Full Power Balanced
X Series Power Amplifiers
700cx, 400cx, 300cx Stereo
750Mcx, 450Mcx, 350Mcx Monaural
with Krell CAST II Technology
THE LEADER IN AUDIO ENGINEERING
Instructions for Use
Owner’s Reference
Krell Industries, Inc.
45 Connair Road
Orange, CT 06477-3650 USA
TEL 203-799-9954
FAX 203-891-2028
E-MAIL krell@krellonline.com
WEB SITE http://www.krellonline.com
This product complies with the EMC directive (89/336/EEC) and the low-voltage
directive (73/23/EEC).
The Full Power Balanced amplifier must be placed on a firm, level surface where it
is not exposed to dripping or splashing.
The ventilation grids on the top of the Full Power Balanced amplifier must be unobstructed at all times during operation. Do not place flammable material on top of or
beneath the component.
Before making connections to the Full Power Balanced amplifier, ensure that it is
off and the preamplifier is in mute or stand-by mode. Make sure all cable terminations are of the highest quality and free from frayed ends, short circuits, or cold
solder joints.
The differential circuitry employed with Full Power Balanced amplifiers requires special
attention when connecting speakers. Do not connect the negative speaker terminals
together. Do not connect the negative speaker terminals to ground or attempt to bridge
the left and right speaker binding posts of Full Power Balanced stereo amplifiers.
Do not connect a Full Power Balanced amplifier to a speaker selector device that
employs a common ground scheme, as it may short-circuit the amplifier output.
THERE ARE NO USER SERVICEABLE PARTS INSIDE ANY KRELL PRODUCT.
Please contact your authorized Krell dealer, distributor, or Krell if you have any ques-
tions not addressed in this reference m anual.
© 2003 by Krell Industries, Inc. All rights reserved P/N 305976
Full Power Balanced
X Series Power Amplifiers
700cx, 400cx, 300cx Stereo
750Mcx, 450Mcx, 350Mcx Monaural
with Krell CAST II Technology
Instructions for Use
v 03.0
CONTACT
INFORMATION
WARNINGS
This product is manufactured in the United States of America. Krell®is a registered trademark of Krell
Industries, Inc., and is restricted for use by Krell Industries, Inc., its subsidiaries, and authorized agents.
Sustained Plateau Bias III™ is a trademark of Krell Industries, Inc. and is a Krell technology based on U.S.
Patent No. 5,331,291. CAST™, CAST II™, Krell Current Mode™, Krell Link™, and Krell Playback System™
are trademarks of Krell Industries, Inc. All other trademarks are registered to their respective companies.
Contents
Krell Full Power Balanced X Series Power Amplifiers iii
Page
INTRODUCTION 1
DEFINITION OF TERMS 2
REVOLUTIONARY KRELL CAST and CAST II TECHNOLOGY 4
UNPACKING 6
PLACEMENT 7
AC Power Guidelines 7
FRONT P ANELDESCRIPTION 8
700cx, 400cx, and 300cx Stereo Power Amplifiers 8
750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers 8
BACK PANEL DESCRIPTION 10
700cx, 400cx, and 300cx Stereo Power Amplifiers 10
750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers 10
CONNECTING THE FULL POWER BALANCED AMPLIFIER
TO YOUR SYSTEM 13
Input and Output Connections 13
Krell Trigger Connections 14
DC Protection Circuitry 14
Using a Tube Preamplifier 15
AMPLIFIER OPERATION 16
On/Off and Stand-by Operation 16
Krell Trigger Operation 17
REMOTE CONTROL OPERATION 18
How to Turn Off the Amplifier LEDs 18
How to Turn On the Amplifier LEDs 18
How to Switch between Krell CAST and XLR Inputs 18
Using a Dedicated Wall Outlet and Switch 18
AMPLIFIER TROUBLESHOOTING 19
How to Troubleshoot System Noise 19
How to Evaluate Amplifier Operation 19
QUESTIONS AND ANSWERS 21
WARRANTY 23
RETURN AUTHORIZA TION PROCEDURE 24
SPECIFICA TIONS 25
Illustrations
Page
FIGURE 1 The Full Power Balanced Stereo Amplifier 8
Front Panel
FIGURE 2 The Full Power Balanced Monaural Amplifier 8
Front Panel
FIGURE 3 The Full Power Balanced Stereo Amplifier 10
Back Panel
FIGURE 4 The Full Power Balanced Monaural Amplifier 10
Back Panel
iv Krell Full Power Balanced X Series Power Amplifiers
Krell Full Power Balanced X Series Power Amplifiers 1
Introduction
Thank you for your purchase of a Full Power Balanced X Series
Power Amplifier.
