fpb x-series power amplifiers owner's reference

Instructions for Use

Owner’s Reference

THE LEADER IN AUDIO ENGINEERING

Full Power Balanced X Series Power Amplifiers

700cx, 400cx, 300cx Stereo

750Mcx, 450Mcx, 350Mcx Monaural

with Krell CAST II Technology

Full Power Balanced X Series Power Amplifiers700cx, 400cx, 300cx Stereo


with Krell CAST II Technology

v 02.0

Krell Industries, Inc.45 Connair RoadOrange, CT 06477-3650 USA

TEL 203-799-9954FAX 203-891-2028E-MAIL [email protected] http://www.krellonline.com

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 Indus-tries, Inc., its subsidiaries, and authorized agents. Sustained Plateau Bias III™ is a trademark of Krell Industries, Inc. and is a Krell technology based onU.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.

© 2002 by Krell Industries, Inc. All rights reserved P/N 305976

This product complies with the EMC directive (89/336/EEC) and the low-voltage directive (73/23/EEC).

WARNINGSThe Full Power Balanced amplifier must be placed on a firm, level surface where it is not exposed to drip-ping or splashing.

The ventilation grids on the top of the Full Power Balanced amplifier must be unobstructed at all times duringoperation. 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 preamplifieris in mute or stand-by mode. Make sure all cable terminations are of the highest quality and free fromfrayed ends, short circuits, or cold solder joints.

The differential circuitry employed with Full Power Balanced amplifiers requires special attention when connect-ing speakers. Do not connect the negative speaker terminals together. Do not connect the negative speaker ter-minals to ground or attempt to bridge the left and right speaker binding posts of Full Power Balanced stereo ampli-fiers.

Do not connect a Full Power Balanced amplifier to a speaker selector device that employs a commonground 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 questions not addressed inthis reference manual.

Page

INTRODUCTION 1

DEFINITION OF TERMS 1

REVOLUTIONARY KRELL CAST and CAST II TECHNOLOGY 3

UNPACKING 4

PLACEMENT 4AC Power Guidelines 5

FRONT PANEL DESCRIPTION 8700cx, 400cx, and 300cx Stereo Power Amplifiers 8750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers 8

BACK PANEL DESCRIPTION 11700cx, 400cx, and 300cx Stereo Power Amplifiers 11750Mcx, 450Mcx, and 350Mcx Monaural Power Amplifiers 12

CONNECTING THE FULL POWER BALANCED AMPLIFIERTO YOUR SYSTEM 13

Input and Output Connections 13Krell Link Connections 13DC Protection Circuitry 14Using a Tube Preamplifier 14

AMPLIFIER OPERATION 15On/Off and Stand-by Operation 15Krell Link Operation 15

REMOTE CONTROL OPERATION 16How to Turn Off the Amplifier LEDs 16How to Turn On the Amplifier LEDs 16How to Switch between Krell CAST and XLR Inputs 16Using a Dedicated Wall Outlet and Switch 16

AMPLIFIER TROUBLESHOOTING 17How to Troubleshoot System Noise 17How to Evaluate Amplifier Operation 17

QUESTIONS AND ANSWERS 19

WARRANTY 20

RETURN AUTHORIZATION PROCEDURE 21

SPECIFICATIONS 22

Krell Full Power Balanced X Series Power Amplifiers iii

Contents

Page

FIGURE 1 Full Power Balanced Stereo Amplifier Front Panel 6

FIGURE 2 Full Power Balanced Monaural Amplifier Front Panel 7

FIGURE 3 Full Power Balanced Stereo Amplifier Back Panel 9

FIGURE 4 Full Power Balanced Monaural Amplifier Back Panel 10

iv Krell Full Power Balanced X Series Power Amplifiers

Illustrations

The Full Power Balanced X Series consists ofthree stereo amplifiers, the Full Power Bal-anced 700cx, 400cx, and 300cx Stereo PowerAmplifiers and three monaural amplifiers, theFull Power Balanced 750Mcx, 450Mcx, and350Mcx Monaural Power Amplifiers. Installa-tion, connection, and operation of all amplifiersin the Full Power Balanced series are identical;however, a pair of Full Power Balanced Monau-ral amplifiers are required for stereo operation.

Full Power Balanced amplifiers can be config-ured to accommodate any sophisticated musicor home theater system and can be operatedby an optional remote control or through theremote control of other Krell components.

This owner’s reference manual contains impor-tant information on placement, installation, andoperation of the Full Power Balanced ampli-fiers. Please read this information carefully. Athorough understanding of these details willhelp ensure satisfactory operation and long lifefor your Full Power Balanced amplifier andrelated system components.

Following are the definitions of key terms usedin your owner’s reference manual.

CONFIGURATIONS

Krell LinkA 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 areused, 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 operationalmode commands from the control componentvia MIDI cables.

INPUT AND OUTPUT CONNECTIONs

Balanced A symmetrical input or output circuit that hasequal impedance from both input terminals to acommon ground reference point. The industrystandard for professional and sound recordinginstallations, balanced connections have 6 dBmore gain than single-ended connections andallow the use of long interconnect cables. Bal-anced connections are completely immune toinduced 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 audiowaveform is transmitted between components inthe current rather than voltage domain. Thespeed and bandwidth provided by Krell CASTand the CAST circuitry update, Krell CAST II,yield accurate, realistic music reproduction. Krellcomponents connected via CAST and CAST IIperform as if they are all part of a single circuit.

