McIntosh C 504 User manual

THEMclNTOSHC 504STEREOPREAMPLIFIER
ReadingTime:30Minutes Price:$2.00

SerialNumber
Purchasedate
ServiceContractNumber
VARIOUSREGULATORYAGENCIESREQUIRETHATWEBRINGTHEFOLLOWING
INFORMATIONTOYOURATTENTION.PLEASEREADITCAREFULLY.
WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNITTO
RAINORMOISTURE.
TheMcintoshyouhavepurchasedisa Model
C504.Ithasa serialnumberlocatedontherearpanel
ofthechassis.Recordthatserialnumberhere:
Themodel,serialnumberandpurchasedateare
importanttoyouforanyfutureservice.Recordthe
purchasedatehere:
Uponapplication,McintoshLaboratoryprovidesa
Three-YearServiceContract.YourMcintoshauthoriz-
edServiceAgencycanexpediterepairswhenyoupro-
videtheServiceContractwiththeinstrumentforre-
pair.Toassist,recordyourServiceContractnumber
here:

YourC 504StereoPreamplifier
willgiveyoumanyyearsofpleasantand
satisfactoryperformance.Ifyou
haveanyquestions,pleasecontact:
CUSTOMERSERVICE
McintoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Phone:[phone]
TakeAdvantageof3 years
ofContractService-
FillintheApplicationNOW.
AnapplicationforA THREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:
1.Mcintoshwillprovideallparts,
materialsandlaborneededtoreturnthe
measuredperformanceoftheinstru-
menttotheoriginalperformancelimits.
TheSERVICECONTRACTdoesnot
coveranyshippingcoststoandfrom
theauthorizedserviceagencyorthe
factory.
2.AnyMcintoshauthorizedserviceagency
willrepairMcintoshinsturmentsatnor-
malservicerates.Toreceiveservice
underthetermsoftheSERVICECON-
TRACT,theSERVICECONTRACTCER-
TIFICATEmustbepresentedwhenthe
instrumentistakentotheserviceagency.
3.Alwayshaveservicedonebya
Mcintoshauthorizedserviceagency.If
theinstrumentismodifiedordamaged
asa resultofunauthorizedrepair,the
SERVICECONTRACTwillbecancelled.
Damagebyimproperuseormishan-
dlingisnotcoveredbytheSERVICE
CONTRACT.
4.TheSERVICECONTRACTisissuedto
youastheoriginalpurchaser.Topro-
tectyoufrommisrepresentation,this
contractcannotbetransferredtoa se-
condowner.
5.ToreceivetheSERVICECONTRACT,
yourpurchasemustbemadefroma
Mcintoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfor
theSERVICECONTRACTmustbe
postmarkedwithin30daysofthedate
ofpurchaseoftheinstrument.
7.ToreceivetheSERVICECONTRACT,all
informationontheapplicationmustbe
filledin.TheSERVICECONTRACTwill
beissuedwhenthecompletelyfilledin
applicationisreceivedbyMcintosh
LaboratoryIncorporatedinBinghamton,
NewYork.
Copyright1980byMcintoshLaboratoryInc.
-1-
Contents
INSTALLATION2,3
HOWTOCONNECTAND
BACKPANELINFORMATION4
FRONTPANELINFORMATION
ANDUSEOFCONTROLS6,7
PERFORMANCELIMITS8
PERFORMANCECHARTS9
TECHNICALDESCRIPTION10
BLOCKDIAGRAM12,13
MclNTOSHTHREEYEARSERVICECONTRACT

