User`s manual | Cambridge Audio 651A Stereo Amplifier User Manual

Your music + our passion
Integrated amplifier
User’s manual
Introduction .............................................................................................. 2
Thank you for purchasing this 651A Amplifier. We are confident that you
will enjoy many years of listening pleasure from it. Like all Cambridge
Audio products the 651A adheres to our three core principles – stunning
performance, ease of use and incredible value.
Important safety instructions.................................................................. 3
Limited warranty ...................................................................................... 4
Rear panel connections .......................................................................... 5
Connections ............................................................................................. 6
Front panel controls................................................................................. 9
Apple device compatibility....................................................................... 10
Remote control......................................................................................... 10
Custom installation (C.I.) use .................................................................. 11
CAP5: Five-way protection system .......................................................... 11
Technical specifications........................................................................... 12
Troubleshooting........................................................................................ 12
Developed as part of our on-going research and development regime,
including extensive listening tests, we have incorporated many subtle
tweaks and improvements to our circuits, components and layouts in the
pursuit of our passion for sound quality.
Very high quality components are used throughout including an Alps
volume pot, polypropylene signal capacitors, gold-plated speaker outputs,
custom-made electrolytic capacitors in critical positions and several new
circuit tweaks. The amplifier is a completely discrete bipolar transistorbased circuit honed over many years powered from a bespoke
audiophile-grade toroidal transformer.
Also featured is an environmentally friendly low power (<1W) standby
circuit. This circuit completely powers down the amplifier circuits in
Standby mode yet is itself totally isolated when the amplifier is on, thus
having no effect on sound quality.
All this proprietary engineering is housed within our low resonance,
acoustically damped chassis. An Azur Navigator remote control is also
provided, giving full remote control of your amplifier in an attractive and
easy to use handset.
Remember your 651A can only be as good as the system it is connected
to. Please do not compromise on your source equipment, speakers or
Naturally we particularly recommend source components from the
Cambridge Audio Azur range which includes CD players, BD/DVD/SACD/
DVD players, iPod docks and Network players which have been designed
to the same exacting standards as this amplifier.
Your dealer can also supply excellent quality Cambridge Audio
interconnects to ensure your system realises its full potential.
Thanks for taking the time to read this manual, we do recommend you
keep it for future reference.
Matthew Bramble
Cambridge Audio Technical Director
and the 651A design team
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This guide is designed to make installing and using this product
as easy as possible. Information in this document has been
carefully checked for accuracy at the time of printing; however,
Cambridge Audio's policy is one of continuous improvement,
therefore design and specifications are subject to change
without prior notice.
This document contains proprietary information protected by
copyright. All rights are reserved. No part of this manual may be
reproduced by any mechanical, electronic or other means, in any
form, without prior written permission of the manufacturer. All
trademarks and registered trademarks are the property of their
respective owners.
© Copyright Cambridge Audio Ltd 2011
Important safety instructions
For your own safety please read the following important safety
instructions carefully before attempting to connect this unit to the mains
power supply. They will also enable you to get the best performance from
and prolong the life of the unit:
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
The lightning flash with the arrowhead symbol within an equilateral
triangle is intended to alert the user to the presence of un-insulated
‘dangerous voltage’ within the product’s enclosure that may be of
sufficient magnitude to constitute a risk of electric shock to persons.
The exclamation point within an equilateral triangle is intended to alert
the user to the presence of important operating and maintenance
instructions in the service literature relevant to this appliance.
6. Clean only with a dry cloth.
7. Do not block any ventilation openings. Install in accordance with the
manufacturer's instructions.
8. Do not install near any heat sources such as radiators, heat registers,
stoves, or other apparatus (including other amplifiers) that produce
9. Do not defeat the safety purpose of the polarized or grounding-type
plug. A polarized plug has two blades with one wider than the other.
A grounding-type plug has two blades and a third grounding prong.
The wide blade or the third prong are provided for your safety. If the
provided plug does not fit into your outlet, consult an electrician for
replacement of the obsolete outlet.
