McIntosh MAC 4100 User manual

THEMCINTOSHMAC4100RECEIVER
ReadingTime: 48Minutes
Price$2.00

VARIOUSREGULATORYAGENCIESREQUIRETHATWEBRINGTHEFOLLOWINGINFOR-
MATIONTOYOURATTENTION.PLEASEREADITCAREFULLY.
WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNITTO
RAINORMOISTURE.
TheMclntoshyouhavepurchasedisa Model
MAC4100.Ithasa serialnumberlocatedontherear
panelofthechassis.Recordthatserialnumber
here:
SerialNumber
Themodel,serialnumberandpurchasedateareim-
portanttoyouforanyfutureservice.Recordthepur-
chasedatehere:
PurchaseDate
Uponapplication,MclntoshLaboratoryprovidesa
Three-YearServiceContract.YourMclntosh
authorizedServiceAgencycanexpediterepairs
whenyouprovidetheServiceContractwiththein-
strumentforrepair.Toassist,recordyourService
Contractnumberhere:
ServiceContractNumber

YourMAC4100SolidStateAM-
FM/FMStereoReceiverwillgiveyou
manyyearsofpleasantand
satisfactoryperformance.Ifyou
haveanyquestions,pleasecontact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Phone:[phone]
Contents
TakeAdvantageof3 years
ofContractService...
FillintheApplicationNOW.
INTRODUCTION...2
INSTALLATION...3
HOWTOCONNECT...5
WHATTHEFRONTPANELCONTROLS
DOANDHOWTOUSE THEM.. .10
PUSHBUTTONS...10
FRONTPANELINDICATORS. . .12
BALANCINGYOURSTEREO. ..13
LISTENINGTOYOURSTEREO. ..13
MAC4100PERFORMANCELIMITS...15
TECHNICALDESCRIPTION. ..16
PERFORMANCECHARTS...20,21,22,23
BLOCKDIAGRAM...24
MCINTOSHTHREEYEARSERVICECONTRACT
Anapplicationfora THREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:
1.Mclntoshwillprovideallparts,
materialsandlaborneededtoreturnthe
measuredperformanceoftheinstru-
menttotheoriginalperformancelimits.
TheCONTRACTdoesnotcoverany
shippingcoststoandfromtheauthoriz-
edserviceagencyorthefactory.
2.AnyMclntoshauthorizedserviceagen-
cywillrepairMclntoshinstrumentsat
normalservicerates.Toreceiveservice
underthetermsoftheSERVICECON-
TRACT,theSERVICECONTRACTCER-
TIFICATEmustbepresentedwhenthe
instrumentistakentotheservice
agency.
3.Alwayshaveservicedonebya
Mclntoshauthorizedserviceagency.If
theinstrumentismodifiedordamaged,
asa resultofunauthorizedrepairthe
SERVICECONTRACTwillbecancelled.
Damagebyimproperuseormishandl-
ingisnotcoveredbytheSERVICECON-
TRACT.
4.TheSERVICECONTRACTisissuedto
youastheoriginalpurchaser.Topro-
tectyoufrommisrepresentationthis
contractcannotbetransferredtoa se-
condowner.
5.ForyourprotectionMclntoshselects
onlydealerswhohavetechnicalcom-
petencetoguidepurchasersfairly,and
provideservicewhennecessary.To
receivetheSERVICECONTRACTyour
purchasemustbemadefroma
Mclntoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfor
aSERVICECONTRACTmustbepost-
markedwithin30daysofthedateof
purchaseoftheinstrument.
7.ToreceivetheSERVICECONTRACTall
informationontheapplicationmustbe
filledin.TheSERVICECONTRACTwill
beissuedwhenthecompletelyfilledin
applicationisreceivedatMclntosh
LaboratoryIncorporatedinBingham-
ton,NewYork.
Copyright1978© byMclntoshLaboratoryInc.
1

Introduction
TheMclntoshMAC4100isa highquality,high
powerAM/FMStereoReceiver.Itsdesignhasbeen
governedbyinsistenceongreatflexibility,sensitivi-
ty,highperformancewithlonglife.Itiseasytouse.
Someofthemanynewimprovementsdesigned
foryourlisteningenjoymentInclude:
Lownoisefieldeffecttransistoranaloginputswit-
chingthatkeepssignalleadsshorttoreducepossi-
blenoiseandhumpickup.Mechanicalcontactnoise
isalsoeliminated.
LEDInputindicatorsshowwhichsourcehasbeen
selectedandhelpmakeinputselectionfaster,
easier,surerandmoreconvenient.
Newlowimpedancetransistortechnology
reduceshumandnoiseinterferenceinthephono
preamplifier.
Electronicallycontrolledtrimmingofthepreci-
sionsteppedvolumecontrolmaintainsa channelto
channelaccuracyof1 dB.Thishighorderofexact-
nessassurescontinuingprogrambalanceasthe
listeningloudnessischanged.
Thefivebandprogramequalizerpermitsthead-
justmentandimprovementofthetonecontrastof
thefivemostimportantlisteningranges.Eachcan
beemphasizedorde-emphasizedtosatisfyyour
tasteorlisteningatmospherewithoutaffectingany
oftheotherranges.
Thehighqualitypowerperformanceiscon-
tinuouslyassuredbyPOWERGUARD.ThePOWER
GUARDcircuitdynamicallypreventspower
amplifiersfrombeingoverdrivenintohardclipping--
-whichprotectsyourspeakersfrompotential
damage- - - whichassuresthattheamplifierwillpro-
duceitsmaximumoutputwithoutincreaseddistor-
tion.Thepowerdeliveredis100wattsperchannelat
4ohmstogiveextradynamiclifetoyourmusic•
evenwhenyou'reusinganycombinationof3 setsof
stereoloudspeakers.
Theselectivelylighteddial pointerlightsonlythe
relevantpartofthetuningindicatortomaketuning
easier.
AutomaticACpowercontrolisprovidedbythe
autoOn/Offcircuitthatconvenientlyshutsoffthe
entiresystemwhentheturntableshutsoff.Noneed
tointerruptyourpleasureattheendoftherecord.
Frontpaneltaperecorderjacksallowsimpleplug
Inofan"outboard"taperecorderwithoutupsetting
yourregularsystemconnections.
Copiesoftapescanbeeasilymadebetweentwo
connectedtaperecorders.Frontpaneltapecopying
controlsfunctionwithoutdisturbingothersound
sources.
Thisoutstandingreceiverwillserveyoubestwhen
youunderstanditsfunctionsandwhatitisdesigned
todo.Sometimeinvestedwiththismanualwillbe
valuableinyourknowledgeofhowitworks.
2