Krell Full Power Balanced X Series Power Amplifiers 1

Definition of TermsIntroduction

2 Krell Full Powered Balanced X Series Power Amplifiers

Definition of Terms, continued

Single-endedA two-wire input or output circuit. Use carewhen using single-ended connections as theground connection is made last and brokenfirst. Turn the system off prior to making orbreaking single-ended connections. Single-ended connections are not recommended forconnections requiring long cable runs.

OPERATION

OffWhen the power switch on the back panel isplaced in the down position and the blue powerLEDs turn off, the component is off.

Operational ModeWhen the power button on the front panel ispressed and the three blue power LEDs illumi-nate, the component is in the operational modeand ready to play music.

Stand-by ModeA low power consumption status that keeps theaudio and regulator circuits at idle. Krell recom-mends leaving the component in the stand-bymode when it is not playing music.

TECHNOLOGY

Krell Current ModeA proprietary Krell circuit topology in which theaudio gain stages of a component operate inthe current rather than voltage domain. Thisunique technology provides the componentwith exceptional speed and a wide bandwidth.

Krell Sustained Plateau Bias IIIA patented microprocessor control system thatmaintains Class A bias operation regardless ofmusical demand. Class A bias is the most accu-rate method used to amplify musical signals.The new Sustained Plateau Bias III software isfeatured in the Full Power Balanced X Seriesamplifiers 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 andheat generation.


Current Audio Signal Transmission, termedCAST, is a revolutionary method of connectinganalog audio components for unparalleledsonic performance. CAST circuitry, and theCAST circuitry update, Krell CAST II, combineinnovative engineering with existing Krell Cur-rent Mode technology to create entire CASTsystems that reproduce music with incrediblerange, tonality, and precision.

Voltage Signal Transmission and the Traditional Audio SystemTraditionally, signal is transmitted in the voltagedomain between two components. In an audiosystem, each component is a discrete entity withunique characteristics that act upon the musicalsignal independently. Each component isunaware of the other components in the system.The cables that connect the components eachhave their own electrical characteristics, whichaffect the sonic presentation of the entire sys-tem.

CAST: A New ApproachCAST circuitry recognizes signal transmitted inthe current domain instead of the voltagedomain between each component. CASTtransmission unifies the individual componentsand their interconnects into an electricallylinked whole. The sonic presentation of theentire system remains intact.

CAST BasicsHere’s how a CAST audio system works. Inter-nally, each CAST source transfers, or amplifies,current using Krell Current Mode circuitry. Thiscurrent signal is then output using CAST cir-cuitry. When the signal is received by a CASTinput, Krell Current Mode circuitry again takesover until the signal reaches the loudspeaker.By maintaining the musical signal in the currentdomain from beginning to end, an entire CASTsystem behaves as if it is one component. With

CAST, anomalies of signal transmission betweencomponents are eliminated. Cable impedancesand their effects on the transmitted signal arenon-existent.

How CAST and Krell Current Mode InteractWhile CAST is a new method of transferring themusical signal between components, its originstems from Krell Current Mode, the technologydeveloped to transfer the musical signal withina component. CAST combined with Krell Cur-rent Mode takes circuitry signal transmission tothe next evolutionary level. In essence, KrellCurrent Mode maintains the integrity of the sig-nal within the component and CAST preservesthe transmitted signal between components.Together, CAST and Krell Current Mode tech-nologies unify separate Krell components into asingle global circuit.

CAST Cable ConstructionA CAST system uses cables manufactured byKrell and other manufacturers speciallylicensed by Krell. Thin and flexible CASTcables are constructed with the same buildquality as other Krell products and are aesthet-ically matched to the components that Krellmanufactures. An all-metal body and lockingconnectors with gold contacts are part of thestandard no-compromise specification devel-oped for every CAST cable made.

The Best Musical PerformanceWhen you operate a CAST system, you willhear significant improvements in every perfor-mance area: speed, precision, dynamic range,depth and width of the sound stage, transientimpact, tonal balance, harmonic distortion, andmore. The goal for CAST is the same companygoal used for all Krell products. Krell strives forthe delivery of the best performance of a musi-cal event for you, using the full expression oftechnology to date.

Revolutionary Krell CAST and CAST II Technology

4 Krell Full Power Balanced X Series Power Amplifiers

Two people are needed to remove the FullPower Balanced amplifier from its shipping boxsafely and easily.

1. Open the shipping box and remove the toplayer of foam. You see these items:

1 Full Power Balanced Amplifier1 Packet containing the owner’s

reference manual and the warranty registration card

2. Orient the shipping box so that one personstands at the front of the amplifier and oneperson stands at the rear of the amplifier.Both people need to grab a pair of the card-board handle cutouts (one pair located at thefront of the amplifier and one pair located atthe rear of the amplifier) and simultaneouslylift the amplifier straight up, out of the carton.