10. Protect the power cord from being walked on or pinched, particularly
at plugs, convenience receptacles and the point where they exit from
the apparatus.
11. Only use attachments/accessories specified by the manufacturer.
12. Use with only the cart, stand, tripod, bracket, or table
specified by the manufacturer, or sold with the apparatus.
When a cart is used, use caution when moving the cart/
apparatus combination to avoid injury from tip-over.
13. Unplug this apparatus during lightning storms or when unused for
long periods of time.
14. Refer all servicing to qualified service personnel. Servicing is required
when the apparatus has been damaged in any way, such as the
power-supply cord or plug having been damaged, liquid has been
spilled or objects have fallen into the apparatus, the apparatus has
been exposed to rain or moisture, does not operate normally, or has
been dropped.
WEEE symbol
The crossed-out wheeled bin is the European Union symbol for
indicating separate collection for electrical and electronic
equipment. This product contains electrical and electronic
equipment which should be reused, recycled or recovered and
should not be disposed of with unsorted regular waste. Please return the
unit or contact the authorised dealer from whom you purchased this
product for more information.
CE mark
This product complies with European Low Voltage
(2006/95/EC), Electromagnetic Compatibility (2004/108/EC)
and Environmentally-friendly design of Energy-related Products
(2009/125/EC) Directives when used and installed according to this
instruction manual. For continued compliance only Cambridge Audio
accessories should be used with this product and servicing must be
referred to qualified service personnel.
C-Tick mark
This product meets the Australian Communications Authority’s
Radio communications and EMC requirements.
Gost-R stamp
This product meets Russian electronic safety approvals.
FCC regulations
– To reduce the risk of fire or electric shock, do not expose this unit to
rain or moisture.
– Batteries (battery pack or batteries installed) shall not be exposed to
excessive heat such as sunshine, fire or the like.
The unit is of Class 1 construction and must be connected to a mains
socket outlet with a protective earthing connection.
The unit must be installed in a manner that makes disconnection of the
mains plug from the mains socket outlet (or appliance connector from
the rear of the unit) possible. Where the mains plug is used as the
disconnect device, the disconnect device shall remain readily operable.
Only use the mains cord supplied with this unit.
Please ensure there is ample ventilation. We recommend that you do not
place the unit in an enclosed space; if you wish to place the unit on a
shelf, use the top shelf to allow maximum ventilation. Do not put any
objects on top of this unit. Do not situate it on a rug or other soft surface
and do not obstruct any air inlets or outlet grilles. Do not cover the
ventilation grilles with items such as newspapers, tablecloths, curtains,
This equipment has been tested and found to comply with the
limits for a Class B digital device, pursuant to Part 15 of the
FCC Rules. These limits are designed to provide reasonable
protection against harmful interference in a residential installation. This
equipment generates, uses and can radiate radio frequency energy and,
if not installed and used in accordance with the instructions, may cause
harmful interference to radio communications. However, there is no
guarantee that interference will not occur in a particular installation.
If this equipment does cause harmful interference to radio or television
reception, which can be determined by turning the equipment off and on,
the user is encouraged to try to correct the interference by one or more
of the following measures:
– Re-orient or relocate the receiving antenna.
– Increase the separation between the equipment and receiver.
– Connect the equipment into an outlet on a circuit different from that to
which the receiver is connected.
– Consult the dealer or an experienced radio/TV technician for help.
This unit must not be used near water or exposed to dripping or splashing
water or other liquids. No objects filled with liquid, such as vases, shall be
placed on the unit.
Limited warranty
IMPORTANT – The unit will become hot when in use. Do not place anything
on top of the unit. Do not place in an enclosed area such as a bookcase
or in a cabinet without sufficient ventilation.
Ensure that small objects do not fall through any ventilation grille. If this
happens, switch off immediately, disconnect from the mains supply and
contact your dealer for advice.