x8"[20.32cm],[seeFig.2].Inaddition,a single3/8"
to1/2"[1cmto1.3cm]screwhole[seeFig.2 and
Fig.3]mustbedrilledintheshelftosecurethe
receiverafterinstallation.Thetopoftheshelfmust
beattachedflushwiththebottomofthecustom
panelcutout.
BOTTOMOFPANELCUTOUTAND
TOPOFSUPPORTSHELFMUSTCOINCIDE
Fig.1 CustomCabinetFrontPanelCutout.
TheMAC4100maybeusedona shelfortabletop
intheenclosureinwhichitcomesormaybeinstall-
edina customcabinet.Inanymethodofuseprovide
adequateventilation.
Thetrouble-freelifeofanelectronicinstrumentis
greatlyextendedbyprovidingsufficientventilation
topreventthebuild-upofhighinternaltemperatures
thatcausedeterioration.Allowenoughclearanceso
thatcoolaircanenteratthebottomofthereceiver
andbeexhausedfromthetopandrear.Withade-
quateventilationtheinstrumentcanbemountedin
anyposition.
TheMAC4100isinstalledfromthefrontofa
customcabinet.Thedesirablespacebehindthe
cabinetpanelis15"[38.1cm]deep,18-1/2"[47cm]
wide,and6"-[15.2cm]high.Theunitfitsanopening
exactly5-1/16"[12.9cm]by17-5/16"[44cm]wide.
Makethiscutoutcarefully.Thereceiver'sfrontpanel
hasa 1/8"[.32cm]overhangonbothsidesanda
3/32"(.24cm)overhangonthetopandbottom,[see
Fig. 1].
Theweightofthereceivermustrestona shelfin
whichthereisa ventilationholecutout15"[38-1cm]
PreparetheMAC4100forcustommountingby
removingthewoodcabinetandfeetasfollows:
1.Remove4 screws"A"[seeFig.4];twofromeach
sidepanel.
2.Toremovetheenclosuretoppanel,thereceiver's
metaltopmustbetemporarilyremoved.Itisat-
tachedtothechassisby4 screws"B"[seeFig.4]
installed2 throughtheflangeonthebackand1
througheachoftheflangesontheside.Remove
these4 screws.Savethescrewstoreinstallthe
metaltopafterremovaloftheenclosuretop
panel.
3.Underthemetaltopare5 screws"C"thatholdthe
enclosuretoppaneltothemetaltop[seeFig.4].
Removethe5 screws"C"thatholdthemetaltop
totheenclosuretoppanel.
4.ReplacethemetaltopontheMAC4100withthe4
screws"B".
5.Onthebottomofthereceiverarethe4 plasticfeet
heldonbyscrews"D"[seeFig.4].Removethese
feet.Donotattempttoremovethe4 plasticbut-
tonglidesastheserestagainsttheshelf,(seeFig.
2and3).Atthispointthereceiverisreadytobe
custominstalled.
Fromthefrontofthecabinet,threadthepower
cordthroughtheopeninginthecabinetpaneland
slidetheMAC4100inontheshelf.Adjusttheposi-
tiontoevenlycoverthecustompanelcutout.Lock
theunitinplacewitha screwandwasherinserted
throughthedrilledholeinthemountingshelf[see
Fig.3].Usea 1-1/4"[3.2cm]screwfor1/2"[1.3cm]
shelfora 1-1/2"[3.8cm]screwfor3/4[1.9cm]shelf.
Donotuselongerscrews.
EDGEOF4100FRONTPANEL
3

MAC4100UNITOUTLINE(DOTTED)
MOUNTINGSURFACE
MOUNTINGPANEL
Fig.2 CustomCabinetShelfMountingCutout.
MOUNTING
SURFACE
15"(36.1cm)
MINIMUMDEPTHREQUIRED
FOR1/2"SHELFUSE1 1/4"SCREW
(1.3cm)(3.2cm)
FOR3/4"SHELFUSE1 1/2"SCREW
(1.9cm)(3.8cm)
MOUNTING
PANEL
PLASTIC
BUTTONS
CUTOUTFOR
VENTILATION
SECUREUNIT
WITHSCREWAND
WASHER
Fig.3 MAC4100CustomMountingProfile
Fig.4 MAC4100EnclosureAssembly
4

HowtoConnect
CONNECTINGTURNTABLES
TheMAC4100hasshortingplugsinthephonoin-
puts.Topreventunwantednoiseremoveonlythe
shortingplugsfrominputjacksthatare10beused
Connectthecablefromtheleftchanneloftheturn-
tableintotheINPU1L PHono1 jack.
Connectthecablefromtherightchannelofthe
turntableintotheINPUTR PHono1 jack.Connect
PHono2 inthesamewayforusewitha secondturn-
table
CONNECTINGTAPERECORDERS
ToRecord
Connecta cablefromtheRECORDERL TAPE1
OUTjacktothelefthighlevelinputofthetape
recorder.Connecta cablefromtheRECORDERR
TAPE1 OUTjacktotherighthighlevelinputofthe
taperecorder.Connecta secondrecorderinthe
samemannertotheRECORDERTAPE2 OUTjacks.
ToPlayback/Monitor.
Connecta cablefromtheleftchanneloutputofa
taperecordertotheRECORDERL TAPE1 INjack.
Connecta cablefromtherightchanneloutputofa
taperecordertotheRECORDERR TAPE1 INjack.
Connecta secondrecorderinthesamemannerto
theRECORDERTAPE2 INjacks.
FrontPanelTapeRecorderJacks:
Taperecorderinputsandoutputsareavailableat
theTAPEIN-OUTjacksonthefrontpanelleftofthe
INPUTSELECTORswitch.Rapid,temporaryconnec-
tionstoTAPE2 facilitiesareeasilymadewithout
gettingattherearpanel.A metalshielded1/4"
stereophoneplugisusedConnectionsaretip:left
signal,ring:rightsignal,and.sleeve:common
ground.
Whena taperecorderispluggedintothefront
jacksallthefacilitiesnormallyassociatedwith
TAPE2 ontherearpanelareautomaticallytransfer-
redtothefrontpaneljacks.
CONNECTINGACPOWER
ThereceiverACpowercordispluggedintoa 120
volt6OHzwalloutlet.
TherearethreetypesofACpoweroutletsonthe
backpaneloftheMAC4100onered.twoblack,and
twogreen
TheredandthegreenACpoweroutletsareonat
alltimes.Theredoutletcanbeusedfora tape
recorderwithitsownACpowerswitch.PlugtheAC
powercablesfromtheturntableintothegreen
TURNTA8LEpoweroutletsontherearpanel
Thetwoblackoutletsareswitchedonandoff
whenthereceiveristurnedonoroff.Thesearein-
tendedforequalizersandotheraccessories.
ThePOWERONpushbuttonsharesACpower
control,withtheACpowerswitchona turntable,
througha currentdetectingswitchcircuitOnme
rearpaneltheTURNTABLEAUTO/MANUALswitch
selectsthemodeofoperation.
WhentheswitchisintheAUTOpositionanda
turntablepluggedintooneofthegreenACpower
outlets,theACpowertothereceiverandtothe
blackACpoweroutletscanbecontrolledbythe
turntableon/offswitch.WhenACpowertotheturn-
tableisturnedon,automaticallythereceiverandthe
SWITCHEDblackACpoweroutletsareturnedon
Thesystemwillremainonuntiltheturntableisturn-
edoil.ThePOWERONpushbuttoncontrolstheAC
powerloranysourceotherthantheturntable.
IntheMANUALpositiononlythePOWERON
pushbuttonwillturnACpoweronoroff
Someturntableshaveelectroniccircuitsthat
drawcurrentallthetime.Tousetheseturntablesthe
AUTO/MANUALswitchmustbeintheMANUAL
position.WiththeAUTO/MANUALswitchinthe
MANUALposition,ACpowertothesystemwillbe
controlledbythefrontpanelPOWERpushbutton
only.
5

