. The front panel’s temperature is an accurate indicator of
“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.
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 rear of the rack, especially if there are other units which
exhaust hot air into it. Also ensure that the exhaust air from the
front of the amplifier is not obstructed by an equipment cabinet
door (or otherwise).
Connect the AC line cord after the amplifier has been installed in the equipment rack. The IEC plug (the rectangular
“block”plug-end of the AC power cord) can only be inserted when it is properly oriented with the IEC receptacle on the
rear panel of the amplifier. Orient the IEC plug correctly and push the plug firmly into the IEC receptacle; it should seat
tightly.
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.
The AC line cord attaches to the IEC connector on the rear panel. 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. The larger AWG number indicates a physically smaller wire; smaller AWG number indicates a physically
larger wire (#12 AWG is able to carry more current than #14AWG).
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. Smaller AWG number means larger wire size (example: #12 AWG is
a larger physical wire size than #14 and able to carry more current). Ensure that all grounding connections are
maintained.
17
The correct AC line voltage is shown on the serial number label.

Unbalanced inputs: Connect the
conductors to the connector as
shown. Make sure that the unused
side of the balanced input is
connected to ground, as shown.
XLR: unbalanced connection
Terminal block: unbalanced connections
XLR : balanced connection
Terminal block: balanced connections
CONNECTIONS: INPUTS- XLR & TERMINAL BLOCK
jumper
shield
Terminal Block Connectors: XLR Connectors:
Each channel has active balanced "Euro-style" terminal block and
XLR input jacks wired in parallel. The input impedance is 20k
ohm balanced or 10 k ohm unbalanced. Unused input jacks may
be daisy chained to additional amplifiers.
Balanced connection is recommended. Balanced signals are less
prone to AC hum and other electrical noise. Unbalanced signals
can be suitable for short cable runs. The signal source's output
impedance should be less than 600 Ohms to avoid high fre-
quency loss in long cables.
If the DataPort V2 is being used for the input signal source, the
XLR and terminal block connections should not be used for
inputs. However, they may be used for daisy chaining the
DataPort V2 input signal to other amplifiers. The signal available
from the XLR and terminal block connections will be about 10 dB
lower than the DataPort V2 signal.
shield
TERMINAL BLOCK
CONNECTORS
XLR CONNECTORS
Balanced inputs: Connect the
conductors to the connector as
shown.
18

CONNECTIONS: INPUTS- DATAPORT V2
The ISA series of amplifiers come with a DataPort V2 connector
that may be used for connecting to accessory QSC DataPort
devices. The V2 (or version 2) DataPort does not have the full
capability of the standard DataPort. The DataPort V2 must be
connected to a QSC DataPort product with a QSC DataPort cable;
similar looking computer data cables will not work and could
damage your QSC equipment. The DataPort V2 connection will
supply the input signals to the amplifier. If using the DataPort V2
connection, do not apply inputs to the XLR or terminal block
connectors.
If the ISA amplifier is being used in a system monitored through
a QSC cinema monitor (or other QSC DataPort product) the
following amplifier information will be provided by the amplifier
DataPort V2:
CH1 and CH2 output voltage
Amplifier AC power status (on or off)
If using the DataPort V2 connection, do not connect any inputs to the XLR or terminal
block connectors. The unused XLR or terminal block inputs may be used for daisy
chaining the DataPort V2 input signal to other amplifiers. The signal level available from
the unused inputs will be about 10 dB lower than the signal applied at the DataPort V2
connector.
How to Connect to the DataPort V2:
Basic Operation Notes:
1- The amplifier Gain controls will need to be set at their anticipated high-level setting. Use reduced level
setting during setup & test.
2- Control of the audio level will be accomplished with the DataPort accessory device to which the amp is
connected.
3- No control of the amplifier’s AC power will be possible via the DataPort V2. Use the amplifier’s POWER
switch to turn the amp on and off.
4- See page 32 for additional DataPort V2 Application information.
If it is an accessory that mounts directly to the rear of the amplifier, orient the accessory correctly
and attach to the amplifier per the accessory’s instructions.
If the accessory attaches with a QSC DataPort cable, orient the HD-15 male plug correctly with
the DataPort V2 socket on the amplifier (it is “D”shaped and will fit only one way). Push the plug onto
the socket firmly and ensure it is seated properly. Finger-tighten the 2 retaining screws. Do not over-
tighten.
19

CONNECTIONS: OUTPUTS- USING THE SCREW TERMINAL CONNECTIONS
GENERAL-
The screw terminal output connections are
protected by a hinged plastic cover.
To make connections to the screw terminals,
you will need to swing the cover door open.
Gently pry the cover with your finger tips on
the side that has the wire openings.
After the door is open, loosen the screws for
the terminals you are planning to use. Do
this by rotating the screw counter-clockwise
with an appropriate screwdriver.
After loosening the screws, slide the tongue
terminals under the head of the screw and
seat the terminal firmly against the screw.
Tighten the screw by rotating it clockwise
with an appropriate screwdriver.
Alternately, wire connections may be made.
Ensure that all wires are neatly terminated
with no loose strands. Do not strip the
insulation back excessively. Loose strands
and exposed wire beyond the terminals may
cause a short circuit and cause protective
muting of the amplifier.
Once all connections have been made, close
the protective cover by swinging it over the
connections and pressing it toward the
amplifier. If you wiring job is messy, you may
need to loosen and reposition some cables
to get a good fit for the cover.
1) Protective cover closed, covering the screw terminals.
2) Protective cover in the open position.
3) Tongue terminals being inserted under loosened screws. Tighten all connec-
tions before closing cover.
4) Protective cover shown closed over exiting cables.
The tongue terminals should
have an overall width (of the
tongue) no larger than 0.320
inch. The opening for the
screw should be no smaller
than 0.135 inch. The wire
insertion barrel should be
sized for the size of speaker
cable used.
#6 is the screw size used on
the ISA output terminals; this
is also the size that tongue
terminal suppliers may use in
their nomenclature.
STACKING OF TONGUE TERMINALS-
If you need to fit two tongue terminals onto one screw, they
should be oriented properly for a good fit and reliable
connection. Refer to the diagram below. Place the flat sides of
the two terminals toward one another, then tighten screw.
If oriented incorrectly, the terminals will bend and possibly not
connect very well. The screw terminal may also be damaged.
20
RECOMMENDED TONGUE TERMINAL SIZE-