Choose the installation location carefully. Avoid placing it in direct sunlight
or close to a source of heat. No naked flame sources, such as lighted
candles, should be placed on the unit. Also avoid locations subject to
vibration and excessive dust, cold or moisture. The unit can be used in a
moderate climate.
This unit must be installed on a sturdy, level surface. Do not place in a
sealed area such as a bookcase or in a cabinet. Do not place the unit on
an unstable surface or shelf. The unit may fall, causing serious injury to
a child or adult as well as serious damage to the product. Do not place
other equipment on top of the unit.
Due to stray magnetic fields, turntables or CRT TVs should not be located
nearby due to possible interference.
Electronic audio components have a running in period of around a week
(if used several hours per day). This will allow the new components to
settle down and the sonic properties will improve over this time.
Power sources
The unit should be operated only from the type of power source indicated
on the marking label. If you are not sure of the type of power-supply to
your home, consult your product dealer or local power company.
This unit can be left in Standby mode when not in use and will draw <1W
in this state. To turn the unit off, switch off at the rear panel. If you do not
intend to use this unit for a long period of time, unplug it from the mains
Do not overload wall outlets or extension cords as this can result in a risk
of fire or electric shock. Overloaded AC outlets, extension cords, frayed
power cords, damaged or cracked wire insulation and broken plugs are
dangerous. They may result in a shock or fire hazard.
Cambridge Audio warrants this product to be free from defects in
materials and workmanship (subject to the terms set forth below).
Cambridge Audio will repair or replace (at Cambridge Audio's option) this
product or any defective parts in this product. Warranty periods may vary
from country to country. If in doubt consult your dealer and ensure that
you retain proof of purchase.
To obtain warranty service, please contact the Cambridge Audio
authorised dealer from which you purchased this product. If your dealer
is not equipped to perform the repair of your Cambridge Audio product,
it can be returned by your dealer to Cambridge Audio or an authorised
Cambridge Audio service agent. You will need to ship this product in either
its original packaging or packaging affording an equal degree of
Proof of purchase in the form of a bill of sale or receipted invoice, which
is evidence that this product is within the warranty period, must be
presented to obtain warranty service.
This Warranty is invalid if (a) the factory-applied serial number has been
altered or removed from this product or (b) this product was not
purchased from a Cambridge Audio authorised dealer. You may call
Cambridge Audio or your local country Cambridge Audio distributor to
confirm that you have an unaltered serial number and/or you made a
purchase from a Cambridge Audio authorised dealer.
This Warranty does not cover cosmetic damage or damage due to acts of
God, accident, misuse, abuse, negligence, commercial use, or
modification of, or to any part of, the product. This Warranty does not
cover damage due to improper operation, maintenance or installation, or
attempted repair by anyone other than Cambridge Audio or a Cambridge
Audio dealer, or authorised service agent which is authorised to do
Cambridge Audio warranty work. Any unauthorised repairs will void this
Warranty. This Warranty does not cover products sold AS IS or WITH ALL
Be sure to insert each power cord securely. To prevent hum and noise, do
not bundle the interconnect leads with the power cord or speaker leads.
Some countries and US states do not allow the exclusion or limitation of
incidental or consequential damages or implied warranties so the above
exclusions may not apply to you. This Warranty gives you specific legal
rights, and you may have other statutory rights, which vary from state to
state or country to country.
For any service, in or out of warranty, please contact your dealer.
To clean the unit, wipe its case with a dry, lint-free cloth. Do not use any
cleaning fluids containing alcohol, ammonia or abrasives. Do not spray an
aerosol at or near the unit.
Battery disposal
Please dispose of any discharged batteries according to local
environmental/electronic waste disposal guidelines.
Before making any connections to loudspeakers, make sure all power is
turned off and only use suitable interconnects.
These units are not user serviceable. Never attempt to repair,
disassemble or reconstruct the unit if there seems to be a problem.
A serious electric shock could result if this precautionary measure is
ignored. In the event of a problem or failure, please contact your dealer.