3. Place the amplifier in a safe location andremove the protective plastic wrapping.

NotesIf any of the items mentioned above are notincluded in the shipping box, please contactyour authorized Krell dealer, distributor, or Krellfor assistance.

Save all packing materials. If you ship your FullPower Balanced amplifier in the future, repackthe unit in its original packaging to prevent tran-sit damage. See Return Authorization Proce-dure, on page 21 for more information.

Before you install the Full Power Balancedamplifier into your system, please follow theguidelines in this section to choose its properlocation. This will facilitate a clean, trouble-freeinstallation.

The Full Power Balanced amplifier requires atleast two inches (5 cm) of clearance on eachside and at least eight inches (20 cm) of clear-ance above the component to provide ade-quate ventilation.

Although Sustained Plateau Bias III circuitryreduces the high heat dissipation and heat out-put of traditional Class A circuitry, Full PowerBalanced amplifiers still can become hot undernormal operation.

When the front and rear of a cabinet are openthe air space between the chassis and shelfmust be unobstructed. If you place the amplifi-er in a closed cabinet, you may need to modifyshelf spacing or use small fans to increase ven-tilation. For the dimensions of your Full PowerBalanced amplifier, see Specifications, onpages 22–23.

Place the amplifier as close to the speakers aspossible. Krell CAST technology permits you touse interconnect cables of any length, see Rev-olutionary Krell CAST and CAST II Technol-ogy on page 3; however, try to keep the cablelength to a minimum.

All Full Power Balanced amplifiers drive thelowest impedances with ease. When imped-ance is added due to long speaker cablelengths, amplifier power is wasted in the cable.Long speaker cables reduce the maximumpower that is delivered in the speakers.

Unpacking Placement


AC POWER GUIDELINES

The Full Power Balanced 300cx and 350Mcxamplifiers need to be operated from a dedicat-ed AC power line rated at a minimum of 15amps. The Full Power Balanced 700cx,750Mcx, 400cx, and 450Mcx amplifiers need to

be operated from a dedicated AC power linerated at a minimum of 20 amps.

Please contact your authorized Krell dealer, dis-tributor, or Krell before using any devicesdesigned to alter or stabilize the AC power forFull Power Balanced amplifiers.

Placement, continued

FIGURE 1 FULL POWER BALANCED STEREO AMPLIFIER FRONT PANEL

1 Power Stand-by LED2 Bias LED3 Power Button

4 Infrared Sensor5 Krell CAST LED6 Regulator LED

1 2 63 54


FIGURE 2 FULL POWER BALANCED MONAURAL AMPLIFIER FRONT PANEL

7 Power Stand-by LED8 Bias LED9 Power Button

10 Infrared Sensor11 Krell CAST LED12 Regulator LED

7 8 129 1110

Krell Full Powered Balanced X Series Power Amplifiers 7


The front panel accesses power on/stand-byand infrared sensor (remote control) functions.The power stand-by, bias, regulator, and KrellCAST LEDs, arranged in a triangle on the frontpanel above the power button, illuminate to indi-cate amplifier status.

FULL POWER BALANCED 700cx, 400cx, AND 300cxSTEREO POWER AMPLIFIERSSee Figure 1 on page 6

1 Power Stand-by LEDThe blue power stand-by LED (top of LED tri-angle) illuminates when the back panel powerbreaker switch has been moved to on, engag-ing the input circuitry and placing the amplifierin stand-by mode.

2 Bias LEDThe blue bias LED (lower left of triangle) illumi-nates after the front panel power button ispressed, indicating that the Sustained PlateauBias III is engaged.

3 Power ButtonUse the silver power button to power on theamplifier from stand-by mode.

4 Infrared SensorThe infrared sensor receives the signal from aremote control.

5 Krell CAST LEDThe red Krell CAST LED (center of triangle) illu-minates when a Krell CAST input on the backpanel is connected to another Krell product witha Krell CAST output.

6 Regulator LEDThe blue regulator LED (lower right of triangle)illuminates after the front panel power button isused to power on from stand-by mode, indicat-ing that the regulator is providing power to theoutput stage.

NoteAn optional remote control is available for FullPower Balanced amplifiers.

FULL POWER BALANCED 750Mcx, 450Mcx, AND 350McxMONAURAL POWER AMPLIFIERSSee Figure 2 on page 7

7 Power Stand-by LEDThe blue power stand-by LED (top of LED tri-angle) illuminates when the back panel powerbreaker switch has been moved to on, engag-ing the input circuitry and placing the amplifierin stand-by mode.

8 Bias LEDThe blue bias LED (lower left of triangle) illumi-nates after the front panel power button ispressed, indicating that the Sustained PlateauBias III is engaged.

9 Power ButtonUse the silver power button to power on theamplifier from stand-by mode.

10 Infrared SensorThe infrared sensor receives the signal from aremote control.

11 Krell CAST LEDThe red Krell CAST LED (center of triangle) illu-minates when a Krell CAST input on the backpanel is connected to another Krell product witha Krell CAST output.

12 Regulator LEDThe blue regulator LED (lower right of triangle)illuminates after the front panel power button isused to power on from stand-by mode, indicat-ing that the regulator is providing power to theoutput stage.

