Benchmark AHB2 Black Manuel utilisateur

Benchmark AHB2

Instruction Manual

Reference Stereo Power Amplifier

100W/channel into 8-Ohms

380W bridged mono into 8-Ohms

AHB2 Instruction Manual Rev G Page 2

Contents

Introduction 3

Product Overview 3

True HRA Performance 3

Virtually Noise Free 3

Virtually Distortion Free 3

Patent Information 3

Licensed THX Patents 3

Important Safety Instructions 4

Safety Symbols 4

Safety Precautions 5

Front Panel 7

Front Panel Layout 7

Rear Panel 8

Rear Panel Layout 8

Quick Start Guide 9

Overview 9

1. Set the MODE Switch 9

2. Set the SENSITIVITY Switch 9

3. Connect the Audio Inputs 10

4. Connect the Speaker Outputs 10

5. Connect the AC Power Cord 11

6. Turn on the Power 11

7. Check the Status Indicators 11

Bidirectional 12 Volt Trigger 12

Linking Multiple Audio Components 12

Trigger Wiring 12

Trigger Cables 12

Automatic Power-Down Feature 12

40 Minute Timer 12

Timer Deactivates the 12V TRIGGER 12

No Warm-Up Required 13

AUTO-ON Feature 13

Rack Mounting 14

Rack Mount Option 14

Rack Mounting Instructions 14

Fault Protection Circuitry 15

Fault-Detection Circuits 15

PROTECT Mode (Both MUTE Lights On) 15

PROTECT Mode - Fault Codes 16

Clipping Fault 17

Over-Current Fault 18

SOA Fault 19

Over-Temperature Fault 20

Power Supply Fault 21

Specifications 22

Rated Output Power 22

Output Current 22

Output Voltage 22

Frequency Response 22

Signal to Noise Ratio 22

Distortion 22

Crosstalk 23

Input Sensitivity 23

Input Impedance 23

Input CMRR 23

Trigger I/O 23

Damping Factor 23

Environmental 23

Mechanical Drawings 24

Dimensions 24

Rack-Mount Dimensions 25

Performance Plots 26

Regulatory Compliance 31

FCC and RoHS Compliance Statements 31

FCC Notice (U.S. Only) 31

RoHS Compliant Information 31

CE Certificate of Conformity 32

Safety 33

Warranty Information 34

Benchmark 1-Year Warranty 34

Benchmark Extended Warranty Options 35

Notes on Warranty Repairs 35

Consignes de Sécurité Importantes

(French) 36

Symboles de Sécurité 36

Mesures de Sécurité 37

Appendix 39

A Radical Approach to Power Amplification

39

AHB2 Instruction Manual Rev G Page 3

Introduction

Thank you for purchasing the Benchmark AHB2 audio power amplifier. To take full advantage of

the extraordinary performance of this amplifier, and to enjoy long and trouble-free use, please read

this manual carefully.

Product Overview

True HRA Performance

The AHB2 is a reference-grade audio power amplifier that is specifically designed to complement

the performance delivered by the finest High Resolution Audio (HRA) recording and playback

systems. The SNR and THD performance of the AHB2 put this amplifier in a class by itself.

Virtually Noise Free

The AHB2 delivers a SNR that exceeds 132 dB A-weighted. This makes the AHB2 15 to 30 dB

quieter than most top-quality power amplifiers. 132 dB is approximately equivalent to the noise

performance of a perfect 22-bit digital system.

Virtually Distortion Free

A THX-patented feed-forward error correction system virtually eliminates all traces of distortion at

all signal level and loading conditions. The AHB2 shows no traces of the crossover distortion that

can occur when push-pull outputs stages switch between output devices. Without crossover

distortion, low-level details are resolved with precision. At high output levels, the AHB2 remains

virtually distortion free while driving heavy loads.

Patent Information

The AHB2 incorporates patented THX® Achromatic™ Audio Amplifier Technology (THX

AAA™) which is licensed from THX Limited.

Licensed THX Patents

 U.S. Patent No. 8,004,355

 U.S. Patent No. 8,421,531

 Mexico Pat. No. 312399

 Mexico Pat. No. 317696

 Canada Pat. No. 2753575

 S. Korea Pat. No. 10-1429804

 Additional Patents Pending

A complete list of applicable patents is available at: http://patents.thx.com/abc/

AHB2 Instruction Manual Rev G Page 4

Important Safety Instructions

Safety Symbols

This symbol alerts the user that there are important operating and maintenance

instructions in the literature accompanying this appliance.