The Full Power Balanced X Series consists of three stereo amplifiers, the Full Power Balanced 700cx, 400cx, and 300cx Stereo
Power Amplifiers and three monaural amplifiers, the Full Power
Balanced 750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers.
Installation, connection, and operation of all amplifiers in the Full
Power Balanced series are identical; however, a pair of Full Power
Balanced Monaural amplifiers are required for stereo operation.
Full Power Balanced amplifiers can be configured 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 important information on
placement, installation, and operation of the Full Power Balanced
amplifiers. Please read this information carefully. Athorough understanding of these details will help ensure satisfactory operation and
long life for your Full Power Balanced amplifier and related system
components.
2 Krell Full Power Balanced X Series Power Amplifiers
Definition of Terms
Following are the definitions of key terms used in your owner’s reference manual.
Krell Trigger
Amethod of synchronizing remote control operation for Krell systems that include multiple preamplifiers, amplifiers, and associated
components. When Krell Trigger in/out connections are used, the
remote capabilities of the linked components are controlled from
one component, called the control component. The linked components respond to stand-by and operational mode commands from
the control component via MIDI cables.
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. Balanced
connections are completely immune to induced noise from the system or the environment.
Krell Current Audio Signal Transmission (CAST)
Aproprietary Krell circuit technology for connecting 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.
Single-ended
A two-wire input or output circuit. Use care when using singleended connections as the ground connection is made last and broken first. Turn the system off prior to making or breaking singleended connections. Single-ended connections are not recommended for connections requiring long cable runs.
CONFIGURATIONS
INPUT AND OUTPUT
CONNECTIONS
Krell Full Power Balanced X Series Power Amplifiers 3
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 illuminate, 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 recommends leaving the component in the
stand-by mode when it is not playing music.
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
A patented microprocessor control system that maintains Class A
bias operation regardless of musical demand. Class Abias is the
most accurate 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 algorithm utilized in the Master Reference Amplifier. Sustained Plateau
Bias III maximizes an amplifier’s efficiency both in power consumption and heat generation.
Definition of Terms,
continued
OPERATION
TECHNOLOGY
4 Krell Full Power Balanced X Series Power Amplifiers
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
Current Mode technology to create entire CAST systems that
reproduce music with incredible range, tonality, and precision.
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 system.
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
Here’s how a CAST audio system works. Internally, each CAST
source transfers, or amplifies, current using Krell Current Mode circuitry. This current signal is then output using CAST circuitry. 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 II system behaves as if it is one component.
With 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 Current Mode takes circuitry
signal transmission to the next evolutionary level. In essence, Krell
Current Mode maintains the integrity of the signal within the compo-
Krell Full Power Balanced X Series Power Amplifiers 5
nent and CAST preserves the transmitted signal between components. Together, CAST and Krell Current Mode technologies unify
separate Krell components into a single global circuit.
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 aesthetically 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
developed for every CAST cable made.
The Best Musical Performance
When you operate a CAST system, you will hear significant
improvements in every performance 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 musical event for you,
using the full expression of technology to date.
Revolutionary CAST Technology,
continued
6 Krell Full Power Balanced X Series Power Amplifiers
Unpacking
Two people are needed to remove the Full Power Balanced amplifier from its shipping box safely and easily.
1. Open the shipping box and remove the top layer of foam. You
see these items:
1 Full Power Balanced Amplifier
1 Packet containing the Quick Setup Guide 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 back of the amplifier.
Both people need to grab a pair of the cardboard handle cutouts
(one pair located at the front of the amplifier and one pair located
at the back of the amplifier) and simultaneously lift the amplifier
straight up, out of the carton.
