Full Power Balanced
X Series Power Amplifiers
THE LEADER IN AUDIO ENGINEERING
700cx, 400cx, 300cx Stereo
750Mcx, 450Mcx, 350Mcx Monaural
with Krell CAST II Technology
Instructions for Use
Owner’s Reference
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Contents
Page
INTRODUCTION
1
1
3
4
DEFINITION OF TERMS
REVOLUTIONARY KRELL CAST and CAST II TECHNOLOGY
UNPACKING
PLACEMENT
4
5
AC Power Guidelines
FRONT PANEL DESCRIPTION
8
8
8
700cx, 400cx, and 300cx Stereo Power Amplifiers
750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers
BACK PANEL DESCRIPTION
11
11
12
700cx, 400cx, and 300cx Stereo Power Amplifiers
750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers
CONNECTING THE FULL POWER BALANCED AMPLIFIER
TO YOUR SYSTEM
13
13
13
14
14
Input and Output Connections
Krell Link Connections
DC Protection Circuitry
Using a Tube Preamplifier
AMPLIFIER OPERATION
On/Off and Stand-by Operation
Krell Link Operation
15
15
15
REMOTE CONTROL OPERATION
16
16
16
16
16
How to Turn Off the Amplifier LEDs
How to Turn On the Amplifier LEDs
How to Switch between Krell CAST and XLR Inputs
Using a Dedicated Wall Outlet and Switch
AMPLIFIER TROUBLESHOOTING
How to Troubleshoot System Noise
How to Evaluate Amplifier Operation
17
17
17
QUESTIONS AND ANSWERS
WARRANTY
19
20
21
22
RETURN AUTHORIZATION PROCEDURE
SPECIFICATIONS
Krell Full Power Balanced X Series Power Amplifiers
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Page
Illustrations
FIGURE 1 Full Power Balanced Stereo Amplifier Front Panel
FIGURE 2 Full Power Balanced Monaural Amplifier Front Panel
FIGURE 3 Full Power Balanced Stereo Amplifier Back Panel
FIGURE 4 Full Power Balanced Monaural Amplifier Back Panel
6
7
9
10
iv
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Introduction
Definition of Terms
The Full Power Balanced X Series consists of
three stereo amplifiers, the Full Power Bal-
anced 700cx, 400cx, and 300cx Stereo Power
Following are the definitions of key terms used
in your owner’s reference manual.
Amplifiers and three monaural amplifiers, the CONFIGURATIONS
Full Power Balanced 750Mcx, 450Mcx, and
350Mcx Monaural Power Amplifiers. Installa-
tion, connection, and operation of all amplifiers
in the Full Power Balanced series are identical;
however, a pair of Full Power Balanced Monau-
ral amplifiers are required for stereo operation.
Krell Link
A method of synchronizing remote control oper-
ation for Krell systems that include multiple pre-
amplifiers, amplifiers, and associated compo-
nents. When Krell Link in/out connections are
used, the remote capabilities of the linked com-
ponents are controlled from one component,
called the control component. The linked com-
ponents respond to stand-by and operational
mode commands from the control component
via MIDI cables.
Full Power Balanced amplifiers can be config-
ured to accommodate any sophisticated music
or home theater system and can be operated
by an optional remote control or through the
remote control of other Krell components.
This owner’s reference manual contains impor-
tant information on placement, installation, and
operation of the Full Power Balanced ampli-
fiers. Please read this information carefully. A
thorough understanding of these details will
help ensure satisfactory operation and long life
for your Full Power Balanced amplifier and
related system components.
INPUT AND OUTPUT CONNECTIONs
Balanced
A symmetrical input or output circuit that has
equal impedance from both input terminals to a
common ground reference point. The industry
standard for professional and sound recording
installations, balanced connections have 6 dB
more gain than single-ended connections and
allow the use of long interconnect cables. Bal-
anced connections are completely immune to
induced noise from the system or the environ-
ment.
Krell Current Audio Signal Transmission
(CAST)
A proprietary Krell circuit technology for connect-
ing analog components, in which the audio
waveform is transmitted between components in
the current rather than voltage domain. The
speed and bandwidth provided by Krell CAST
and the CAST circuitry update, Krell CAST II,
yield accurate, realistic music reproduction. Krell
components connected via CAST and CAST II
perform as if they are all part of a single circuit.
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Definition of Terms,
continued
Single-ended
TECHNOLOGY
A two-wire input or output circuit. Use care
when using single-ended connections as the
ground connection is made last and broken
first. Turn the system off prior to making or
breaking single-ended connections. Single-
ended connections are not recommended for
connections requiring long cable runs.
Krell Current Mode
A proprietary Krell circuit topology in which the
audio gain stages of a component operate in
the current rather than voltage domain. This
unique technology provides the component
with exceptional speed and a wide bandwidth.
Krell Sustained Plateau Bias III
OPERATION
A patented microprocessor control system that
maintains Class A bias operation regardless of
musical demand. Class A bias is the most accu-
rate method used to amplify musical signals.
The new Sustained Plateau Bias III software is
featured in the Full Power Balanced X Series
amplifiers and was developed from the algo-
rithm utilized in the Master Reference Amplifier.
Sustained Plateau Bias III maximizes an ampli-
fier’s efficiency both in power consumption and
heat generation.
Off
When the power switch on the back panel is
placed in the down position and the blue power
LEDs turn off, the component is off.
Operational Mode
When the power button on the front panel is
pressed and the three blue power LEDs illumi-
nate, the component is in the operational mode
and ready to play music.
Stand-by Mode
A low power consumption status that keeps the
audio and regulator circuits at idle. Krell recom-
mends leaving the component in the stand-by
mode when it is not playing music.