ThegreenACpoweroutletsareprotectedwitha
oneampfuse.Anyincreaseinthevalueofthisfuse
willaffecttheprotectionofthesensingcircuitand
maycausedamage.
AVHF-TVantennacanbeeffectivewhenitis
designedforbothFMandTVreception.Connectthe
twoleadsfromtheVHF-TVantennatotheANTEN-
NA300WFMpushconnectors.
CONNECTINGPROGRAMSOURCEGROUNDS
AsingleGROUNDpostisprovidedtowhich
groundsforturntables,recordchangers,tapedecks,
etc.areconnected.Topreventhumpickup,theleft
andrightprogramcablesandthegroundwirefrom
thatsourceshouldbewoundortwistedtogether.
Makesurethegroundwiredoesnotmakeanycon-
nectiontotheshieldsoftheleftandrightprogram
cablesbetweenthesourceandtheinputoftheMAC
4100.
FMPRESELECTORSWITCH
FMreceiverscanbeoverloadedbyverylarge
antennainputsignalswhenthereceiverislocated
veryneartoa FMbroadcastingstationorwhena
highgaindirectionalantennaisusedina
metropolitanarea.
Thepreselectormaybeswitchedintooroutofthe
FMRFcircuitbya slideswitchlocatedontheMAC
4100rearpanelneartheAMantenna.
WerecommendthattheFMPreselectorswitchbe
usedinthe"out"positionforallFMlisteningcondi-
tionsexceptwherethereisevidenceofoverloadby
strongstations.Inthatcase,the"in"positionwill
immunizeagainstoverload.Formoststationsthere
willbenolisteningdifferencebetweenthetwo
switchpositions.
MAC4100receiverswithserialnumbersbelow
BY3000donothavetheFMpreselectorswitch
describedabove.
CONNECTINGANFMANTENNA
Oneofthreeantennasystemscanbeused:[1]an
outdoorFMantenna,or[2]a VHF-TVantenna,or[3]
theindoordipolesupplied.
Anoutdoorantennaisrecommendedforoptimum
performanceinallareas,Infringe[outlying]areas,
bestresultswillbeobtainedwitha highlydirec-
tionalFMantennausedinconjunctionwitha
rotator.Iftheantennausesa 300ohmlead,connect
ittotheANTENNA3000FMpushconnectors.
Thecoaxialcableofanunbalanced75ohmanten-
naconnectstotherearpanelANTENNA750FM
typeF coaxialconnector.
Anoutsideantennasystemshouldnotbelocated
inthevicinityofoverheadpowerlinesorotherelec-
triclightorpowercircuits,orwhereitcanfallinto
suchpowerlinesorcircuits.Wheninstallinganout-
sideantennasystem,extremecareshouldbetaken
tokeepfromtouchingsuchpowerlinesorcircuits
ascontactwiththemmightbefatal.
CONNECTINGANINDOORDIPOLEANTENNA
Theflexiblefoldeddipoleantenna[300ohm]isfor
useinurbanorhighstrengthsignalareas.Connect
thetwoleadsfromthedipoletotheANTENNA300W
FMpushconnector.
Theflexibilityofthetwinflatwireassemblyper-
mitsittobeplacedundera rug,tackedbehindthe
stereo...orplacedinanyotherconvenientlocation.
Insomecases,itmaybenecessaryto"position"the
antennaforbestsignalreception.Thisshouldbe
donebeforeitispermanentlylocated.
Avoidlocatingtheantennanexttootherwiresor
metalobjects.Anyindoorantennamaybeineffec-
tiveinhouseshavingmetalsidingormetalfoilin-
sulation.
AMANTENNA
ForlocalandmostmoderatelydistantAMrecep-
tionthebuilt-inferriteloopstickantennamaybeus-
ed.TheAMloopstickantennaisona swivelbase
andmustbeadjustedawayfromthechassisforbest
reception.
Distantreceptioncanbeimprovedwiththeuseof
acopperantennawire50to150feetinlength.Sus-
pendthewireina straightlineashighaspossible.
Attachthewireateachendwithsuitableglassor
ceramicinsulators.Connecta lead-inwireatany
convenientpointontheantenna.Itisrecommended
thata lightningarresterbeusedwithanoutdoorAM
antenna.Thearrestershouldbewellgroundedtoa
groundrodorcoldwaterpipe.
CONNECTINGA MAXIMUM
PERFORMANCEINDICATOR
ThescopeTP1andTP2jacksontherearpanelare
usedtoconnecta Mclntoshmaximumperformance
indicatororanoscilloscope.Followdirections
outlinedinthemaximumperformanceindicator
owner'smanual.
FUSES
A4-ampSLOBLOfuseprotectsthereceivercir-
cuits.Thefusedoesnotprotectadditionalequip-
mentconnectedtotherearpanelACpoweroutlets.
Aoneampfuseprotectstheturntableautooncir-
cuit.Ifthisfuseopens,powertothegreenoutlets
willbeinterrupted.
6

7

CONNECTINGLOUDSPEAKERSFORSTEREO
Allspeakersareconnectedtothepushconnec-
torsontherearpanel.Whenstereospeakershave
beenconnectedtotheproperpushconnectors,the
correspondingfrontpanelpushbuttonsturnthe
speakersonoroff.
Selectionoftheproperguagewiretoconnectthe
loudspeakerspreservesthequalityofsoundrepro-
ductionforwhichtheloudspeakershavebeende-
signed.Ifundersizewireisused,resistanceisadded
tothereceiver/loudspeakercombinationwhich
adverselyaffectstheperformance.Addedresis-
tancecausesreductionofdampingcharacteristics,
modificationoffrequencyresponseandreductionin
poweroutput.
Uselampcord,bellwire,orwirewithsimilartype
ofinsulationtoconnectthespeakerstotheam-
plifier,inallcases,theleadstoandfromthespeaker
shouldbetwinconductorortwistedtogether.When
using8 ohmspeakersandforthenormallyshort
distancesofunder30feetbetweentheamplifierand
speaker.No.18wireorlargercanbeused.For
distancesover30feetbetweenthereceiverand
speakeruselargerdiameterwire.Selectthecorrect
sizewireforthewirelengthfromthechart.Itis
recommendedthattheDCresistanceofthespeaker
leadsbelessthan5%ofthespeakerimpedance.Up
to10%canbetolerated.Resistanceoftheleads
shouldbecomputedforthelengthofwirebothto
andfromthespeakerorspeakers.Theheaviergauge
wiresmaynotfitintotheholesinthespeakerand
receiverterminals.Attacha shortpieceoflighter
gaugewireandthenconnecttotheterminals.
MAXIMUMWIRELENGTHS
WireFor4 OhmLoadFor8 OhmLoad
Gauge
22
20
18
16
14
12
10
Wirelengthsaboverepresentthewireresistanceequalto5%
ofthespeakerimpedance
Formultiplespeakeroperation,runseparate
leadsfromthereceivertothespeakers.
Connecttheleadsfromtheleftmainloudspeaker
totheSPEAKER1 LeftandCommonpushconnec-
tors.Connecttheleadfromtherightmain
Feet
6
10
15
25
40
60
100
Meters
1.8
3.1
4.6
7.6
12.2
18.3
30.5
Feet
12
20
30
50
80
120
200
Meters
3.7
6.1
9.1
15.2
24.4
36.6
66.0
loudspeakertotheSPEAKERI RightandCommon
pushconnectors.Connecttheleadsfroma second
leftloudspeakertotheSPEAKER2 LeftandCom-
monpushconnectors.Connecttheleadfroma se-
condrightloudspeakertotheSPEAKER2 Rightand
Commonpushconnectors.Connecttheleadsfrom
athirdleftloudspeakertotheSPEAKER3 Leftand
Commonpushconnectors.Connecttheleadfroma
thirdrightloudspeakertotheSPEAKER3 Rightand
Commonpushconnectors.
CONNECTINGONELOUDSPEAKERFORMONO
TheleftandrightoutputsoftheMAC4100mustcon-
necttoseparateloudspeakers.Donotparallelthe
outputconnectionsfora singleloudspeaker.Ifthe
leftandrightoutputsareconnectedtogetherex-
cessiveheatisgeneratedinthepoweramplifiers
whichcausesdamageeventhoughtheMODE
SELECTORpushbuttonisintheMONOposition.If
youwishtodrivea singleloudspeaker,putthe
MODESELECTORinMONOandconnecttheloud-
speakertotheleftortherightspeakerpushconnec-
torsonly.Itisnotnecessarytoconnecta loadtothe
otherchanneloutput.
CONNECTINGAMCINTOSHEQUALIZER
OntheJUMPERpanel,removethejumpersbet
weenthePREAMPOUTjacksandPOWERAMPIN-
putjacks.Theenvironmentalequalizerisconnected
betweenthesejacks.Standardshieldcablescon-
nectthePREAMPOUTtotheinputoftheequalizer.
ConnecttheoutputoftheequalizertothePOWER
AMPINputjack.
CONNECTINGOTHERPOWERAMPLIFIERS
ExternalpoweramplifiersmaybefedtotheMAC
4100intwoways:
1.FedfromtheRECORDERTAPEOUT.Theout-
putatthispointisnotaffectedbythevolumeor
equalizingcontrolsoftheMAC4100.Usethisoutput
todriveanamplifierwhichhasitsowncontrols.A
possibleusewouldbetooperateanindependent
systemina remotelocationwherevolumere-
quirementsneedtobelocallycontrolled.
2.FedfromtheAMPLIFIER- PREAMPOUT
jacks.Theoutputatthesejacksisaffectedbythe
VOLUME,EQUALIZER,BALANCE,andLOUDNESS
controls.Usethisconnectiontodriveanamplifier
withoutcontrolsofitsown.orwheretheinfluenceof
thecontrolsoftheMAC4100arewantedonall
loudspeakers.
8

