Benchmark AHB2 User manual

Benchmark AHB2
Instruction Manual
Reference Stereo Power Amplifier
100W/channel into 8-Ohms
380W bridged mono into 8-Ohms

AHB2 Instruction Manual Rev F 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
45 Minute Timer 12
Activates the 12V TRIGGER 12
No Warm-Up Required 12
Rack Mounting 13
Rack Mount Option 13
Rack Mounting Instructions 13
Fault Protection Circuitry 14
Fault-Detection Circuits 14
PROTECT Mode (Both MUTE Lights On) 14
PROTECT Mode - Fault Codes 15
Clipping Fault 16
Over-Current Fault 17
SOA Fault 18
Over-Temperature Fault 19
Power Supply Fault 20
Specifications 21
Rated Output Power 21
Output Current 21
Frequency Response 21
Signal to Noise Ratio 21
Distortion 21
Crosstalk 22
Input Sensitivity 22
Input Impedance 22
Input CMRR 22
Trigger I/O 22
Damping Factor 22
Environmental 22
Mechanical Drawings 23
Dimensions 23
Rack-Mount Dimensions 24
Performance Plots 25
Regulatory Compliance 30
FCC and RoHS Compliance Statements 30
FCC Notice (U.S. Only) 30
RoHS Compliant Information 30
CE Certificate of Conformity 31
Safety 32
Warranty Information 33
Benchmark 1-Year Warranty 33
Benchmark Extended Warranty Options 34
Notes on Warranty Repairs 34
Consignes de Sécurité Importantes
(French) 35
Symboles de Sécurité 35
Mesures de Sécurité 36
Appendix 38
A Radical Approach to Power Amplification
38

AHB2 Instruction Manual Rev F 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 F 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 F 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 F 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 F Page 7
Front Panel
Front Panel Layout
Left to Right:
Power Switch
Power Indicator
Channel 1 Clip Indicator
Channel 1 Temperature Indicator
Channel 1 Mute Indicator
Channel 2 Mute Indicator
Channel 2 Temperature Indicator
Channel 2 Clip Indicator

AHB2 Instruction Manual Rev F 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 F 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 F 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 F 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.
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 indicator, Off = Normal, On = Fault
MUTE (one per channel) - Channel-mute indicator, Off = Normal, On = PROTECT
POWER - Power Status Indicator
Off = Power is Off
On = Normal Operation
Flash = Fault Condition, Power Supply has Shut Down
CLIP - Audio Clipping Indicators
Off = Normal
Occasional Flash = Some Clipping is Occurring
On = Fault Condition, Excessive Clipping has Occurred
TEMP - Over-Temperature Indicators
Off = Normal
Left On = Fault - Left Channel Overheated
Right On = Fault - Right Channel Overheated
Both On = Other Fault Conditions
MUTE - Audio Mute Indicators
Off = Normal
Both On During Start Up or Shut Down = Normal, Audio is Muted
Both On = PROTECT Mode, a Fault has Occurred, Audio is Muted
Note: Audio will automatically mute on startup and shutdown to protect the speakers and eliminate
unwanted transients.

AHB2 Instruction Manual Rev F 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
45 Minute Timer
The AHB2 has an audio signal presence detector on each input channel. If no audio is detected for
a period of 45 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.
Activates 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.
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.

AHB2 Instruction Manual Rev F Page 13
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 F Page 14
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 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 for at least
10 seconds before normal operation can resume. Identify and correct the cause of the
fault before restarting the amplifier.

AHB2 Instruction Manual Rev F Page 15
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 for at least 10 seconds before normal
operation can resume. Identify and correct the cause of the fault before restarting the
amplifier.
POWER
CLIP
TEMP
MUTE
MUTE
TEMP
CLIP
Status
OFF
OFF
OFF
OFF
OFF
OFF
OFF
Power off, or no AC input
ON
ON
ON
ON
ON
ON
ON
AC Startup - lamp test
ON
OFF
OFF
ON
ON
OFF
OFF
Mute on - startup or shutdown
ON
OFF
OFF
OFF
OFF
OFF
OFF
Normal operation, no errors
ON
FLASH
OFF
OFF
OFF
OFF
OFF
Channel 1 clipping
ON
OFF
OFF
OFF
OFF
OFF
FLASH
Channel 2 clipping
FLASH
ON
OFF
ON
ON
OFF
OFF
Channel 1 - Clipping Fault
FLASH
OFF
OFF
ON
ON
OFF
ON
Channel 2 - Clipping Fault
FLASH
ON
OFF
ON
ON
OFF
ON
Chan. 1&2 - Clipping Fault
ON
ON
OFF
ON
ON
OFF
OFF
Channel 1 - Over-Current Fault
ON
OFF
OFF
ON
ON
OFF
ON
Channel 2 - Over-Current Fault
ON
ON
OFF
ON
ON
OFF
ON
Chan. 1&2 - Over-Current Fault
FLASH
OFF
ON
ON
ON
OFF
OFF
Channel 1 over temperature
FLASH
OFF
OFF
ON
ON
ON
OFF
Channel 2 over temperature
FLASH
ON
ON
ON
ON
ON
ON
Power Supply fault or loss of AC
ON
ON
ON
ON
ON
ON
ON
SOA Fault

AHB2 Instruction Manual Rev F Page 16
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
One or both CLIP lights are On
Both TEMP lights are Off
Both MUTE lights are On
Typical Causes:
The sensitivity switch may be set too high
Speaker cables may be shorted
Required Actions:
Check for shorted speaker cables
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 F Page 17
Over-Current Fault
The output current of each channel is constantly monitored. If either channel reaches an output
current of 18 Amperes, 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 TEMP lights are Off
Both MUTE lights are On
One or both CLIP 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 18 Amp limit can be reached if the load impedance dips below
about 2 Ohms. In MONO mode, at full output, the 18 Ampere limit can be reached if the load
impedance dips below about 4 Ohms.

AHB2 Instruction Manual Rev F Page 18
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 CLIP lights are On
Both TEMP lights are On
Both MUTE 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 F Page 19
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 CLIP lights are Off
One TEMP light is On
Both MUTE lights are 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

AHB2 Instruction Manual Rev F Page 20
Power Supply Fault
The power supply has a number of sensors that monitor voltage, current, and temperature. If any
parameter exceeds safe limits, both channels are muted to protect the amplifier and speakers. This
fault may indicate that the AC power has been interrupted. It may also indicate that the power
supply has overheated. It may also indicate the detection of an overload on one of the power
supply rails. It may also indicate a fault condition in the power supply system. All high-power
subsystems are shut down. A power reset will be required.
Fault Display:
POWER light is Flashing
Both CLIP lights are On
Both TEMP lights are On
Both MUTE lights are On
This fault display will only persist if AC is present.
In the event of a total loss of AC power, this error display will stay on for about 15-30
seconds and then all lights will turn off.
Typical Causes:
The AC line voltage may have dropped below allowable limits for a few seconds
AC power has been lost (if all lights turn off after about 15-30 seconds)
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:
Check the AC power source
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
If unit is hot, allow time to cool
Turn down the audio source
Restart the amplifier