2
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Revolutionary Krell CAST
and CAST II Technology
Current Audio Signal Transmission, termed
CAST, is a revolutionary method of connecting
analog audio components for unparalleled
sonic performance. CAST circuitry, and the
CAST circuitry update, Krell CAST II, combine
innovative engineering with existing Krell Cur-
rent Mode technology to create entire CAST
systems that reproduce music with incredible
range, tonality, and precision.
CAST, anomalies of signal transmission between
components are eliminated. Cable impedances
and their effects on the transmitted signal are
non-existent.
How CAST and Krell Current Mode Interact
While CAST is a new method of transferring the
musical signal between components, its origin
stems from Krell Current Mode, the technology
developed to transfer the musical signal within
a component. CAST combined with Krell Cur-
rent Mode takes circuitry signal transmission to
the next evolutionary level. In essence, Krell
Current Mode maintains the integrity of the sig-
nal within the component and CAST preserves
the transmitted signal between components.
Together, CAST and Krell Current Mode tech-
nologies unify separate Krell components into a
single global circuit.
Voltage Signal Transmission
and the Traditional Audio System
Traditionally, signal is transmitted in the voltage
domain between two components. In an audio
system, each component is a discrete entity with
unique characteristics that act upon the musical
signal independently. Each component is
unaware of the other components in the system.
The cables that connect the components each
have their own electrical characteristics, which
affect the sonic presentation of the entire sys-
tem.
CAST Cable Construction
A CAST system uses cables manufactured by
Krell and other manufacturers specially
licensed by Krell. Thin and flexible CAST
cables are constructed with the same build
quality as other Krell products and are aesthet-
ically matched to the components that Krell
manufactures. An all-metal body and locking
connectors with gold contacts are part of the
standard no-compromise specification devel-
oped for every CAST cable made.
CAST: A New Approach
CAST circuitry recognizes signal transmitted in
the current domain instead of the voltage
domain between each component. CAST
transmission unifies the individual components
and their interconnects into an electrically
linked whole. The sonic presentation of the
entire system remains intact.
CAST Basics
The Best Musical Performance
Here’s how a CAST audio system works. Inter-
nally, each CAST source transfers, or amplifies,
current using Krell Current Mode circuitry. This
current signal is then output using CAST cir-
cuitry. When the signal is received by a CAST
input, Krell Current Mode circuitry again takes
over until the signal reaches the loudspeaker.
By maintaining the musical signal in the current
domain from beginning to end, an entire CAST
system behaves as if it is one component. With
When you operate a CAST system, you will
hear significant improvements in every perfor-
mance area: speed, precision, dynamic range,
depth and width of the sound stage, transient
impact, tonal balance, harmonic distortion, and
more. The goal for CAST is the same company
goal used for all Krell products. Krell strives for
the delivery of the best performance of a musi-
cal event for you, using the full expression of
technology to date.
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Unpacking
Placement
Two people are needed to remove the Full
Power Balanced amplifier from its shipping box
safely and easily.
Before you install the Full Power Balanced
amplifier into your system, please follow the
guidelines in this section to choose its proper
location. This will facilitate a clean, trouble-free
installation.
1. Open the shipping box and remove the top
layer of foam. You see these items:
The Full Power Balanced amplifier requires at
least two inches (5 cm) of clearance on each
side and at least eight inches (20 cm) of clear-
ance above the component to provide ade-
quate ventilation.
1 Full Power Balanced Amplifier
1 Packet containing the owner’s
reference manual and the warranty
registration card
2. Orient the shipping box so that one person
stands at the front of the amplifier and one
person stands at the rear of the amplifier.
Both people need to grab a pair of the card-
board handle cutouts (one pair located at the
front of the amplifier and one pair located at
the rear of the amplifier) and simultaneously
lift the amplifier straight up, out of the carton.
Although Sustained Plateau Bias III circuitry
reduces the high heat dissipation and heat out-
put of traditional Class A circuitry, Full Power
Balanced amplifiers still can become hot under
normal operation.
When the front and rear of a cabinet are open
the air space between the chassis and shelf
must be unobstructed. If you place the amplifi-
er in a closed cabinet, you may need to modify
shelf spacing or use small fans to increase ven-
tilation. For the dimensions of your Full Power
Balanced amplifier, see Specifications, on
pages 22–23.
3. Place the amplifier in a safe location and
remove the protective plastic wrapping.
Notes
If any of the items mentioned above are not
included in the shipping box, please contact
your authorized Krell dealer, distributor, or Krell
for assistance.
Place the amplifier as close to the speakers as
possible. Krell CAST technology permits you to
use interconnect cables of any length, see Rev-
olutionary Krell CAST and CAST II Technol-
ogy on page 3; however, try to keep the cable
length to a minimum.
Save all packing materials. If you ship your Full
Power Balanced amplifier in the future, repack
the unit in its original packaging to prevent tran-
sit damage. See Return Authorization Proce-
dure, on page 21 for more information.
All Full Power Balanced amplifiers drive the
lowest impedances with ease. When imped-
ance is added due to long speaker cable
lengths, amplifier power is wasted in the cable.
Long speaker cables reduce the maximum
power that is delivered in the speakers.
4
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Placement,
continued
be operated from a dedicated AC power line
rated at a minimum of 20 amps.
AC POWER GUIDELINES
The Full Power Balanced 300cx and 350Mcx
amplifiers need to be operated from a dedicat-
ed AC power line rated at a minimum of 15
amps. The Full Power Balanced 700cx,
750Mcx, 400cx, and 450Mcx amplifiers need to
Please contact your authorized Krell dealer, dis-
tributor, or Krell before using any devices
designed to alter or stabilize the AC power for
Full Power Balanced amplifiers.
