Perreaux Prisma 750 User manual

Prisma 750
Monoblock Power Amplifier
Owners Manual

2
Perreaux Industries Limited makes no warranty for the use of its products, other than those
expressly contained in the warranty detailed herein. The Company assumes no responsibility for
any errors which may appear in this document, reserves the ri ht to chan e products or
specifications detailed herein at any time without notice, and does not make any commitment to
update the information contained herein. No licenses to patents or other intellectual property of
Perreaux are ranted by the Company in connection with the sale of Perreaux products, expressly or
by implication.
mboob^ru
®
is a re istered trademark of Perreaux Industries Ltd.
Terms and product names in this document may be trademarks of others.

3
i
ii
i Introducing the Perreaux
750 Power Amplifier
Con ratulations on your Perreaux 750 purchase. To realise the full potential of
your unit you need to appreciate all aspects of its operation.
Before installin the 750 into your system, read the entire manual carefully.
Endeavour to un
derstand every detail by familiarisin yourself with the controls
and features as you read. You will find it easier to install usin the relevant
sections of this manual as a reference.
We have attempted to explain every feature and operation facet clearl
y and
concisely. Your Perreaux dealer will be happy to assist if you encounter any
unforeseen problems.
Read this manual, install your unit correctly and realise the sonic si nificance of
your investment in Perreaux.
Perreaux products are desi ned to prov
ide the utmost in sonic realism and
electronic reliability with a functional yet ele ant appearance that reflects the
care and craftsmanship applied durin all sta es of construction.
Features at a
Glance
 Balanced and Unbalanced inputs
 Ru ed build quality
 Ultra-stiff power supply
 Soft-Start circuit
 Hybrid Class A/AB output sta es
 MOSFET output devices
 Hi hly powered
 Dual bindin posts
 Remote tri er input and output
 Multiple protection systems
 Advanced PCB desi n and earthin techniques
 Earth isolation switch
To maintain the consistently hi h quality that you expect from us, and we expect
from ourselves, Perreaux products are essentially handcrafted.
We maintain the human-
link throu hout, from desi n and construction, throu h
to the ultimate test, your music, your system, your ears.
Because we too listen to our products, we know that with your Perreaux you will
discover many more of the musical secrets we strive to reveal.
From all of us at Perreaux Industries Limited, thank you for choosin the
Perreaux Prisma Series 750 monoblock power amplifier.

4
ii
iiii
ii Important Safety Instructions
Note:
All safety and operation instructions should be read carefully before the
750 is operated. Keep the Owners Manual in a safe place for future
reference.
 The 750 should
not be used near water, for example near a bathtub, kitchen
sink, in a wet basement, near a swimmin pool, etc.
 Mountin to a wall or ceilin should be via a heavy-duty bracket or shelf
desi ned for audio equipment use.
 The 750 should be situated away from heat sources such as radiators,
stoves, or other appliances that produce excessive amounts of heat.
 Always ensure the 750 heat sinks have adequate ventilation enablin air
circulation both above and below.
 DO NOT place the 750 directly onto carpeted surfaces.
 Avoid exposin the 750 to extremely hi h or low temperatures.
 The 750 should be connected to a mains power supply only of the type
described in the operatin instructions, or as marked on the rear of the unit.
 DO NOT disconnect the mains earth from the system.
 The mains power supply cord should be routed so that it is not likely to be
walked on or pinched by items placed on or a ainst it.
 The power cord of the 750 should be unplu ed from the mains outlet
when the unit is to be left unused for lon periods or when attemptin to
connect or disconnect cables and before cleanin your unit.
 Care should be taken so that objects and/or liquids do not accidentally fall
inside the 750.
 Please keep electrical equipment out of reach of children.
 Please unplu sensitive electronic equipment durin electrical storms.
 Please replace any fuse with the value and type specified.
 Avoid operatin the 750 with the cover removed.
 DO NOT bypass any fuse.

5
 DO NOT attempt to repair the 750. In the event of a problem, please
contact your Perreaux dealer.
 DO NOT operate this product in an explosive atmosphere.
Caution!
he 750 is an extremely high powered, convection cooled amplifier. he
finned outer heat sinks may become very hot when delivering high
volume levels –
to avoid injury; care should be taken not to touch the
heat sinks during operation.
DO NO , UNDER ANY CIRCUMS ANCES, EAR H EI HER OU PU OF
HE 750 – SERIOUS DAMAGE MAY OCCUR IF HIS IS NO ADHERED O.