3. Place the amplifier in a safe location and remove the protective
plastic wrapping.
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.
Save all packing materials. If you ship your Full Power Balanced
amplifier in the future, repack the unit in its original packaging to
prevent transit damage. See Return Authorization Procedure on
page 24, for more information.
Notes
Krell Full Power Balanced X Series Power Amplifiers 7
Placement
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.
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 clearance above the component to provide adequate ventilation.
Although Sustained Plateau Bias III circuitry reduces the high heat
dissipation and heat output of traditional Class Acircuitry, 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 amplifier in a closed cabinet, you may need to modify shelf
spacing or use small fans to increase ventilation. For the dimensions of your Full Power Balanced amplifier, see Specifications,
on pages 25–26.
Place the amplifier as close to the loudspeakers as possible. Krell
CAST technology permits you to use interconnect cables of any
length, see Revolutionary CAST II Technology, on page 4; how-
ever, try to keep the cable length to a minimum.
All Full Power Balanced amplifiers drive the lowest impedances
with ease. When impedance 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.
The Full Power Balanced 300cx and 350Mcx amplifiers need to be
operated from a dedicated AC power line rated at a minimum of 15
amps. The Full Power Balanced 700cx, 750Mcx, 400cx, and
450Mcx amplifiers need to be operated from a dedicated AC power
line rated at a minimum of 20 amps.
Please contact your authorized Krell dealer, distributor, or Krell
before using any devices designed to alter or stabilize the AC
power for Full Power Balanced amplifiers
AC Power Guidelines
8 Krell Full Power Balanced X Series Power Amplifiers
Figure 1 The Full Power Balanced Stereo Amplifier Front Panel
Figure 2 The Full Power Balanced Monaural Amplifier Front Panel
Krell Full Power Balanced X Series Power Amplifiers 9
Front Panel Description
The front panel accesses power on/stand-by and remote control
functions. The power stand-by , bias, regulator, and Krell CAST II LEDs,
arranged in a triangle on the front panel above the power button,
illuminate to indicate amplifier status.
1 Power Stand-by LED
The blue power stand-by LED (top of LED triangle) illuminates
when the back panel power breaker switch has been moved to
on, engaging the input circuitry and placing the amplifier in
stand-by mode.
2 Bias LED
The blue bias LED (lower left of triangle) illuminates after the
front panel power button is pressed, indicating that the
Sustained Plateau Bias III is engaged.
3 Power Button
The silver power button powers on the amplifier from stand-by
mode.
4Infrared Sensor
The infrared sensor receives the signal from a remote control.
5Krell CAST LED
The red Krell CAST LED (center of triangle) illuminates when a
Krell CAST input on the back panel is connected to another
Krell product with a Krell CAST output.
6Regulator 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, indicating that the regulator is providing power to the
output stage.
An optional remote control is available for Full Power Balanced
amplifiers.
Note
10 Krell Full Power Balanced X Series Power Amplifiers
Figure 3 The Full Power Balanced Stereo Amplifier Back Panel
Figure 4 The Full Power Balanced Monaural Amplifier Back Panel
Krell Full Power Balanced X Series Power Amplifiers 11
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.
13 Left and Right Loudspeaker Binding Posts
Stereo. These amplifiers are equipped with four pairs of loud-
speaker binding posts (upper left, lower left, upper right, and
lower right).
Monaural. These amplifiers are equipped with two pairs of
loudspeaker binding posts.
Two pairs of loudspeaker 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 loudspeakers
having two pairs of binding posts. For biwiring applications, with loudspeakers having more than one pair of binding posts, use both upper
and lower pairs of loudspeaker binding posts. See the loudspeaker’s
instruction manual for biwiring connections.
Loudpeaker 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.
14 Krell CAST Inputs
The Krell CAST inputs allow the Full Power Balanced amplifier to
be connected to the KPS 25sc Krell Playback System and other
CAST-equipped components.
Stereo. These amplifiers are equipped with one left Krell CAST
input and one right Krell CAST input via 4-pin bayonet connectors.
Monaural. These amplifiers are equipped with one Krell CAST
input via 4-pin bayonet connectors.