This symbol alerts the user to the presence of uninsulated voltages within the unit that can

cause dangerous electric shocks.

This symbol alerts the user to the presence of voltages at the output connectors that can

cause dangerous electric shocks.

This symbol alerts the user that the product can only be used safely at altitudes lower than

2,000 meters.

This symbol alerts the user that the product can only be used safely in non-tropical

climates.

AHB2 Instruction Manual Rev G Page 5

Safety Precautions

Important Operating and Maintenance Instructions

1. Read these instructions.

2. Keep these instructions.

3. Heed all warnings.

4. Do not use this apparatus near water.

5. Do not spray any liquid onto any surface, as this may cause a dangerous condition. Clean only

with a damp cloth.

6. This apparatus produces heat when operated normally. Operate in a well-ventilated area. Do

not block the heat-sink fins located on either side of the unit. These emit heat and must be well

ventilated.

7. Do not install near any heat sources such as radiators, heat registers, stoves or other apparatus

that produce heat.

8. Use only with attachments and accessories specified by the manufacturer.

9. Use only with a stand, rack, or table designed to support the weight of this apparatus. Make

sure that injury or damage will not result from cables pulling on the apparatus or its mounting.

Speaker Output Voltage Warning

10. The speaker outputs are capable of producing dangerous voltages. Use insulated speaker

connections. Unplug the apparatus before making changes to the speaker output connections.

Hazardous Internal Voltage Warnings

11. Refer all servicing to qualified service personnel. There are no user-serviceable parts inside the

unit. There are exposed high voltages inside the unit and these may persist after the unit is

unplugged. Do not attempt to open any of the covers, and do not remove any fasteners.

Opening the unit will void the warranty.

12. Certain parts are safety related, or are required to meet certain regulations. All parts must be

replaced with exact replacements unless written approval is granted by Benchmark.

Unauthorized substitutions and modifications can create unsafe or non-compliant operating

conditions and will void the warranty. Unauthorized modifications may cause fire and shock

hazards. Unauthorized modification may cause the unit to emit excessive radio and magnetic

interference. Modifications may reduce the immunity to external interference. Do not refer

servicing to personnel who offer product modification services.

AHB2 Instruction Manual Rev G Page 6

Line Cord and Fuse Warnings

13. The AC line cord is removable. Use a grounded 3-prong line cord that is appropriate for your

region. Your dealer can provide you with the correct line cord.

14. Do not defeat the purpose of the grounded power plug. The ground prong is provided for your

safety. When a 3-prong outlet is not available, please consult an electrician for replacement of

the obsolete outlet. Do not use 2-prong to 3-prong adapters. Do not attempt to solve AC hum

problems by lifting the AC safety ground!

15. Unplug this apparatus during lightning storms or when unused for long periods of time.

16. This apparatus is equipped with an auto-ranging power supply. There is no internal voltage

selection switch - do not attempt to open the unit. Operating voltage ranges are 100 to 120 Vac

+/- 10%, and 220 to 240 Vac +/- 10%. Operating frequency is 50 to 60 Hz. All operating

voltages use the same fuse size.

17. For continued fire and shock protection always replace the fuses with the correct size and type

(T 8A H 250V, 5x20mm), (T = time lag, 8A = eight Amps, H = high breaking capacity, 250V =

voltage rating, 5x20mm = cartridge size). High-breaking fuses use a ceramic body. Use Bel

Fuse 5HT 8-R, or Schurter 0001.2513, or an exact equivalent. The fuse drawer includes two

fuses. Always replace both fuses at the same time.

Operating Environment Warnings

18. This product can only be used safely at altitudes lower than 2,000 meters.

19. This product can only be used safely in non-tropical climates.

AHB2 Instruction Manual Rev G Page 7

Front Panel

Front Panel Layout

Left to Right:

 Power Switch

 Power Indicator

 Channel 1 Clip Indicator

 Channel 1 Temperature and High-Current Indicator

 Channel 1 Mute Indicator

 Channel 2 Mute Indicator

 Channel 2 Temperature and High-Current Indicator

 Channel 2 Clip Indicator

AHB2 Instruction Manual Rev G Page 8

Rear Panel

Rear Panel Layout

Top Row, Left to Right:

 Channel 2 Speaker Binding Posts

 AC Power Entry with Fuse Drawer

 Channel 1 Speaker Binding Posts

Bottom Row, Left to Right:

 12 Volt Trigger Input / Output Connector

 3-Position Sensitivity Switch - Sets Gain

 Balanced XLR Input for Channel 2

 NL4 Speaker Output for Channel 2

 NL4 Speaker Output for Bridged Mono Operation

 NL4 Speaker Output for Channel 1, or Channels 1 and 2

 Balanced XLR Input for Channel 1, or for Bridged Mono

 2-Position Mode Switch - Enables Bridged Mono Mode

 12 Volt Trigger Input / Output Connector

AHB2 Instruction Manual Rev G Page 9

Quick Start Guide

Overview

 Connect all cables before turning the unit on.

 Check the settings of the MODE and SENSITIVITY switches before turning the unit on.

 Turn down the audio source before turning the unit on for the first time.

1. Set the MODE Switch

The MODE switch is very important, make sure it is set correctly for your application. An incorrect

setting will not cause damage, but it may cause low output levels, a missing channel, or a polarity

inversion.

The AHB2 power amplifier can be run in two modes:

 STEREO mode - Two output channels

 MONO mode - One output channel in bridged mono

The bridged MONO mode will deliver almost 4 times as much power into an 8-Ohm speaker, and

will do so without any increase in distortion. The MONO mode is an excellent choice for high-power

applications. In MONO mode, two amplifiers will be required for stereo operation.

 Set this switch to STEREO if the AHB2 is driving a stereo pair of speakers.

 Set this switch to STEREO if the AHB2 is driving two channels of a multi-channel system.

 Set this switch to STEREO if the AHB2 is driving a biamped two-way speaker.

 Set this switch to MONO if the AHB2 is driving one speaker.

2. Set the SENSITIVITY Switch

The SENSITIVITY switch must be set properly in order to maximize the signal to noise ratio of

your audio system. If this switch is set too low, you will not be able to drive the amplifier to its

rated output. If this switch is set too high, the noise produced by your preamplifier will be amplified

more than is necessary.

 If you are using an unbalanced input, you must use one of the top two switch positions.

 If you are using a balanced input, you will usually need to use one of the bottom two switch

positions.

 Set this switch all the way down if you are using professional balanced sources.

 Raise the switch to increase the output level.

 Lower the switch to decrease the output level.

When set properly, you should be able to drive the amplifier to the onset of clipping when your

volume control is set near maximum.

AHB2 Instruction Manual Rev G Page 10

3. Connect the Audio Inputs

There are two balanced XLR audio inputs on the AHB2:

 1 IN/MONO IN

 2 IN

Special adapter cables are required if balanced sources are not available. The adapter cables

extend a three-wire balanced connection back to an unbalanced RCA output. The adapter cables

are available from Benchmark.

 Use 1 IN/MONO IN for the left channel of a stereo system.

 Use 2 IN for the right channel of a stereo system.

 Use 1 IN/MONO IN for all MONO mode applications.

Please note that unbalanced sources will limit the overall performance of the playback system. This

is not due to any limitations in the AHB2. It is due to the noise limitations of unbalanced output

drive stages. High-level balanced interconnects are required in low-noise systems. We highly

recommend balanced interconnects.

4. Connect the Speaker Outputs

The AHB2 has twist-lock NL4 SpeakON connectors that provide very high-quality speaker

connections. These connectors outperform most binding posts, have very low resistance, and are

designed to reliably carry high current. These jacks are compatible with two-pole NL2 plugs or four

pole NL4 plugs. For best performance, make all speaker connections using twist-lock SpeakON

connectors. Binding posts are included to provide compatibility with existing speaker cables.

 Use 1+ and 1- for the channel 1 output in STEREO mode.

 Use 2+ and 2- for the channel 2 output in STEREO mode.

 Use M+ and M- for the output in MONO mode.

The 1&2 OUT NL4 jack provides access to channels 1 and 2. If an NL2 plug is inserted into this

jack, it will have access to channel 1 only. Use this jack with a two-pole cable to connect the

channel 1 output to the left speaker in a stereo system.

The 2 OUT NL4 jack provides access to channel 2 only. Use this jack with a two-pole cable to

connect the channel 2 output to the right speaker in a stereo system.

The BRIDGED MONO OUT NL4 jack provides a dedicated output for bridged mono applications.

Use this jack with a two-pole cable to connect the bridged output to a single speaker.