9

WhattheFrontPanelControlsdo
andHowtouseThem
INPUTSELECTOR
ThesixpositionIN-
PUTSELECTORcon-
trolsDCvoltagefedto
FETanalogswitches
whichchoosetheinput
programselected.The
INPUTSELECTORis
turnedto:
AUX1:toconnecttheoutputfromanyhighlevel
programsourcerequiringflatamplificationtothe
highlevelinputstage.Sucha sourcecouldbe
anothertaperecorder,a televisionset,etc.Theinput
impedanceis100,000ohms
AUX2:sameasAUX1
AM:toconnecttheAMtunercircuitstothe
amplifiersandloudspeakers
FM:toconnecttheFMtunercircuitstothe
amplifiersandloudspeakers
PHono1:toconnecttheoutputofmagnetic
phonocartridgepluggedintoPHono1 tothelow
levelamplifyingstages.Theresponseofthese
stageshasbeenshapedtopreciselyconformto
revisedRIAAstandards.Theinputimpedanceis
47,000ohms,87pf
PHono2:SameasPHono1
Pushbuttons
IMPORTANT:WhentheMAC4100isoperatedwith
eitherMONITORpushbuttonattheinposition,the
programheardwillbethatfromthetaperecorders
only.Signalfromanyothersourcewillnotbeheard
fromtheloudspeakers.Tohearanyothersource,
makesuretheMONITORpushbuttonsareOUT.
TheMONITORswitchesaremechanicallyin-
terlockedtopreventsimultaneousmonitoringfrom
twotaperecorders.Ifonebuttonisattheinposi-
tion,itmustbepushedagaintoreleaseittotheout
positionbeforetheotherbuttoncanbepushed.
TheMAC4100isdesignedsoitmaybeusedwith
twotaperecorders.Thefourupperleftpushbuttons
onthefrontpanelcontrolthesignaloutputofthese
recorders.Theypermitplaybackofeitherrecorder,
monitorofeitherrecorderasrecordingsarebeing
made,orcopyingoftapesfromonerecorderto
anotherwhilelisteningtoa separateprogram.
MONITORTAPE1 pushbuttonout:Theprogram
sourceasselectedbytheINPUTSELECTORisfed
tothepoweramplifiersandheardthroughthe
loudspeakers;pushbuttonin:Signalfroma tape
recorderpluggedintoTAPE1 INIsfedtothepower
amplifiersandheardthroughtheloudspeakers.
MONITORTAPE2 pushbutton:Functionssimilarly
tomonitorTape1.Italsocontrolstheprogramfrom
ataperecorderpluggedintothefrontpanelTAPEIN
andOUTjacks.Whena taperecorderispluggedinto
thefrontJacksallthefacilitiesnormallyfedtoTAPE
2ontherearpanelareautomaticallytransferredto
thefrontpanel.Thetaperecorderpluggedintothe
TAPE2 INandOUTjacksontherearpanelIs
automaticallydisconnected.
TAPECOPYT1- T2pushbuttonin:connectsthe
outputfromtaperecorder1 totheinputoftape
recorder2 withoutaffectingtheprogrambeing
10

heardfromthespeakers.Inthispositiona copyof
theprogramontaperecorder1 canbemadeontape
recorder2.TomonitortheoriginaluseMONITOR
TAPE1 pushbuttonandtomonitorthecopyuse
MONITORTAPE2 pushbutton.
TAPECOPYT2- T1pushbuttonin:connectsthe
outputfromtaperecorder2 totheinputoftape
recorder1 withoutaffectingtheprogrambeing
heardfromthespeakers.InthispositionA copyof
tapeprogramonrecorder2 canbemadeonrecorder
1.TomonitortheoriginaluseMONITORTAPE2
pushbuttonandtomonitorthecopyuseMONITOR
TAPE1 pushbutton.
MONO:TheMONOpushbuttonswitchestheaudio
sectionsofthereceiverfromstereomodetoMONO.
WhentheINPUTSELECTORisintheFMposition
theFMmultiplexlightwillremainonwhentunedto
aFMstereostationregardlessofthepositionofthe
MONOpushbutton.Theprogramheardwillbe
mono.TheTAPEOUTjacksarenotaffectedbythe
MONOpushbutton.
FMMUTE:Withthepushbuttonin,interstationnoise
andweakerstationsaresuppressed;pushbutton
out:noisebetweenstations,aswellasveryweak
stations,willbeheardasyoutuneacrossthedial.
SPEAKERS1,2 and3:Wheneachofthesepushbut-
tonsispushedin,a pairofloudspeakersiscon-
nectedtothepoweramplifieroutputs.Speaker1,2
and3 maybeselectedoneata time,anycombina-
tionorallatonce.
POWERON:ThePOWERONpushbuttonsharesAC
powercontrol,througha currentsensingswitchcir-
cuit,withtheACpowerswitchona turntable.Onthe
rearpaneltheTURNTABLEAUTO/MANUALswitch
selectsthemodeofoperation.
WhentheswitchisintheAUTOpositionanda
turntableispluggedintooneofthegreenACpower
outlets,theACpowertothereceiverandtothe
blackACpoweroutletscanbecontrolledbythe
turntableon/offswitch.WhenACpowertotheturn-
tableisturnedon.automaticallythereceiverandthe
SWITCHEDblackACpoweroutletsareturnedon.
Thesystemwillremainonuntiltheturntableisturn-
edoff.ThePOWERONpushbuttoncontrolstheAC
powerforanysourceotherthantheturntable.
IntheMANUALpositiononlythePOWERON
pushbuttonwillturnreceiverACpoweronoroff.
EQUALIZERFREQUENCYCONTROLS
EachoffiveEQUALIZERFREQUENCYcontrols
modifiesupwardordownwardthetonebalanceofa
bandoffrequenciescenteredonthefrequency
markedabovethecontrol.Theflatpositionofthe
controlhasa detentforeasyreference.Eachcontrol
provides12dBboostorcutatthespecifiedcenter
frequency.
UsetheEQUALIZERFREQUENCYcontrolsto
modifythesoundandtonebalanceofprogram
material.Herearesomesuggestionsfromwhichto
start:
ProblemEqualizerCorrection
BasstooweakRaise30and/or150
MalevocalistneedsreinforcingRaise150
FemalevocalistreinforcingRaise500
HumonprogramReduce30
Violins,trumpetsdullRaise1500
Drum"brushes"notaudibleRaise10K
BALANCEand
LOUDness
TheBALANCEand
LOUDnesscontrolsare
concentric.TheBAL-
ANCEcontrol[large
outerknob]adjustsfor
equalvolumeofeither
theleftorrightchan-
nels.Thevolumeofthechannelscanbevaried
relativetoeachotherwithoutaffectingtheircombin-
edvolume.
left...turningthecontroltotheleftaccentstheleft
channelbyreducingtherightchanneloutput.
right. ..turningthecontroltotherightaccentsthe
rightchannelbyreducingtheleftchanneloutput.
TheLOUDnesscontrol[smallcenterknob]in-
creasesbothbassandtreblefrequenciesofboth
channelsasitisturnedclockwise.Adjustmentof
theLOUDnesscontrolallowslife-likefrequency
balancewhenplayingmusicsoftly.Itscontouristhe
11