15 Back Panel Power Breaker Switch
Place the back panel power breaker switch in the up position to
put the amplifier in stand-by mode.
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).
Notes
Note
12 Krell Full Power Balanced X Series Power Amplifiers
16 Balanced Inputs
Stereo. These amplifiers are equipped with one left balanced
input and one right balanced input via XLR connectors.
Monaural. These amplifiers are equipped with one balanced
input via XLR connectors.
17 Krell Trigger Out/In
(Labeled
KRELL LINK on the back panel.)
Krell Trigger remote out/in connectors that allow a remote control
to operate a linked amplifier configuration. See Krell Trigger
Connections, on page 14 for more information.
An optional remote control is available for Full Power Balanced amplifiers.
18 AC Mains Power Cord
All Full Power Balanced amplifiers are equipped with a permanently attached AC power cord.
19 Handles
The handles help to move the amplifier easily and safely.
Stereo. These amplifiers are equipped with two handles,
beside the loudspeaker binding posts.
Monaural. These amplifiers are equipped with one handle,
beside the loudspeaker binding posts.
Back Panel Description,
continued
Note
Krell Full Power Balanced X Series Power Amplifiers 13
Connecting the Full Power Balanced
Amplifier to Your System
Krell recommends using its proprietary Krell CAST system for
unparalleled sonic performance between the Full Power Balanced
amplifiers and other CAST-equipped components and the
KPS 25sc Krell Playback System.
Full Power Balanced amplifiers also offer balanced 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.
Aone piece RCA-to-XLR adapter is available from Krell Industries, to
allow single-ended operation using the balanced XLR inputs.
The following steps describe how to connect cables to the Full Power
Balanced Amplifiers.
1. Turn all pwer sources and components off before connecting
inputs and outputs.
2. Neatly arrange and organize wiring to and from the amplifier
and all components. Separate AC wires from audio cables to
prevent hum or other unwanted noise from being introduced
into the system.
3. Connect the Krell CAST cables from your CAST-enabled pre-
amplifier/source component to the left and right Krell CAST
4-pin bayonet inputs (14) on the amplifier back panel. For balanced operation, connect the interconnect cable from your preamplifier to the left and right balanced XLR input (16) on the
amplifier back panel.
4. Connect the loudspeaker cables to the Full Power Balanced
amplifier’s loudspeaker binding posts (13), located on the amplifier back panel. Loudspeaker binding posts for both stereo and
monaural amplifiers accept spade lugs only.
5. Insert the end of the AC mains power cord (18) into the AC wall
receptacle.
6. Proceed with Krell Trigger Connections, if desired, or turn to
Amplifier Operation, on page 16.
INPUT AND OUTPUT
CONNECTIONS
CONNECTION STEPS
14 Krell Full Power Balanced X Series Power Amplifiers
Krell Trigger remote out/in connectors (17) on the back panel of the
Full Power Balanced amplifier (labeled
KRELL LINK) allow you to syn-
chronize remote control operation for systems that include multiple
amplifiers and associated components. When the Krell Trigger
remote out/in connectors are used, the remote capabilities of the
linked components 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.
Krell Trigger uses standard five pin MIDI communication 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. 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 component. The control
component must be in plain view for proper remote control operation.
3. Connect one end of the MIDI cable to the Krell Trigger out con-
nector (17) on the back panel of the component.
4. Connect the other end of the MIDI cable to the Krell Trigger in
connector on the next component.
To link another component, connect a second MIDI cable to the
Krell Trigger out connector on the back panel of the second component. Connect the remaining end of the MIDI cable to the Krell
Trigger in connector on the back panel of a third component.
5. To link additional components, if desired, see Steps 3 and 4.
The components are now ready for operation with Krell Trigger.
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
coupling capacitors from the audio signal path. Coupling capacitors
block damaging DC but have sonic characteristics that corrupt sound
reproduction.
For more information about DC protection circuitry features, see Amplifier
Troubleshooting, on page 19.
How to Connect
Components Using
Krell Trigger
Note
Note
KRELL TRIGGER
CONNECTIONS
DC PROTECTION
CIRCUITRY
Connecting,
continued
Krell Full Power Balanced X Series Power Amplifiers 15
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, speakers, 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.