The 1&2 OUT NL4 jack can also be used for biamp applications. Use this jack with a four-pole

cable to connect both output channels to the high and low drivers in a biamped 2-way

speaker.

AHB2 Instruction Manual Rev G Page 11

5. Connect the AC Power Cord

The AC input connector accepts standard IEC input cables. Use a grounded cable that is

appropriate for your location. The AC input is auto ranging and may be used internationally without

changing any settings or fuse sizes. Fuses are located in a drawer at the top of the AC input

connector.

6. Turn on the Power

 Turn down the audio source before turning the unit on for the first time.

 Press the POWER button to turn the unit on or off.

Note: Audio will automatically mute on startup and shutdown to protect the speakers and

eliminate unwanted transients.

7. Check the Status Indicators

The amplifier has the following status indicators:

 POWER - Power-status indicator, On = Normal, Flashing = Fault

 CLIP (one per channel) - Audio-clip indicator, Flash = Clip, Off = Normal, On = Fault

 TEMP (one per channel) - Over-temperature/current indicator, Off = Normal, On = Fault

 MUTE (one per channel) - Channel-mute indicator, Off = Normal, On = PROTECT or MUTE

POWER - Power Status Indicator

 Off = Power is Off

 On = Normal Operation

 Flash = Fault Condition, Power Supply has Shut Down, PROTECT

CLIP - Audio Clipping Indicators

 Off = Normal

 Left or Right Flashing = Some Clipping is Occurring

 On = Fault Condition, Excessive Clipping has Occurred, PROTECT

TEMP - Over-Temperature Indicators

 Off = Normal

 Left or Right Flashing = Peak-Current Warning

 Left or Right On and POWER On = Over-Current Fault, PROTECT

 Left or Right On and POWER Flashing = Over-Temperature Fault, PROTECT

 Both On = Other Fault Conditions, PROTECT

MUTE - Audio Mute Indicators

 Off = Normal

 Both On During Start Up or Shut Down = Normal, Audio is Muted

 Both On = PROTECT or MUTE Mode, Audio is Muted

AHB2 Instruction Manual Rev G Page 12

Bidirectional 12 Volt Trigger

Benchmark has reinvented the 12 volt trigger by adding bidirectional signaling. The trigger

connection on the AHB2 can be used as an input, an output, or both. It is compatible with any

common 12 volt trigger input or output. The 12V TRIGGER can be used to turn the AHB2 power

amplifier on or off automatically in sequence with other audio system components. The AHB2 can

also turn other connected components on and off.

Linking Multiple Audio Components

Two or more AHB2 power amplifiers can be linked together with 12V TRIGGER CABLES, so that

all units power up and down together. This group of amplifiers can be linked to a group of

Benchmark DAC2 D/A converters. In such a system, any power button can be used to turn the

system on or off.

Trigger Wiring

The AHB2 has two bi-directional 12V TRIGGER I/O jacks. These jacks are 1/8" (3.5 mm) TRS

connectors. The tip is wired to the 12V TRIGGER I/O bus. The sleeve is wired to chassis ground.

There is no connection to the ring.

Trigger Cables

The AHB2 includes one 3-foot (1 m) 12V TRIGGER CABLE. This cable has a 1/8" (3.5 mm) TRS

connector at each end.

Automatic Power-Down Feature

40 Minute Timer

The AHB2 has an audio signal presence detector on each input channel. If no audio is detected on

either input for a period of 40 minutes, the AHB2 will automatically shut down to save energy. This

feature is required by law in many countries, and can contribute to significant energy savings.

This auto-off feature is programmable. Starting with the unit on, press and hold the POWER button

for 7 seconds to toggle this feature (press and hold the POWER button until the MUTE lights turn

off). This setting is stored in memory and is recalled when the unit is turned on.

Press and hold the power button for 1 second to view the status of this feature. If the timer is

enabled, the TEMP lights will turn on while the POWER button is pressed.

Timer Deactivates the 12V TRIGGER

When the AHB2 executes an automatic power down, it will pull the 12V TRIGGER low to shut

down any equipment attached to the trigger bus. The timer is only active when the system is

started using the POWER button on the front of the AHB2.

AHB2 Instruction Manual Rev G Page 13

No Warm-Up Required

Unlike most power amplifiers, the AHB2 reaches its full rated performance very quickly. Full rated

performance is reached in less than one minute. For this reason, there is absolutely no reason to

keep the AHB2 powered on when not in use. The feed-forward error correction circuits in the

AHB2 keep it very stable over a wide range of operating temperatures.