Krell Full Power Balanced X Series Power Amplifiers
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FIGURE 1
FULL POWER BALANCED STEREO AMPLIFIER FRONT PANEL
1
2
3
4
5
6
1 Power Stand-by LED
2 Bias LED
3 Power Button
4 Infrared Sensor
5 Krell CAST LED
6 Regulator LED
6
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FIGURE 2 FULL POWER BALANCED MONAURAL AMPLIFIER FRONT PANEL
7
8
9
10 11 12
7 Power Stand-by LED
8 Bias LED
9 Power Button
10 Infrared Sensor
11 Krell CAST LED
12 Regulator LED
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Front Panel Description
The front panel accesses power on/stand-by
and infrared sensor (remote control) functions.
The power stand-by, bias, regulator, and Krell
CAST LEDs, arranged in a triangle on the front
Note
An optional remote control is available for Full
Power Balanced amplifiers.
panel above the power button, illuminate to indi- FULL POWER BALANCED
cate amplifier status.
750Mcx, 450Mcx, AND 350Mcx
MONAURAL POWER AMPLIFIERS
FULL POWER BALANCED
700cx, 400cx, AND 300cx
STEREO POWER AMPLIFIERS
See Figure 2 on page 7
7 Power Stand-by LED
See Figure 1 on page 6
The blue power stand-by LED (top of LED tri-
angle) illuminates when the back panel power
breaker switch has been moved to on, engag-
ing the input circuitry and placing the amplifier
in stand-by mode.
1 Power Stand-by LED
The blue power stand-by LED (top of LED tri-
angle) illuminates when the back panel power
breaker switch has been moved to on, engag-
ing the input circuitry and placing the amplifier
in stand-by mode.
8 Bias LED
The blue bias LED (lower left of triangle) illumi-
nates after the front panel power button is
pressed, indicating that the Sustained Plateau
Bias III is engaged.
2 Bias LED
The blue bias LED (lower left of triangle) illumi-
nates after the front panel power button is
pressed, indicating that the Sustained Plateau
Bias III is engaged.
9 Power Button
Use the silver power button to power on the
amplifier from stand-by mode.
3 Power Button
Use the silver power button to power on the
amplifier from stand-by mode.
10 Infrared Sensor
The infrared sensor receives the signal from a
remote control.
4 Infrared Sensor
The infrared sensor receives the signal from a
remote control.
11 Krell CAST LED
The red Krell CAST LED (center of triangle) illu-
minates when a Krell CAST input on the back
panel is connected to another Krell product with
a Krell CAST output.
5 Krell CAST LED
The red Krell CAST LED (center of triangle) illu-
minates when a Krell CAST input on the back
panel is connected to another Krell product with
a Krell CAST output.
12 Regulator LED
The blue regulator LED (lower right of triangle)
illuminates after the front panel power button is
used to power on from stand-by mode, indicat-
ing that the regulator is providing power to the
output stage.
6 Regulator LED
The blue regulator LED (lower right of triangle)
illuminates after the front panel power button is
used to power on from stand-by mode, indicat-
ing that the regulator is providing power to the
output stage.
8
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FIGURE 3
FULL POWER BALANCED STEREO AMPLIFIER BACK PANEL
19 13
14
15 16
17
18
16
14
13 19
13 Left and Right Speaker Binding Posts
14 Krell CAST Inputs
16 Left and Right Balanced Inputs
17 Krell Link Out/In
15 Back Panel Power Breaker Switch
18 AC Mains Power Cord
19 Handles
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FIGURE 4
FULL POWER BALANCED MONAURAL AMPLIFIER BACK PANEL
20
21
22
23
24
25
26
20 Handle
24 AC Mains Power Cord
25 Krell Link Out/In
26 Back Panel Power
Breaker Switch
21 Speaker Binding Posts
22 Krell CAST Input
23 Balanced Input
10
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Back Panel Description
The back panel provides connections for all
inputs and outputs, power on/off, and remote
control links. The back panel also has handles
that allow you to safely and easily move the
amplifier.
15 Back Panel Power Breaker Switch
Full Power Balanced amplifiers are equipped
with a back panel power breaker switch, for
powering on the amplifier. Placing the back
panel power breaker switch in the up position
places the amplifier in stand-by mode, where it
remains until the front panel power button (3) is
pressed.
FULL POWER BALANCED
700cx, 400cx, AND 300cx
STEREO POWER AMPLIFIERS
Note
See Figure 1 on page 6
Krell recommends that the amplifier remain on,
in stand-by mode, even when not in use, once
it is powered on from the back panel power
breaker switch (15).
13 Left and Right Speaker Binding Posts
Full Power Balanced 700cx, 400cx, and 300cx
stereo amplifiers are equipped with four pairs of
speaker binding posts (upper left, lower left,
upper right, and lower right).
16 Left and Right Balanced Inputs
Full Power Balanced 700cx, 400cx, and 300cx
stereo amplifiers are equipped with one left bal-
anced input and one right balanced input via
XLR connectors.
Notes
Two pairs of speaker binding posts are used for
each channel of amplification. On the stereo or
monaural Full Power Balanced amplifiers,
either the upper or the lower pair can be used
with speakers having two pairs of binding posts.
For biwiring applications, with speakers having
more than one pair of binding posts, use both
upper and lower pairs of speaker binding posts.
See the speaker’s instruction manual for
biwiring connections.
17 Krell Link Out/In
Full Power Balanced amplifiers are equipped
with Krell Link Remote out/in connectors that
allow the remote control to operate a linked
amplifier configuration. See Krell Link Connec-
tions, on page 13 for more information.
Note
An optional remote control is available for Full
Power Balanced amplifiers.
Speaker binding posts for stereo and monaural
amplifiers accept spade lugs only. Bare wire,
banana lugs, or pins will not work. Use the red
terminal for the positive connection and the
blue terminal for the negative connection.
18 AC Mains Power Cord
All Full Power Balanced amplifiers are equipped
with a permanently attached AC power cord.
14 Krell CAST Inputs
19 Handles
Full Power Balanced 700cx, 400cx, and 300cx
stereo amplifiers are equipped with one left Krell
CAST input and one right Krell CAST input via 4-
pin bayonet connectors. The Krell CAST inputs
allow the Full Power Balanced amplifier to be
connected to the KPS 25sc Krell Playback Sys-
tem and other CAST-equipped components.