mendedminimumspaceforinstallationis15inches
(38.1cm)deep,17inches(43.2cm)wide,and4 ½ in-
ches(11.4cm)high.
Toinstalltheinstrumentina Mcintoshcabinet,
followtheinstructionsthatareenclosedwiththe
cabinet.Foranyothertypeofinstallationfollow
theseinstructions:
1.OpenthecartonandremovethePANLOC
brackets,hardwarepackage,andmountingtemplate
fromthecarton.RemovetheC 504fromitsplastic
bagandplaceitupsidedownontheshippingpallet;
unscrewthefourplasticfeetfromthebottomofthe
chassis.
2.Markthecabinetpanel.
Placethemountingtemplateinthepositiononthe
cabinetpanelwheretheinstrumentistobeinstalled,
andtapeitinplace.Thebrokenlinesthatrepresent
theoutlineoftherectangularcutoutalsorepresent
theoutsidedimensionsofthechassis.Makesure
theselinesclearshelves,partitions,oranyequip-
ment.Withthetemplateinplace,firstmarkthesixA
andB holesandthefoursmallholesthatlocatethe
cornersofthecutout.Then,jointhefourcornermark-
ingswithpencillines,usingtheedgeofthetemplate
asa straightedge.
3.DrillHoles.
Usea drillwitha 3/16inchbitheldperpendicularto
thepanelanddrillthesixA andB holes.Then,usinga
drillbitslightlywiderthanthetipofyoursawblade,
drilloneholeateachoftwodiagonallyoppositecor-
ners.Theholesshouldbarelytouchtheinsideedgeof
thepenciledoutline.Beforetakingthenextstep,make
surethatthesixA andB holeshavebeendrilled.
4.SawthePanelCutout.
Sawcarefullyontheinsideofthepenciledlines.First
makethetwolongcutsandthenthetwoshortcuts.
Aftertherectangularopeninghasbeencutout,usea
filetosquarethecornersandsmoothanyir-
regularitiesinthecutedges.
ThePANLOCsystemofinstallingequipmentcon-
venientlyandsecurelyisa productofMcintosh
research.BydepressingthetwoPANLOCbuttonson
thefrontpanel,theinstrumentcanbelockedfirmlyin
placeoritcanbeunlockedsothatthechassiscan
slideforward,givingyoueasyaccesstothetopand
rearpanels.
Thetrouble-freelifeofanelectronicinstrumentis
greatlyextendedbyprovidingsufficientventilationto
preventthebuildupofhighinternaltemperaturesthat
causedeterioration.Allowenoughclearancesothat
coolaircanenteratthebottomofthecabinetandbe
ventedfromthetop.Withadequateventilationthein-
strumentcanbemountedinanyposition.Therecom-
-2-

5.InstalltheMountingStrips.
Inthehardwarepackageyouwillfindtwomounting
strips,four6-32x 1-1/4inchfillisterheadscrewsand
two4-40x 1-1/4inchflatheadscrews.Thesearelong
enoughforanycabinetpanelthicknessuptoone
inch.
Startingattheright-handsideofthepanel,inserta
4-40x 1-1/4inchflatheadscrewintothecenterholein
thepanel,markedB onthetemplate.Onthebackof
thepanel,aligna mountingstripwiththeholesinthe
panelandtightenthescrewuntilthescrewheadis
pulledslightlyintothewood.
Repeatthisproceduretoattachthemountingstrip
totheleftsideofthepanel.
6.AttachthePANLOCBrackets.
Usingtwoofthe6-32x 1-1/4inchfillisterheadscrews
intheA holesoneachside,attachthePANLOC
bracketstothecabinetpanel;theshortflangeis
mountedagainstthefront(face)ofthecabinetpanel.
ThescrewspassthroughthePANLOCbracketflange,
thecabinetpanel,andthenthroughthemounting
stripspreviouslymounted.
7.InstalltheInstrument.
GuidetheACpowercordthroughthepanelopening
tothebackofthecabinet;then,slidetheinstrument
intotheopeningcarefullysothattherailsonthebot-
tomofeachsideofthechassisengagethetrackson
themountingbrackets.Continuetoslidetheinstru-
mentintothecabinetuntilitisstoppedbytheadjust
positionlatches.Pressthelatchesinward,thisper-
mitstheinstrumenttoslideintothecabinetuntilits
frontpanelisflushwiththecabinetpanel.Depress
thePANLOCbuttonsatthelowerleftandrightcor-
nersoftheinstrumentpaneltolocktheunitfirmlyin
thecabinet.DepressingthePANLOCbuttonsagain
willunlocktheinstrumentsothatitcanslideforward
totheadjustposition;ifyoupressinwardonthead-
justpositionlatchesthenyoucanremovetheinstru-
mentfromthecabinet.
-3-