Front Panel Description

FIGURE 3 FULL POWER BALANCED STEREO AMPLIFIER BACK PANEL

13 Left and Right Speaker Binding Posts14 Krell CAST Inputs15 Back Panel Power Breaker Switch

16 Left and Right Balanced Inputs17 Krell Link Out/In18 AC Mains Power Cord19 Handles

13 1716 161519 191814 14 13

Krell Full Powered Balanced X Series Power Amplifiers 9

FIGURE 4 FULL POWER BALANCED MONAURAL AMPLIFIER BACK PANEL

20 Handle21 Speaker Binding Posts22 Krell CAST Input23 Balanced Input

24 AC Mains Power Cord25 Krell Link Out/In26 Back Panel Power

Breaker Switch

21 2523 2420 2622



The back panel provides connections for allinputs and outputs, power on/off, and remotecontrol links. The back panel also has handlesthat allow you to safely and easily move theamplifier.

FULL POWER BALANCED 700cx, 400cx, AND 300cxSTEREO POWER AMPLIFIERSSee Figure 1 on page 6

13 Left and Right Speaker Binding PostsFull Power Balanced 700cx, 400cx, and 300cxstereo amplifiers are equipped with four pairs ofspeaker binding posts (upper left, lower left,upper right, and lower right).

NotesTwo pairs of speaker binding posts are used foreach channel of amplification. On the stereo ormonaural Full Power Balanced amplifiers,either the upper or the lower pair can be usedwith speakers having two pairs of binding posts.For biwiring applications, with speakers havingmore than one pair of binding posts, use bothupper and lower pairs of speaker binding posts.See the speaker’s instruction manual forbiwiring connections.

Speaker binding posts for stereo and monauralamplifiers accept spade lugs only. Bare wire,banana lugs, or pins will not work. Use the redterminal for the positive connection and theblue terminal for the negative connection.

14 Krell CAST InputsFull Power Balanced 700cx, 400cx, and 300cxstereo amplifiers are equipped with one left KrellCAST input and one right Krell CAST input via 4-pin bayonet connectors. The Krell CAST inputsallow the Full Power Balanced amplifier to beconnected to the KPS 25sc Krell Playback Sys-tem and other CAST-equipped components.

15 Back Panel Power Breaker SwitchFull Power Balanced amplifiers are equippedwith a back panel power breaker switch, forpowering on the amplifier. Placing the backpanel power breaker switch in the up positionplaces the amplifier in stand-by mode, where itremains until the front panel power button (3) ispressed.

NoteKrell recommends that the amplifier remain on,in stand-by mode, even when not in use, onceit is powered on from the back panel powerbreaker switch (15).

16 Left and Right Balanced InputsFull Power Balanced 700cx, 400cx, and 300cxstereo amplifiers are equipped with one left bal-anced input and one right balanced input viaXLR connectors.

17 Krell Link Out/In Full Power Balanced amplifiers are equippedwith Krell Link Remote out/in connectors thatallow the remote control to operate a linkedamplifier configuration. See Krell Link Connec-tions, on page 13 for more information.


18 AC Mains Power CordAll Full Power Balanced amplifiers are equippedwith a permanently attached AC power cord.

19 HandlesAll Full Power Balanced stereo amplifiers areequipped with two handles, located beside thespeaker binding posts, to help you easily andsafely move the amplifier.

Back Panel Description


FULL POWER BALANCED 750Mcx,450Mcx, AND 350Mcx MONAURALPOWER AMPLIFIERSSee Figure 4 on page 10

20 HandleAll Full Power Balanced monaural amplifiers areequipped with a handle, located beside thespeaker binding posts, to help you easily andsafely move the amplifier.

21 Speaker Binding PostsFull Power Balanced 750Mcx, 450Mcx, and350Mcx monaural amplifiers are equipped withtwo pairs of speaker binding posts (one upperpair and one lower pair). For stereo operation,two monaural amplifiers are required.

22 Krell CAST InputFull Power Balanced 750Mcx, 450Mcx, and350Mcx monaural amplifiers are equipped withone Krell CAST input via a 4-pin bayonet con-nector. The Krell CAST input allows the FullPower Balanced amplifier to be connected tothe KPS 25sc Krell Playback System and otherCAST-equipped components.

23 Balanced InputFull Power Balanced 750Mcx, 450Mcx, and350Mcx monaural amplifiers are equipped withone balanced input via an XLR connector.

24 AC Mains Power CordAll Full Power Balanced amplifiers are equippedwith a permanently attached AC power cord.

25 Krell Link Out/In Full Power Balanced amplifiers are equippedwith Krell Link Remote out/in connectors thatallow the remote control to operate a linkedamplifier configuration. See Krell Link Connec-tions, on page 13 for more information.


26 Back Panel Power Breaker SwitchFull Power Balanced amplifiers are equippedwith a back panel power breaker switch, forpowering on the amplifier. Powering on usingthe back panel power breaker switch places theamplifier in stand-by mode, where it remainsuntil the front panel power button is pressed.

NoteKrell recommends that, once the amplifier ispowered on from the back panel power breakerswitch, it remains on, in stand-by mode, evenwhen not in use.