Coupling capacitors must be inserted into the signal path by your
authorized Krell dealer, distributor, or Krell before you can use your
Full Power Balanced amplifier with a tube preamplifier.
Please read Warranty, on page 23, to understand the warranty limitations of Full Power Balanced amplifiers when used with tube preamplifiers.
USING A TUBE
PREAMPLIFIER
Connecting,
continued
IMPORTANT
16 Krell Full Power Balanced X Series Power Amplifiers
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 preamplifier output, or bumping or miscuing a source can generate large transients at low frequencies. Full Power Balanced amplifiers may generate enough power with these transients to damage
loudspeakers.
Always mute or fully attenuate the preamplifier level when switching
sources.
Do not change input connections to the amplifier when the amplifier
is on.
Use care when setting high playback levels. Because of their tremendous reserves of clean power, Full Power Balanced amplifiers can
safely drive speakers to higher sound pressure levels than other
amplifiers. Lower the volume level at the first sign of loudspeaker distress.
When powering on any system, turn on amplifiers last. Turn off amplifiers first.
1. Move the back panel power breaker switch (15) to the up position
to engage the input circuitry and place the amplifier into the
stand-by mode. The front panel blue power stand-by LED (1) illuminates.
2. Press the silver power button (3) on the amplifier front panel. The
blue regulator LED (6) illuminates. Once the regulator provides
power to the output stage, the blue bias LED (2) illuminates. The
Sustained Plateau Bias III 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.
If the Krell CAST input is being used, the Krell CAST red LED (5)
illuminates and remains illuminated at all times during stand-by or
on modes.
3. With the preamplifier muted or volume control completely low-
ered, select a source. Increase the volume control to the desired
listening level.
4. To turn the amplifier off, place the Full Power Balanced amplifier
in the stand-by mode by pressing the power button on the front
panel. It is now safe to turn off the rest of the system.
For best Full Power Balanced amplifier performance, leave the back
panel power breaker switch on at all times.
ON/OFF AND STAND-BY
OPERATION
Note
IMPORTANT
Krell Full Power Balanced X Series Power Amplifiers 17
1. When all components are linked, see How to Connect Com-
ponents Using Krell Trigger, on page 14, 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.
2. When the components are in stand-by, switch the control com-
ponent to the operational mode from the control component’s
front panel or by using the component’s remote control.
The linked components switch to the operational mode simultaneously.
KRELL TRIGGER
OPERATION
Operation,
continued
18 Krell Full Power Balanced X Series Power Amplifiers
Remote Control Operation
Full Power Balanced amplifiers are compatible with the remote controls included with Krell preamplifiers, the Home Theater Standard
7.1, and the KPS 25sc Krell Playback System.
Please contact your authorized Krell dealer, distributor, 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 Trigger Connections, on page 14.
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.
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
breaker 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.
Press the meter key on a Krell remote to switch between CAST
inputs and the balanced XLR inputs.
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.
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, distributor, or Krell for
more information before you connect your Full Power Balanced
amplifier to a dedicated AC wall outlet with a switch.
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
Krell Full Power Balanced X Series Power Amplifiers 19
Amplifier Troubleshooting
AC grounding becomes critical when connecting 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 loudspeakers. This often occurs when introducing a
new component into a system.
If a low frequency hum emanates from the loudspeakers when you
place the Full Power Balanced amplifier into the system, follow
these simple troubleshooting steps:
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 interconnects inserted, there may be a defective cable. Have the interconnect cables checked before proceeding.
2. If the interconnect cables are sound, you may be experiencing
a ground loop. This can often be easily eliminated. Please contact your authorized Krell dealer, distributor, or Krell for suggestions on how to solve this problem.
Full Power Balanced amplifiers are protected by a series of nonintrusive 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 Balanced amplifier is designed to prevent damage to the amplifiers or loudspeakers
caused by other defective components, faulty wiring, system mishandling, or amplifier failure.
In addition, when a Full Power Balanced amplifier’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.
The Krell CAST LED illuminates only if a Krell CAST input is being used.
There are no output fuses in Full Power Balanced amplifiers.