same,regardlessofthepositionofthevolumecon-
trol.Thiscontourisaccuratelymodelledafterthe
familyof"EqualLoudness"curvesidentifiedby
FletcherandMunson.
Theloudnesscircuitryiscompletelyindependent
ofthevolumecontrol.Therefore,anydesired
amountofcompensationcanbeintroduced
regardlessofvolumecontrolposition.
VOLUMECONTROL
TheVOLUMEcon-
trolisa precisionstep
controlmanufactured
forMclntoshLabora-
tory.Ithas32steps
witha 70dBrange,
plusvolumeoff.Left
andrightchannel
trackingarewithin
1dB.Thisextremeaccuracyisobtainedthrough
specialelectronicallycontrolledresistanceelement
trimming.Sincetheswitchcommutatortoucheson-
lycontactpadsandnottheprecisionresistor
elements,trackingaccuracyispermanentlymain-
tainedandisnoisefree.
HEADPHONEJACKS
ThefrontpanelHEADPHONEjackshavebeen
designedtofeedlowimpedancedynamichead-
phones.Electrostaticheadphonesgenerallyrequire
higherpowerthandynamicheadphones.Theymust
beconnectedtothespeakerpushconnectorsonthe
rearpanel.
PlugheadphonesintothefrontpanelHEAD-
PHONEjack.AdjustthefrontpanelVOLUMEcontrol
forcomfortableheadphonelistening.
Signaltotheheadphonejacksisnotaffectedby
theSPEAKERswitches.
FrontPanelindicators
TheMAC4100hasthreedialscales:
1.AM- marked550to1600kHz
2.FM- marked88to108MHz
3.LoggingScale- 0-100
Asthetuningknobisturned,thetuningindicator
movesacrossthedial.Tomaketuningeasieronly
theportionoftheindicatordirectlybehindtheap-
propriatedialscaleislighted.OnFM,theupperpor-
tionoftheindicatorislighted.OnAM,thelowerpor-
tionislighted.
Theloggingscalecanbeusedtoaccurately
retuneanystation.Youmayfinditeasiertokeepa
recordofyourfavoritestationsbyuseofthelogging
scale.
FMTUNINGMETER
AnFMstationiscorrectly
tunedwhenthemeterneedleis
intheblackareaoftheFMtun-
ingmeterandtheAFLin-
dicatorlightislighted.
SIGNALSTRENGTHMETER
WhentuningeitheranFMorAMsignalthesignal
strengthmeterindicatesthestrengthofthesignal
asreceivedfromtheantenna.Thehighertheindica-
tionthestrongerthesignal.
AMPLIFIERPOWER
OUTPUTINDICATORS
TheamplifierPOWERoutputin-
dicatorsaretotheleftofthetuning
dial.Therearetwoverticalcolumns
ofsevenyellowLightEmittingDiode
[LED]indicators- theleftcolumnfor
theleftchannelandrightcolumnfor-
therightchannel.
Aspowertotheloudspeakersisincreased,more
LEDsareturnedon,vertically,indicatingthein-
crease.Eachrowisindependentoftheother.The
LEDsprovideconstantandinstantinformationon
theamountofpowerbeingfedtoyourspeakers.
POWERGUARD
POWERGUARDassuresthattheamplifiercannot
12

beoverdrivensoamplifieroutputclippingis
eliminated.Clippingiscausedwhentheamplifieris
askedtoproducemorepoweroutputthanitcan
deliverwithlowdistortion.Amplifiersarecapableof
deliveringlargequantitiesofpowerwhentheyare
driventoclippingandcanhavemorethan40%har-
monicdistortion.Theextraenergycontentofthe
clippedsignalwilldamagemostspeakers.A Mcln-
toshadvancementhelpstoprotectyourspeaker
fromthiskindofdamage.TheMAC4100hasa built
in"waveformcomparator"thatcomparesthewave
shapeoftheinputsignalwiththeoutputsignal.If
thenon-linearitybetweenthetwosignalsexceeds
0.5%thePOWERGUARDcircuitoperates.Opera-
tionisindicatedwhentheLEDsatthetopofthe
amplifierpowerindicatorarelightedinred.Aslong
astheamplifieroperateswithoutoverloadtheNOR-
MALindicatorilluminates.WithPOWERGUARD
operatingtheoutputwaveformdistortionislimited
to1 %.
INPUTINDICATORS
Atthebottomrightofthetuningdialareaare
eightLEDs,sixindicatethestatusoftheINPUT
SELECTORswitch.TheilluminatedLEDindicates
theprogramsourceselected.
ThetworemainingLEDsindicateAFLandFM
MPX.AFLindicatestheoperationoftheautomatic
frequencylockcircuitshowingthatthetuneriscor-
rectlytunedtothecenterfrequencyoftheFMsta-
tion.
FMMPX- indicatestheFMstationisbroad-
castinga 19kHzpilotsignalnecessaryforthe
transmissionofFMstereoprograms.Itdenotesthe
stationisbroadcastingstereo.
BalancingYourStereo
Theperformanceandenjoymentofa stereo
systemisgreatlyincreasedwhenthesoundispro-
perlybalanced.Thebalanceofthestereosystemis
affectedbymanythingsincludingroomacoustics,
furnitureplacement,roomshape,smalldifferences
inloudspeakersetc.Factorsthataffectproper
stereobalancearecorrectphaseforbothchannels
andequalprogramloudness.
TOADJUSTPHASE
PresstheMONOpushbutton.TurntheBALANCE
controlto12o'clock.StandabouttenfeetInfrontof
andmidwaybetweentheloudspeakers.Thesound
shouldappeartocomedirectlyfrominfrontofyou.
Ifthesoundisnotdirectlyinfrontofyou,reversethe
leadsononeoftheloudspeakersonly.Whenthe
soundcomesfromthemidpointbetweenthe
speakerstheyareinphase.
TOBALANCELOUDNESS
PresstheMONOpushbutton.Playa familiar
recording.TurntheBALANCEcontroltothe12
o'clockposition.Whiletheprogramisplayingstand
betweenthetwoloudspeakers.Listenfora dif-
ferenceinloudnessbetweenspeakers.Ifthereisa
differenceinloudness,turntheBALANCEcontrol
towardthespeakerthatisnotasloud.Adjustthe
BALANCEcontroluntilthesoundisbalancedbet-
weenbothspeakers.
ListeningtoYourStereo
FORALLLISTENING
Setthe"SPEAKERS"pushbuttonsinforopera-
tionofthedesiredspeakers.Setthemonitor
pushbuttonsoutexceptfortapelistening.Turnon
powerbypressingthePOWERONbuttonin.
LISTENINGTOASTEREORECORD
TurntheINPUTSELECTORtoPHono1 orPHono2
whicheverisconnectedtotheturntableyouwishto
hear.SettheMONOpushbuttonoutforstereo.Ad-
justtheVOLUMEcontroltodesiredvolume.Adjust
theLOUDnesscontrolforanydesiredcompensa-
tion.
LISTENINGTOA MONOPHONICRECORD
PushtheMONOpushbuttoninforMONO.Adjust
theVOLUMEcontroltodesiredvolume.Adjustthe
LOUDnesscontroltoanydesiredcompensation.
LISTENINGTOASTEREOTAPERECORDER
PushineitherMONITORTAPE1 orTAPE2,
whicheverisconnectedtothetaperecorderyou
13