All Full Power Balanced stereo amplifiers are
equipped with two handles, located beside the
speaker binding posts, to help you easily and
safely move the amplifier.
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Back Panel Description,
continued
24 AC Mains Power Cord
All Full Power Balanced amplifiers are equipped
with a permanently attached AC power cord.
FULL POWER BALANCED 750Mcx,
450Mcx, AND 350Mcx MONAURAL
POWER AMPLIFIERS
See Figure 4 on page 10
25 Krell Link Out/In
Full Power Balanced amplifiers are equipped
with Krell Link Remote out/in connectors that
allow the remote control to operate a linked
amplifier configuration. See Krell Link Connec-
tions, on page 13 for more information.
20 Handle
All Full Power Balanced monaural amplifiers are
equipped with a handle, located beside the
speaker binding posts, to help you easily and
safely move the amplifier.
Note
21 Speaker Binding Posts
An optional remote control is available for Full
Power Balanced amplifiers.
Full Power Balanced 750Mcx, 450Mcx, and
350Mcx monaural amplifiers are equipped with
two pairs of speaker binding posts (one upper
pair and one lower pair). For stereo operation,
two monaural amplifiers are required.
26 Back Panel Power Breaker Switch
Full Power Balanced amplifiers are equipped
with a back panel power breaker switch, for
powering on the amplifier. Powering on using
the back panel power breaker switch places the
amplifier in stand-by mode, where it remains
until the front panel power button is pressed.
22 Krell CAST Input
Full Power Balanced 750Mcx, 450Mcx, and
350Mcx monaural amplifiers are equipped with
one Krell CAST input via a 4-pin bayonet con-
nector. The Krell CAST input allows the Full
Power Balanced amplifier to be connected to
the KPS 25sc Krell Playback System and other
CAST-equipped components.
Note
Krell recommends that, once the amplifier is
powered on from the back panel power breaker
switch, it remains on, in stand-by mode, even
when not in use.
23 Balanced Input
Full Power Balanced 750Mcx, 450Mcx, and
350Mcx monaural amplifiers are equipped with
one balanced input via an XLR connector.
12
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Connecting the Full Power Balanced
Amplifier to Your System
4. Insert the end of the AC mains power cord
INPUT AND OUTPUT
CONNECTIONS
into the AC wall receptacle.
5. Proceed with Krell Link Connections, if
desired, or turn to Amplifier Operation, on
page 15.
Krell recommends using its proprietary Krell
CAST system for unparalleled sonic perfor-
mance between the Full Power Balanced
amplifiers and other CAST-equipped compo-
nents and the KPS 25sc Krell Playback Sys-
tem.
KRELL LINK CONNECTIONS
Krell Link Remote out/in connectors on the
back panel of the Full Power Balanced amplifi-
er allow you to synchronize remote control
operation for systems that include multiple
amplifiers and associated components. When
the Krell Link Remote out/in connectors are
used, the remote capabilities of the linked com-
ponents are controlled from one amplifier or
preamplifier, called the control component. The
linked components respond to stand-by and
operational mode commands from the control
component via MIDI cables.
Full Power Balanced amplifiers also offer bal-
anced operation. The circuitry and connections
associated with balanced operation not only
can minimize sonic loss but also are immune to
induced noise, especially for installations using
long cables.
A one piece RCA-to-XLR adapter is available
from Krell Industries, to allow single-ended oper-
ation using the balanced XLR inputs.
The following steps describe how to connect
cables to the Full Power Balanced Amplifiers.
Note
Krell Link uses standard five pin MIDI commu-
nication cables, sometimes referred to as MIDI
Plus cables. MIDI cables can be purchased
from your authorized distributor or dealer, or
from an audio supply store.
1. Neatly arrange and organize wiring to and
from the amplifier and all components. Sep-
arate AC wires from audio cables to prevent
hum or other unwanted noise from being
introduced into the system.
2. Connect the Krell CAST cables from your
CAST-enabled preamplifier/source compo-
nent to the left and right Krell CAST 4-pin
bayonet inputs on the amplifier back panel.
For balanced operation, connect the inter-
connect cable from your preamplifier to the
left and right balanced XLR input on the
amplifier back panel.
How to Connect Components
through Krell Link
1. Turn all components off, using the back
panel power breaker switch. This ensures
that the components are synchronized when
the MIDI cable is connected.
2. Select the component to be the control com-
ponent. The control component must be in
plain view for proper remote control opera-
tion.
3. Connect the speaker cables to the Full
Power Balanced amplifier’s speaker binding
posts, located on the amplifier back panel.
Speaker binding posts for both stereo and
monaural amplifiers accept spade lugs only.
3. Connect one end of the MIDI cable to the
Krell Link out connector on the back panel of
the component.
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Connecting,
continued
4. Connect the other end of the MIDI cable to
the Krell Link in connector on the next com-
ponent.
USING A TUBE PREAMPLIFIER
The high DC output of tube preamplifiers may
exceed the DC protection circuitry of Full
Power Balanced amplifiers. Excessive DC
level in a signal can damage amplifiers, speak-
ers, or both. The coupling capacitors in Full
Power Balanced amplifiers must be engaged
when using a tube preamplifier. An authorized
Krell dealer, distributor, or Krell must activate
these capacitors.
To link another component, connect a sec-
ond MIDI cable to the Krell Link out con-
nector on the back panel of the second
component. Connect the remaining end of
the MIDI cable to the Krell Link in connec-
tor on the back panel of a third component.
5. Link additional components, if desired, as
described in Steps 3 and 4.
Coupling capacitors must be inserted into the
signal path by your authorized Krell dealer, dis-
tributor, or Krell before you can use your Full
Power Balanced amplifier with a tube preampli-
fier.
