McIntosh C27 User manual

THEMcINTOSHC27SOLIDSTATESTEREOPREAMPLIFIER
ReadingTime:28MinutesPrice:$2-00

WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNITTO
RAINORMOISTURE.
TheMclntoshyouhavepurchasedhasa serialnumberlocatedon
therearpanelofthechassis.
Recordthatserialnumberhere
forfuturereferences.Themodelandserialnumberareimportant
toyouforanyfutureservice.

YourC 27StereoPreamplifierwillgiveyou
manyyearsofpleasantandsatisfactory
performance.Ifyouhaveanyquestions,
pleasecontact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Phone:[phone]
TakeAdvantageof3 years
ofFREEService...
FillintheApplicationNOW.
SERVICECONTRACT. . . . 1
INTRODUCTION. . . . 2
HOWTOINSTALL....2
HOWTOCONNECT....4
WHATTHEFRONTPANELCONTROLS
ANDHOWTOUSETHEM....8
BALANCINGYOURSTEREO....11
PERFORMANCELIMITSANDRATINGS. . . . 12
PERFORMANCECHARTS. . . . 13
TECHNICALDESCRIPTION....14
BLOCKDIAGRAM....15
1.Mclntoshwillprovideailparts,materialsand
laborneededtoreturnthemeasuredperfor-
manceoftheinstrumenttotheoriginalper-
formancelimitsfreeofanycharge.The
SERVICECONTRACTdoesnotcoverany
shippingcoststoandfromtheauthorized
serviceagencyorthefactory.
2.AnyMclntoshauthorizedserviceagencywill
repairallMclntoshinstrumentsatnormal
servicerates.Toreceivethefreeservice
underthetermsoftheSERVICECONTRACT,
theSERVICECONTRACTCERTIFICATEmust
accompanytheinstrumentwhentakento
theserviceagency.
3.Alwayshaveservicedonebya Mclntosh
authorizedserviceagency.Iftheinstrument
ismodifiedordamaged,asa resultofun-
authorizedrepairtheSERVICECONTRACT
willbecancelled.Damagebyimproperuseor
THREEYEARSERVICECONTRACT
Anapplicationfora FREETHREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:mishandlingisnotcoveredbytheSERVICE
CONTRACT.
4.TheSERVICECONTRACTisissuedtoyouas
theoriginalpurchaser.Toprotectyoufrom
misrepresentationthiscontractcannotbe
transferredtoa secondowner.
5.ForyourprotectionMclntoshselectsonly
dealerswhohavetechnicalcompetenceto
guidepurchasersfairly,andprovideservice
whennecessary.ToreceivetheSERVICE
CONTRACTyourpurchasemustbemade
froma Mclntoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfora
SERVICECONTRACTmustbepostmarked
within30daysofthedateofpurchaseofthe
instrument.
7.ToreceivetheSERVICECONTRACTallin-
formationontheapplicationmustbefilled
in.TheSERVICECONTRACTwillbeissued
whenthecompletelyfilledinapplicationis
receivedatMclntoshLaboratoryIncorporated
inBinghamton,NewYork.
Copyright© 1977byMclntoshLaboratoryInc.
Contents

