McIntosh C28 User manual

OWNER'SMANUAL
C28
SOLIDSTATE
STEREOPREAMPLIFIER
Price$1.25

MclntoshLaboratoryIncorporatedguaranteesthisinstrumenttobecapable
ofperformanceasadvertised.Wealsoguaranteethemechanicalandelec-
tricalworkmanshipandcomponentstobefreeofdefectsfora periodof90
daysfromdateofpurchase.Ifsuchdefectsoccur,MclntoshLaboratoryor
oneofitsauthorizedagencieswillrepairthedefectatnocosttothepur-
chaser.Thisguaranteedoesnotextendtocomponentsdamagedbyimproper
usenordoesitextendtotransportationtoandfromthefactoryorservice
agency.
THREEYEARFACTORYSERVICECONTRACT
Anapplicationfora FREETHREEYEARFACTORYSERVICECONTRACTis
includedwiththismanual.Thetermsofthecontractare:
ForThreeYearsfromdateofpurchase
1.Mclntoshwillprovideallparts,materialsandlaborneededtoreturn
themeasuredperformanceoftheinstrumenttotheoriginalfactory
specificationsfreeofanycharge.TheSERVICECONTRACTdoesnot
coveranyshippingcoststoandfromtheauthorizedserviceagency
orthefactory.
2.AnyMclntoshauthorizedserviceagencywillrepairallMclntoshInstru-
mentsatnormalservicerates.Toreceivethefreeserviceunderthe
termsoftheSERVICECONTRACT,theSERVICECONTRACTCER-
TIFICATEmustaccompanytheinstrumentwhentakentotheservice
agency.
3.Alwayshaveservicedonebya Mclntoshauthorizedserviceagency.
Iftheinstrumentismodifiedordamagedasa resultofunauthorized
repairtheSERVICECONTRACTwillbecancelled.
4.TheSERVICECONTRACTisissuedtoyouastheoriginalpurchaser.
Toprotectyoufrommisrepresentationthiscontractcannotbetrans-
ferredtoa secondowner.
5.TheSERVICECONTRACTisgiventothepurchaserswholiveinthe
50UnitedStatesorCanadaonly.
6.ForyourprotectionMclntoshselectsitsdealerscarefully-Therequire-
mentsareverystrict.Onlyonedealerinsevenapplicantsqualifiesfor
aMcIntoshfranchise.ToreceivetheSERVICECONTRACTyourpur-
chasemustbemadefroma Mclntoshfranchiseddealer.
7.Yourcompletelyfilledinapplicationfora SERVICECONTRACTmust
bepostmarkedwithin30daysofthedateofpurchaseoftheinstru-
ment.
8.ToreceivetheSERVICECONTRACTallinformationontheapplica-
tionmustbefilledin.TheSERVICECONTRACTwillbeissuedwhen
thecompletelyfilledinapplicationisreceivedatMclntoshLaboratory
IncorporatedinBinghamton,NewYork.Iftheapplicationisnotre-
ceivedatMclntoshLaboratory,onlytheserviceofferedunderthe90-
dayguaranteewillapply.
GUARANTEE

YourC 28stereopreamplifierwillgive
youmanyyearsofpleasantand
satisfactoryperformance.Ifyouhave
anyquestionsconcerningoperationor
maintenancepleasecontactthedealer
fromwhomyoupurchasedthis
instrumentor:—
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Ourtelephonenumberis607-723-3512
CONTENTS
Guarantee
Installation2-3
IfYou'reInA Hurry4
HowToConnect5-8
AdjustingTheTopPanelControls...9
UsingTheFrontPanelControls10,11
UsingThePushbuttons12,13
Specifications14,15
PerformanceCharts16,17
TechnicalDescription18,19
BlockDiagram20
TAKEADVANTAGEOF3 YEARSOFFREEFACTORYSERVICE
FILLINTHEAPPLICATIONNOW!
C28
SOLIDSTATE STEREOPREAMPLIFIER