6
iii
iiiiii
iii Table of Contents
i
ii
i Introducing the Perreaux 750 Power Amplifier ........................................................3
ii
iiii
ii Important Safet Instructions ........................................................................................4
iii
iiiiii
iii Table of Contents ..............................................................................................................6
1
11
1 Unpacking and Placement..............................................................................................7
2
22
2 Instant Install......................................................................................................................9
3
33
3 Front Panel Functions................................................................................................... 11
4
44
4 Rear Panel Functions..................................................................................................... 12
5
55
5 Special Design Philosophies ........................................................................................ 16
6
66
6 Special Design Features................................................................................................ 18
7
77
7 Maximising S stem Potential ...................................................................................... 20
8
88
8 The Power MOSFET....................................................................................................... 22
9
99
9 Care and Maintainance................................................................................................ 25
10
1010
10 Warrant Information and Obtaining Service........................................................ 26
11
1111
11 Extended Warrant Registration Form.................................................................... 27
12
1212
12 Faultfinding Your S stem............................................................................................. 28
13
1313
13 Specifications................................................................................................................... 33
14
1414
14 Ph sical Dimensions ...................................................................................................... 36
15
1515
15 Contact Details................................................................................................................ 37

7
Unpacking and Placement
The 750 is packa ed for maximum protection. Please carefully read the
instructions below before proceedin to unpack the unit. Be extremely careful.
Unpacking
Procedure
 Inspect both ends of the cardboard box and open at the end without the
central staple by slittin the reinforced tape at either side.
 Fold back the flaps and tip the packa e on end and the inner box will
slide out.
 Lay the inner box down flat and upri ht, open it conventionally by
separatin the top tray from the bottom.
 The product can now be removed from the bottom packa in . This will
be easier if you have someone to help you by holdin the base of the
box.
 Alternately, the bottom tray and amplifier could be tipped upside down
and the bottom packa in removed. If opened in this manner, please
ensure that you turn the contents over a ain.
Note:
Be very careful to secure the unit if you are planning to flip the package
upside down.
 Remove the two white polystyrene protectors off either side of the
amplifier, leavin the black material coverin .
 Pull back the material and remove the protective black tissue from the
front panel.
The amplifier is now unpacked and ready for further installation.
Note:
Please retain all packaging material for future transport.
Box
Contents
1 x 750 Power amplifier
1 x 750 Product manual
1 x Detachable AC power cord
3 x Performance analysis charts
Placing
Your 750
The 750 should enerally be placed close to your preamplifier, keepin the
interconnect cablin short.
We stron l
y recommend keepin the 750 on it’s own separate shelf to allow for
proper ventilation.

8
Ventilation
Requirements
The 750 is a hi h-powered amplifier. For optimal performance, the unit M UST
receive adequate ventilation.
 Please do not install in a sealed cabinet.
 Please do not stack products directly on top of the unit.
 Please do not cover the product with a cloth or similar.
 Please do not mount the 750 directly onto carpeted surfaces.
 As a “rule of thumb”, allow 80-100mm (3-4 inches) around all sides of
the product and mount the 750 on a flat surface, ensurin that the unit
has adequate access to free flowin air.
 In the event that the 750 is to be incorporated into custom cabinetry,
please refer to Chapter 14 “Physical Dimensions”.
Note:
Please ta
ke all necessary steps to ensure that the unit receives adequate
ventilation

9
2
22
2 Instant Install
If you are like us, the first thin you will want to do is to play your favourite
piece of music throu h your new 750. The followin instructions are writte
n to
enable you to achieve this as quickly as possible. These are not comprehensive
instructions, but are desi ned to enable you to play music now!
Note:
Please take the time to read the 750 manual thoroughly as it incorporates
many features, which will enhance its operation.
Placement
The 750 is a hi h-
power amplifier and best results will be achieved when placed
on a solid surface with adequate ventilation. DO NOT place on
a carpeted floor
or cover the amplifier!
Turn off associated components
This
minimises the potential to dama e any other components when connectin
your 750 into the system.
Connect preamplifier to 750
Connect the output of your preamplifier to either the balanced (XLR
) or
unbalanced (RCA) input at the rear of the 750 and set th
e input confi uration
to le switch at the rear to the correct position.
Note:
ry to keep all interconnect cables as far from loudspeaker cables as
possible and well away from all AC mains leads.
Connect speaker cables to the speaker terminals
We recom
mend usin hi h quality connectors for your speaker cables, spade
lu s are the preferable option as they combine a lar er surface area with the
possibility of a stron mechanical connection; however, hi h quality banana
terminals are also acceptable.
Note:
Be careful to maintain phase integrity, positive (+) to positive (+), negative
(-) to negative (-).
Switch on preamplifier
Turn on the preamplifier and set the volume to the minimum level. Select the
respective input to which your source component is connected.
Switch on 750
After checkin the supply volta e compatibility with the volta e ratin on the
750 rear panel, insert the power cord-
set supplied into the rear of the unit and
into the wall. Switch on the socket at the wall and power up the 750
usin the
switch on the rear panel.