HowtoConnect
CONNECTINGA TURNTABLETOPHONO1
Connectthecablefromthe"left"channeloftheturn-
tableintotheL PHONO1 INPUTjack.
Connectthecablefromthe"right"channeloftheturn-
tableintotheR PHONO1 INPUTjack.
PHONO2 isprovidedfortheuseofa secondturntable.
Connectthecablefromthe"left"channeloftheturn-
tableintotheL PHONO2 INPUTjack.
Connectthecablefromthe"right"channeloftheturn-
tableintotheR PHONO2 INPUTjack.
PlugtheACpowercablefromtheturntableintothered
unswitchedPOWERoutletontherearpanel.Thered
receptacleisonatalltimes.Itisnecessarytoturnoffthe
turntablewithitsownACpowerswitch.Thisarrangement
protectstheturntable.
ThefourblackACpoweroutletsarecontrolledbythe
frontpanelPOWERswitch.Usetheseoutletsfora tuner,
taperecorder,etc.
GROUNDCONNECTION
Asinglegroundpostisprovided.Groundsforturntables,
recordchangers,tapedecks,etc.aretobeconnectedto
thispost.Theleftandrightprogramcablesandtheground
wirefromthatsourceshouldbewoundortwistedtogether.
Toavoidhummakesurethegroundwiredoesnotmake
anyconnectionstotheshieldsoftheleftandrightprogram
cablesbetweentheprogramsourceandtheC 27.
CONNECTINGA STEREOTUNER
Connectthecablefromthe"left"channeltuneroutput
totheL TUNERINPUTjack.
Connectthecablefromthe"right"channeltuneroutput
totheR TUNERINPUTjack.
AUX—Anyhighlevelprogramsourcesuchasa tuner,
aTVsetora taperecordercanbeconnectedtotheAUX1
and2 INPUTjacks.Theconnectingprocedureisthesame
asforthetunerinput.
CONNECTINGTAPERECORDERS
ToRecord:
Connecta cablefromtheL TAPE1 OUTPUTjacktothe
lefthighlevelinputofthetaperecorder.
Connecta cablefromtheR TAPE1 OUTPUTjacktothe
righthighlevelinputofthetaperecorder.
Connecta secondrecorderinthesamemannertothe
TAPE2 OUTPUTjacks.
ToPlayback/Monitor:
Connecta cablefromtheleftchanneloutputofa tape
recordertotheL TAPE1 INPUTjack.
Connecta cablefromtherightchanneloutputofa tape
recordertotheR TAPE1 INPUTjack.
Connecta secondrecorderinthesamemannertothe
TAPE2 INPUTjacks.
4

ACPOWERTO
TUNERS,TAPE
RECORDERSAND
POWERAMPLIFIERS
CONNECTIONSFORTUNERS,TURNTABLES,ANDTAPERECORDERS
TAPE
RECORDER
2
TAPE
RECORDER
1
ACPOWER
TOTURNTABLES
5
TURNTABLE#1
FMANTENNA
TUNERTURNTABLE#2

SPEAKERSYSTEM#1
CONNECTIONSFORPOWERAMPLIFIERANDLOUDSPEAKERS
SPEAKERSYSTEM#2
6
LOUDSPEAKER
ENVIRONMENTAL
EQUALIZER
POWERAMPLIFIER

CONNECTINGTHEC 27TOPOWERAMPLIFIERS
ConnecttheMAINOUTPUTjackstotheinputofa
stereopoweramplifier.TheLeftMAINjackisconnected
totheleftamplifierinputjack.TheRightMAINjackis
connectedtotherightamplifierinputjack.
AsecondpairofMAINOUTPUTjackshavebeensupplied
tofeeda secondpoweramplifier.Intheeventitisdesired
totaperecordafterthetonefilterandvolumecontrols
thesecondsetofMAINOUTPUTjackscanbeconnected
tothetaperecorderinput.Thecontrolsarethenallavail-
abletoalterthesignalbeforerecording.Remember,any
changeinthesettingofthecontrolswillchangethepro-
gramtothetaperecorder.Sincetherecordingsignal
availableattheMAINOUTPUTismuchhigherthanthe
outputavailablefromtheTAPE1 orTAPE2 OUTPUT
jacks,besurenottooverloadthetaperecorderinput.It
willnotbepossibletomonitorfromthetaperecordervia
theTAPEMONITORpushbuttonswhilefeedingtherecorder
fromtheMAINOUTPUTjacks.DepressingtheTAPE
MONITORpushbuttonwilldisconnecttheprogramsource
andmaycausefeedbackoscillation.
CablesaresuppliedwiththeC 27tointerconnectto
thepoweramplifier.Longercablescanbeusedifneeded.
Thelengthofthecableislimitedbythecapacityofthe
cable.Thetotalcapacitymustnotexceed1,000pF.For
instance:cableswitha capacityof25pFperfootmaybe
40feetlong.13.5pFperfootcablemaybe75feetlong.
Theinputimpedanceoftheamplifiersshouldbe22k
ohmsorgreater.
CTRCHAN
UsetheCenTeRCHANneloutputtofeedleftplusright
signaltoa separatepoweramplifierformonophonicback-
groundmusicorfora centerchannel.
CONNECTINGFORSPEAKERSWITCHINGAND
HEADPHONE
Whenthepoweramplifieroutputisproperlyconnected
totherearpanelFROMAMPLIFIERpushconnectors,
speakersintwoseparateareascanbeturnedonoroff
andtheC 27frontpanelHEADPHONEjackwillreceive
theprogramsignal.
Connecta wirefromtheproperimpedanceoutput
connectiononthepoweramplifiertotheFROMAMPLIFIER
pushconnectorsontheC 27rearpanel.Connectthefirst
pairofspeakerstotherearpanelSPEAKER1 pushcon-
nectorsanda secondpairofspeakerstotheSPEAKER2
pushconnectors.Whenconnectingthespeakersandpower
amplifieritisimportanttoconnectthepoweramplifier
outputimpedancetapfortheparallelimpedancecom-
binationofthetwospeakersystemsused.Thefrontpanel
SPEAKERswitchpermitsroutingprogramtoeither
SPEAKER1,SPEAKER2,both1 and2,orOFF.Inthe
SPEAKEROFFposition,theprogramisfedonlytothe
HEADPHONEjackforprivatelistening.
ACOUTLETS
Thereare4 blackACoutletsandoneredACoutlet.The
powertotheblackACoutletsiscontrolledbythefront
panelACpowerswitch.Usetheseoutletsfora tuner,tape
recorder,etc.ThetotalcapacityofallACpoweroutletsis
600watts.Theredreceptacleisonatalltimestofeed
ACpowertoa turntablesothatitcanbeturnedonoroff
withitsownACswitch.
FUSE
A0.5AMPfuseprotectsthepreamplifiercircuits.The
fusedoesnotprotectadditionalequipmentconnectedto
thebackpanelACoutlets.
7