Installation
Adequateventilationextendsthetrouble-freelifeofelectronic
instruments.Itisgenerallyfoundthateach10"centigrade(18°F)
riseintemperaturereducesthelifeofelectricalinsulationbyone
half.Adequateventilationisaninexpensiveandeffectivemeans
ofpreventinginsulationbreakdownduetounnecessarilyhighop-
eratingtemperature.Thedirectbenefitofadequateventilationis
longer,trouble-freelife.
ThesuggestedminimumspaceformountingtheC 28is15
inchesdeepx 17½widex 6 incheshigh.Itcanbemounted
eitherhorizontallyorvertically.
TopreparetheC 28forinstallationremovetheplasticpro-
tectivecovering.TurntheC 28upsidedownsothatitrestsonits
topontheshippingpallet.Removethefourplasticfeetfastened
tothebottomofthechassis.
Nextplacethemountingbrackets,thepartsbagandthemount-
ingtemplateforeasyaccessibility.
Theprofessionalmountingdesigneliminatestheneedforyou
toprovideanyshelforbrackettosupporttheC 28.Itiscompletely
supportedbyitsownmountingbrackets.
Positiontheplasticmountingtemplateovertheareaofthepanel
tobecutoutforinstallation.
Thedesignofthemountingtemplateallowsyoutopositionor
locatethecutoutfromthefrontorrearofthepaneltowhichthe
instrumentistobemounted.
Ifthecutoutistobelocatedfromtherearofthepanel,the
followingstepswillhelpyou:
Onthebackofthecabinetpanel,scribea verticalcenter-
linethroughtheexactcenteroftheareainwhichthecutout
istobemade.
Placethetemplateagainstthebackofthepanelandmatch
thetemplatecenterlinewiththecenterlineonthecabinetpanel.
Makesurethatthereisatleast¼ inchclearancebetweenthe
bottomofthedashedlineofthecutoutareaonthetemplate
andanyshelforbracebelowtheproposedcutout.
Markthetwolocatingholes("C"holesonthemountingtem-
plate).
Drillthetwolocatingholes.Becertainthedrillisperpendicular
tothepanel.
Nowpositionthetemplateonthefrontofthepanelbyalign-
ingthe"C"locatingholesonthetemplatewiththedrillholes.
2

Withthetemplateinplaceagainstthecabinetpanel,markthe
"A"and"B"drillholesandthefoursmallholesthatidentifythe
cornersofthecutout.Jointhecornermarkswitha pencil.The
edgeofthetemplatecanbeusedasa straightedge.
IMPORTANT:DRILLTHE6 HOLESBEFOREMAKINGTHECUT-
OUT.
Accuratelydrilleachofthethreeholesontheleftandthe
rightsideofthecutoutareawitha 3/16inchdrill.
WiththesawontheINSIDEOFTHEPENCILLINEScarefully
cutouttherectangularopening.
Securethemountingstripstotherearofthecabinetpanel
usingtwoscrewsfromthehardwarepackage.
Insertthescrewsinthecenterholesofthecabinetpanel
{"B"holesonthetemplate)andtighten.Thescrewheadshouldpull
intothewoodslightly.(Usetwo¾ inchlongscrewsforpanels
under½ inch,ortwoVAinchlongscrewsforpanels½ inchor
thicker.)
Attachthemountingbracketstothecabinetpanelusingfour
screws.
Placethetemplateoverthemountingscrews.Themounting
screwsshouldbecenteredinthe"A"and"B"holesonthetem-
plate.Thesidesofthemountingbracketsshouldmatchthevertical
dashlinesonthetemplate.Ifnecessary,loosenthescrewsand
pushthebracketsintoalignmentandretighten.
Insertthepowercordthroughtheopeningsotherailsonthe
bottomoftheequipmentslideinthetrackofthemounting
brackets.Continuetoslidetheinstrumentinuntilthefrontpanel
isagainstthecabinetpanel.
AtthebottomfrontcornersofthePANLOCinstrumentsare
thePANLOCbuttons.
DepressingthePANLOCbuttonswilllocktheinstrumentfirmly
intheinstallation.
DepressingthePANLOCbuttonsa secondtime(aswitha ball-
pointpen)willreleasetheinstrument.Youcanthenslidethein-
strumentforwardtotheinspection-adjustmentposition.
Depressingtheinspection-adjustmentpositionlatcheswillallow
theinstrumenttoslidecompletelyoutoftheinstallation.
VERTICALINSTALLATION
Inthehardwarepacketaretwohelicalsprings.Fastenthe
springstothesmallflangesattherearofthePANLOCbrackets.
Theflangehasa notchanda holetomountthespring.Thesprings
assistintheremovalofverticallymountedPANLOCequipment.
DONOTUSETHESPRINGSONHORIZONTALLYMOUNTED
EQUIPMENT.
3

