McIntosh C28 User manual

THEMCINTOSHC 28SOLIDSTATESTEREOPREAMPLIFIER
ReadingTime:37Minutes Price$1.25

TakeAdvantageof3 years
ofFREEService. . .
FillintheApplicationNOW.
ServiceContract..1
Installation..2,3
HowtoConnect..4,5,6,7
AdjustingTheTopPanelControls..8
UsingTheFrontPanelControls..9,10
UsingthePushbuttons..11
BalancingYourStereo..12,13
ListeningToYourStereo..13
PerformanceLimitsandRatings..14,15
PerformanceCharts..16
TechnicalDescription..18
BlockDiagram..20
1.Mclntoshwillprovideallparts,materialsand
laborneededtoreturnthemeasuredperform-
anceoftheinstrumenttotheoriginalper-
formancelimitsfreeofanycharge.The
SERVICECONTRACTdoesnotcoveranyship-
pingcoststoandfromtheauthorizedservice
agencyorthefactory.
2.AnyMclntoshauthorizedserviceagencywill
repairallMclntoshinstrumentsatnormal
servicerates.Toreceivethefreeserviceunder
thetermsoftheSERVICECONTRACT,the
SERVICECONTRACTCERTIFICATEmustac-
companytheinstrumentwhentakentothe
serviceagency.
3.Alwayshaveservicedonebya Mclntosh
authorizedserviceagency.Iftheinstrument
ismodifiedordamaged,asa resultofun-
authorizedrepairtheSERVICECONTRACT
willbecancelled.Damagebyimproperuse
THREEYEARSERVICECONTRACT
Anapplicationfora FREETHREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:ormishandlingisnotcoveredbytheSERV-
ICECONTRACT.
4.TheSERVICECONTRACTisissuedtoyouas
theoriginalpurchaser.Toprotectyoufrom
misrepresentationthiscontractcannotbe
transferredtoa secondowner.
5.ForyourprotectionMclntoshselectsonly
dealerswhohavetechnicalcompetenceto
guidepurchasersfairly,andprovideservice
whennecessary.ToreceivetheSERVICE
CONTRACTyourpurchasemustbemade
froma Mclntoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfora
SERVICECONTRACTmustbepostmarked
within30daysofthedateofpurchaseof
theinstrument.
7.ToreceivetheSERVICECONTRACTallin-
formationontheapplicationmustbefilled
in.TheSERVICECONTRACTwillbeissued
whenthecompletelyfilledinapplication
isreceivedatMclntoshLaboratoryIncor-
poratedinBinghamton,NewYork.
Copyright(c)1970ByMclntoshLaboratoryInc.
1
YourMC28StereoPreamplifier
willgiveyoumanyyearsofpleasant
andsatisfactoryperformance.Ifyou
haveanyquestions,pleasecontact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Phone:[phone]
WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNIT TORAIN
ORMOISTURE.
CONTENTS

HowToConnect
CONNECTINGA RECORDPLAYERTO PHONO1
Connectthecablefromthe"left"channelofthe
recordplayerintothe"L"PHONO1 inputjack.
Connectthecablefromthe"right"channelofthe
recordplayerintothe"R"PHONO1 jack.
PHONO2 isprovidedfortheuseofa secondrecord
player.
Connectthecablefromthe"left"channelofthe
recordplayerintothe"L"PHONO2 inputjack.
Connectthecablefromthe"right"channelofthe
recordplayerintothe"R"PHONO2 inputjack.
CONNECTINGA MICROPHONE
Connectthecablefromthe"left"microphoneto
the"L"MICinputjack.Connectthecablefromthe
"right"microphonetothe"R"MICinputjack.
CONNECTINGA TAPEDECKFORPLAYBACK
Connectthecablefromthe"left"taperecorderhead
onthetapedeck(onewithoutitsownelectronics)
tothe"L"TAPEHEADinput.Connectthecable
fromthe"right"taperecorderheadtothe"R"TAPE
HEADinput.
CONNECTINGA STEREOTUNER
Connectthecablefromthe"left"channeltunerout-
puttothe"L"tunerinputjack.
Connectthecablefromthe"right"channeltuner
outputtothe"R"TUNERjack.
AUX
Anyhighlevelprogramsourcesuchasanothertuner
ora TVsetcanbeconnectedtotheinputjacks
marked"AUX."
CONNECTINGA TAPERECORDER
ToRecord:
Connecta cablefromthe"L"TAPEOUTPUTjack
markedTAPE1 tothe"left"highlevelinputtape
recorder.
Connecta cablefromthe"R"TAPEOUTPUTjack
markedTAPE1 tothe"right"highlevelinputofthe
taperecorder.
Connecta secondtaperecorderinthesamefashion
totheTAPE2 outputs.
ToPlaybackMonitor:Connectthecablefromthe
"left"channeloutputofa taperecordertothehigh
levelinputs. . . "L"TAPE1.
Connectthecablefromthe"right"channeloutputof
ataperecordertothehighlevelinput. . . "R"TAPE.
Connecta secondtaperecorderinthesamefashion
totheTAPE2 inputjacks.
4