WhattheFrontPanelcontrolsDo
andHowtouseThem
INPUTSELECTOR
TheINPUTSELECTORisa fivepositionswitchthat
connectsthechoseninputprogramtothepropercircuits
intheC 27.
AUX1:Connectstothehighlevelinput,anyoutput
froma highlevelprogramsourcerequiringflatamplifica-
tion.Sucha sourcecouldbea televisionset,playbackfrom
anothertaperecorder,anadditionaltuner,etc.Inthe
AUX1 positionthegainis20dBtotheMAINoutputs,
0dBtotheTAPEoutputs.Theinputimpedanceis100k
ohms.
AUX2:SameasAUX1 butfora secondhighlevel
programsource.
TUNER:ConnectstheoutputfromanyAM,FMorMPX
FMtunertothehighlevelinputstage.IntheTUNERposi-
tiontheC 27hasflatamplification.Thereis20dBof
gaintotheMAINoutputs,0 dBtotheTAPEoutputs.The
inputimpedanceis100kohms.
PHONO1:Connectstheoutputofanymagneticphono
cartridgetothelowlevelinputstage.Theresponsehas
beenshapedaccordingtotheRIAAstandardtocompensate
forthecharacteristicsofa magneticphonocartridge.The
gainat1KHzis62dBtotheMAINoutputs,42dBtothe
TAPEoutputs.Theinputimpedanceis47kohmsand
100pF.
PHONO2:SameasPHONO1 butfora secondphono
system.
MODESELECTOR
LtoL & R:Connectstheleftinputtobothloudspeak-
ers.R toL & R:Connectstherightinputtobothloud-
speakers.StereoRev:Connectstheleftinputtotheright
loudspeakerandtherightinputtotheleftloudspeaker.
Stereo:Connectstheleftinputtotheleftloudspeaker
andtherightinputtotherightloudspeaker.
Mono(L+ R):Addstheleftinputandtherightinput
andthenconnectstheL + R programtobothloud-
speakers.
L+ R toL:Addstheleftandrightprogramtogether
andconnectsthecombinedprogramtotheleftloud-
speakeronly.
L+ R toR:Addstheleftandrightprogramtogether
andconnectsthecombinedprogramtotherightloud-
speakeronly.
PRECISETRACKINGVOLUMECONTROL
TheVOLUMEcontrolisa precisionstepattenuator
whichhaslefttorighttrackingaccuracywithin1 dB
throughoutitsentirerange.Suchextremelyaccuratematch-
ingisachievedthroughelectronicallycontrolledtrimming
oftheresistancematerialdepositedonpairsofprinted
circuits.Sincetheswitchcommutatortouchesonlycontact
padsandnottheactualresistanceelement,trackingac-
curacyisnotdegradedwithuseasinordinaryvolume
controls.Clockwiserotationincreasesvolume.TheVOLUME
controlintheC 27hasbeendesignedandmanufactured
forMclntoshLaboratory.
FILTERS/SPEAKERS
ThesmallcenterknoboftheconcentricFILTER/
SPEAKERScontrolshapestheC 27frequencyresponseto
reduceorfilterobjectionablelowfrequencynoiseand/or
objectionablehighfrequencynoise.Thelargeouterknob
8