HowtoConnectand
BackPanelInformation
Refertothedrawingonpage5.
Rearpanelinputjacksareprovidedfora stereo
highlevelsource(AUX),2 stereoturntables(PH1 and
PH2),2 stereotaperecorders(TAPE1 andTAPE2),
anda stereotuner.
Rearpaneloutputjacksareprovidedtofeed2
stereotaperecorders(TAPE1 andTAPE2),anda
stereopoweramplifier(MAIN).
AFrontpanelheadphonejackisprovidedwhichis
fedbyanamplifierintheC 504.
CONNECTINGTURNTABLES
Connectthecablefromtheleftchanneloftheturn-
tableintotheINPUTPHono1 Leftjack.Connectthe
cablefromtherightchanneloftheturntableintothe
INPUTPHono1 Rightjack.TheC 504hasshorting
plugsinthePhono2 inputstopreventunwanted
noise.Removetheshortingplugsfromtheinputjacks
onlywhentheyaretobeused.Fora secondturntable,
connectPHono2 inthesameway,afterremovingthe
shortingplugs.
CONNECTINGTAPERECORDERS
ToRecord:
Connecta cablefromtheOUTPUTTAPE1 Leftjack
tothelefthighlevelinputofthetaperecorder.Con-
necta cablefromtheOUTPUTTAPE1 Rightjackto
therighthighlevelinputofthetaperecorder.Con-
necta secondrecorderinthesamemannertothe
OUTPUTTAPE2 jacks.
ToPlayback/Monitor:
Connecta cablefromtheleftchanneloutputofa
taperecordertotheTAPEINPUT1 Leftjack.Connect
acablefromtherightchanneloutputofa tape
recordertotheTAPEINPUT1 Rightjack.Connecta
secondrecorderinthesamemannertotheTAPEIN-
PUT2 jacks.
CONNECTINGA STEREOTUNER
Connecta cablefromthelefttuneroutputtotheL
TUNERINPUTjack.Connecta cablefromtheright
tuneroutputtotheR TUNERINPUTjack.
CONNECTINGAUX
Connecttheleftchannelcablefromanyhighlevel
source(tuner,TVset,taperecorder,etc.)totheINPUT
AUXleftjack.Connecttherightchannelcabletothe
INPUTAUXRightjack.
CONNECTINGTOPOWERAMPLIFIERS
Connectthejackslabeled"OUTPUTSMAIN"tothe
inputofa stereopoweramplifier.TheLeftMAINjack
isconnectedtotheleftamplifierinputjack.TheRight
MAINjackisconnectedtotherightamplifierinput
jack.
CONNECTINGPROGRAMSOURCEGROUNDS
AsingleGROUNDpostisprovidedtowhich
groundsforturntables,recordchangers,tapedecks,
etc.areconnected.Topreventhumpickup,theleft
andrightprogramcablesandthegroundwirefrom
thatsourceshouldbewoundortwistedtogether.
Makesurethegroundwiredoesnotmakeanycon-
nectiontotheshieldsoftheleftandrightprogram
cablesbetweenthesourceandtheinputoftheC 504.
ACPOWEROUTLETS
Thereare4 blackACpoweroutlets,and2 redAC
poweroutlets.TheACpowertotheblackoutletsis
controlledbythefrontpanelswitch.Usethese
outletsfora poweramplifier,tuner,taperecorders,
etc.Theredreceptaclesareonatalltimes.Usethe
redoutletsforturntablesorrecordchangers.Turn-
tablesareprotectedbythisarrangement.Itis
necessarytoturnoffa turntableorrecordchanger
withitsownACpowerswitch.
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LEFT
SPEAKER
TUNER
-5-
POWER
AMPLIFIER
RIGHT
SPEAKER
TAPERECORDER
#1
TAPERECORDER
#2
TURNTABLE#2
TURNTABLE#1
FMANTENNA
ACPOWER
TOTURNTABLE
ACPOWERTO
TUNER,TAPERECORDERS,
POWERAMP,ETC.