The components are now ready for operation with
Krell Link.
DC PROTECTION CIRCUITRY
Full Power Balanced amplifiers use unobtrusive
direct current (DC) protection circuitry that
strips DC from the signal without corrupting
sound reproduction. Full Power Balanced
amplifiers feature direct coupled circuitry from
input to output. This topology eliminates all cou-
pling capacitors from the audio signal path.
Coupling capacitors block damaging DC but
have sonic characteristics that corrupt sound
reproduction.
IMPORTANT
Please read the Warranty, on page 20, to
understand the warranty limitations of Full
Power Balanced amplifiers when used with
tube preamplifiers.
Note
For more information about DC protection cir-
cuitry features, see Amplifier Troubleshooting,
on page 17.
14
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Amplifier Operation
Full Power Balanced amplifiers are easy to
install and operate. However, it is important to
exercise care during operation, due to the
amplifiers’ enormous power output. Switching
between active sources (such as a CD player,
tape monitor, or VCR) without muting the pre-
amplifier output, or bumping or miscuing a
source can generate large transients at low fre-
quencies. Full Power Balanced amplifiers may
generate enough power with these transients
to damage loudspeakers.
If the Krell CAST input is being used, the
Krell CAST red LED illuminates and
remains illuminated at all times during the
stand-by or power on modes.
3. With the preamplifier muted or volume con-
trol completely lowered, select a source.
Increase the volume control to the desired
listening level.
4. When turning off the system, mute or com-
pletely lower the preamplifier volume, or
place the Full Power Balanced amplifier in
the stand-by power mode by pressing the
power button on the front panel. It is now
safe to turn off the rest of the system.
IMPORTANT
Always mute or fully attenuate the preamplifier
level when switching sources.
Do not change input connections to the amplifi-
er when the amplifier is on.
Note
For best performance of Full Power Balanced
amplifiers, leave the back panel power breaker
switch on at all times.
Use care when setting high playback levels.
Because of their tremendous reserves of clean
power, Full Power Balanced amplifiers can safe-
ly drive speakers to higher sound pressure lev-
els than other amplifiers. Always lower the vol-
ume level at the first sign of speaker distress.
KRELL LINK OPERATION
1. When all components are linked, place
each component in the stand-by mode by
moving the back panel power breaker
switch to the up position. This ensures that
all components will be synchronized when
signals from the control component are sent
to the linked components in the system.
ON/OFF AND STAND-BYOPERATION
When powering on any system, turn on ampli-
fiers last. Turn off amplifiers first.
1. Move the back panel power breaker switch
to the up position to engage the input cir-
cuitry and place the amplifier into the stand-
by mode. The front panel blue power stand-
by LED illuminates.
2. When the components are in stand-by,
switch the control component to the opera-
tional mode from the control component’s
front panel or by using the component’s
remote control.
2. Press the silver power button on the amplifi-
er front panel. The blue regulator LED illumi-
nates. Once the regulator provides power to
the output stage, the blue bias LED illumi-
nates. The Sustained Plateau Bias II system
is now engaged. After the protection circuitry
has confirmed that safe operating conditions
exist, the input relays engage. You hear a
click. The amplifier is ready for operation.
The linked components switch to the oper-
ational mode simultaneously.
A linked component can be switched between
the operational mode and stand-by, individual-
ly, from its front panel. Switching a linked com-
ponent temporarily breaks the chain of linked
components. To re-establish linked operation,
return all components to stand-by.
Krell Full Power Balanced X Series Power Amplifiers
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Remote Control
Operation
Full Power Balanced amplifiers are compatible
with the remote controls included with Krell pre-
amplifiers, the Home Theater Standard 7.1, and
the KPS 25sc Krell Playback System.
HOW TO TURN ON
THE AMPLIFIER LEDs
With the amplifier in the stand-by mode, turn
the rear panel power breaker switch to the off
position. Then turn the rear panel power break-
er switch back to the on position. The next time
the amplifier is powered up from the front panel
or the remote control, the blue LEDs illuminate
during the turn-on sequence.
Please contact your authorized Krell dealer, dis-
tributor, or Krell to purchase a remote control for
Full Power Balanced amplifiers.
Full Power Balanced amplifiers can be located
in a room or space close to the speakers but out
of sight, and powered on or off remotely from
the listening room, through a control amplifier.
See Krell Link Connections, on page 13.
HOW TO SWITCH BETWEEN
KRELL CAST AND XLR INPUTS
Press the meter key on a Krell remote to switch
between CAST inputs and the balanced XLR
inputs.
HOW TO TURN OFF
THE AMPLIFIER LEDs
The amplifier must be in the stand-by mode
with the rear panel power breaker switch on.
While holding the silver power button in, press
the power key on the remote control. After the
amplifier finishes its turn-on sequence, the front
panel blue LEDs turn off. The blue LEDs remain
off throughout normal operation as long as the
amplifier’s rear panel power breaker switch is
not turned off.
Full Power Balanced amplifiers default to CAST
operation upon startup, if the amplifier is turned
off from the rear panel power breaker switch and
a CAST source and cable are connected to the
CAST inputs. The operational mode does not
change if the Full Power Balanced amplifier is in
stand-by mode.
USING A DEDICATED WALL
OUTLET AND SWITCH
Full Power Balanced amplifiers can be powered
on from an AC wall receptacle with a dedicated
switch, rather than from the front panel power
button or optional remote control.
Please contact your authorized Krell dealer, dis-
tributor, or Krell for more information before you
connect your Full Power Balanced amplifier to a
dedicated AC wall outlet with a switch.
16
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Amplifier Troubleshooting
HOW TO TROUBLESHOOT
SYSTEM NOISE
HOW TO EVALUATE AMPLIFIER
OPERATION
The amplifiers are protected by a series of non-
intrusive circuits that constantly evaluate the
amplifier’s operation. This circuitry protects
against damaging DC input or output and short
circuits, see also DC Protection Circuitry, on
page 14, and monitors regulator operation,
ensuring constant voltage to the output stage.