10
Start our source component
Switch on the source component both at the wall and on its front panel. Ensure
you have some source material inserted and press play.
Increase the volume
Slowly increase the preamplif
ier volume control to achieve a comfortable
listenin level.
CONGRATULATIONS!
Now that you have achieved your first objective, sit back, relax and please read
the rest of the manual at your own pace, in your favourite armchair, whilst
sippin a lass of wine
. You’ll find the whole experience much more
pleasurable whilst listenin to music.

11
3
33
3 Front Panel Functions
Power Indicator
The indicator li ht is an LED that shows the status of your 750 monoblock
power amplifier.
Off
This indicates that
the amplifier is either not connected to the mains supply, or
the unit is in standby.
The unit not bein connected to the mains supply could be due to the power
switch at the rear of the unit bein set to the OFF position, or power not bein
supplied to t
he mains power cord (e. . unplu ed, switched OFF at the wall
socket, tripped circuit breaker, etc.).
Standby occurs when the unit is connected to the mains supply with the power
switch bein set to ON and a master device, connected via the remote tri er
input at the rear of the unit, is set to OFF. To brin the unit out of standby the
master device needs to be set to ON.
For more information on the remote tri er, please refer to Chapter 4 “Rear
Panel Functions”.
Blue
When the LED is blue, the amplifier is ON and ready to be used.

12
4
44
4 Rear Panel Functions
Caution!
Please make all changes at minimum volume setting. Only increase the
volume after the connections have been made.
Serial Number
The serial number is unique to your 750. Please record
this number and store it
in a safe place. For any service related enquiry, please be prepared to quote the
product serial number to Perreaux personnel or their service representative.
Input Voltage and Fuse Rating
Input Voltage
It is important that th
e 750 be operated from the correct AC mains volta e. This
unit is factory set for the volta e applicable to the ori inal country of
destination.
The 750 will operate satisfactorily within a volta e variation of up to ±5% of
that volta e at which the unit has been set.
If you require the volta e settin to be altered, e. . relocation to another area,
city or country, or extraordinarily hi h or low volta es, please contact your
Perreaux dealer. Qualified service personnel can only perform this modification.
Caution!
Never attempt to connect the unit to the incorrect voltage. Severe
damage can result from applying incorrect voltage to the unit.

13
Fuse Rating
The fuse ratin displayed here, refers to the ratin of the mains inlet fuse.
For more informatio
n on fuse ratin s, please refer to Chapter 13
“Specifications”.
Caution!
Never replace the fuses with any other ratings other than the one
specified.
AC Mains Input
An IEC-
standard mains input is provided at the rear of the unit. The AC cord set
is removable, allowin you to up rade to a cord set of your preference.
Caution!
Prior to connection to the AC mains, please check the voltage label on
the rear panel to ensure that your unit conforms to the power supply in
your area. Never attempt to conne
ct the unit to the incorrect voltage.
Severe damage can result from applying incorrect voltage to the unit.
Earth Lift Switch
This switch enables the user to isolate the internal si nal earth of the amplifier
from the mains earth and is useful if system hum is a problem
. Settin this
switch DOWN connects the internal si nal earth to mains earth and is the normal
position. Settin to UP disconnects the si nal earth from the mains earth.
Note:
Activating this switch has no effect on chassis earth, ma
intaining the
connection to mains earth.
Mains Fuse
The 750 is equipped with a user serviceable AC mains fuse. In the event of fuse
failure, always replace with the same type and value fuse. Remember, fuses do
not usually blow without a reason. Any
doubts about fuse failure should be
conveyed directly to your Perreaux dealer.
For more information on fuse ratin s, please refer to Chapter 13
“Specifications”.
Caution!
his is the ONLY user accessible fuse.
Never replace the fuses with any other ratin
gs other than the one
specified on the rear panel.
Always ensure your 750 is disconnected from the mains supply before
attempting to change the mains fuse.
Master Trigger Input
The master tri er input is used to take the 750 in and out of standby. T
he
master tri er input is desi ned to accept a 3.5mm diameter male plu . The
volta e ratin is +5V to +12V DC level ON and 0V DC level OFF.