Back Panel Description, continued


INPUT AND OUTPUT CONNECTIONS

Krell recommends using its proprietary KrellCAST system for unparalleled sonic perfor-mance between the Full Power Balancedamplifiers and other CAST-equipped compo-nents and the KPS 25sc Krell Playback Sys-tem.

Full Power Balanced amplifiers also offer bal-anced operation. The circuitry and connectionsassociated with balanced operation not onlycan minimize sonic loss but also are immune toinduced noise, especially for installations usinglong cables.

A one piece RCA-to-XLR adapter is availablefrom Krell Industries, to allow single-ended oper-ation using the balanced XLR inputs.

The following steps describe how to connectcables to the Full Power Balanced Amplifiers.

1. Neatly arrange and organize wiring to andfrom the amplifier and all components. Sep-arate AC wires from audio cables to preventhum or other unwanted noise from beingintroduced into the system.

2. Connect the Krell CAST cables from yourCAST-enabled preamplifier/source compo-nent to the left and right Krell CAST 4-pinbayonet inputs on the amplifier back panel.For balanced operation, connect the inter-connect cable from your preamplifier to theleft and right balanced XLR input on theamplifier back panel.

3. Connect the speaker cables to the FullPower Balanced amplifier’s speaker bindingposts, located on the amplifier back panel.Speaker binding posts for both stereo andmonaural amplifiers accept spade lugs only.

4. Insert the end of the AC mains power cordinto the AC wall receptacle.

5. Proceed with Krell Link Connections, ifdesired, or turn to Amplifier Operation, onpage 15.

KRELL LINK CONNECTIONS

Krell Link Remote out/in connectors on theback panel of the Full Power Balanced amplifi-er allow you to synchronize remote controloperation for systems that include multipleamplifiers and associated components. Whenthe Krell Link Remote out/in connectors areused, the remote capabilities of the linked com-ponents are controlled from one amplifier orpreamplifier, called the control component. Thelinked components respond to stand-by andoperational mode commands from the controlcomponent via MIDI cables.

NoteKrell Link uses standard five pin MIDI commu-nication cables, sometimes referred to as MIDIPlus cables. MIDI cables can be purchasedfrom your authorized distributor or dealer, orfrom an audio supply store.

How to Connect Components through Krell Link

1. Turn all components off, using the backpanel power breaker switch. This ensuresthat the components are synchronized whenthe MIDI cable is connected.

2. Select the component to be the control com-ponent. The control component must be inplain view for proper remote control opera-tion.

3. Connect one end of the MIDI cable to theKrell Link out connector on the back panel ofthe component.

Connecting the Full Power BalancedAmplifier to Your System


4. Connect the other end of the MIDI cable tothe Krell Link in connector on the next com-ponent.

To link another component, connect a sec-ond MIDI cable to the Krell Link out con-nector on the back panel of the secondcomponent. Connect the remaining end ofthe MIDI cable to the Krell Link in connec-tor on the back panel of a third component.

5. Link additional components, if desired, asdescribed in Steps 3 and 4.

The components are now ready for operation withKrell Link.

DC PROTECTION CIRCUITRY

Full Power Balanced amplifiers use unobtrusivedirect current (DC) protection circuitry thatstrips DC from the signal without corruptingsound reproduction. Full Power Balancedamplifiers feature direct coupled circuitry frominput to output. This topology eliminates all cou-pling capacitors from the audio signal path.Coupling capacitors block damaging DC buthave sonic characteristics that corrupt soundreproduction.

NoteFor more information about DC protection cir-cuitry features, see Amplifier Troubleshooting,on page 17.

USING A TUBE PREAMPLIFIER

The high DC output of tube preamplifiers mayexceed the DC protection circuitry of FullPower Balanced amplifiers. Excessive DClevel in a signal can damage amplifiers, speak-ers, or both. The coupling capacitors in FullPower Balanced amplifiers must be engagedwhen using a tube preamplifier. An authorizedKrell dealer, distributor, or Krell must activatethese capacitors.

Coupling capacitors must be inserted into thesignal path by your authorized Krell dealer, dis-tributor, or Krell before you can use your FullPower Balanced amplifier with a tube preampli-fier.

IMPORTANTPlease read the Warranty, on page 20, tounderstand the warranty limitations of FullPower Balanced amplifiers when used withtube preamplifiers.

Connecting, continued


Full Power Balanced amplifiers are easy toinstall and operate. However, it is important toexercise care during operation, due to theamplifiers’ enormous power output. Switchingbetween active sources (such as a CD player,tape monitor, or VCR) without muting the pre-amplifier output, or bumping or miscuing asource can generate large transients at low fre-quencies. Full Power Balanced amplifiers maygenerate enough power with these transientsto damage loudspeakers.

IMPORTANTAlways mute or fully attenuate the preamplifierlevel when switching sources.

Do not change input connections to the amplifi-er when the amplifier is on.

Use care when setting high playback levels.Because of their tremendous reserves of cleanpower, 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.

ON/OFF AND STAND-BYOPERATIONWhen powering on any system, turn on ampli-fiers last. Turn off amplifiers first.