The protection circuitry in a Full Power Bal-
anced amplifier is designed to prevent damage
to the amplifiers or speakers caused by other
defective components, faulty wiring, system
mishandling, or amplifier failure.
AC grounding becomes critical when connect-
ing high performance audio components. When
you mix and match audio components, each
with its own ground potential, a low frequency
hum may occur in one or both speakers. This
often occurs when introducing a new compo-
nent into a system.
If a low frequency hum emanates from the
speakers when you place the Full Power Bal-
anced amplifier into the system, follow these
simple troubleshooting steps:
Note
In addition, when a Full Power Balanced ampli-
fier’s DC protection circuitry senses a problem
within the system, it identifies, then indicates the
problem by illuminating the front panel blue
LEDs, as described in the following table.
During these steps, the back panel power
breaker switch remains in the on position.
1. Check all input and output connections,
making sure they are of sound construction.
With the amplifier in stand-by mode, remove
the interconnect cables, then press the front
panel power button. If the hum disappears,
press the power button to return to stand-by
mode, and reinsert one of the interconnect
cables. Press the power button again. If the
hum reappears with one or both intercon-
nects inserted, there may be a defective
cable. Have the interconnect cables checked
before proceeding.
Notes
The Krell CAST LED illuminates only if a Krell
CAST input is being used.
There are no output fuses in Full Power Bal-
anced amplifiers.
2. If the interconnect cables are sound, you
may be experiencing a ground loop. This
can often be easily eliminated. Please con-
tact your authorized Krell dealer, distributor,
or Krell for suggestions on how to solve this
problem.
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If the course of action listed in the table below does not correct the situation, please con-
tact your authorized Krell dealer, distributor, or Krell.
AMPLIFIER CONDITION
The output mutes during
playback and the following
LEDs illuminate: Power
Stand-by, and
POSSIBLE CAUSES
Excessive DC at the
amplifier input
COURSE OF ACTION
Have source unit and
preamplifier checked for high
DC output
Regulator Bias
If preamplifier is a tube
model, see Using a Tube
Preamplifier, on page 14.
The amplifier switches to
stand-by mode and the
Power Stand-by LED
illuminates
Electrical short in speaker
cables or inside speaker
Check all speaker cables for
any cuts or frayed edges that
might form a connection
between the positive and neg-
ative speaker binding post ter-
minals
The amplifier switches to
stand-by at high volumes
and the Power Stand-by
LED illuminates
Insufficient AC current from
the wall outlet
Make sure the AC line is at
least 15 amps for 300cx and
350Mc amplifiers; 400cx,
450Mcx, 700cx, and 750Mcx
amplifiers should be
operated from a dedicated
20-amp line.
Excessive heat
Allow amplifier to cool before
resuming operation. See
Placement, on page 4 for ven-
tilation requirements
The amplifier powers down
completely and no LEDs
illuminate
DC present at the output
stage
Contact your authorized Krell
dealer, distributor, or Krell
Contact your authorized Krell
dealer, distributor, or Krell
Internal amplifier problem
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Questions and Answers
Q. Should I leave my Full Power Balanced
amplifier on at all times?
device that employs a common ground
scheme, as it may short-circuit the amplifier
output.
A. For maximum amplifier performance, leave
the back panel power breaker switch on at all
times. This places the amplifier in stand-by
mode. Full Power Balanced amplifiers are
designed to be powered on and off from stand-
by, using the front panel power button. This
eliminates “cold start” degradations. The ampli-
fier will operate at full performance within min-
utes.
Q. My speakers have only one pair of binding
posts, but my Full Power Balanced stereo
amplifier has two pairs. Which pair of speaker
binding posts should I use, the upper or the
lower?
A. The upper and lower pair of speaker bind-
ing posts on Full Power Balanced stereo ampli-
fiers are identical. You can use either the upper
or lower pair; they work and sound the same.
See Connecting the Full Power Balanced
Amplifier to Your System, on page 13.
Q. When I turn on the amplifier there is a loud
hum through the speakers. What should I do?
A. When a new component is introduced, a low
frequency hum may occur in one or both speak-
ers. Check all input and output connections and
cables, making sure they are of sound con-
struction. See How to Troubleshoot System
Noise, on page 17. If the interconnects and
cables are sound, you may be experiencing a
ground loop. This can often be easily eliminat-
ed. Please contact your authorized Krell dealer,
distributor, or Krell for suggestions on how to
solve this problem.
Q. My speakers are rated for 150 Watts. Are
the Full Power Balanced 400cx or 700cx mod-
els too powerful for them?
A. No. A speaker seldom is damaged from
overdriving. More often, damage occurs when
an amplifier that lacks sufficient power is asked
to handle heavy demand situations such as
high playback levels. These amplifiers may
have very high 8 Ohm power ratings, but in
heavy demand situations they can be driven
into clipping (in which DC current goes to
speakers due to loss of amplifier power). Clip-
ping can damage speakers. Avoid damage to
your speakers by reviewing your speaker’s
specifications and exercise caution in heavy
demand situations.
Q. My system includes multiple pairs of speak-
ers. Can I connect them to my Full Power Bal-
anced amplifiers through a speaker selector
box?
A. No. Most speaker selector boxes use a com-
mon ground scheme. The differential circuitry in
Full Power Balanced amplifiers prohibits the use
of these devices. Do not connect a Full Power
Balanced amplifier to a speaker selector
Krell Full Power Balanced X Series Power Amplifiers
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Warranty
This Krell product has a limited warranty of five years for
parts and labor on circuitry. Should this product fail to per-
form at any time during the warranty, Krell will repair it at
no cost to the owner, except as set forth in this warranty.
Freight to the factory is your responsibility. Return freight
within the United States (U.S.A.) is included in the warranty.