14
The plu must follow the specifications as per the followin dia ram:
Slave Trigger Output
A parallel s
lave tri er output is provided to switch on or off any connected
peripherals to the 750. The slave tri er output is desi ned to accept a 3.5mm
diameter male plu . The volta e ratin is +12V DC level ON and 0V DC level
OFF.
The plu must follow the specifications as per the dia ram below:
Power Switch
Set this switch ri ht (I
) to turn power ON. Mute relay circuitry is employed in
the 750 so output is muted momentarily after the power switch is actuated. Set
the switch left (O) to turn the unit o
ff, at which time the outputs will be
disconnected.
Unbalanced Inputs
Accepts a standard sin le-
ended input pair (RCA) from preamplifiers with
sin le-
ended outputs. The connectors are hi h quality old plated sockets which
are hi hly conductive, corr
osion resistant, and provide less potential for
corrosion induced distortion.
Refer to Chapter 13 “Specifications”, for detail on input sensitivity and
impedance.
Note:
Please set the input configuration switch to the appropriate setting.
Input Configuration Switch
This to le switch allows selection of either the balanced or unbalanced inputs.
Note:
Input leads should be connected to one type of input only, i.e. do not
connect to both the unbalanced and balanced inputs at one time.
Balanced Inputs
Accepts a si nal from a preamplifier with balanced outputs via a hi h quality
XLR connector.
The use of ood quality balanced line cable into the balanced
input cause the input si nal to be relatively immune to noise and external effects
caused
by the use of lon interconnect cables, helps reduce hum loop noise and
aids in the cancellation of distortion products.

15
Refer to Chapter 13 “Specifications”, for detail on input sensitivity and
impedance.
Note:
Please set the input configuration switch to the appropriate setting.
The pin assi nments of the balanced XLR connectors are as follows:
Pin 1: Signal ground
Pin 2: Signal + (non-inverting)
Pin 3: Signal – (inverting)
Shield ground: Chassis ground
Note:
Please refer to the operating ma
nuals of your balanced output line level
source to verify that the pin assignments of the output connectors
correspond to the 750 balanced inputs. In the event that they are not
compatible, the interconnecting cable will need to be altered to suit.
For mo
re information re ardin balanced interconnects, please refer to Chapter 7
“Maximisin System Potential”.
Speaker Output Terminals
The 750 is equipped with two sets of output terminals, to enable easy hook-
up
for bi-wirin of loudspeakers or additiona
l loudspeakers. All terminals are
clearly marked and colour coded RED Positive (+) and BLACK Ne ative (-
).
This polarity must be observed when connectin loudspeakers, i.e. positive
terminal of the 750 to the positive terminal of the loudspeaker and ne a
tive
terminal of the 750 to the ne ative terminal of the loudspeaker.
Caution!
Never connect the amplifier’s output terminals to any device other than a
loudspeaker.
Please do not short circuit the amplifier’s output terminals.
Never connect the output of
one amplifier to the output terminals of
another amplifier.
Do not over-tighten the binding posts on your amplifier.
DO NO , UNDER ANY CIRCUMS ANCES, EAR H EI HER OU PU OF
HE 750 – SERIOUS DAMAGE MAY OCCUR IF HIS IS NO ADHERED O.