willturnmainorremoteloudspeakersonoroffwhena
poweramplifierhasbeenproperlyconnectedtotheC 27
rearpanel.
FILTEROPERATION
OUT:Filterdisconnected,programnotmodifiedby
eitherhighorlowfrequencyfilters.
LF(LOWFREQUENCYFILTER)
UsetheLFpositiontoreduceobjectionablelow-
frequencynoisecreatedbya turntableorrecordchanger
oracousticallycoupledfeedback.Responseisrolledoff
below50Hz.
HF(HIGHFREQUENCYFILTER)
UsetheHFpositiontoreduceobjectionablehigh-
frequencynoisesuchasrecordscratch.Responseis
rolledoffabove5,000Hz.
LF-HF
Bothhighandlowfrequencyfiltersareactivated.
SPEAKERSOPERATION
OUT:Allspeakersaredisconnected.Programisfedonly
totheHEADPHONEjackforprivatelistening.
1:ProgramisfedonlytotherearpanelSPEAKER1 con-
nectorsandtheHEADPHONEjack.SPEAKER2 is
disconnected.
1& 2:ProgramisfedtotherearpanelSPEAKER1 and
2connectorsandtheHEADPHONEjack.
2:Programmaterialisfedonlytotherearpanel
SPEAKER2 connectorsandtheHEADPHONEJACK.
SPEAKER1 isdisconnected.
BASS
Concentric,11position,tonecontrolswitchesadjust
thebass.Theouterknobadjuststherightchannelbass
response.Thecenterknobadjuststheleftchannelbass
response.
Left:Adjuststhebassloudnessfromtheleftloudspeaker.
Clockwiserotationincreasesthebassloudnesswhilecoun-
terclockwiserotationdecreasesthebassloudness.Each
stepofthetonecontroladjuststhebassloudnessabout4
dB.
Right:Hasthesameeffectonthesoundfromtheright
loudspeaker.
TREBLE
Concentric,11position,tonecontrolswitchesadjust
thetreble.Theouterknobadjuststherightchannelre-
sponse.Thecenterknobadjuststheleftchanneltreble
response.
Left:Adjuststhetrebleloudnessfromtheleftloud-
speaker.Clockwiserotationincreasesthetrebleloudness
whilecounterclockwiserotationdecreasesthetrebleloud-
ness.Eachstepofthetonecontroladjuststhetreble
loudnessabout4 dB.
Right:Hasthesameeffectonthesoundfromtheright
loudspeaker.
LOUD/BALANCE
LOUDNESS:
Usetheloudnesscontrolforfullfrequencyrangelisten-
ingateventhesoftestlisteninglevels.TheLOUDness
control(thesmallcenterknoboftheconcentriccontrol)
provideslow-frequencyboosttocompensatefora hearing
characteristicofthehumanearatlowlisteninglevels.
Theearbecomeslesssensitivetolowfrequenciesasvolume
isreduced.Increasedloudnesscompensationistherefore
desirableatlowerlisteninglevels.Theloudnesscontrol
booststhelowfrequenciessothattheearhearsapproxi-
matelythesamemusicalbalanceasitwouldathigher
listeninglevels.
FLAT:(Maximumcounterclockwiserotation)Fullvolume
withflatfrequencyresponse.Theloudnesscompensation
isinoperativeinthisposition.
TurningthecontrolclockwisetowardMAXreducesthe
listeningvolume,andautomaticallyincreasesthecompen-
sationbyboostingbass.
BALANCE
TheBALANCEcontroladjustsforunequalvolumein
eithertheleftorrightchannels.Thevolumeofthechan-
nelscanbevariedrelativetoeachotherwithoutaffecting
theircombinedvolume.
Turningthecontroltotheleftaccentstheleftchannel
9