1. Move the back panel power breaker switchto 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. Press the silver power button on the amplifi-er front panel. The blue regulator LED illumi-nates. Once the regulator provides power tothe output stage, the blue bias LED illumi-nates. The Sustained Plateau Bias II systemis now engaged. After the protection circuitryhas confirmed that safe operating conditionsexist, the input relays engage. You hear aclick. The amplifier is ready for operation.

If the Krell CAST input is being used, theKrell CAST red LED illuminates andremains illuminated at all times during thestand-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 desiredlistening level.

4. When turning off the system, mute or com-pletely lower the preamplifier volume, orplace the Full Power Balanced amplifier inthe stand-by power mode by pressing thepower button on the front panel. It is nowsafe to turn off the rest of the system.

NoteFor best performance of Full Power Balancedamplifiers, leave the back panel power breakerswitch on at all times.

KRELL LINK OPERATION1. When all components are linked, place

each component in the stand-by mode bymoving the back panel power breakerswitch to the up position. This ensures thatall components will be synchronized whensignals from the control component are sentto the linked components in the system.

2. When the components are in stand-by,switch the control component to the opera-tional mode from the control component’sfront panel or by using the component’s remote control.

The linked components switch to the oper-ational mode simultaneously.

A linked component can be switched betweenthe operational mode and stand-by, individual-ly, from its front panel. Switching a linked com-ponent temporarily breaks the chain of linkedcomponents. To re-establish linked operation,return all components to stand-by.

Amplifier Operation


Full Power Balanced amplifiers are compatiblewith the remote controls included with Krell pre-amplifiers, the Home Theater Standard 7.1, andthe KPS 25sc Krell Playback System.

Please contact your authorized Krell dealer, dis-tributor, or Krell to purchase a remote control forFull Power Balanced amplifiers.

Full Power Balanced amplifiers can be locatedin a room or space close to the speakers but outof sight, and powered on or off remotely fromthe listening room, through a control amplifier.See Krell Link Connections, on page 13.

HOW TO TURN OFF THE AMPLIFIER LEDs

The amplifier must be in the stand-by modewith the rear panel power breaker switch on.While holding the silver power button in, pressthe power key on the remote control. After theamplifier finishes its turn-on sequence, the frontpanel blue LEDs turn off. The blue LEDs remainoff throughout normal operation as long as theamplifier’s rear panel power breaker switch isnot turned off.

HOW TO TURN ON THE AMPLIFIER LEDs

With the amplifier in the stand-by mode, turnthe rear panel power breaker switch to the offposition. Then turn the rear panel power break-er switch back to the on position. The next timethe amplifier is powered up from the front panelor the remote control, the blue LEDs illuminateduring the turn-on sequence.

HOW TO SWITCH BETWEENKRELL CAST AND XLR INPUTS

Press the meter key on a Krell remote to switchbetween CAST inputs and the balanced XLRinputs.

Full Power Balanced amplifiers default to CASToperation upon startup, if the amplifier is turnedoff from the rear panel power breaker switch anda CAST source and cable are connected to theCAST inputs. The operational mode does notchange if the Full Power Balanced amplifier is instand-by mode.

USING A DEDICATED WALLOUTLET AND SWITCH

Full Power Balanced amplifiers can be poweredon from an AC wall receptacle with a dedicatedswitch, rather than from the front panel powerbutton or optional remote control.

Please contact your authorized Krell dealer, dis-tributor, or Krell for more information before youconnect your Full Power Balanced amplifier to adedicated AC wall outlet with a switch.

Remote Control Operation


HOW TO TROUBLESHOOT SYSTEM NOISE

AC grounding becomes critical when connect-ing high performance audio components. Whenyou mix and match audio components, eachwith its own ground potential, a low frequencyhum may occur in one or both speakers. Thisoften occurs when introducing a new compo-nent into a system.

If a low frequency hum emanates from thespeakers when you place the Full Power Bal-anced amplifier into the system, follow thesesimple troubleshooting steps:

NoteDuring these steps, the back panel powerbreaker 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, removethe interconnect cables, then press the frontpanel power button. If the hum disappears,press the power button to return to stand-bymode, and reinsert one of the interconnectcables. Press the power button again. If thehum reappears with one or both intercon-nects inserted, there may be a defectivecable. Have the interconnect cables checkedbefore proceeding.

2. If the interconnect cables are sound, youmay be experiencing a ground loop. Thiscan often be easily eliminated. Please con-tact your authorized Krell dealer, distributor,or Krell for suggestions on how to solve thisproblem.

HOW TO EVALUATE AMPLIFIER OPERATIONThe amplifiers are protected by a series of non-intrusive circuits that constantly evaluate theamplifier’s operation. This circuitry protectsagainst damaging DC input or output and shortcircuits, see also DC Protection Circuitry, onpage 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 damageto the amplifiers or speakers caused by otherdefective components, faulty wiring, systemmishandling, or amplifier failure.

In addition, when a Full Power Balanced ampli-fier’s DC protection circuitry senses a problemwithin the system, it identifies, then indicates theproblem by illuminating the front panel blueLEDs, as described in the following table.

NotesThe Krell CAST LED illuminates only if a KrellCAST input is being used.

There are no output fuses in Full Power Bal-anced amplifiers.