Plug-fitting Instructions (UK only)
The cord supplied with this appliance is factory-fitted with a UK mains plug fitted with
a 5-amp fuse inside. If it is necessary to change the fuse, it is important that a
5-amp fuse is used. If the plug needs to be changed because it is not suitable for
your socket, or becomes damaged, it should be cut off and an appropriate plug
fitted following the wiring instructions below. The plug must then be disposed of
safely, as insertion into a mains socket is likely to cause an electrical hazard. Should
it be necessary to fit a 3-pin BS mains plug to the power cord, the wires should be
fitted as shown in this diagram. The colours of the wires in the mains lead of this
appliance may not correspond with the coloured markings identifying the terminals
in your plug. Connect them as follows:
The wire which is coloured BLUE must be
connected to the terminal which is marked with
the letter ‘N’ or coloured BLACK.
The wire which is coloured BROWN must be
connected to the terminal which is marked with
the letter ‘L’ or coloured RED.
The wire which is coloured GREEN/YELLOW must
be connected to the terminal which is marked
with the letter ‘E’ or coloured GREEN.
If a standard 13-amp (BS 1363) plug is used, a 5-amp fuse must be fitted or, if any
other type of plug is used, a 5-amp fuse must be fitted, either in the plug or adaptor,
or on the distribution board.
Rear panel connections
Power On/Off
Switches the unit on and off. This switch is a master on/off control that
completely powers down the unit.
AC power socket
Once you have completed all connections to the amplifier, plug the
AC power cable into an appropriate mains socket and turn the unit on.
Your amplifier is now ready for use.
Loudspeaker terminals
Two sets of loudspeaker terminals are available, A (main loudspeaker
terminals, top row) and B (secondary switchable loudspeaker terminals,
bottom row). Connect the wires from your left channel loudspeaker to the
LEFT positive and negative terminals, and the wires from the right
channel loudspeaker to the RIGHT positive and negative terminals.
In each case, the red terminal is the positive output and the black
terminal is the negative output.
Care should be taken to ensure no stray strands of wire are shorting
speaker outputs together. Please ensure that the loudspeaker terminals
have been tightened adequately to provide a good electrical connection.
It is possible for the sound quality to be affected if the screw terminals are
The use of A and B speakers affords you an easy and inexpensive way to
create a simple multi-room system.
Note: When using two pairs of speakers, use speakers with a minimum
nominal impedance of 8 ohms.
IR (Infrared) Emitter In
Allows modulated IR commands from multi-room systems or IR repeater
systems to be received by the amplifier. Commands received here are not
looped out of the Control Bus. Refer to the ‘Custom Installation’ section
for more information.
Control Bus
In Allows un-modulated commands from multi-room systems or other
components to be received by the unit.
These outputs can be used to connect to the inputs on an external power
amplifier or an active subwoofer, etc.
Record Out 1/2
These two identical output sockets can be connected to a tape deck or
to the analogue Record In sockets on a MiniDisc or CD recorder etc.
These inputs are suitable for any 'line level' source equipment such as
BD/DVD players, DAB or FM/AM tuners, CD players, Netwok Players, iPod
docks, MP3 players, etc.
Note: These inputs are for analogue audio signals only. They should not
be connected to the digital output of a CD player or any other digital
Connecting a turntable
If it is desired to connect a turntable without a built-in phono stage, an
external phono stage such as our 551P or 651P models should be used.
Contact your Cambridge Audio dealer for more details.
Note: A very few turntables have built-in phono stages, in which case it is
not necessary to use a separate phono stage amplifier. If you’re unsure,
please consult your turntable user manual.
USB interface
A USB B type socket is fitted to the 651A to enable the playback of audio
from a personal computer running either Microsoft Windows or Apple Mac
OS X operating systems. Some builds of Linux are also suitable.
Note: Always use a certified cable for USB Audio preferably one that
displays an official mark. USB cable connections longer than 3m may
result in inconsistent audio performance.