HOW TO
TROUBLESHOOT
SYSTEM NOISE
HOW TO EVALUATE
AMPLIFIER OPERATION
Notes
Note
20 Krell Full Power Balanced X Series Power Amplifiers
If the course of action listed in the table below does not correct the situation, please contact your
authorized Krell dealer, distributor, or Krell.
Amplifier Operation,
continued
AMPLIFIER CONDITION
The output mutes during playback and the following LEDs
illuminate: power stand-by,
and regulator bias
The amplifier switches to
stand-by mode and the
power stand-by LED
illuminates
The amplifier switches to
stand-by at high volumes and
the power stand-by LED illuminates
The amplifier powers down
completely and no LEDs illuminate
POSSIBLE CAUSES
Excessive DC at the
amplifier input
Electrical short in loudspeaker
cables or inside loudspeaker
Insufficient AC current from
the wall outlet
Excessive heat
DC present at the output
stage
Internal amplifier problem
COURSE OF ACTION
Have source unit and
preamplifier checked for high
DC output
If preamplifier is a tube
model, see Using a Tube
Preamplifier, on page 15.
Check all loudspeaker cables
for any cuts or frayed edges
that might form a connection
between the positive and negative speaker binding post terminals
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.
Allow amplifier to cool before
resuming operation. See
Placement, on page 7, for
ventilation requirements
Contact your authorized Krell
dealer, distributor, or Krell
Contact your authorized Krell
dealer, distributor, or Krell
Krell Full Power Balanced X Series Power Amplifiers 21
Questions and Answers
Q. Should I leave my Full Power Balanced amplifier on at all times?
A. For maximum amplifier performance, leave the back panel power
breaker switch on at all times. This places the amplifier in standby 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 amplifier will
operate at full performance within minutes.
Q. When I turn on the amplifier there is a loud hum through the loud-
speakers. What should I do?
A. When a new component is introduced, a low frequency hum may
occur in one or both loudspeakers. Check all input and output
connections and cables, making sure they are of sound construction. See How to Troubleshoot System Noise, on page 19. If
the interconnects and cables are sound, you may be experiencing a ground loop. This can often be easily eliminated. Please
contact your authorized Krell dealer, distributor, or Krell for suggestions on how to solve this problem.
Q. My system includes multiple pairs of loudspeakers. Can I connect
them to my Full Power Balanced amplifiers through a loudspeaker selector box?
A. No. Most loudspeaker selector boxes use a common 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 loudspeaker selector device
that employs a common ground scheme, as it may shortcircuit the amplifier output.
Q. My loudspeakers have only one pair of binding posts, but my Full
Power Balanced stereo amplifier has two pairs. Which pair of
loudspeaker binding posts should I use, the upper or the lower?
A. The upper and lower pair of loudspeaker binding posts on Full
Power Balanced stereo amplifiers 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. My loudspeakers are rated for 150 Watts. Are the Full Power
Balanced 400cx or 700cx models too powerful for them?
A. No. Aloudspeaker 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
22 Krell Full Power Balanced X Series Power Amplifiers
power ratings, but in heavy demand situations they can be driven
into clipping (in which DC current goes to the loudspeakers due
to loss of amplifier power). Clipping can damage loudspeakers.
Avoid damage to your speakers by reviewing your loudspeaker
specifications and exercise caution in heavy demand situations.
Questions and Answers,
continued
Krell Full Power Balanced X Series Power Amplifiers 23
Warranty
This Krell product has a limited warranty of five years for parts and labor on circuitry. Should
this product fail to perform at any time during the warranty, Krell will repair it at no cost to the
owner, except as set forth in this warranty.
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 warranty, expressed or implied, includ-
ing, but not limited to, any implied warranty of merchantability or fitness for a particular 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 purchase, use, or inability to
use this product, even if Krell has been advised of the possibility of such damages.
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 warranty, based on the
original date of manufacture.
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.
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.
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 forwarder of your choice.
Freight and other charges to ship the unit from the freight forwarder to you are also your
responsibility.
Krell is not responsible for any damage incurred in transit. Krell will file claims for damages as
necessary for units damaged 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 products returned to Krell for exchange become the
property of Krell.
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 factory and can only be changed by an
authorized Krell distributor 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.