Amplifier Troubleshooting

AMPLIFIER CONDITIONThe output mutes duringplayback and the followingLEDs illuminate: PowerStand-by, and Regulator Bias

The amplifier switches tostand-by mode and the Power Stand-by LED illuminates

The amplifier switches tostand-by at high volumesand the Power Stand-byLED illuminates

The amplifier powers downcompletely and no LEDsilluminate

POSSIBLE CAUSESExcessive DC at the amplifier input

Electrical short in speakercables or inside speaker

Insufficient AC current fromthe wall outlet

Excessive heat

DC present at the outputstage

Internal amplifier problem

COURSE OF ACTIONHave source unit and preamplifier checked for highDC output

If preamplifier is a tube model, see Using a Tube Preamplifier, on page 14.

Check all speaker cables forany cuts or frayed edges thatmight form a connectionbetween the positive and neg-ative speaker binding post ter-minals

Make sure the AC line is atleast 15 amps for 300cx and350Mc amplifiers; 400cx,450Mcx, 700cx, and 750Mcxamplifiers should be operated from a dedicated 20-amp line.

Allow amplifier to cool beforeresuming operation. SeePlacement, on page 4 for ven-tilation requirements

Contact your authorized Krelldealer, distributor, or Krell

Contact your authorized Krelldealer, distributor, or Krell


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.


Q. Should I leave my Full Power Balancedamplifier on at all times?

A. For maximum amplifier performance, leavethe back panel power breaker switch on at alltimes. This places the amplifier in stand-bymode. Full Power Balanced amplifiers aredesigned to be powered on and off from stand-by, using the front panel power button. Thiseliminates “cold start” degradations. The ampli-fier will operate at full performance within min-utes.

Q. When I turn on the amplifier there is a loudhum through the speakers. What should I do?

A. When a new component is introduced, a lowfrequency hum may occur in one or both speak-ers. Check all input and output connections andcables, making sure they are of sound con-struction. See How to Troubleshoot SystemNoise, on page 17. If the interconnects andcables are sound, you may be experiencing aground loop. This can often be easily eliminat-ed. Please contact your authorized Krell dealer,distributor, or Krell for suggestions on how tosolve this problem.

Q. My system includes multiple pairs of speak-ers. Can I connect them to my Full Power Bal-anced amplifiers through a speaker selectorbox?

A. No. Most speaker selector boxes use a com-mon ground scheme. The differential circuitry inFull Power Balanced amplifiers prohibits the useof these devices. Do not connect a Full PowerBalanced amplifier to a speaker selector

device that employs a common groundscheme, as it may short-circuit the amplifieroutput.

Q. My speakers have only one pair of bindingposts, but my Full Power Balanced stereoamplifier has two pairs. Which pair of speakerbinding posts should I use, the upper or thelower?

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 upperor lower pair; they work and sound the same.See Connecting the Full Power BalancedAmplifier to Your System, on page 13.

Q. My speakers are rated for 150 Watts. Arethe Full Power Balanced 400cx or 700cx mod-els too powerful for them?

A. No. A speaker seldom is damaged fromoverdriving. More often, damage occurs whenan amplifier that lacks sufficient power is askedto handle heavy demand situations such ashigh playback levels. These amplifiers mayhave very high 8 Ohm power ratings, but inheavy demand situations they can be driveninto clipping (in which DC current goes tospeakers due to loss of amplifier power). Clip-ping can damage speakers. Avoid damage toyour speakers by reviewing your speaker’sspecifications and exercise caution in heavydemand situations.

Questions and Answers

This Krell product has a limited warranty of five years forparts and labor on circuitry. Should this product fail to per-form at any time during the warranty, Krell will repair it atno cost to the owner, except as set forth in this warranty.

The warranty does not apply to damage caused by acts ofGod 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 exceedbeyond those described in this document. If this productdoes not perform as warranted herein, the owner’s soleremedy shall be repair. In no event will Krell be liable forincidental or consequential damages arising from pur-chase, use, or inability to use this product, even if Krell hasbeen advised of the possibility of such damages.

IMPORTANTThe user is responsible for notifying his or her Krell deal-er, distributor, or Krell that a tube preamplifier will be usedwith the Full Power Balanced amplifier, so that the Krelldealer, 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 FullPower Balanced amplifier’s coupling capacitor engaged,Krell reserves the right to refuse warranty related servicedue to DC-related damage.

Proof of purchase in the form of a bill of sale or receiptedinvoice substantiating that the unit is within the warrantyperiod must be presented to obtain warranty service. Thewarranty begins on the date of the original retail purchase,as noted on the bill of sale or receipted invoice from anauthorized Krell dealer or distributor. Previously ownedequipment, when re-purchased from an authorized Krelldealer or distributor, has the balance of the original war-ranty, based on the original date of manufacture.

The warranty for Krell products is valid only in the country towhich they were originally shipped, through the authorizedKrell distributor for that country, and at the factory. Theremay be restrictions on or changes to Krell’s warrantybecause of regulations within a specific country. Pleasecheck with your distributor for a complete understanding ofthe warranty in your country.

If a unit is serviced by a distributor who did not import theunit, there may be a charge for service, even if the productis within the warranty period.