Always turn the Volume to minimum, or turn the
651A off before plugging/unplugging cables to the
USB input or whilst booting up your PC/Mac.
Out Loop out for control bus commands to another unit.
This output can be used to connect to a subwoofer, if desired.
Note: Before making any connections, make sure that the 651A is turned
When designing our amplifiers we include features that allow you to
connect your system in various ways. The inclusion of features such as
Pre-Out and Speaker B connections mean that you can flexibly configure
your system depending on your requirements.
Basic connection
The diagram below shows the basic connection of your amplifier to a
CD player and a pair of loudspeakers.
Red Black Black Red
CD player
Record out connection
The diagram below shows how to connect the amplifier to a tape recorder
or other component with a record function. Please note that either of the
record outputs can be used (as they are both the same signal in parallel).
Tape/MD player
Speaker B connections
The Speaker B connections on the back of the amplifier allow for a second
set of speakers to be used (i.e. speakers located in another room).
The Speaker A/B button on the remote control allows the two sets of
speakers to be toggled on and off. Refer to the Remote Control section of
this manual for more information on the Speaker A/B operation.
Set either A or B, or both A and B may be selected for use.
Note: When using two pairs of speakers, use speakers with a minimum
nominal impedance of 8 ohms each.
Speaker A
Main Room
Speaker B
Room Two
Pre-Out connections
The Pre-Out sockets are for connecting to the input sockets of a power
amplifier, or active subwoofer. The diagram below shows how to connect
the amplifier to an active subwoofer via either a mono Sub in or Stereo
Line In inputs on the subwoofer.
Connections cont.
USB audio connections
The diagram below shows how to connect the amplifier to a personal
computer via USB connection. Connect a USB ‘B-A’ type lead from the
651A USB input to one of the USB ports on the PC.
The 651A is USB 1.1 (Full-speed) USB port compatible and support USB
Audio 1.0, which works with nearly all common operating systems
(Windows XP, Vista or 7 and Mac OS X 10.5 or higher) and computer types
without drivers and allows 16 bit audio at 32kHz, 44.1kHz and 48kHz to
be received.
The 651A also works with most builds of Linux using the native Audio 1.0
driver. Because Linux builds vary according to their creator’s choice of
software components including drivers, it is not possible to guarantee
operation and Audio drivers may need to be loaded.
‘Class drivers’ as they are called for generic support of Audio Class 1.0
device may be available from the Linux community as we do not supply
these drivers.
Note: Always use a certified cable for USB Audio preferably one that
displays an official mark. USB cable connections longer than 3m may
result in inconsistent audio performance.
Always turn the Volume to minimum, or turn the
651A off before plugging/unplugging cables to the
USB input or whilst booting up your PC/Mac.
Front panel controls
Switches the unit between Standby mode (indicated by dim power LED)
and On (indicated by bright power LED). Standby is an eco power mode
where the power consumption is less than one watt. The unit is designed
so that it can be left safely in Standby mode when not in use.
Infrared sensor
Receives IR commands from the supplied Azur remote control. A clear,
unobstructed line of sight between the remote control and the sensor is
LED flashes to indicate activation of CAP5 protection system. Refer to the
CAP5 section of this manual for more information.
Speaker LEDs
Indicator shows the speaker terminals that are selected. The speaker
terminals selected are changed with the remote control.
This control gives the audio signal a more direct path to the power
amplifier stage of your amplifier, bypassing the bass and treble control
circuits for the purest possible sound quality.
Use to increase or decrease the level of the sound from the outputs of the
amplifier. This control affects the level of the loudspeaker output, the preamp output and the headphone output. It does not affect the Rec Out
connections. It is advisable to turn the Volume control fully anti-clockwise
before switching the amplifier on.
Allows for the connection of headphones with a ¼" jack plug connector.
Headphones with an impedance of between 32 and 600 ohms are
recommended. When the headphones are connected, the output to the
loudspeakers is switched off (both speakers A and B).
