4.3Coolingrequirements
Itis
essentialthataircancirculate
freely
aroundtheamplifierto keep
itcool.
Therearfanwill drawairinto
theamplifiercase,forcingitoverthelargetransverseheatsinkinorderto keepthe
power
devicescool,
and
exhaustthroughthefrontvent.Thefront
and
rear
oftheunitmust
not
beobstructed
inanywayto prevent
this.
lftheunitismounted
ina rack,
caremustbetakenthattherackissufficientlv
open
atthefrontand
backto allowa sufficientflowof airthrough
the
rack.lfthe
airflow isrestrictedin any
way
aseparatefan
shouldbemountedonthebackto draw
airinside
the
rack.
Similarlythe
front
oftherack
mustnotbeobstructed,forexample,someracksinfixed
installations
utilise
perspexfrontdoors
toprevent
tampering.
These
mustnotbeusedasthey
wouldrestrict
the
exhaustofthe
air,trappingit inside
therack,andincreasing
the
risk
ofthermaloverload.
Inadditiontokeepingthe
amplifiercoolthefans
will
alsodrawdustanddirt
intotheamplifiercasing,which
mayremainthere.lfthisdustisallowed
to buildup insidetheamplifier
it will reducetheeffectivenessof
theheatsinksandtheamplifiermay
produce
lowerthannormaloutput
levels.
(see
5.7).
Toreducedustintake
intotherack,airventsin therear
of the rack
should
havedustfilterswhichare
periodically
cleaned.
In
certainenvironmentsthedustlevelwill bemuchhigherthanisnormale.g..
in discotheques
whichhave
smokemachineslocatedneartheamplifiers.
Some
smokeoils
depositacorrosiveresiduewhichovertime
attacksthecomponentleadsandPrintedCircuit
traces.Care
shouldbe
taken
notto usesuchsmokeoils
In
thepresence
of theseamplliers
(damage
causedinthiswaywill notbecoveredbythewarranty).Insuch
circumstances
stepsshould
betakento locate
theamplifiersasfarawayfroma potential
dust
sourceasis
practical,
andthismustbeborneinmindwhen
considering
serviceintervals.
4.4CableLooms
Whentheamplifiersarehousedin a rack
the input
andoutputconnections
areusuallyterminatedon a
connecting
panel.Typically
whenmultiplesofamplifiersarehousedinarackthe
panel
maybeconfigured
with multipininputconnectors,whichwill havea variety
of signalsources,usually
beingoutputsfroma
crossover
frequency
dividingnetwork)ina PA
system,or variousmonitoroutputsfromthemixingconsole
in a studioapplication.Theconnection
panel
will thus
normally.havea numberof inputandoutput
connectors,together
withanACinput,
andcablesfromthese
connectors
will connect
witheachamplifier.
It isimportant
thattheappropriate
type
of cable
isusedandthatcare
is
taken
withthewayin whichthe
cablesare routed
roundthe rack
and tied together.
Poor
cabling
mayresultin reduced
performance,
amplifierfailure,unreliability,andincreased
hum.
To
reducethese
possibilities
all
cablesshould
beloomed
togetherwithcablesperforming
similar
functions,
butnotwithothercables.Forexampleifarackishousing
sixSTiSeriesamplifiers,therewill be12signal
cablesconnecting
the
amplifiers
totheconnector
panel.
These12cablesshouldutilise
screened
pair
cableandtheyshouldbetiedtogether
inabundleusingplastic
cabletiesor lacingcord,
andalsotiedtotherear
rack
rails,sotheycannot
move
around
insidetherack.lf
signalcablesareleftfree
andnottieda magnetic
humfieldmaybe createdandthepossibility
of them
causinghumthrough
ground
loopsisincreased.
Theback
panel
oftheSTISerieshasbeenlaid
outsuchthat
allsignal
inputcablescanbeloomedtogether
uponesideoftherack,and
allspeaker
outputscanbeloomeduptheotherside.SimilarlyallACcables
shouldbecarefullyloomed
and
positioned,
asthesetoomayalsocausegroundloops
whichproducehum.
Theuseofthe
ground
liftswitch
(3.4,
4.16)may
beof assistance,butcare
shouldbetakento ensurethat
the
AC
cables
areinan
optimum
position
beforethisistried.