FrontPanelInformationand
UseofControls
INPUTSELECTOR
Thefourposition
INPUTSELECTOR
choosestheinput
programselected.
TheINPUTSELEC-
TORisturnedto:
AUX:Connectsthe
outputfromany
highlevelprogramsourcerequiringflatamplification
connectedtotheAuxinputjackstothehighlevelin-
putstage.Sucha sourcecouldbeanothertape
recorder,a televisionset.etc.
TUNER:ConnectstheoutputfromanAMorFM
tunertothehighlevelinputstage.Inthispositionthe
C504hasflatamplification.
PHono1:Connectstheoutputofa magneticphono
cartridgepluggedintoPHono1 tothephonoamplify-
ingstages.Theresponseofthesestageshasbeen
shapedtopreciselyconformtoRIAAstandards.
PHono2:SameasPHono1 fora secondturntable.
PUSHBUTTONS
POWERON:ThePOWERONpushbuttonenergizes
theC 504circuitsandconnectspowertotheblackAC
poweroutletsontherearpanel.
TheC 504isdesignedsoitmaybeusedwithtwo
taperecorders.Thefourcenterpushbuttonsonthe
frontpanelcontrolthesignaltoandfromthese
recorders.Theypermitplaybackofeither
recorder,monitorofeitherrecorderasrecordingsare
beingmade,orcopyingoftapesfromonerecorderto
anotherwhilelisteningtoa separateprogram.
MONITORTAPE1 pushbuttonout:Theprogram
sourceasselectedbytheINPUTSELECTORisfedto
thepoweramplifiersandheardthroughtheloud-
speakers.Pushbuttonin:Signalfroma taperecorder
pluggedintoTAPE1 INisfedtothepoweramplifiers
andheardthroughtheloudspeakers.
MONITORTAPE2 pushbutton:Functionssimilarly
toMONITORTAPE1 fora secondtaperecorder.
IMPORTANT:WhentheC 504isoperatedwith
eitherMONITORpushbuttonattheinposition,the
programheardwillbethatfromthetaperecorderson-
ly.Signalfromanyothersourcewillnotbeheard.To
hearanyothersource,makesuretheMONITOR
pushbuttonsareOUT.
TheMONITORswitchesaremechanicallyin-
terlockedtopreventsimultaneousmonitoringfrom
twotaperecorders.Ifonebuttonisattheinposition,
itmustbepushedagaintoreleaseittotheoutposi-
tionbeforetheotherbuttoncanbepushed.
TAPECOPYT1T2pushbuttonout:Theprogram
sourceselectedbytheINPUTSELECTORisfedtothe
inputoftaperecorder2.Pushbuttonin:Connectsthe
outputfromtaperecorder1 totheinputoftape
recorder2 withoutaffectingtheprogrambeingheard
fromthespeakers.Inthispositiona copyofthepro-
gramontaperecorder1 canbemadeontaperecorder
2.TomonitortheoriginaluseMONITORTAPE1
-6-