If you have purchased your Krell product outside the U.S.A.
and wish to have it serviced at the factory, all freight and
associated charges to the factory are your responsibility.
Krell will pay return freight to the U.S.A.-based freight for-
warder of your choice. Freight and other charges to ship the
unit from the freight forwarder to you are also your respon-
sibility.
The warranty does not apply to damage caused by acts of
God or nature.
The warranty on this page shall be in lieu of any other war-
ranty, expressed or implied, including, but not limited to,
any implied warranty of merchantability or fitness for a par-
ticular purpose. There are no warranties which exceed
beyond those described in this document. If this product
does not perform as warranted herein, the owner’s sole
remedy shall be repair. In no event will Krell be liable for
incidental or consequential damages arising from pur-
chase, use, or inability to use this product, even if Krell has
been advised of the possibility of such damages.
Krell is not responsible for any damage incurred in transit.
Krell will file claims for damages as necessary for units dam-
aged in transit to the factory. You are responsible for filing
claims for shipping damages during the return shipment.
Krell does not supply replacement parts and/or products to
the owner of the unit. Replacement parts and/or products
will be furnished only to the distributor performing service on
this unit on an exchange basis only; any parts and/or prod-
ucts returned to Krell for exchange become the property of
Krell.
IMPORTANT
The user is responsible for notifying his or her Krell deal-
er, distributor, or Krell that a tube preamplifier will be used
with the Full Power Balanced amplifier, so that the Krell
dealer, distributor, or Krell can activate the coupling capac-
itors. If the user does not notify the Krell dealer, distributor,
or Krell and uses a tube preamplifier without the Full
Power Balanced amplifier’s coupling capacitor engaged,
Krell reserves the right to refuse warranty related service
due to DC-related damage.
No expressed or implied warranty is made for any Krell
product damaged by accident, abuse, misuse, natural or
personal disaster, or unauthorized modification.
Any unauthorized voltage conversion, disassembly,
component replacement, perforation of chassis,
updates, or modifications performed to the unit will
void the warranty.
The operating voltage of this unit is determined by the fac-
tory and can only be changed by an authorized Krell distrib-
utor or at the factory. The voltage for this product in the
U.S.A. cannot be changed until six months from the original
purchase date.
Proof of purchase in the form of a bill of sale or receipted
invoice substantiating that the unit is within the warranty
period must be presented to obtain warranty service. The
warranty begins on the date of the original retail purchase,
as noted on the bill of sale or receipted invoice from an
authorized Krell dealer or distributor. Previously owned
equipment, when re-purchased from an authorized Krell
dealer or distributor, has the balance of the original war-
ranty, based on the original date of manufacture.
In the event that Krell receives a product for warranty ser-
vice that has been modified in any way without Krell autho-
rization, all warranties on that product will be void. The prod-
uct will be returned to original factory layout specifications
at the owner’s expense before it is repaired. All repairs
required after the product has been returned to original fac-
tory specifications will be charged to the customer, at cur-
rent parts and labor rates.
The warranty for Krell products is valid only in the country to
which they were originally shipped, through the authorized
Krell distributor for that country, and at the factory. There
may be restrictions on or changes to Krell’s warranty
because of regulations within a specific country. Please
check with your distributor for a complete understanding of
the warranty in your country.
All operational features, functions, and specifications and
policies are subject to change without notification.
To register your product for warranty benefits,
please complete and return the Warranty Reg-
istration Card enclosed in the shipping box
within 15 days of purchase. Thank you.
If a unit is serviced by a distributor who did not import the
unit, there may be a charge for service, even if the product
is within the warranty period.
20
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Return Authorization
Procedure
If you believe there is a problem with your com-
ponent, please contact your dealer, distributor, or
the Krell factory to discuss the problem before
you return the component for repair. To expedite
service, you may wish to complete and e-mail
the Service Request Form in the Service Section
of our website at:
To return this product to Krell, please follow
this procedure so that we may serve you
better:
1. Obtain a Return Authorization Number (R/A
number) and shipping address from the
Krell Service Department.
2. Insure and accept all liability for loss of or
damage to this product during shipment to
the Krell factory and prepay all shipping
charges. Please see the Warranty page in
this manual, concerning liability for shipping
damage and shipping charges.
To contact the Krell Service Department
TEL
203-799-9954
Monday-Friday
This product may also be hand delivered if
arrangements with the Service Department
have been made in advance. Proof of purchase
may be required for warranty validation at the
time of hand delivery.
9:00 AM to 5:00 PM EST
FAX
203-799-9796
E-MAIL
IMPORTANT
Full Power Balanced X Series Amplifier
Use the original packaging to ensure safe tran-
sit of this product to the dealer, distributor, or
factory. Krell may, at its discretion, return this
product in new packaging and bill the owner for
such packaging if the product received by Krell
was boxed in non-standard packaging or if the
original packaging was so damaged that it was
unusable. If Krell determines that new packag-
ing is required, the owner will be notified before
this product is returned.
PRODUCT NAME
MODEL NUMBER
SERIAL NUMBER
To purchase additional packaging, please con-
tact your authorized Krell dealer, distributor, or
the Krell Service Department.