Bass and Treble
These controls allow subtle adjustments to the tonal balance of the
sound. In the central position these controls have no effect. They only
modify the sound through your loudspeakers and the Pre-Out sockets,
and do not affect the signals sent through the Rec Out connections.
With well-produced source material and a good system, the tone controls
are unnecessary and can be switched out by the ‘Direct’ switch. If the
musical recording is of poor quality or other factors are affecting the
sound quality, it may be necessary to adjust the tone controls to
This control allows you to adjust the relative output levels of the left and
right channels. In the central position the output from each channel is
equal. This control only modifies the sound through your loudspeakers
and the Pre-Out sockets – it does not affect the signals sent through the
Rec Out connections.
S1/MP3 input
This source input allows you to connect a portable audio device such as
an MP3 player, plugged into either the rear panel ‘S1’ Phono/RCA input
pair or the front panel 3.5mm stereo-jack input (labelled ‘MP3 In’).
Press the S1 button on the front panel to select the input, or insert a
device into the front panel socket which automatically selects the input
and overrides the rear Phono/RCA sockets.
Note: Whilst plugging a device into the front panel automatically selects
the MP3 input, any other input can still be selected once this has been
done. As a result you may, if desired, leave a device permanently plugged
into the front panel.
S2-S5 Source inputs
Push the appropriate input selection button to select the source
component that you wish to listen to. The signal selected is also fed to the
Rec Out sockets so that it may be recorded. The input should not be
changed whilst recording.
This source input allows connection of a personal computer via USB.
Remote control
The 651A is supplied with an Azur Navigator remote control that operates
both this amplifier and Cambridge Audio Azur range CD players. Insert
the supplied AAA batteries to activate. The functions relevant to the
amplifier are as follows:
Press the relevant button to play, stop or pause the CD.
Switches the amplifier between On
and Standby mode.
Right Skip Press to skip forward by one track on the CD.
Left Skip Press to skip backward by one track on the CD.
Cycles through the amplifier’s source
Press and hold to scan within the selected track. Hold down for seven
seconds to increase scan speed. Press the right button to fast forward,
the left button to rewind.
Mutes the audio on the amplifier. The
mute mode is indicated by the
source LED flashing. Press again to
cancel mute.
Note: The speaker outputs, Pre-out
and headphone outputs will all
be muted. The Record outputs are
Used with CDs that support CD-text. In stop mode, press to toggle
between album name and total time on the display. During playback,
press to toggle between track name and track time.
Alters the brightness of the display backlight. There are three levels of
brightness: Bright, Dim and Off.
Speaker A/B
Toggles the speaker terminals on the
rear panel to output speaker A only,
speaker B only, both speakers A and
B or no speaker output at all. The
speaker indicators on the front panel
of the amplifier show which speaker
terminals are selected.
Note: The ‘no speaker output’ option
allows the 651A to be used as a
preamplifier only.
Volume controls
Increases or decreases the volume
of the amplifier output.
The six source select buttons are
used to directly select the input
source to the amplifier.
Read the ‘Operating Instructions’ section of the Azur CD manual for
information on the functions of these buttons.
Note: these buttons will function only when the display backlight is in
either ‘Bright’ or ‘Dim’ modes. If it is set to ‘Off’, the functions do not
Apple device compatibility
The Azur 651AC Navigator remote control can control the basic functions
of Apple devices such as Apple TV and Apple’s iPod/iPhone/iPad range
when docked in a Cambridge Audio or Apple dock.
Press and hold the source button that corresponds to the input that the
Apple product is connected to whilst also pressing one of the buttons
The functions are slightly different depending on the Apple product.
The remaining buttons are reserved
for use with Cambridge Audio Azur
CD players.
Stop or Menu
Press briefly to skip or navigate left or right. Press and hold to
scan forwards or backwards.
Used to control volume and/or navigate menus.
