GAS Thaedra - Hum Reduction Tips

We‖
―
shieidedcab:eisrecommendedforconnectingtothecartridge
andisusua‖
ysuppliedaspartoftheturntableorchanger.Where
longerdistancesaredesiredforthisconnection,itisnotrecommended
thephonocab!esexceed5feet,otherwiseaudibledegradationofhigh
frequenciesmightbeencountered.Specialcaremustbetakenthata‖
connectionsaretightandsecure.
Ordinari:y′
anadditionalgroundingwireisprovidedwiththeturntable
whichshouldbeconnectedtothegroundingpostlocatedbetweenthe
phonoinputsontherearpanel.:nsomesystems′
itmightbefoundthat
thisconnectioncreateshum.!nthiscase′ nogroundconnectionshould
bemade..Becarefultokeepa‖
largetransformers(suchasfoundin
povveramplifiers)avvayfrOmthephonocartridgetopreventmagneti‐
ca‖
y‐
inducedhum.
HEADAMP:Thisinputisforusewithlow‐
outputmo宙 ng― coil
cartridges.THAEDRAhasspeciaicircuitswith67microvoltsensitivity
(OVerload:4.7mV}whichWi!!accommodatetheseverylow‐
output
cartridgeswithouttheneedfortransformersorpre―
preannplifiers.The
inputimpedanceis6000hms・
(withO.luFshuntcapacitance),v〆
hich
providesnegligiblesignaliossandfrequencyresponsernodificationvvith
moving‐
coiltypecartridges.
Althoughcab!esupto15feetmavbeusedwithoutaffectingthe
cartridgefrequencyrespOnse,specialcaremustbetakentopreventhum
pickupinthecables.Theymustnoton:ybewe‖
―
shielded′
butthe
cablesmustbekeptawayfromanvACpowertransformers.lfanyhum
isheard′
trymovingthecablestosomeotherposition′ routingitasfar
aspossiblefromanypotentialmagneticfields.Thetwoleftandright
channelsshouldbekepttogetherandtvvistedafewtimes.:fhumstill
persistsragainbecertainthat″
ο!argepowertransformersarenearthe
:eftsideofTHAEDRA.
SPECiALNOTESONHUMREDUC丁
iON
Probablythemostfrustratingproblemvvithlovv‐
outputmoving‐ coil
cartridgesishum.Agreatpercentageofthetimeitistheresultof
irnproperinsta‖
ationandlackofcarewhenorientingcomponents.
Unfortunateiy′
eitherbypoordesignortheverynatureofthecom―
ponent,somecomponentsaremorepronetohumthanothers,and770
cablemadeisentirelyimmunetoradiatedmagneticf!ux(hum).it
fo‖ owsthen′
that
σ〃cablesinthesystemmustbeorientedforthe
lowestlevelofhum.
Theconnectingcab:esfromtheturntablewi‖
pickupfar″
0′θhurn
thananyothersourceoThesecab:esmustbeorientedformaxirnum
humcance‖ ation.И
ノ7vvirescarryingACpowershouldbelocatedasfar
avvayfromtheturntableandpre― ampinputasisphysica‖
ypossible.
さnder17ο
εirc″隔 じancθsshou!dyougroundtheturntableorgrounding
pOsttOawaterpipeorothersuchground.(Dnly
オカ′ο
J9/7the
ρ
O、
νθ
′
′
η
p/iFiarshou!dyoursystembegroundedtoearth.lfyourpower
ampiifierdoesnothaveathird‐ wireground′
weadviseyouhavea
qualifiedtechnicianinsta‖
oneasasafetyfeature.
Aithoughsometimesawkward′
rotatingthepoweramplifieratright
anglestothepreamp‖ fierllvi‖
altertheradiationfieldfromitspO、 ver
transformer.Placingmetalsheetsbetweenunitswi‖
notaidinthe
reductionofhumbecausethemagneticfluxfie!dwillextendaround
theshie!d.
Humcanaisobeintroducedbyapoorcableconnectorcontactwiththe
outergroundingshe‖ oftheplug.Makesurethattheoutershe‖
sonthe
RCAphonop!ugsaresqueezedtogetherenoughtoprovidean
absolute!yso!idgroundconnection.Tryrotatingtheplugstoobtainthe
bestpossibleground.