Freight to the factory is your responsibility. Return freightwithin 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 andassociated 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 theunit from the freight forwarder to you are also your respon-sibility.

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 filingclaims for shipping damages during the return shipment.

Krell does not supply replacement parts and/or products tothe owner of the unit. Replacement parts and/or productswill be furnished only to the distributor performing service onthis unit on an exchange basis only; any parts and/or prod-ucts returned to Krell for exchange become the property ofKrell.

No expressed or implied warranty is made for any Krellproduct damaged by accident, abuse, misuse, natural orpersonal disaster, or unauthorized modification.

Any unauthorized voltage conversion, disassembly,component replacement, perforation of chassis,updates, or modifications performed to the unit willvoid 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 theU.S.A. cannot be changed until six months from the originalpurchase date.

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 specificationsat the owner’s expense before it is repaired. All repairsrequired after the product has been returned to original fac-tory specifications will be charged to the customer, at cur-rent parts and labor rates.

All operational features, functions, and specifications andpolicies 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 boxwithin 15 days of purchase. Thank you.

Warranty


If you believe there is a problem with your com-ponent, please contact your dealer, distributor, orthe Krell factory to discuss the problem beforeyou return the component for repair. To expediteservice, you may wish to complete and e-mailthe Service Request Form in the Service Sectionof our website at:

www.krellonline.com

To return this product to Krell, please followthis procedure so that we may serve youbetter:

1. Obtain a Return Authorization Number (R/Anumber) and shipping address from theKrell Service Department.

2. Insure and accept all liability for loss of ordamage to this product during shipment tothe Krell factory and prepay all shippingcharges. Please see the Warranty page inthis manual, concerning liability for shippingdamage and shipping charges.

This product may also be hand delivered ifarrangements with the Service Departmenthave been made in advance. Proof of purchasemay be required for warranty validation at thetime of hand delivery.

IMPORTANTUse the original packaging to ensure safe tran-sit of this product to the dealer, distributor, orfactory. Krell may, at its discretion, return thisproduct in new packaging and bill the owner forsuch packaging if the product received by Krellwas boxed in non-standard packaging or if theoriginal packaging was so damaged that it wasunusable. If Krell determines that new packag-ing is required, the owner will be notified beforethis product is returned.

To purchase additional packaging, please con-tact your authorized Krell dealer, distributor, orthe Krell Service Department.

To contact the Krell Service Department

TEL 203-799-9954Monday-Friday9:00 AM to 5:00 PM EST

FAX 203-799-9796

E-MAIL [email protected]

WEBSITE www.krellonline.com

Full Power Balanced X Series AmplifierPRODUCT NAME

MODEL NUMBER SERIAL NUMBER

Return AuthorizationProcedure

SpecificationsFull Power Balanced 300cx, 400cx, 700cx 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 WEACH 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 Peak 170 V Peak to Peak 240 VRMS 49 V RMS 60 V RMS 84 V

POWER CONSUMPTION Stand-by 60 W Stand-by 75 W Stand-by 85 WIdle 175 W Idle 350 W Idle 430 WMax. 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 connectors1 pair CAST via 4-pin 1 pair CAST via 4-pin 1 pair CAST via 4-pinbayonet connectors bayonet connectors bayonet connectors

OUTPUTS 4 pair (upper left, 4 pair (upper left, 4 pair (upper leftSPEAKER 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

DIMENSIONSINCHES 19.0w x 10.3h x 17.0d 19.0w x 10.3h x 19.7d 19.0w x 10.3hx 25.5dCENTIMETERS 48.3w x 26.2h x 43.2d 48.3w x 26.2h x 50.0d 48.3wx 26.2hx 64.8d

WEIGHTSHIPPING 107.0 lb., 48.6 kg 127.0 lb., 57.7 kg 200.0 lb., 90.9 kgUNIT 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.



SpecificationsFull Power Balanced 350Mcx, 450Mcx, 750Mcx 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 WEACH 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 Peak 170 V Peak to Peak 240 VRMS 49 V RMS 60 V RMS 84 V

POWER CONSUMPTION Stand-by 30 W Stand-by 37.5 W Stand-by 42.5 WIdle 150 W Idle 175 W Idle 220 WMax. 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 connectors1 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

DIMENSIONSINCHES 12.5w x 10.5h x 16.0d 12.5w x 10.5h x 19.0d 12.5w x 10.5h x 25.0dCENTIMETERS 31.8w x 26.7h x 40.6d 31.8w x 26.7h x 48.3d 31.8w x 26.7h x 67.3d

WEIGHTSHIPPING 79.0 lb., 35.9 kg 110.0 lb., 50.0 kg 155.0 lb., 70.5 kgUNIT ONLY 68.0 lb., 31.0 kg 98.0 lb., 44.5 kg 140.0 lb., 63.6 kg

Krell Industries, Inc.45 Connair RoadOrange, CT 06477-3650 USA

TEL 203-799-9954FAX 203-891-2028E-MAIL [email protected] SITE http://www.krellonline.com

Full Power Balanced X Series Power Amplifiers

700cx, 400cx, 300cx Stereo


with Krell CAST II Technologyv 02.0

fpb x-series power amplifiers owner's reference

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