Opens and closes the disc tray
Numerical track select
Press the number of the desired
track. The track will then play
automatically from the start of the
Track select
To select a track number greater
than nine, press -/-- followed by the
track number. Playback of the
chosen track starts automatically.
Used to navigate menus.
In addition, the Azur remote can be paired with up to six specific Apple
devices using any of the six source buttons. This can be useful if you have
more than one Apple product.
For more information on pairing refer to your Apple device’s instruction
Pairing – To pair with an Apple device, press and hold the required source
button along with the button for six seconds. Some devices like Apple
TV have visual indication once pairing is achieved.
Un-pairing – To un-pair an Apple device, press and hold any of the source
buttons along with the button for six seconds.
Cambridge Audio has developed a proprietary protection system to
ensure reliability and long life of its amplifiers. This protection system
comprises five main protection methods:
1. DC detection
Indicator – Unit has switched off during operation, protection LED
constantly flashes in single bursts.
Description – CAP5 offers loudspeaker protection if the output of the
amplifier goes to a high constant voltage (DC). This is a rare fault, although
detecting it could just save those expensive loudspeakers.
Remedy – Due to the necessary sensitivity of the DC protection circuit,
hard clipping of the amplifier may cause DC protection to be triggered.
If this fault occurs please switch the unit off, power up again and check
operation with a reduced volume level. If the DC fault occurs again please
contact your dealer for service.
CAP5: Five-way protection system
5. Intelligent clipping detection
Indicator – Volume is nudged down automatically.
Description – CAP5 has the ability to detect when the amplifier starts to
clip or overdrive at its output, which can damage loudspeakers and
degrade the sound. Clipping distortion is caused at high volume levels
when the output signal briefly goes outside the maximum voltage that
the amplifier can provide, causing the tops of the signal to flatten off.
When CAP5 detects clipping, the volume will be automatically nudged
down until CAP5 detects an undistorted output.
The clipping detection is disabled by default. However, to enable the
clipping detection, hold down the Standby/On button during power up
(whilst switching on the unit at the rear panel power switch). The unit will
indicate this by flashing the protection LED for several seconds.
2. Over temperature detection
Indicator – Unit has switched off during operation, protection LED
constantly flashes in bursts of two.
Description – CAP5 includes temperature detection which constantly
monitors the heat generated by the output transistors. If the monitored
temperature reaches a high level (suitably within the limits of the output
devices) the amplifier will automatically switch into a fault mode. If the
loudspeaker impedance is low, the temperature of the amplifier may rise
faster as the amplifier is working harder. If the amplifier is mounted in a
cabinet or the ventilation slots are obstructed, the over-temperature
detection may activate/reactivate after a short listening time.
Remedy – The unit is not damaged, although it should be left for 15
minutes to cool down before being switched out of Standby.
3. Overvoltage/overcurrent detection
Indicator – Unit has switched off during operation, protection LED
constantly flashes in bursts of three.
Description – CAP5 offers V/I protection by constantly monitoring the
output transistors to keep them working inside their Safe Operating
Area (SOA). The SOA is a set of limits given by the output transistor
manufacturer to ensure reliability. V/I also protects the amplifier against
short-circuits on the speaker terminals during use.
Remedy – The amplifier is being used outside its performance envelope.
Reduce the volume. Also check to see if there is a short- or partial shortcircuit between the loudspeaker terminals.
Note: If the indication remains the same and multiple loudspeakers are
being used on each loudspeaker output, then please remove a pair and
retry. If too many loudspeakers are connected to any amplifier, causing
the load resistance to drop too low, the amplifier will be overdriven. CAP5
will detect this situation. If the indication remains the same with only one
set of loudspeakers connected, there may be a fault with one or both of
the loudspeakers.
4. Short-circuit detection
Indicator – As the unit attempts to come out of Standby mode, the
protection LED flashes in bursts of four.
Description – During power up from Standby, CAP5 performs a check on
the loudspeaker terminals to see if a short across the terminals has
been accidentally introduced. If the resistance measured across the
loudspeaker terminals is too low, the unit will remain in Standby mode
until the fault has been removed and power up is re-attempted.