wishtohear.SettheMONOpushbuttonoutfor
stereo.AdjusttheVOLUMEtodesiredvolume.Ad-
justtheLOUDnesscontroltoanydesiredcompensa-
tion.
TAPEMONITORING
ToMONITORtheprogrambeingrecorded,pressthe
correspondingMONITORTAPEpushbuttonin.
Aprogrambeingrecordedmaybemonitoredfrom
theplaybackheadofthetaperecorderasthepro-
gramisbeingrecordedifthetaperecorderhas
separateplaybackheadsandassociated
preamplifiers.
Aprogrammaybemodifiedwithequalizer,
balanceandloudnesscontrolsbeforerecording,by
connectingthetaperecorderinputstotheJUMPER
PREAMPOUTjacksontherearpanel.Allfrontpanel
controls,then,influencetheoutputofthetape
recorder.Notethatoncerecordinghasstarted,ad-
justmentofthecontrolswillchangetheprogramto
thetaperecorder.Inaddition,theavailablesignal
outputismuchhigherthantheoutputavailablefrom
theRECORDERTAPEOUTjacks.Besurethesignal
doesnotoverloadthetaperecorderinput.Tohear
theprogramfromtheloudspeakersa "Y"connector
mustbeusedtojointhetaperecorder,the
preamplifieroutputandpoweramplifierinput.
choice.Formostaccuratefinetuningofthestation,
adjustthetuningknobuntiltheAFLindicatorlights;
asureindicationthatthestationisexactlytuned
andlockedin.AdjusttheVOLUMEtoa comfortable
level.TheFMmutingcircuitsuppressesnoisebet-
weenstations.Italsosuppressesweakerstations
notstrongenoughtooverridethebackgroundnoise.
Mutingthreshold,carefullyadjustedtooptimumat
thefactory,determinesthestrengthofthesignal
whichcanbeheardwithmutinginoperation.While
tuningyoumaynoticethetuningindicatorwillshow
astationyetnoprogramisheardfromthe
loudspeakers.Themutingcircuitinthetunerhasre-
jectedthestationbecausethereisnoiseaccompa-
nyingtheweaksignal.PushtheFMMUTEpushbut-
tontotheoutpositionandthestationwillbeheard.
Mostprogramsthatcanbetunedinthismannerare
ofpoorqualityduetointerferingnoise.
LISTENINGTOAM
TurntheINPUTSELECTORtoAM.Rotatethetun-
ingknobsothestationofyourchoiceshowsmax-
imumdeflectionoftheSIGNALstrengthmeter.Ad-
justtheVOLUMEtoa comfortablelevel.
LISTENINGTOFMORFMSTEREO
TurntheINPUTSELECTORtoFM.SettheMONO
pushbuttoninthestereooroutposition.TheMAC
4100usesa Mclntoshdevelopedautomatic
mono/stereoswitchingcircuit.Theswitchingis
electronicandswitchessmoothlyandsilently
withoutclicksortransients.Whenthe19kHzpilot
signalforstereotransmissionisreceivedthe
automaticcircuitryswitchestheMAC4100tostereo
andtheFMMPXLEDindicatoristurnedon.Ifthe
FMstationis"notbroadcastinga 19kHzpilotsignal
theFMMPXIndicatorwillremainoffandthetuner
willautomaticallyswitchtomono.
Rotatethetuningknobtothestationofyour
14

MAG4100PerformanceLimits
WepromiseyouthattheMAC4100youbuyis
capableofperformanceatorexceedingtheselimits
atthetimeofpurchaseoryougetyourmoneyback.
MclntoshPERFORMANCELIMITSarethemaximum
departurefromperformanceperfectionpermitted
fora Mclntoshinstrument.
Performance
Mclntoshaudiopowerratingsareinaccordance
withtheFederalTradeCommissionRegulationof
November4,1974concerningpoweroutputclaims
foramplifiersusedinhomeentertainmentproducts.
POWEROUTPUT
100wattsminimumsinewavecontinuousaverage
poweroutput,perchannel,bothchannelsoperating
into4 ohms20Hzto20kHz,withnomorethan.05%
totalharmonicdistortion.
75wattsminimumsinewavecontinuousaverage
poweroutput,perchannel,bothchannelsoperating
into8 ohms20Hzto20kHz,withnomorethan.05%
totalharmonicdistortion.
OUTPUTLOADIMPEDANCE
4ohms,8 ohms
RATEDPOWERBAND
20Hzto20kHz
TOTALHARMONICDISTORTION
.05%maximumatanypowerlevelfrom250
milliwattstoratedpowerperchannel,20Hzto20
kHz,bothchannelsoperating.
INTERMODULATIONDISTORTION
.05%maximumatanypowerlevelfrom250
milliwattstoratedpower-perchannelbothchannels
operatingforanycombinationoffrequencies20Hz
to20 kHz.
FREQUENCYRESPONSE
20Hzto20kHz+0,-0.5dBatratedpower
HUMANDNOISE
PowerAmp:100dBIHFA,95dBunweighted,below
ratedoutput
TapeandAuxInput:95dBIHFA,90dBunweighted,
belowratedoutput
PhonoInput:90dBIHFA,80dBunweighted,below
10mVinput
DAMPINGFACTOR
Greaterthan30
INPUTSENSITIVITYANDIMPEDANCE
PowerAmp:2.5V;22,000ohms
TapeandAux:250mV;100,000ohms
Phono:2 mV;47,000ohms;87pF
TAPEOUTPUT
Tuner:1.0Vat100%modulation[FM]
Tape:250mVwithratedinput
Phono:250mVwithratedinput
PROGRAMEQUALIZER
±12dBat30,150,500,1500,and10,000Hz
AMSECTION
SENSITIVITY
75µVIHF[Externalantenna]
SIGNALTONOISERATIO
45dBminimumIHF,55dBat100%modulation
HARMONICDISTORTION
1%maximumat30%modulation
FREQUENCYRESPONSE
3500Hz© -6dB
ADJACENTCHANNELSELECTIVITY
30dBminimumIHF
IMAGEREJECTION
65dBminimum,540kHzto1600kHz
FMSECTION
SENSITIVITY
2.5uV[13dBF]IHFminimum
SIGNALTONOISERATIO
70dBIHFminimum
HARMONICDISTORTION
Mono:0.18%IHFmaximum
Stereo:0.38%IHFmaximum
FREQUENCYRESPONSE
20Hzto15kHz+0,-1dB
CAPTURERATIO
1.8dB
SELECTIVITY
75dBIHFminimum
SPURIOUSREJECTION
90dBIHFminimum
15