AUTO-ON Feature

The AHB2 has a programmable AUTO-ON feature. When this feature is enabled, the AHB2 will

automatically turn on whenever AC power is applied. The 40-minute timer is automatically disabled

when this feature is activated. The POWER button will act as a MUTE button when this feature is

enabled. When AUTO-ON is enabled, the POWER button will toggle MUTE on and off. In MUTE

MODE, the POWER light and MUTE lights are on, and all other lights are off.

To enable the AUTO-ON feature, start with the unit off. Then press and hold the POWER button for

3 seconds. The CLIP lights will turn on at the end of 3 seconds. Release the POWER button as soon

as the CLIP lights turn on. Press the POWER button to verify that the AUTO-ON mode is enabled. If

it is enabled, the POWER button will toggle MUTE on and off.

To disable the AUTO-ON feature, start with the unit on. Then press and hold the POWER button for

3 seconds. The clip lights will turn off at the end of 3 seconds. Release the Power button as soon as

the CLIP lights turn off. The unit should now turn off (verifying that the feature has been disabled).

AHB2 Instruction Manual Rev G Page 14

Rack Mounting

The AHB2 is available in a rack-mount version. The AHB2 is magnetically shielded, and will not

interfere with sensitive equipment mounted above or below the AHB2.

Rack Mount Option

Rack Mounting Instructions

The AHB2 runs very cool when idle and runs very cool under most load conditions. However, it can

produce significant heat when heavily loaded. Make sure the rack is adequately ventilated. Make

sure the side heat sinks have an unobstructed air flow.

Some power amplifiers can emit very strong magnetic fields. These amplifiers should be kept at

least two rack units above or below the AHB2. Magnetic interference can produce hum problems.

If the AHB2 is mounted directly above another piece of equipment, it may be necessary to remove

the feet from the AHB2. Save the feet for future needs. Replacement feet may be purchased

directly from Benchmark or through most authorized Benchmark dealers.

AHB2 Instruction Manual Rev G Page 15

Fault Protection Circuitry

The AHB2 is designed to detect overloads, short circuits, clipping, excessive temperatures, high

DC offsets, and low AC input voltages. When a potentially-damaging fault occurs, the amplifier

enters a special "PROTECT" mode to prevent damage.

The amplifier has a comprehensive set of fault-detection circuits that will activate the PROTECT

mode to protect against damage to the amplifier or speakers.

Fault-Detection Circuits

 Temperature sensor on each output channel

 Temperature sensor on main power supply

 Current sensor on each output channel

 Voltage clip detector on each output channel

 DC offset detector on each output channel

 SOA (safe operating area) detector on each output channel

 Load sensor on main power supply

 Fault sensors on all power supplies

 AC line under-voltage fault sensor on AC input

PROTECT Mode (Both MUTE Lights On)

In PROTECT mode, both MUTE lights are on. The CLIP, TEMP, and POWER lights identify

the cause of the fault.

The PROTECT mode is only activated when a potentially damaging fault condition has occurred. To

protect against damage, both audio outputs are muted. In some fault conditions, all high-power

circuits are shut off. A small auxiliary power supply remains active so that the error condition can

be displayed on the front panel.

If the POWER light is flashing, all high-power circuits have been shut down as an additional

precaution.

If a fault has triggered the PROTECT mode, the amplifier must be turned off before

normal operation can resume. Identify and correct the cause of the fault before

restarting the amplifier.

AHB2 Instruction Manual Rev G Page 16

PROTECT Mode - Fault Codes

The following table provides a summary of all possible status display conditions. The MUTE lights

will turn on and stay on whenever a fault condition has triggered the PROTECT mode.

If a fault has occurred, power must be turned off before normal operation can resume.

Identify and correct the cause of the fault before restarting the amplifier.