Custom installation (C.I.) use
The 651A feature a Control Bus input/output that allow un-modulated
remote control commands (positive logic, TTL level) to be received
electrically by the unit and looped to another unit if desired. These control
commands are typically generated by custom installation (multi-room)
systems or remote IR receiver systems. The Control Bus sockets are
colour-coded orange.
An IR Emitter Input is also provided that allows modulated IR remote
control commands to be received electrically by the unit. Commands on
this input operate the unit only and are not looped out demodulated on
the Control Bus Output.
In addition the units feature 'direct' IR/Control codes as well as toggle
codes for some of their features to simplify programming custom
installation systems. Special direct On/Off and Mute commands can be
accessed on the supplied remote control for teaching into C.I. systems
as follows:
1. Press and hold the Standby button. The remote first generates its
standby (toggle) command. Keep holding the button down and after
12 seconds an amplifier “On” command will be generated. If the
button is held down for a further 12 seconds, an amplifier “Off”
command is generated.
2. Press and hold the Mute button. The remote first generates its
mute (toggle) command. Keep holding the button down and after
12 seconds a “Mute On” command will be generated. If the button is
held down for a further 12 seconds, a “Mute Off” command is
A full code table for this product is available on the Cambridge Audio
website at
Remedy – User-related fault. There may be a short-circuit between the
loudspeaker terminals. Check all loudspeaker connections before
attempting to switch the unit out of Standby.
Technical specifications
There is no power
Power output
75 watts (into 8Ω)
Ensure the AC power cord is connected securely.
THD (unweighted)
<0.002% @ 1kHz, 80% of rated power
<0.03% 20Hz - 20kHz, 80% of rated
<0.02% 20Hz - 20kHz @ 10W
Ensure the plug is fully inserted into the wall socket and is switched on.
Check the unit is switched on at the rear panel.
Check fuse in the mains plug or adaptor.
Frequency response (-1dB)
5Hz - 50kHz
S/N ratio (ref 1W)
>92dB (unweighted)
Input impedances
Power Amp damping factor
Max. power consumption
Standby power consumption
<1W @ rated mains
Check that the correct speaker outputs are switched on (‘Speaker A/B’
button on the remote control).
Bass/Treble controls
Shelving, ultimate boost/cut
+/- 7.5dB @ 20Hz and 20kHz
If source LED is flashing, turn ‘Mute’ off.
USB input
USB Audio 1.0
16 bit 32kHz, 44.1kHz, 48kHz.
There is no sound on one channel
Dimensions (H x W x D)
120 x 430 x 350mm
(4.7 x 16.9 x 13.8”)
Check speaker connections.
8.4kg (18.5lbs)
There is no sound
Make sure the unit is not in Standby mode.
Check that the source component is properly connected.
Check that your speakers are properly connected.
Ensure that balance control is in the correct position.
Check interconnects.
There is a loud buzz or hum
Check turntable or tone arm for ground and connection lead fault.
Ensure no interconnects are loose or defective.
Ensure that your tape deck or turntable is not too close to the amplifier.
Unable to make tape recordings
Check that ‘Rec Out’ has been connected correctly.
There is weak bass or diffused stereo imaging
Ensure that speakers are not wired out of phase.
The sound is distorted
Check that the volume or tone controls are not set too high.
Protection LED flashing
See section on CAP5 protection system.
The remote handset will not function
Check that the batteries have not expired.
Ensure that nothing is blocking the remote sensor.
In the event that the above solutions do not remedy your problem, please
consult our frequently asked questions (FAQ) section on our website:
For all servicing, in or out of warranty, please contact your dealer.
Cambridge Audio is a brand of Audio Partnership Plc
Registered Office: Gallery Court, Hankey Place
London SE1 4BB, United Kingdom
Registered in England No. 2953313
© 2011 Cambridge Audio Ltd
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