16
5
55
5 Special Design Philosophies
Perreaux has been desi nin and manufacturin only the hi hest quality audio
componentry for more than a quarter of a century. Technolo y has continued to
evolve rapidly over that time and our knowled e and application of desi n,
materials an
d manufacturin techniques has advanced in tandem with this.
Today’s Perreaux ran e comes closer to fulfillin our shared vision than at any
other time in the past.
To follow is a discussion on some of Perreaux desi n philosophies that have
been incorporated into the entire ran e.
Minimalist
Design
Leadin British architect, John Pawson, writes:
“The Minimum can be defined as the perfection that an object
achieves when it is no longer possible to improve it by subtraction.
This is the uality that an object has when every component, every
detail, and every junction has been reduced or condensed to the
essentials. It is the result of the omission of the inessentials”.
Perreaux has historically embraced the minimalist ethic from an audio desi n
perspective
only. The concept of “less equatin to more” has been at the heart
of all Perreaux audio desi ns for more than a quarter of a century.
Minimalist Electronics
We wish to maximise the quality of your listenin pleasure by keepin the
componentry and si na
l path as uncluttered, short and clean possible. All
components in the si nal path, even those of the hi hest quality have an effect
on the si nal, thereby alterin the quality of the reproduction in some way. Our
aim is to recreate in its entirety, the
ori inal performance by not addin or
subtractin anythin , irrespective of the source.
Minimalist User Interface
We carefully study the user interface and par down the number of buttons and
associated clutter leavin just the essential and no more. How t
emptin it has
been over the years to loose si ht of our core values as technolo y or trends
have made it possible. That is one of the reasons why our older products still
have such a hi h resale value today. The user interface has and always will
remain simple, free from adornments, clean and uncluttered.
Minimalist Aesthetics
Our products appeal to those who seek the ultimate in audio exclusivity, namely
the perfect blend of “form and function”.

17
“Form and function” are both tou h masters. That
is why our amplifier heat
sinks are not hidden, but instead feature prominently in all our desi ns. We
make no excuses for producin some of the most distinctive hi h-
end audio
products on the planet. We let “form and function” blend to ether in perfect
harmony. This surely is the essence of true minimalist utilisation.
Minimalism in a Wider Context
John Pawson writes:
“Clearly simplicity has dimensions to it that go beyond the purely
aesthetic: it can be seen as the reflection of some innate, inner
uality, or the pursuit of philosophical or literary insight into the
nature of harmony, reason, and truth”.

18
6
66
6 Special Design Features
Rugged Build
Qualit
Mechanical stren th has been a hallmark of Perreaux products since the
company first started producti
on back in 1974. The concept behind the physical
desi n and construction is that each structural member should contribute to both
ri idity and performance.
Ultra Stiff
Power Suppl
The 750 incorporates a massive custom desi ned, toroidal power transforme
r,
employin unusually heavy au e wire that reduces copper losses to a
minimum. An electrostatic shield prevents AC line borne interference from
enterin the si nal path. The power supply filter capacitors, totalin 60,00
0µF,
have exceptionally low inductance and internal resistance. They char e and
dischar e in response to load demand far more rapidly than conventional stora e
capacitors and are capable of deliverin the instantaneous current required by the
output sta e
s, providin optimum dynamic ran e and transient response. The
wirin from the power supplies to the output boards is desi ned for unimpeded
transmission of the required current and volta e and utilizes heavy au e, tinned
copper wire cables. Since power
supply leads radiate at si nal frequencies, all
wirin is carefully loomed to minimise this effect.
H brid Class
A/AB
The bi-
polar transistors used in the 750 are run in Class A mode. This avoids the
crossover notch distortion and the resultin odd-orde
r harmonics present, to
some de ree, in all other classes of operation. The devices used in the 750
output sta e are M OSFETs, which with hi h quiescent current circuitry, are run
in the equivalent of Class A to 10 watts. Beyond this point the output clas
s is
technically Class AB (hence the hybrid nomenclature), but with a major
difference. The combination of MOSFET characteristics and their application in
this circuitry, result in crossover distortion so minimal that it is virtually non-
existent.
MOSFET
Output Stage
The 750 output sta e takes full advanta e of the unique qualities of M OSFET
devices and in many ways they are superior to bi-
polar transistors. A major
advanta e is their tendency to draw less current over a lar e section of the power
bandwi
dth as their temperature rises (Ne ative Temperature Coefficient), hence
self stabilisin thermally, whereas bi-
polar transistors draw more current as their
temperature rises (Positive Temperature Coefficient) and protection circuits
become mandatory to pr
event thermal runaway and eventual self destruction.
MOSFETs have the ability to swin fully across the amplifier’s internal DC
volta e and are therefore true "rail-to-
rail" devices. Usin MOSFETs
encoura es the hi hest performance from the balance of th
e internal amplifier
circuitry.
Multiple
Protection
S stems
The 750 is equipped with a number of protection systems, isolated from all
si nal carryin circuits via opto-couplers, to protect both itself and ancillary
equipment.