pushbuttonandtomonitorthecopyuseMONITOR
TAPE2 pushbutton.
TAPECOPYT2T1pushbuttonout:Theprogram
sourceselectedbytheINPUTSELECTORisfedtothe
inputoftaperecorder1.Pushbuttonin:Connectsthe
outputfromtaperecorder2 totheinputoftape
recorder1 withoutaffectingtheprogrambeingheard
fromthespeakers.Inthispositiona copyofthepro-
gramonrecorder2 canbemadeonrecorder1.To
monitortheoriginaluseMONITORTAPE2 pushbut-
tonandtomonitorthecopyuseMONITORTAPE1
pushbutton.
MONO:TheMONOpushbuttonswitchestheaudio
circuitsfromstereomodetoMONO.Theprogram
heardwillbemonophonic.TheTAPEOUTjacksare
notaffectedbytheMONOpushbutton.
EQUALIZERFREQUENCYCONTROLS
EachofthreeEQUALIZERFREQUENCYcontrols
modifiesupwardordownwardthetonebalanceofa
bandoffrequenciescenteredonthefrequencymark-
edabovethecontrol.Theflatpositionofthecontrol
hasa detentforeasyreference.Eachcontrolprovides
12dBboostorcutatthespecifiedcenterfrequency.
UsetheEQUALIZERFREQUENCYcontrolsto
modifythesoundandtonebalanceofprogram
material.Herearesomesuggestionsfromwhichto
start:
Problem
Basstooweak
Malevocalistneedsreinforcing
Humonprogram
Femalevocalistreinforcing
Violins,trumpetsdull
Drum"brushes"notaudible
Hissand/ornoiseonprogram
EqualizerCorrection
Raise30
Raise30
Reduce30
Raise750
Raise750
Raise10K
Reduce10K
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.Adjustmentofthe
LOUDnesscontrolallowslife-likefrequencybalance
whenplayingmusicsoftly.Itscontouristhesame,
regardlessofthepositionofthevolumecontrol.This
contourisaccuratelymodeledafterthefamilyof
"EqualLoudness"curvesidentifiedbyFletcherand
Munson.Theflatresponsepositionofthecontrolhas
adetentforeasyreference.
Theloudnesscircuitryiscompletelyindependent
ofthevolumecontrol.Therefore,anydesiredamount
ofcompensationcanbeintroducedregardlessof
volumecontrolposition.
VOLUMECONTROL
TheVOLUMEcon-
trolisa precisionstep
controlmanufactured
forMcintoshLabora-
tory.Ithas32steps
witha 70dBrange,
plusvolumeoff.Left
andrightchannel
trackingarewithin
1dB.Thisextremeaccuracyisobtainedthrough
specialelectronicallycontrolledresistanceelement
trimming.Trackingaccuracyispermanentlymain-
tainedandoperationisnoisefree.
HEADPHONEJACK
AHEADPHONEjackisprovidedtodrivelowim-
pedancedynamicheadphonesfromaninternalpower
amplifier.
-7-

PerformanceLimits
PerformanceLimits
Performancelimitsarethemaximumdeviationfrom
perfectionpermittedfora Mcintoshinstrument.We
promiseyouthatwhenyoupurchasea newC 504
froma McintoshFranchiseddealeritwillbecapable
ofperformanceatorexceedingtheselimitsoryou
canreturntheunitandgetyourmoneyback.
Mcintoshistheonlymanufacturerthatmakesthis
statement.
FREQUENCYRESPONSE
+0 -0.5dbfrom20Hzto20kHz
RATEDOUTPUTLEVELS
MainOut2.5V
Headphone750mV
TapeOut250mV
DISTORTION
0.02%maximumat2.5Voutputfrom
20Hzto20kHz
INPUTSENSITIVITYANDGAIN
InputtoMainOut
Phono1 and2
OUTPUTIMPEDANCE
MainOut
Headphone
TapeOut
lessthan100W(tooperate
into5kWorgreater)
8W
lessthan200W(tooperate
into5kWorgreater)
Tuner,Tape1 and2,
Aux
InputtoHeadphoneOut
Phono1 and2
Tuner,Tape1 and2,
Aux
InputtoTapeOut
Phono1 and2
Tuner,Tape1 and2,
Aux
SIGNALTONOISE
Phono1 and2
Tuner,Tape1 and2,
Aux
INPUTIMPEDANCE
Phono1 and2
Tuner,Tape1 and2,
Aux
2.2mVinfor2.5Vout
(61.1dBgainat1 kHz)
250mVinfor2.5Vout
(20dBgainat1 kHz)
2.2mVinfor750mVout
(50.7dBgainat1 kHz)
250mVinfor750mVout
(9.5dBgainat1 kHz)
2.2mVinfor250mVout
(41.1dBgainat1 kHz)
250mVinfor250mVout
(0dBgainat1 kHz)
-90dBIHFA-weighted,
below10mVinput
-80dBunweighted,
below10mVinput
-100dBIHFA-weighted,
below250mVinput
-90dBunweighted,
below250mVinput
47kWand50pF
47kW
EQUALIZERCONTROLRESPONSE
CenterFre-
quencies30,750,and10kHz
BoostandCut± 12dB
GENERALINFORMATION
POWERREQUIREMENT
120Volts50/60Hz,25Watts
SEMICONDUCTORCOMPLEMENT
15Transistors
14FieldEffectTransistors
11SiliconDiodes
11IntegratedCircuits
MECHANICALINFORMATION
SIZE
SIZE:Frontpanelmeasures16incheswide(40.6
cm)by3 5/8incheshigh(9.2cm).Chassis
measures143/4incheswide(37.5cm)by2 3/8
incheshigh(6.0cm)by141/2inchesdeep(36.8
cm),includingconnectors.Knobclearancere-
quiredis1 1/4inches(3.2cm)infrontofmoun-
tingpanel.
FINISH:
Frontpanelisanodizedgoldandblackwith
specialgold/tealnomenclatureillumination.
Chassisisblack.
MOUNTING:
ExclusiveMcintoshdevelopedprofessional
PANLOC
WEIGHT:
14pounds(6.4kg)net,25pounds(11.3kg)in
shippingcarton.
-8-