Krell Full Power Balanced X Series Power Amplifiers
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Specifications
Full Power Balanced 300cx, 400cx, 700cx Stereo Amplifiers
FPB 300cx
FPB 400cx
FPB 700cx
FREQUENCY RESPONSE
20 Hz to 20 kHz
+0 dB, -0.05 dB
20 Hz to 20 kHz
+0 dB, -0.05 dB
20 Hz to 20 kHz
+0 dB, -0.05 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
SIGNAL TO NOISE RATIO
“A” WEIGHTED
113 dB
117 dB
120 dB
26.4 dB
GAIN
26.4 dB
26.4 dB
TOTAL HARMONIC
1 kHz <0.03%
20 kHz <0.16%
1 kHz <0.03%
20 kHz <0.16%
1 kHz <0.03%
20 kHz <0.16%
DISTORTION (THD)
ALL BALANCED, UNWEIGHTED
INPUT IMPEDANCE
INPUT SENSITIVITY
100 kOhms
2.34 Vrms
100 kOhms
2.71 Vrms
100 kOhms
3.58 Vrms
OUTPUT POWER
EACH CHANNEL DRIVEN
8 Ohms 300 W
4 Ohms 600 W
2 Ohms 1200 W
8 Ohms 400 W
4 Ohms 800 W
2 Ohms 1,600 W
8 Ohms 700 W
4 Ohms 1,400 W
2 Ohms 2,800 W
OUTPUT VOLTAGE
Peak to Peak138 V
Peak to Peak170 V
Peak to Peak240 V
RMS
49 V
RMS
60 V
RMS
84 V
POWER CONSUMPTION
Stand-by
Idle
60 W
175 W
Stand-by
Idle
75 W
350 W
Stand-by
Idle
85 W
430 W
Max.
1,700 W
Max.
3,000 W
Max.
6,000 W
INPUTS
1 pair balanced via
XLR connectors
1 pair balanced via
XLR connectors
1 pair balanced via
XLR connectors
1 pair CAST via 4-pin
bayonet connectors
1 pair CAST via 4-pin
bayonet connectors
1 pair CAST via 4-pin
bayonet connectors
OUTPUTS
SPEAKER BINDING POSTS
4 pair (upper left,
lower left, upper right
lower right)
4 pair (upper left,
lower left, upper right
lower right)
4 pair (upper left
lower left, upper right
lower right)
REMOTE CONTROL
Optional
Optional
Optional
DIMENSIONS
INCHES
CENTIMETERS
19.0w x 10.3h x 17.0d
48.3w x 26.2h x 43.2d
19.0w x 10.3h x 19.7d
48.3w x 26.2h x 50.0d
19.0w x 10.3hx 25.5d
48.3wx 26.2hx 64.8d
WEIGHT
SHIPPING
UNIT ONLY
107.0 lb., 48.6 kg
90.0 lb., 40.9 kg
127.0 lb., 57.7 kg
110.0 lb., 50.0 kg
200.0 lb., 90.9 kg
180.0 lb., 81.8 kg
All operational features, functions, specifications, and policies are subject to change without notification.
22 Krell Full Power Balanced X Series Power Amplifiers
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Specifications
Full Power Balanced 350Mcx, 450Mcx, 750Mcx Monaural Amplifiers
FPB 350Mc
FPB 450Mc
FPB 750Mc
FREQUENCY RESPONSE
20 Hz to 20 kHz
+0 dB, -0.05 dB
20 Hz to 20 kHz
+0 dB, -0.05 dB
20 Hz to 20 kHz
+0 dB, -0.05 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
0.1 Hz to 240 kHz
+0 dB, -3 dB
SIGNAL TO NOISE RATIO
“A” WEIGHTED
114 dB
118 dB
121 dB
26.4 dB
GAIN
26.4 dB
26.4 dB
TOTAL HARMONIC
1 kHz <0.03%
20 kHz <0.16%
1 kHz <0.03%
20 kHz <0.16%
1 kHz <0.03%
20 kHz <0.16%
DISTORTION (THD)
ALL BALANCED, UNWEIGHTED
INPUT IMPEDANCE
INPUT SENSITIVITY
100 kOhms
2.53 Vrms
100 kOhms
2.87 Vrms
100 kOhms
3.71 Vrms
OUTPUT POWER
EACH CHANNEL DRIVEN
8 Ohms 350 W
4 Ohms 700 W
2 Ohms 1,400 W
8 Ohms 450 W
4 Ohms 900 W
2 Ohms 1,800 W
8 Ohms 750 W
4 Ohms 1,500 W
2 Ohms 3,000 W
OUTPUT VOLTAGE
Peak to Peak138 V
Peak to Peak170 V
Peak to Peak240 V
RMS
49 V
RMS
60 V
RMS
84 V
POWER CONSUMPTION
Stand-by
Idle
30 W
150 W
Stand-by
Idle
37.5 W
175 W
Stand-by
Idle
42.5 W
220 W
Max.
1,700 W
Max.
3,000 W
Max.
6,000 W
INPUTS
1 balanced via
XLR connectors
1 balanced via
XLR connectors
1 balanced via
XLR connectors
1 Krell CAST via 4-pin
bayonet connectors
1 Krell CAST via 4-pin
bayonet connectors
1 Krell CAST via 4 pin
bayonet connectors
OUTPUTS
SPEAKER BINDING POSTS
2 pair (one upper,
one lower)
2 pair (one upper,
one lower)
2 pair (one upper,
one lower)
REMOTE CONTROL
Optional
Optional
Optional
DIMENSIONS
INCHES
CENTIMETERS
12.5w x 10.5h x 16.0d
31.8w x 26.7h x 40.6d
12.5w x 10.5h x 19.0d
31.8w x 26.7h x 48.3d
12.5w x 10.5h x 25.0d
31.8w x 26.7h x 67.3d
WEIGHT
SHIPPING
UNIT ONLY
79.0 lb., 35.9 kg
68.0 lb., 31.0 kg
110.0 lb., 50.0 kg
98.0 lb., 44.5 kg
155.0 lb., 70.5 kg
140.0 lb., 63.6 kg
Krell Full Power Balanced X Series Power Amplifiers
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Krell Industries, Inc.
45 Connair Road
Orange, CT 06477-3650 USA
Full Power Balanced
X Series Power Amplifiers
700cx, 400cx, 300cx Stereo
TEL 203-799-9954
750Mcx, 450Mcx, 350Mcx Monaural
FAX 203-891-2028
E-MAIL [email protected]
with Krell CAST II Technology
v 02.0
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