In the event that Krell receives a product for warranty service that has been modified in any
way without Krell authorization, all warranties on that product will be void. The product 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 factory specifications will be
charged to the customer, at current parts and labor rates.
All operational features, functions, specifications, and policies are subject to change without
notification.
IMPORTANT
The user is responsible for notifying his or her Krell dealer, 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 capacitors. 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 DCrelated damage.
To register your product for
warranty benefits, please
complete and return the
Warranty Registration Card
enclosed in the shipping box
within 15 days of purchase.
Thank you.
24 Krell Full Power Balanced X Series Power Amplifiers
Return Authorization Procedure
If you believe there is a problem with your component, 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:
http://www.krellonline.com
To return a product to Krell, please follow this procedure so that we
may serve you better:
1. Obtain a Return Authorization Number (R/Anumber) and shipping address from the Krell Service Department.
2. Insure and accept all liability for loss or damage to the product
during shipment to the Krell factory and ensure all freight (shipping) charges are prepaid.
The product may also be hand delivered if arrangements with the
Service Department have been made in advance. Proof of purchase
will be required for warranty validation at the time of hand delivery.
Use the original packaging to ensure the safe transit of the product to
the factory, dealer, or distributor. Krell may, at its discretion, return a
product in new packaging and bill the owner for such packaging if the
product received by Krell was boxed in nonstandard packaging or if
the original packaging was so damaged that it was unusable. If Krell
determines that new packaging is required, the owner will be notified
before the product is returned.
HOW TO RETURN
A PRODUCT
IMPORTANT
To purchase additional packaging, please contact your authorized
Krell dealer, distributor, or the Krell Service Department for assistance.
HOW TO PURCHASE
ADDITIONAL PACKING
To contact the Krell Service Department:
TEL 203-799-9954
Monday-Friday, 9:00 am to 5:00 pm EST
FAX 203-799-9796
E-MAIL service@krellonline.com
WEB SITE http://www.krellonline.com
HOW TO EXPEDITE
SERVICE
Krell Full Power Balanced X Series Power Amplifiers 25
Specifications for Full Power Balanced
X-Series Stereo Amplifiers
FPB 300cx FPB 400cx FPB 700cx
FREQUENCY RESPONSE 20 Hz to 20 kHz 20 Hz to 20 kHz 20 Hz to 20 kHz
+0 dB, -0.05 dB +0 dB, -0.05 dB +0 dB, -0.05 dB
0.1 Hz to 240 kHz 0.1 Hz to 240 kHz 0.1 Hz to 240 kHz
+0 dB, -3 dB +0 dB, -3 dB +0 dB, -3 dB
SIGNAL TO NOISE RATIO 113 dB 117 dB 120 dB
“A” WEIGHTED
GAIN 26.4 dB 26.4 dB 26.4 dB
TOTAL HARMONIC 1 kHz <0.03% 1 kHz <0.03% 1 kHz <0.03%
DISTORTION (THD) 20 kHz <0.16% 20 kHz <0.16% 20 kHz <0.16%
ALL BALANCED, UNWEIGHTED
INPUT IMPEDANCE 100 kOhms 100 kOhms 100 kOhms
INPUT SENSITIVITY 2.34 Vrms 2.71 Vrms 3.58 Vrms
OUTPUT POWER 8 Ohms 300 W 8 Ohms 400 W 8 Ohms 700 W
EACH CHANNEL DRIVEN 4 Ohms 600 W 4 Ohms 800 W 4 Ohms 1,400 W
2 Ohms 1200 W 2 Ohms 1,600 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 60 W Stand-by 75 W Stand-by 85 W
Idle 175 W Idle 350 W Idle 430 W
Max. 1,700 W Max. 3,000 W Max. 6,000 W
INPUTS 1 pair balanced via 1 pair balanced via 1 pair balanced via
XLR connectors XLR connectors XLR connectors
1 pair CAST via 4-pin 1 pair CAST via 4-pin 1 pair CAST via 4-pin
bayonet connectors bayonet connectors bayonet connectors
OUTPUTS 4 pair (upper left, 4 pair (upper left, 4 pair (upper left
SPEAKER BINDING POSTS lower left, upper right lower left, upper right lower left, upper right
lower right) lower right) lower right)
REMOTE CONTROL Optional Optional Optional
DIMENSIONS
INCHES 19.0w x 10.3h x 17.0d 19.0w x 10.3h x 19.7d 19.0w x 10.3hx 25.5
CENTIMETERS 48.3w x 26.2h x 43.2d 48.3w x 26.2h x 50.0d 48.3wx 26.2hx 64.8d
WEIGHT
SHIPPING 107.0 lb., 48.6 kg 127.0 lb., 57.7 kg 200.0 lb., 90.9 kg
UNIT ONLY 90.0 lb., 40.9 kg 110.0 lb., 50.0 kg 180.0 lb., 81.8 kg
All operational features, functions, specifications, and policies are subject to change without notification.