POWER

CLIP

TEMP

MUTE

TEMP

CLIP

Status

OFF

Power off, or no AC input

ON

AC Startup - lamp test

ON

OFF

ON

OFF

Mute on - startup or shutdown

ON

OFF

Normal operation, no errors

ON

FLASH

OFF

Channel 1 - Clipping

ON

OFF

FLASH

Channel 2 - Clipping

ON

OFF

FLASH

OFF

Channel 1 - Current warning

ON

OFF

FLASH

OFF

Channel 2 - Current warning

FLASH

ON

OFF

ON

OFF

Channel 1 - Clipping Fault

FLASH

OFF

ON

OFF

ON

Channel 2 - Clipping Fault

FLASH

ON

OFF

ON

OFF

ON

Chan 1&2 - Clipping Fault

ON

OFF

ON

OFF

Channel 1 - Over-Current Fault

ON

OFF

ON

OFF

Channel 2 - Over-Current Fault

ON

OFF

ON

OFF

Chan 1&2 - Over-Current Fault

FLASH

OFF

ON

OFF

Channel 1 - Over Temperature

FLASH

OFF

ON

OFF

Channel 2 - Over Temperature

FLASH

ON

Power Supply Fault, Loss of AC

ON

SOA Fault

AHB2 Instruction Manual Rev G Page 17

Clipping Fault

The input and output audio signals are compared to determine when clipping is occurring.

Occasional clipping will cause the CLIP lights to flash and will not trigger this fault. However, if a

severe overdrive condition occurs, this fault is triggered to prevent damage to speakers. This fault

indicates that the amplifier has been driven very hard into voltage clipping. Both channels are

muted to protect the amplifier and speakers. A power reset will be required.

Fault Display:

 POWER light is Flashing

 Both MUTE lights are On

 One or both CLIP lights are On

 Both TEMP lights are Off

Typical Causes:

 The sensitivity switch may be set too high

 Output of preamplifier or DAC is too high

Required Actions:

 Check the position of the SENSITIVITY switch

 Move the sensitivity switch down one or two positions if necessary

 Turn down the audio source

 Restart the amplifier

AHB2 Instruction Manual Rev G Page 18

Over-Current Fault

The output current of each channel is constantly monitored. If either channel exceeds a safe output

current, this fault is triggered and both channels are muted to protect the amplifier and speakers. A

power reset will be required.

Fault Display:

 POWER light is On

 Both MUTE lights are On

 Both CLIP lights are Off

 One or both TEMP lights are On

Typical Causes:

 The load impedance of the speakers may be too low

 Speaker cables may be shorted

Required Actions:

 Check for shorted speaker cables

 Make sure the nominal Stereo load impedance is 3 Ohms or higher

 Make sure the nominal Bridged Mono load impedance is 6 Ohms or higher

 Turn down the audio source

 Restart the amplifier

Speaker impedance always varies with frequency. Speaker impedance may be much lower than the

rated "nominal" impedance at certain frequencies. The over-current fault detection circuits prevent

potential damage that can be caused by driving very high signal levels into very low impedances.

In STEREO mode, at full output, the current limit can be reached if the load impedance dips below

about 1.3 Ohms. In MONO mode, at full output, the current limit can be reached if the load

impedance dips below about 2.6 Ohms.

AHB2 Instruction Manual Rev G Page 19

SOA Fault

The SOA (Safe Operating Area) of the output power devices is constantly monitored. If this safe

operating area is violated, both channels are muted to protect the amplifier and speakers. A power

reset will be required.

Fault Display:

 POWER light is On

 Both MUTE lights are On

 Both CLIP lights are On

 Both TEMP lights are On

Typical Causes:

 The load impedance of the speakers may be too low

 Speaker cables may be shorted

 Amplifier has been overloaded with a high-amplitude test tone

Required Actions:

 Check for shorted speaker cables

 Make sure the nominal STEREO load impedance is 3 Ohms or higher

 Make sure the nominal Bridged MONO load impedance is 6 Ohms or higher

 Turn down the audio source

 Restart the amplifier

AHB2 Instruction Manual Rev G Page 20

Over-Temperature Fault

The temperature of the left and right heat sinks are constantly monitored. If either heat sink

reaches the maximum allowable temperature, both channels are muted to protect the amplifier and

speakers. All high-power subsystems are shut down to accelerate the cooling process. One or both

heat sinks will be very hot. After the unit cools, a power reset will be required.

Fault Display:

 POWER light is Flashing

 Both MUTE lights are On

 Both CLIP lights are Off

 One TEMP light is On

Typical Causes:

 The load impedance of the speakers may be too low

 Heat sinks may be obstructed

 Amplifier has been overloaded with a high-amplitude test tone

Required Actions:

 Make sure the nominal STEREO load impedance is 3 Ohms or higher

 Make sure the nominal Bridged MONO load impedance is 6 Ohms or higher

 Maintain adequate clearance around heat sinks

 Allow time for the amplifier to cool

 Turn down the audio source

 Restart the amplifier

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