IMAGEREJECTION
80dBIHFminimum
STEREOSEPARATION
45dBminimumat1 kHz
SCAREJECTION
60dBminimum
GENERAL
SEMICONDUCTORCOMPLEMENT
45Transistors
31IntegratedCircuits
62Diodes
1SiliconControlledRectifier
MECHANICALINFORMATION
SIZE:
Incabinet:18-5/8inches(473.1mm)wide,6-1/2in-
ches(165.1mm)high,15-1/2inches(393.7mm)deep.
Withoutcabinet:Frontpanelmeasures17-9/16in-
ches(446.1mm)wideby5-1/4inches(133.4mm}high.
Chassismeasures17-1/8inches(435mm)wideby
4-15/16inches(125.4mm)highby13-1/2inches
(342.9mm)deep.Knobandhandleclearancere-
quiredis1-1/16inches(27mm)infrontofthemoun-
tingsurface.
FINISH:
Frontpanelisclearanodizedtoproducea brushed
satin- silverfinishwithblackanodizedtrim.Cabinet
iswalnutgrainedvinyl
WEIGHT:
42pounds(19kg)net
56pounds(25.4kg)inshippingcarton
TechnicalDescription
Engineeringdirectiondictateda receiverdesign
governedbyinsistenceona preamplifierwithex-
cellentflexibility,a FMsectionwithgreatsensitivity
andhighselectivity,anAMsectionwhoseperfor-
mancemaximizesreceptioncapabilitiesanda high
performance,highpowerstereopoweramplifier.
Thesevalueswereachievedandtheyretainthe
Mclntoshreputationoflonglifeandreliability.
FMSECTION
Theradiofrequency[RFsection]housesthecom-
pleteFM-RFfrontendandpartoftheAM-RFcir-
cuitry.A sevensectionvariablecapacitoristhe
heartoftheRFsection.Foursectionsofthevariable
capacitorareusedforFM.Theremainingthreeare
usedintheAMsection.Byinterleavingthesections:
AM/FM/AM/FMetc.,spuriousresponseshavebeen
significantlyreduced.Theuseofthelateststateof
theartMOSfieldeffecttransistorsaswellasa
carefullydesignedvariabletuningcapacitorhaspro-
videda highdegreeofRFselectivityandexcellent
spuriousresponserejection.Imagerejectionand
spuriousresponseshavebeenbroughttoa
minimumintheRFsection.A dualinsulatedgate
metaloxidesiliconfieldeffecttransistor[MOS-FET]
isusedasthefirstRFamplifier.Eachgateofthe
transistorisinternallyprotectedbyzenerdiodes
againstincomingexternallygeneratedtransients.
UseoftheMOS-FETgreatlyreducescrossmodula-
tionovera widerdynamicrange.Thisdynamicrange
permitstheinputcircuittoacceptextremelystrong
signalswithoutoverload.Themixerhasbeen
designedtouseanotherMOS-FETforhighsensitivi-
ty,lowcrossmodulation,andfreedomfrom
overload.Lowtemperatureco-efficientcomponents
areusedintheFMlocaloscillatortopreventfre-
quencydrift.Thisassuresthatyouareproperlytun-
edtothestation.Foroptimumsignaltransferand
lowerdistortion,a specialmatchingtransformerhas
beendesignedtointerfacetheFM-RFtotheFM-IF
amplifier.Thismatchingtransformerimproves
phaselinearityoftheIFamplifier.
AlloftheRFcircuitstotheFMsectionsofthe
variablecapacitorareencasedina metalmodule.
WithinthemetalmoduleeachFM-RFsectionis
separatelyshieldedbymetalpartitions.Thisex-
tremeshieldinggivesprotectionagainstradiationor
interference.
Antennaconnectionsforeither300ohmtwinlead
transmissionlineor75ohmcoaxialcableareprovid-
edontherearpanel.Thenormalinputimpedanceof
theRFamplifieris75ohms.Impedancematchto
300ohmsisprovidedbya Mclntoshdesignedbalun
transformer.Connectionsfora 300ohmlineare
madewithpushtypeterminalsthatdonotrequire
theuseoftools.Forthe75ohminput,a typeF con-
nectorisprovided.
TheFM-IFsectionconsistsoffiveintegratedcir-
cuitsandfourpiezo-electricfilters.Theycombineto
givea totalgainofover140dB.Thesignalis
amplifiedtenmilliontimes.Theresponsecurvehas
nearlylinearphasecharacteristics.Theskirtsofthe
responsecurveareverysteep.Themaximumwidth
is170kHzat3 dBand500kHzat60dB.The
responseissymmetricaleachsideofthecenterfre-
quency.Thefiltersarepermanentlysealedand
neverrequireadjustmentandcannotdriftnorvibrate
outofadjustment.Theexceptionallyhighgainof
thefiveintegratedcircuitsassureshardlimitingat
16

verylowlevelsofInputsignal.
AFoster-Seeleydiscriminatorhasbeendesigned
tocomplementtheintegratedcircuitIFsection.The
detectedoutputofthediscriminatorisextremely
lowindistortion.
FMSTEREOMULTIPLEX
Theheartofthemultiplexsectionisa newthird
generationphaselockloop(PLL)stereodecoderin-
tegratedcircuit(IC).ThisPLLICincorporatestwo
specialsystems,anautomaticvariableseparation
controlcircuittoreducebackgroundnoisewhen
receivingweakstereostations,anda tri-leveldigital
waveformgenerationwhicheliminatesinterference
fromSCAsignalsandfromthesidebandsofadja-
centchannelFMsignals.
Thevariableseparationcontrolisoperatedfrom
theIFamplifier'ssignalstrengthdetectorsystem.A
smoothtransitionisprovidedfrommonotostereoor
visaversaatweaksignallevelstoprovidetheop-
timumsignaltonoiseratioandbeststereosepara-
tionfortheprevailingsignalconditions.Thecircuit
operatesonlyduringstereoreception,Itswitches
automaticallytomonauralifthe19kHzpilottoneis
absent.
InthePLLtheinternaloscillatoroperatesat228
kHzlockedtothe19kHzpilottone.The228kHz
feedsa 3 stageJohnsoncounterviaa binarydivider
togeneratea seriesofsquarewaves.Suitablycon-
nectedNANDgatesandexclusiveORgatesproduce
thetri-leveldrivewaveformforthevariousde-
modulatorsinthecircuit.Theusualsquarewave-
formshavebeenreplacedinthePLLanddecoder
sectionsbytri-levelwaveforms.Thesetri-levelforms
containnoharmonicswhicharemultiplesof2 or3.
Thiseliminatesfrequencytranslationanddetection
ofinterferencefromtheside-bandsofadjacentsta-
tionssincethethirdharmonicofthesub-carrier(114
kHz)isexcludedandinterferencefromSCAbroad-
castssincethethirdharmonicofthepilottone(57
kHz)isexcluded.Unwantedspuriousaudiblecom-
ponentsandphasejitterinthePLLwithconsequent
intermodulationdistortionareinherentlyeliminated
bythistechnique.
Additionaladvantagesofthephaselockedloop
stereodemodulationaretheeliminationofinduc-
torstominimizedrift,integrallampdrivingcapabili-
tytoindicatethepresenceofthe19kHzpilotcarrier,
excellentchannelseparationovertheentireaudio
frequencyrange,extremelylowdistortion,lowout-
putimpedance,andtransient-freemono/stereoswit-
ching.
Aftermultiplexdetection,19kHzpilotand38kHz
carriersuppressioncircuitsareusedtopreventtape
recorderinterference.
TheFMmutingcircuitisunusual.Itoperatesboth
bydetectingultrasonicnoiseandbysensingcorrect
tuningofthedetectorcircuit.To'un-mute'itis
necessaryforthesignaltohaveanadequatesignal-
to-noiseratioandtobetunedtothecenteroftheFM
carrier.TheMUTINGcircuitcanbeactivatedor
defeatedbythefrontpanelmutingpushbutton.The
switchingonandoffoftheaudiosignalisdonewith
FETanalogswitches.
AMSECTION
TheAM-RFamplifiercircuitincludesa threesec-
tionvariabletuningcapacitorina metalenclosure.
Thisthreesectionvariablecapacitorisusedfor
greaterspuriousrejection.TheMclntoshAMRF
amplifiercircuitisunique.Ithasconstantsensitivi-
ty,constantselectivityandhighimagerejection
acrossthecompleteAMband.OrdinaryAM-RFcir-
cuitscannotdoallofthissimultaneously.This
designachievesequalsensitivityevendowntothe
lowendoftheband.Spurious,imageandin-
termediatefrequencyrejectionareallsuperior.The
samecircuitdeliversequalselectivityacrosstheen-
tireband.TheMclntoshcircuitisuniqueina super
heterodyneAMreceiver.Inaddition,thereisnoloss
ofaudiofrequencyresponseatthelowendofthe
band.AnotheradvantageoftheMclntoshcircuitis
freedomfromcrossmodulationandoverloadingby
stronglocalstations.A highqualityloopstickanten-
naisprovidedandcanberotatedformaximumper-
formanceover180degrees.EachMAC4100
loopstickisindividuallytunedforoptimumperfor-
mance.Aftertuning,theloopstickissealed.This
custommatchingoftheloopsticktotheAM-RFfront
endmaximizestheperformanceoftheloopstick
antenna.
Arearpanelantennaconnectorisprovidedfor
connectinganexternalantennaifdesired.Tomain-
taintheexcellentimagerejectionandspurious
crossmodulationoftheAM-RFamplifier,an
autodynecircuitwasusedfortheAMmixer.TheAM-
IFusestwodoubletunedIFtransformersdesigned
toobtaina highdegreeofselectivityyetallowing
goodaudiofidelity.A 10kHzactivefiltereliminates
thewhistleandirritatingmonkeychattercausedby
anadjacentstation.Thefrequencyresponseofall
stationsisnearlyflatfrom20Hzto3,500Hzthen
rolloffbegins.Becauseoftheactivefilterthe10kHz
whistleelementsaredownover30dBorone-
thousandthofwhattheywouldbewithouta filter.
Theautomaticvolumecontrolsystemwasdesigned
topreventburstingorthumpswhentheAMistuned
througha strongsignal.Distortionatlowaudiofre-
quenciesisminimizingbyusinga two-sectionfilter
insteadoftheconventionalsinglesection.
INPUTSELECTORSWITCHING
Lowlevel,noisesensitiveinputselectorswitching
isdoneelectronicallyusingfieldeffectanalogswit-
ches.Thefrontpanelselectorsimplyswitchessmall
17