5

CONNECTINGTHEC 28TOPOWERAMPLIFIERS
ConnecttheMAINoutputjackstotheinputofa
stereopoweramplifier.The"L"jackisconnectedto
the"left"amplifierinputjack.The"R"jackiscon-
nectedtothe"right"amplifierinputjack.
TheoutputimpedanceattheMAINoutletis100
ohms.Longercablesthanaresuppliedcanbecon-
nectedbetweentheC 28andtheamplifiers.The
lengthofthecableislimitedbythecapacityofthe
cable.Thetotalcapacitymustnotexceed1000pF.
Forinstance:cableswitha capacityof25pFper
footmaybe40feetlong.13.5pFperfootcable
maybe75feetlong.Theinputimpedanceofthe
amplifiersshouldbe47,000ohmsorgreater.
CTROUTPUT
UsetheCTRoutputtofeedleftplusrightsignaltoa
separatepoweramplifierformonophonicback-
groundmusicorfora centerchannelspeaker.
SPEAKERCONTROLRELAY
Tocontrolmainandremoteloudspeakersfromthe
frontpaneloftheC 28anaccessoryMclntoshSCR
controlisneeded.PlugthecablefromtheSCRcon-
trolintheSPEAKERCONTROLRELAYreceptacle.
ThespeakersarethenconnectedtotheSCRcon-
trol.TheACoutletsontheSCRhavea totalcapa-
cityof2400watts.
ACOUTLETS
Thereare4 blackACoutlets,2 greenACoutlets,
andoneredACoutlet.ThepowertotheblackAC
outletsiscontrolledbythefrontpanelswitch.Use
theseoutletsfora tuner,taperecorder,etc.The
greenoutletsarecontrolledbythetoppanelswitch
marked"PowerAmplifier."Thetotalcapacityofall
ACpoweroutletsis600watts.Topreventburnout,
usetheACoutletsontheCRforpowerrequirements
exceeding600watts.Theredreceptacleisonatall
times.Usetheredoutletfora turntableorrecord
changer.Theturntableisprotectedbythisarrange-
ment.Itisnecessarytoturnofftheturntableorrec-
ordchangerwithitsownACswitch.
GROUNDCONNECTION
Asinglegroundpostisprovided.Groundsforturn-
tables,recordchangers,tapedecks,etc.shouldbe
connectedtothispost.Theleftandrightprogram
cablesandthegroundwirefromthatsourceshould
bewoundortwistedtogether.Toavoidhum,make
surethegroundwiredoesnotmakeanyconnec-
tionstotheshieldsoftheleftandrightprogram
cablesbetweentheprogramsourceandtheC 28.
6