byreducingtherightchanneloutputandturningthecon-
troltotherightaccentstherightchannelbyreducingthe
leftchanneloutput.
PANLOC
DepressingthetwoPANLOCbuttonsonthefrontpanel
permitstheC 27tobeeitherlockedfirmlyinplaceor
unlockedsothatthechassiscanbeslidforward,untilit
isstoppedbythemid-positionlatches.Pressthelatches
onthesideoftheC 27inwardtopermittheinstrumentto
slideinoroutofthecabinet.WiththeC 27frontpanel
flushwiththecabinetpanel,pressingthePANLOCbuttons
willlocktheunitfirmlyinthecabinet.
THEPUSHBUTTONS
TheC 27isdesignedtobeusedwithoneortwotape
recorders.Thefrontpanelpushbuttonspermitnormal
playbackofeitherrecorder,monitorasrecordingsare
beingmadeoneitherrecorder,orcopyingtapesfromone
recordertoanotherwhilelisteningtoa separateprogram.
TAPEMONITOR
Tomonitorwhilerecordingfromanysourcechosenon
theINPUTSELECTOR,yourtaperecordermusthavesepa-
raterecordandplaybackheadsandseparateelectronics.
TheMONITORswitchesletyoumonitorthequalityoftape
recordingsmadeduringtherecordingprocess.Whenthe
chosenTAPEMONITORpushbuttonisintheINposition
thesoundfromthetapeasitpassestheplaybackheadis
hearda momentafteritisrecorded.Therecordingprocess
continuesasusual.WhentheswitchisintheOUTposition,
theprogramthatisbeingrecordedisheard.
TAPE1 MONITOR
PUSHBUTTONOUT...Theprogramsourceselectionby
theINPUTSELECTORisfedtothepoweramplifiersand
heardthroughtheloudspeakers.
PUSHBUTTONIN...Theprogramsourcebecomesthe
recordedtapeontherecorderconnectedtoTAPE1 INPUT.
Therecordedprogramfromtaperecorder1 isfedtothe
poweramplifiersandheardfromtheloudspeakers.
InthePUSHBUTTONINposition,a rectangleislighted
abovethepushbutton.Whenthelightisononlythetape
willbeheard.Tolistentoothersourcesthepushbutton
mustbeoutandthelightoff.
TAPE2 MONITOR
Asecondtaperecordercanbeoperatedinthesame
mannerusingpushbuttonTAPE2 MONITOR.
UsethefrontpanelpushbuttonTAPE2 toplaybackfrom
ataperecorderpluggedintotherearpanelTAPE2 INPUT
jacks.
HOWTOCOPYTAPE,TAPECOPY1 ->2
Putthetapetobecopiedontherecorderconnectedto
TAPE1 INPUT.PressintheTAPECOPY1 ->2 pushbutton.
ThesignalavailableattheTAPE2 OUTPUTjacksisthe
playbackofTAPE1.Recordontherecorderconnectedto
TAPE2 OUTPUT.Thesourcetapeontaperecorder1 can
beheardbypressingintheTAPE1 MONITORpushbutton.
TherecordingcanbemonitoredbypressingintheTAPE2
MONITORpushbutton.Instantaneouscomparisononthe
recordedprogramwiththeoriginalcanbeheard.
TAPECOPY2 ->1
WhenpushedINtheTAPE2 OUTPUTjacksarecon-
nectedtotheTAPE1 INPUTjackswithoutaffectingthe
programheardfromthespeakers.Inthispositiona copy
oftheprogramontaperecorder2 canbemadeontape
recorder1.
TomonitorthetapecopyproceduresusetheTAPE
MONITORpushbuttons.
POWER
ThePOWERswitchenergizestheC 27circuitsandcon-
nectsACpowertotheblackrearpanelACpoweroutlets.
TheblackACpoweroutletsarenotfused.A lightedrec-
tangleabovetheONPOWERswitchindicatestheAC
powertothesystemisturnedon.
HEADPHONES
ThefrontpanelHEADPHONEjackhasbeendesignedto
feedlowimpedancedynamicheadphones.Electrostatic
headphonesgenerallyrequirehigherpowerthandynamic
headphones.Theymustbeconnectedtotheoutputcon-
nectorsonthepoweramplifier.
PlugheadphonesintothefrontpanelHEADPHONE
jack.AdjusttheVOLUMEcontrolforcomfortablehead-
phonelistening.Theoutputofanexternalpoweramplifier
mustbeproperlyconnectedtotheC 27backpanelfor
programmaterialtobeavailableattheHEADPHONEjack.
10