19
DC Offset Protection
Th
is system senses if any direct current (DC) is present at the 750 output
terminals and disconnects the output to avoid potential speaker dama e. DC
may be present due to ancillary equipment feedin DC into the input or an
amplifier fault.
Short-Circuit/Overdrive Protection
This system senses if there is a short circuit across the 750 output terminals and
disconnects the output to avoid amplifier dama e. It also senses if the 750 is
bein driven outside acceptable operational parameters. An example of thi
s
would be drivin a 1Ω speaker at very hi h levels.
Note:
After the short circuit or overdrive source is removed, the 750 must be
turned off then back on to reset and resume operation.
hermal Protection
This system senses if the 750 is overheatin and d
isconnects the output until a
safe operatin temperature is reached, at which time the unit will automatically
resume normal operation.
Earthing
Perreaux en ineers pay particular attention to desi nin the product to ensure
maximum separation between inte
rnal si nal and power earths, only meetin at a
central starred point.
Earth
Isolation
Switch
The to le switch on the rear of the 750 allows the internal circuitry to be
isolated from the mains earth, whilst still maintainin an earth connection to the
chassis. This ensures the potentially fatal practice of usin an AC cord-
set with
no earth connection, to alleviate system hum, is not required.
Highest
Qualit PCBs
and
Components
Quality fibre lass PCBs, featurin heavy copper tracks and hi h-
rade
comp
onents, are used throu hout the 750. This provides added stability under
variable thermal or electrical loads and assures maximum si nal inte rity,
separation and product life.
Bi-Wiring
Made Eas
Dual pairs of bindin posts allow bi-wirin of speakers to be conducted easily.
Soft-Start
Circuitr
The 750 utilises soft-
start circuitry to protect the fuses and/or circuit breakers in
your home’s mains power supply. Without this circuit, the hu e inrush current
required to char e the 60,000µF of power suppl
y smoothin capacitance can
blow the fuses or trip the circuit breakers.
Highl
Powered
Capable of continuously deliverin 750W
RMS
into 8Ω (1300W
RMS
into 4Ω
), the
750 is hi hly powered. Utilisin sixteen hi h current Toshiba M OSFETs, the
750 handles even the most difficult loads with ease.

20
7
77
7 Maximising System Potential
Interconnects
and Speaker
Cables
An often-
i nored area in hi h fidelity systems is the cablin connectin the
various
components. Interconnect leads should be hi h quality cable with
su
bstantial terminations. Gold plate is inherently resistant to corrosion, and an
excellent conductor. The presence of corrosion induces distortion and poor
conductivity will seriously interfere with sound quality. Terminations must plu
snu ly into socke
ts to maintain maximum conductivity and to avoid annoyin
earthin problems.
Speaker cablin is equally critical. Use only solidly constructed cable of hi h
purity copper or silver content. A ain, old plated terminations are
recommended, of the spade or
banana plu type. Use cables of equal len th and
as short as possible to maintain uniform electrical resistance at the lowest
possible level. If your amplifier is closer to one of your speakers than the other,
avoid coilin the lon er lead as this can c
reate inductance, with the potential of
reduced hi h frequency performance. Keep all connections clean, firm and
ti ht. The traditional ada e that a chain is only as stron as its weakest link
most certainly applies to audio systems.
Bi-amping
Bi-ampin
uses two similarly powered amplifiers, with exactly the same input
sensitivity so that, when the same input si nal is provided to each of them, the
output level will be exactly the same. This can often be done with one power
amplifier connected to the tw
eeters and another to the woofers, as it spreads the
power requirement between the two amplifiers. Bi-
ampin can achieve reater
control, dynamics and resolution than if you try to run everythin from a sin le
stereo amplifier.
Balanced
Interconnects
The
use of the balanced si nal inputs and outputs can have the effect of cleanin
up hums, buzzes, radio frequency interference (RFI) and eneral extraneous
rubbish that can enter an audio system. A balanced si nal input system operates
on the principle of d
ifferential amplification. The positive and ne ative inputs
are contrasted a ainst one another and the difference between them is amplified.
Noise enterin the system is imposed equally on the positive and ne ative
si nals and therefore will not be amplified, as no differential volta e exists.
The term used to describe the quality of the effect is called Common M ode
Rejection Ratio (CM RR). CM RR is an equipment and system specification,
which describes how well unwanted common mode si nals are counteracte
d
when used in conjunction with balanced connections. CM RR action prevents
the e ress and build up of extraneous hum; buzzes and RFI when analo ue
si nals are conveyed down cables and between equipment powered from
different locations and is widely used in professional audio applications.