26 Krell Full Power Balanced X Series Power Amplifiers
Specifications for Full Power Balanced
X-Series Monaural Amplifiers
FPB 350Mc FPB 450Mc FPB 750Mc
FREQUENCY RESPONSE 20 Hz to 20 kHz 20 Hz to 20 kHz 20 Hz to 20 kHz
+0 dB, -0.05 dB +0 dB, -0.05 dB +0 dB, -0.05 dB
0.1 Hz to 240 kHz 0.1 Hz to 240 kHz 0.1 Hz to 240 kHz
+0 dB, -3 dB +0 dB, -3 dB +0 dB, -3 dB
SIGNAL TO NOISE RATIO 114 dB 118 dB 121 dB
“A” WEIGHTED
GAIN 26.4 dB 26.4 dB 26.4 dB
TOTAL HARMONIC 1 kHz <0.03% 1 kHz <0.03% 1 kHz <0.03%
DISTORTION (THD) 20 kHz <0.16% 20 kHz <0.16% 20 kHz <0.16%
ALL BALANCED, UNWEIGHTED
INPUT IMPEDANCE 100 kOhms 100 kOhms 100 kOhms
INPUT SENSITIVITY 2.53 Vrms 2.87 Vrms 3.71 Vrms
OUTPUT POWER 8 Ohms 350 W 8 Ohms 450 W 8 Ohms 750 W
EACH CHANNEL DRIVEN 4 Ohms 700 W 4 Ohms 900 W 4 Ohms 1,500 W
2 Ohms 1,400 W 2 Ohms 1,800 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 30 W Stand-by 37.5 W Stand-by 42.5 W
Idle 150 W Idle 175 W Idle 220 W
Max. 1,700 W Max. 3,000 W Max. 6,000 W
INPUTS 1 balanced via 1 balanced via 1 balanced via
XLR connectors XLR connectors XLR connectors
1 Krell CAST via 4-pin 1 Krell CAST via 4-pin 1 Krell CAST via 4 pin
bayonet connectors bayonet connectors bayonet connectors
OUTPUTS 2 pair (one upper, 2 pair (one upper, 2 pair (one upper,
SPEAKER BINDING POSTS one lower) one lower) one lower)
REMOTE CONTROL Optional Optional Optional
DIMENSIONS
INCHES 12.5w x 10.5h x 16.0d 12.5w x 10.5h x 19.0d 12.5w x 10.5h x 25.0d
CENTIMETERS 31.8w x 26.7h x 40.6d 31.8w x 26.7h x 48.3d 31.8w x 26.7h x 67.3d
WEIGHT
SHIPPING 79.0 lb., 35.9 kg 110.0 lb., 50.0 kg 155.0 lb., 70.5 kg
UNIT ONLY 68.0 lb., 31.0 kg 98.0 lb., 44.5 kg 140.0 lb., 63.6 kg
All operational features, functions, specifications, and policies are subject to change without notification.
Krell Industries, Inc.
45 Connair Road
Orange, CT 06477-3650 USA
TEL 203-799-9954, FAX 203-891-2028
E-MAIL krell@krellonline.com
WEB SITE www.krellonline.com
Full Power Balanced
X Series Power Amplifiers
700cx, 400cx, 300cx Stereo
750Mcx, 450Mcx, 350Mcx Monaural
with Krell CAST II Technology
v03.0
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