Krell Industries 700cx User manual

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 [phone]
FAX [phone]
E-MAIL [email protected]
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 unob-
structed 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 termina-
tions 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 manual.
©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 PANEL DESCRIPTION 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 AUTHORIZATION PROCEDURE 24
SPECIFICATIONS 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 ampli-
fiers, 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 oper-
ated 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. A thorough under-
standing of these details will help ensure satisfactory operation and
long life for your Full Power Balanced amplifier and related system
components.

2Krell Full Power Balanced X Series Power Amplifiers
Definition of Terms
Following are the definitions of key terms used in your owner’s ref-
erence manual.
Krell Trigger
Amethod of synchronizing remote control operation for Krell sys-
tems 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 compo-
nents respond to stand-by and operational mode commands from
the control component via MIDI cables.
Balanced
Asymmetrical 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 con-
nections and allow the use of long interconnect cables. Balanced
connections are completely immune to induced noise from the sys-
tem or the environment.
Krell Current Audio Signal Transmission (CAST)
Aproprietary Krell circuit technology for connecting analog compo-
nents, in which the audio waveform is transmitted between compo-
nents 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 com-
ponents connected via CAST and CAST II perform as if they are all
part of a single circuit.
Single-ended
Atwo-wire input or output circuit. Use care when using single-
ended connections as the ground connection is made last and bro-
ken first. Turn the system off prior to making or breaking single-
ended connections. Single-ended connections are not recommend-
ed 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
Alow 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
Aproprietary 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
Apatented microprocessor control system that maintains Class A
bias operation regardless of musical demand. Class A bias 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 algo-
rithm utilized in the Master Reference Amplifier. Sustained Plateau
Bias III maximizes an amplifier’s efficiency both in power consump-
tion and heat generation.
Definition of Terms, continued
OPERATION
TECHNOLOGY

4Krell 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 compo-
nents 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 intercon-
nects 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 cir-
cuitry. 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 main-
taining 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 transmit-
ted 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 com-
ponent. 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 compo-
nents. Together, CAST and Krell Current Mode technologies unify
separate Krell components into a single global circuit.
CAST Cable Construction
ACAST system uses cables manufactured by Krell and other man-
ufacturers 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, dynam-
ic 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

6Krell Full Power Balanced X Series Power Amplifiers
Unpacking
Two people are needed to remove the Full Power Balanced amplifi-
er from its shipping box safely and easily.
1. Open the shipping box and remove the top layer of foam. You
see these items:
1Full Power Balanced Amplifier
1Packet 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 ship-
ping 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 sys-
tem, 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 ventila-
tion.
Although Sustained Plateau Bias III circuitry reduces the high heat
dissipation and heat output of traditional Class A circuitry, Full
Power Balanced amplifiers still can become hot under normal oper-
ation.
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 dimen-
sions 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 speak-
ers.
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

8Krell 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.
1Power 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 ampli-
fiers, either the upper or the lower pair can be used with loudspeakers
having two pairs of binding posts. For biwiring applications, with loud-
speakers 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 connec-
tors.
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 ampli-
fiers.
18 AC Mains Power Cord
All Full Power Balanced amplifiers are equipped with a perma-
nently 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 bal-
anced operation, connect the interconnect cable from your pre-
amplifier 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 ampli-
fier 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 compo-
nent 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 oper-
ation.
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 com-
ponent. 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 pro-
tection 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 deal-
er, 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 limi-
tations of Full Power Balanced amplifiers when used with tube pre-
amplifiers.
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. How-
ever, 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 gener-
ate large transients at low frequencies. Full Power Balanced ampli-
fiers 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 tremen-
dous 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 dis-
tress.
When powering on any system, turn on amplifiers last. Turn off ampli-
fiers 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) illu-
minates.
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 pro-
tection 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