Performance
Charts
EQUALIZERFREQUENCYRESPONSE:
CONTROLSSETATMAXIMUM
ANDMINIMUM
LOUDNESSCONTROLRESPONSE:
FORVARIOUSCONTROL
POSITIONS
HARMONICDISTORTION:
IN:AUX;OUT:MAIN
INTERMODULATIONDISTORTION:
IN:AUX;OUT:MAIN
INPUTFREQUENCY:60Hz& 7 kHz:
RATIO:4:1
-9-

TechnicalDescription
TheC 504iscomprisedofsixbasicsections.They
are:phonoamplifier,highlevelamplifier,equalizer
amplifier,output/headphoneamplifier,inputselector
switching,andpowersupply.Theircircuitdescrip-
tionsfollow.
PHONOAMPLIFIER
Thephonoamplifierusesa hightechnologyin-
tegratedcircuitoperationalamplifier.Itsdifferential
inputstagehasbeenoptimizedforlownoiseandlow
distortionperformance.Openloopgainofthisin-
tegratedcircuitis100,000.Withhighopenloopgaina
largeamountofnegativefeedbackcanbeused
aroundthephonoamplifiertofurtherreducenoise
anddistortion.Thefeedbacknetworkalsoprovides
precisionRIAAfrequencycompensation.Thenet-
workuses1%metalfilmresistorsand5%polyfilm
capacitors.Toachievelownoiseperformanceitis
essentialthatthefeedbacknetworkhaveverylowim-
pedance.Asa consequence,thepreamplifiermustbe
capableofoperatingasa poweramplifiertodrivethis
impedance.Theactualpoweroutputcapabilityofthis
preamplifierstageismorethan100milliwatts,a great
marginbeyondthatwhichisrequired.
Inputsensitivityofthephonoamplifieris2.2
millivolts.Thegainoftheamplifieris41.1dBat1000
Hz.Thephonoamplifierhasa verywidedynamic
range.At1000Hzthephonoinputcircuitwillaccept
100millivoltswithoutoverload,a voltagefargreater
thantheoutputofanycurrentmagneticphonocar-
tridge.Phonoinputoverloadthereforeisvirtuallyim-
possible.A signallevelof10millivoltsatthephono
inputat1000Hzwillproduce1.13voltsatthetape
output.Thetapeoutputhasa sourceimpedanceof
200ohmsandisdesignedtooperateintoa loadim-
pedanceof5,000ohmsorgreater.
HIGHLEVELAMPLIFIER
Attheinputtothehighlevelorloudnessamplifier
thesignalpassesthroughtheMONO/stereoswitch,
thenthroughthevolumecontrol,andintothe
amplifier.Inthepast,loudnesscontrolshavetypical-
lyusedsimplepassivecircuitsconnectedtoa tapon
thevolumecontrol.Asa consequence,compensation
accuracywasdependentonmanyvariablessuchas
volumecontrolpositionanddifferencesintheinput
level.TheC 504usesactivecircuitry.Thesametype
ofintegratedcircuitoperationalamplifierthatisused
inthephonoamplifierisusedhere.Ithastwofeed-
backloops.Onefeedbackloopisflat.Theotherfeed-
backloopconformstotheFletcher-Munsonequal
loudnesscompensation.A potentiometerisplaced
betweenthesetwofeedbackloopsmakingitpossible
toselectanycombinationofthetwofroma flat
responsetofullloudnesscompensation.Theoverall
gainofthestageis20dBatmid-frequenciesandis
-10-