amountsofDCwhichturntheFETanalogswitches
offoron.Thedesigneliminatesdegradationoffre-
quencyresponseandnoisepickupfromlongsignal
pathsnecessarywithconventionalswitching.
PHONOAMPLIFIER
Thephonoamplifierusesa hightechnologyin-
tegratedcircuitoperationalamplifier.Itsdifferential
inputstagehasbeenoptimizedforlownoiseand
lowdistortionperformance.Openloopgainofthis
integratedcircuitis100,000-Withhighopenloop
gaina largeamountofnegativefeedbackcanbeus-
edaroundthephonoamplifiertofurtherreduce
noiseanddistortion.Thefeedbacknetworkalsopro-
videsprecisionRIAAfrequencycompensation.The
networkuses1%metalfilmresistorsand5%poly
filmcapacitors.Toachievelownoiseperformanceit
isessentialthatthefeedbacknetworkbeverylow
impedance.Asa consequence,thepreamplifier
mustbecapableofoperatingasa poweramplifierto
drivethisimpedance.Theactualpoweroutput
capabilityofthispreamplifierstageismorethan100
milliwatts,a greatmarginbeyondthatwhichisre-
quired.
Inputsensitivityofthephonoamplifieris2
millivolts.Thegainoftheamplifieris42dBat1000
Hz.Thephonoamplifierhasa verywidedynamic
range.At1000Hzthephonoinputcircuitwillaccept
100millivoltswithoutoverload,a voltagefargreater
thantheoutputofanycurrentmagneticphonocar-
tridge.Phonoinputoverloadthereforeisvirtuallyim-
possible.A signallevelof10millivoltsatthephono
inputat1000Hzwillproduce1.2voltsatthetape
output.Thetapeoutputhasa sourceimpedanceof
200ohms,designedtooperateintoa loadim-
pedanceof47,000ohmsorgreater.
HIGHLEVELAMPLIFIER
Attheinputtothehighlevelorloudnessamplifier
thesignalpassesthroughtheMONO/stereoswitch,
thenthroughthevolumecontrol,andintothe
amplifier.Inthepastloudnesscontrolshavetypical-
lyusedsimplepassivecircuitsconnectedtoa tap
onthevolumecontrol.Asa consequence,compen-
sationaccuracywasdependentonmanyvariables
suchasvolumecontrolpositionanddifferencesin
inputlevel.TheMAC4100usesactivecircuitry.The
sametypeofintegratedcircuitoperationalamplifier
thatisusedinthephonoamplifierisusedhere.It
hastwofeedbackloops.Onefeedbackloopisflat.
TheotherfeedbackloopconformstotheFletcher-
Munson equalloudnesscompensation.A poten-
tiometerisplacedbetweenthesetwofeedback
loopsmakingitpossibletoselectanycombination
ofthetwofroma flatresponsetofullloudnesscom-
pensation.Theoverallgainofthestageis20dBand
isnotaffectedbythepositionoftheloudnesscon-
trol.
EQUALIZERAMPLIFIER
Theequalizeramplifieruseshightechnologyin-
tegratedcircuitoperationalamplifiers.It'soutput
stagehasbeenoptimizedforthebesttransientper-
formanceandminimumdistortion.Fiveotheropera-
tionalamplifiersareeacharrangedina circuitcon-
figurationthataretheequivalentofseriestunedcir-
cuits,oneateachofthefivecenterfrequencies.
Eachseriestunedcircuitisinsertedviathecontrol
potentiometerineithertheinputcircuitorfeedback
circuitoftheoperationalamplifiertherebyproviding
aboostandcutcapabilityof12dBforeachbandof
frequencies.
POWERAMPLIFIER
Theinputimpedanceofthepoweramplifieris
22,000ohms.Itrequires2.5voltsRMStodrivethe
amplifiertoratedoutput.Attheinputofthepower
amplifiertwotransistorsareconnectedasa dif-
ferentialamplifier.Thetwoinputsignalstothedif-
ferentialpairaretheinputsignalandthenegative
feedbacksignalfromthepoweramplifier.Thedif-
ferentialamplifierpermitsthebestuseofnegative
feedbacktomaintainlownoiseandlowdistortion
performance.Theoutputsofthedifferential
amplifierarecombinedina currentmirrortoa single
output.Thiscombinedsignalfeedsa linearvoltage
amplifierwhichinturndrivestwomediumpower
drivertransistors.Thedrivertransistorsfeedtheout-
putstages.Theoutputsectionisarrangedasa fully
complementarydirectcoupledseriespush/pull
amplifier.Thepowertransistorsusedintheoutput
circuitareselectedfortheirhighpowerdissipation
capability,widefrequencyresponse,andlargesafe
operatingarea.Thepowertransistorsaremounted
onlargeblackanodizedheatsinkstoassurethat
undernormaloperatingconditionsthetransistors
willoperateata lowtemperature.Ifoperating
temperaturesshouldincreaseduetoa shorted
speakerorrestrictedventilation,anautomaticsens-
ingdeviceturnsthespeakercircuitoff.Thespeaker
circuitwillturnonagainwhenthetemperaturehas
returnedtoitsnormallimits.Thisadditionalprotec-
tionassuresyouofreliabilityevenunderthemost
extremeoperatingconditions.Tofurtherinsure
reliabilitya specialpoweroutputSENTRY
MONITORINGCIRCUITpreventsfailureofthepower
amplifiertransistorsduetoexcessivemismatchor
shortingoftheoutput.WhentheMAC4100operates
normallytheSENTRYMONITORINGCIRCUIThas
noeffectonsignalspassingthroughthepower
amplifier.Ifthepowerdissipationintheoutputtran-
sistorsshouldriseabovenormaldesignlimitsthe
SENTRYMONITORINGCIRCUITrestrictsthedrive
totheoutputstagewhichreducesthedissipationin
theoutputtransistors.TheSENTRYMONITORING
CIRCUITactsinstantaneouslyforanyinputsignalor
loadcombination.Thisarrangementassurescircuit
reliability.OnlyMclntoshgivesyouthisdegreeof
protection.
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