7

AdjustingTheTopPanelControls
Youwillenjoythebestinstereoperformancemore
whenthestereosystemisproperlybalanced.For
properbalanceeachchannelmustbeequalinloud-
nessandsimilarinfrequencyresponse.Usethetop
panelLEVELcontrolstobalancesystemloudness
andthetoppanelBASSTRIMcontrolstobalancefor
frequencyresponsedifferencesatlowfrequencies.
DonotusethefrontpanelBALANCEcontrolto
correctforsystemunbalance.TheBALANCEcontrol
isusedtoadjustforanyunbalanceinthesource
material,therecord,etc.
BeforeattemptingtobalancetheoutputoftheC 28
makecertainthefrontpanelcontrolsaresetproperly.
TurntheVOLUMEcontroltotheOFF(totallycoun-
ter-clockwise)position.
SettheMODESELECTORtoSTEREOandthe
BALANCEcontrolatthecenteror12o'clockposition.
Turnthetonecontrolstothecenteror12o'clock
position.TheHFandLFpushbuttonsshouldbein
theOUTpositionandtheCOMPensationcontrolin
theFLATposition.TurntheINPUTSELECTORto
TUNER.
DepressthePANLOCbuttonsandpullthepre-
amplifierouttotheadjustposition.Thecontrolson
thetoppanelarenoweasilyadjusted.
OnthetoppanelturntheBASSTRIMcontrols
counter-clockwise.Turnallthelevelcontrolstothe
clockwiseposition.TurnthePOWERAMPLIFIER
switchon.
Withthetunerturnedon,turnuptheVOLUME
controlonthefrontpaneluntila comfortableroom
loudnessisreached.
ThenswitchtheINPUTSELECTORtoPHONO1,
theMODESELECTORtoL TOL & R,usea mono-
phonicrecordandturndownthetoppanelLEFT
PHONO1 LEVELcontroltomatchtheloudnessofthe
tuner.RepeattheprocedurewiththeRIGHTPHONO
1LEVELcontrol.Whenthechannelsareequallyloud
thesystemisbalancedforloudness.
RepeatthesamestepsforPHONO2.
BassTrim
Acontrolhasbeenprovidedineachchannelthat
adjuststhebassloudness.Thesecontrolsareused
tocompensateforthedifferencesinloudspeakerre-
sponseatlowfrequenciesorfortheroominwhich
theyareused.Theyarevariablecontrolsthatprovide
upto6 dBofboostbelow100Hz.Withthecontrol
inthecounter-clockwisepositiontheresponseisflat.
Clockwiserotationincreasesthebassloudness.Ad-
justonechannelata time.
HeadphoneLevel
Acontrolhasbeenprovidedineachchannelto
adjusttheloudnessoftheprogramwhenusinghead-
phones.Thecontrolsadjusttheoutputineachchan-
neltotheHEADPHONEjackonlyanddonotaffect
theprogramloudnessfromtheloudspeakers.Toad-
justforcomfortableheadphonelisteningfirstadjust
theVOLUMEcontroltothefrontpaneltonormal
roomloudness.Then,whilewearingtheheadphones,
adjusttheHEADPHONELEVELcontroltothedesired
loudnesslevel.
OutputLevel
Acontrolhasbeenprovidedineachchannelthat
adjuststheoutputofthepreamplifier.Usethesecon-
trolstocompensateforminordifferencesinloud-
speakerefficiencyoramplifiergain.Thesecontrols
adjusttheleveltotheMAINOUTPUTSonly.
WiththeMODESELECTORintheMONO(L+ R)
positionsettheBALANCEcontrolto12o'clock.Ad-
justthetoppanelOUTPUTLEVELcontrolsuntilthe
loudnessfromeachloudspeakerisequal.
CenterChannelLevel
Acontrolhasbeenprovidedthatadjuststhecom-
binedleftplusrightprogramleveltotheCTRoutput
jacks.
PowerAmplifierOn/Off
Aswitchhasbeenprovidedthatwillcontrolthe
ACpowertothegreenPOWERAMPLIFIERrecepta-
clesindependentlyoftheC 28frontpanelcontrol.
Usethisswitchtoturnofftheamplifierwhenlisten-
ingtotheheadphones,etc.
IMPORTANT:TOHEARTHEPROGRAMFROMTHE
LOUDSPEAKERSTHISSWITCHMUSTBEINTHE
ONPOSITION.
8