notaffectedbythepositionoftheloudnesscontrol.
EQUALIZERAMPLIFIER
Theequalizeramplifierisconstructedwithanother
ofthesametypelownoiseoperationalamplifieras
usedinthephonoamplifier.Threeotheroperational
amplifiersarearranagedincircuitconfigurationsthat
aretheequivalentofthreeseriestunedcircuits.One
isresonantateachofthethreeequalizercenterfre-
quencies.Theseseriestunedcircuitsareinsertedvia
thecontrolpotentiometersineithertheinputcircuit
orfeedbackcircuitoftheequalizeramplifierthereby
providinga boostandcutcapabilityof12dBforeach
bandoffrequencies.Theequalizeramplifierhasa flat
responsegainof0 dB.
OUTPUT/HEADPHONEAMPLIFIER
Theoutputamplifierisa push-pullcomplementary
classABamplifierusinga signalinvertingdifferential
stageatitsinput.Thisamplifierdrivesthemainout-
putsandtheheadphonejack.Morethan10voltsRMS
outputcanbeproducedwithtypicallynomorethan
0.003%harmonicdistortion.
Aturn-ondelaycircuitislocatedaheadoftheout-
putamplifier.Thiscircuitusesa lightemitting
diode/lightdependentresistornetworkthatfunctions
totransmitnosignaluntiltwosecondsafterthe
powerswitchisturnedonandtoremovetheoutput
signalalmostinstantlyuponpowerturn-off.Thusthe
turn-onandturn-offistransientandnoisefree.
INPUTSELECTORSWITCHING
Lowlevel,noisecriticalinputselectorswitchingis
doneelectronicallyusingfieldeffecttransistor
analogswitches.Thefrontpanelselectorsimplyswit-
chessmallamountsofcontrolDCwhichturntheFET
analogswitchesofforon.Thisdesigneliminates
degradationoffrequencyresponseandnoisepickup
fromlongsignalpathsnecessarywithconventional
switching.
POWERSUPPLY
Tominimizemagnetichumradiationandthusim-
provesignaltonoiseratiotheC 504power
transformeristripleshielded.Shieldingincludesa
copperstrap,a siliconsteelstrap,andfinallya steel
outershell.Thetransformeroutputvoltageisfedtoa
fullwavebridgerectifierand3,300microfaradfilter
capacitorstoprovidethe+24voltsforpoweringthe
plusregulatorand-24voltsfortheminusregulator.
Integratedcircuitvoltageregulatorssupplythe±18
voltsneededforlowlevelamplifierstages.
-11-

BlockDiagram
MclNTOSHC 504
-12-

STEREOPREAMPLIFIER
-13-

MclNTOSHLABORATORYINC.
2CHAMBERSST.,BINGHAMTON,N.Y.13903
607-723-3512
Thecontinuousimprovementofitsproductsisthepolicyof
McintoshLaboratoryIncorporatedwhoreservetherightto
improvedesignandpricewithoutnotice.
PrintedinU.S.A.
039243