UsingTheFrontPanelControls
Intheupperleftofthefrontpanelisa concentric
control.ThelargeouterknobistheBALANCEcon-
trol.ThesmallcenterknobistheCOMPENSATION
control.
BALANCE
TheBALANCEcontroladjustsforunequalloud-
nessineithertheleftorrightchannels.Theloud-
nessofthechannelscanbevariedrelativetoeach
otherwithoutaffectingtheircombinedloudness.
Left. . . turningthecontroltotheleftaccentsthe
leftchannelbyreducingtherightchanneloutput.
Right. . . turningthecontroltotherightaccents
therightchannelbyreducingtheleftchannelout-
put.
COMPENSATION
TheCOMPENSATIONcontrolisa threeposition
switch.
Pres:Intheleftofcenterpositiontheresponseof
theC28isshapedtoemphasizetheuppermid-
frequencies.
Flat:InthecenterpositiontheresponseoftheC 28
isunmodified.
Loud:TheLOUDnesscontrolautomaticallypro-
videsthecorrectamountofbassrequiredtocom-
pensateforthechangeinresponseofthehuman
earatlowloudnesslevels.
Whenthevolumeisreduced,themusicwill
seemtolosemuchofitsbassandsomeofits
treble.Thiseffectisduetothesensitivitycharac-
teristicofhumanhearing.Theresponseofthehu-
maneartobassandtreblepitchdecreasesmore
rapidlythanitsresponsetopitchcenteredinthe
mid-tonalrange.TheLOUDnessswitchconverts
thevolumecontroltoa loudnesscompensated
control.UseLOUDnesstolistenatlowvolumeand
stillhearfull-frequencyrange.
INPUTSELECTOR
Aux:Connectstheoutputfromanyhighlevelpro-
gramsourcerequiringflatamplificationtothehigh
levelinputstage.Sucha sourcecouldbea tele-
visionset.IntheAUXpositionthegainis20dBto
theMAINoutputs,0 dBtotheTAPEoutputs,and
17.5dBtotheLINEoutputs.Theinputimpedance
is250,000ohms.
Tuner:ConnectstheoutputfromanyAM,FMor
MPXFMtunertothehighlevelinputstage.Inthe
TUNERpositiontheC 28hasflatamplification.
Thereis20dBofgaintotheMAINoutputs,0 dB
totheTAPEoutputsand17.5dBtotheLINEout-
puts.Theinputimpedanceis250,000ohms.
Phono1:Connectstheoutputofanymagnetic
phonocartridgetothelowlevelinputstage.The
responsehasbeenshapedtocompensateforthe
characteristicsofthemagneticphonocartridge.
Thegainat1,000Hzis62dBtotheMAINoutputs,
42dBtotheTAPEoutputsand59.5dBtotheLINE
outputs.Theinputimpedanceis47,000ohms.
Phono2:SameasPHONO1.
Mic:Connectstheoutputofanyhighimpedance
microphonetothelowlevelinputstage.IntheMIC
positiontheC 28hasflatamplification.Thegain
is60dBtotheMAINoutputs,40dBtotheTAPE
outputsand57.5dBtotheLINEoutputs.Theinput
impedanceis500,000ohms.
TapeHd:Connectstheoutputofanytapehead(a
tapedeckwithoutitsownelectronics)tothelow
levelinputstages.Theresponsehasbeenshaped
tocompensateforthecharacteristicsofthetape
head.Thegainat500Hzis64dBtotheMAINout-
puts,44dBtotheTAPEoutputsand61.5dBtothe
LINEoutputs.Theinputimpedanceis500,000
ohms.
MODESELECTORConnectstheprogramtothe
loudspeakerinthefollowingsevenways:
LtoL & R:Connectsthe"left"inputtobothloud-
speakers.
RtoL & R:Connectsthe"right"inputtobothloud-
speakers.
StereoRev:Connectsthe"left"inputtothe"right"
loudspeakerandthe"right"inputtothe"left"
loudspeaker.
Stereo:Connectsthe"left"inputtothe"left"loud-
speakerandthe"right"inputtothe"right"loud-
speaker.
Mono(L+ R):addsthe"left"inputandthe"right"
inputandthenconnectstheL + R programtoboth
amplifiersandloudspeakers.
L+ R toL:Connectsthe"leftplusright"program
tothe"left"loudspeakeronly.
L+ R toR:Connectsthe"leftplusright"program
tothe"right"loudspeakeronly.
9

VOLUMEON/OFF
TurningtheVOLUMEtotallycounter-clockwise
turnstheC28OFF.TheVOLUMEcontrolregulates
theloudnessinbothchannels.TheVOLUMEcon-
trolhasbeenprecisiontrackedthroughoutthelis-
teningrange(0to-65dB)foraccuratestereo
balance.
BASS
TheC 28hasseparate11positiontonecontrol
switchesineachchannelforbassandtreble.
Left:Adjuststhebassloudnessfromtheleftloud-
speaker.Clockwiserotationincreasesthebass
loudnesswhilecounter-clockwiserotationde-
creasesthebassloudness.Eachstepofthetone
controladjuststhebassloudness4 dB.
Right:Hasthesameeffectonthesoundfromthe
rightloudspeaker.
TREBLE
Left:Adjuststhetrebleloudnessfromtheleftloud-
speaker.Clockwiserotationincreasesthetreble
loudnesswhilecounterclockwiserotationde-
creasesthetrebleloudness.Eachstepofthetone
controladjuststhetrebleloudnessabout4 dB.
Right:Hasthesameeffectonthesoundfromthe
rightloudspeaker.
PANLOC
MclntoshdevelopedPANLOCmountingbringspro-
fessionalinstallationtechniquetostereo.Depress-
ingthePANLOCbuttonfaswitha ballpointpen)
willreleasetheinstrument.Itcanthenbepulled
towardyoutothe"adjustment"position.Inthis
positionthetoppanelcontrolscanbeadjusted.
10