IfYou'reInA Hurry
A-BALANCE(outerring)make
onespeakerlouderthantheother.Permits
theadjustmentforunequalsoundcaused
byroomacousticsorprogrammaterial.
B-COMPcenterknob). . threeposition
switch.FLATisthecenterposition.PRES
(theleftofcenterposition)increasesthe
mid-frequencies.LOUD(therightofcenter
position)adjustsfrequencyresponseas
volumeisreducedtocompensateforhear-
inglossesatlowvolumes.
C-INPUTSELECTOR
AUX...foranydeviceconnectedtothe
AUXinputsonback.
TUNER...forFMstereoorAM/FMtuner.
PHONO1 ...forrecordplayer.
PHONO2 ...forrecordplayer.
MIC...formicrophone.
TAPEHD...fortapedeckwithoutelec-
tronics.
D-MODESELECTOR
UsetheSTEREOorSTEREOREVERSE
positionsforallstereoprograms.Allother
positionsaredesignedtohandlemono-
phonicprograms.
E-VOLUMEON/OFF
TurnstheACtotheC 28on,adjustsloud-
nessofsoundtosuityourtaste.
F-BASS
Modifythelowfrequencyprogramma-
terialtosuityourtaste.Rightchannelis
therightknob,theleftchannelistheleft
knob.
G-TREBLE
Modifythehighfrequencyprogramma-
terialtosuityourtaste.Rightchannelis
therightknob,theleftchannelistheleft
knob.
H-PUSHBUTTONS
TAPE1;Pushin- Monitortherecorded
programonTAPErecorder1;Out-Hear
theprogrambeingrecordedonTAPEre-
corder
TAPE2:Pushin- Monitortherecorded
programonTAPErecorder2;Out-Hear
theprogrambeingrecordedonTAPEre-
corder2.
MUSTBEINOUTPOSITIONTOHEAR
ANYOTHERPROGRAMSOURCE.
I-1 2/21 ...copyfromTAPE1 toTAPE
2orfromTAPE2 toTAPE1,whentwo
taperecordersareused.
J-LF...FILTERin...reduceslowfrequency
noisesuchasturntablerumble,OUT- flat
response.
K-HF...FILTERin...reduceshighfre-
quencynoisesuchasrecordsurfacenoise,
OUT-flatresponse.
L-MAIN(mustbeusedwiththeaccessory
SCR).Turnsthemainloudspeakeronor
off.
M-REMOTE(mustbeusedwiththeacces-
sorySCR).Turnstheremoteloudspeaker
onoroff.
N-JACKS
TAPEINPUT
Foruseasanothertaperecorderinput.
Usesthefunctionsnormallyconnectedto
TAPE2.
O-TAPEOUTPUT
Foruseasanothertaperecorderoutput.
Usesthefunctionsnormallyconnectedto
TAPE2.
P-HEADPHONE...toconnecta setof
stereoheadphones.
4

HowToConnect
CONNECTINGA RECORDPLAYERTOPHONO1
Connectthecablefromthe"left"channeloftherecord
playerintothe"L"PHONO1 inputjack.
Connectthecablefromthe"right"channeloftherecord
playerintothe"R"PHONO1 jack.
PHONO2 isprovidedfortheuseofa secondrecordplayer.
Connectthecablefromthe"left"channeloftherecord
playerintothe"L"PHONO2 inputjack.
Connectthecablefromthe"right"channeloftherecord
playerintothe"R"PHONO2 inputjack.
CONNECTINGA MICROPHONE
Connectthecablefromthe"left"microphonetothe"L"MIC
inputjack.Connectthecablefromthe"right"microphone
tothe"R"MICinputjack.
CONNECTINGA TAPEDECKFORPLAYBACK
Connectthecablefromthe"left"taperecorderheadonthe
tapedeck(onewithoutitsownelectronics)tothe"L"TAPE
HEADinput.Connectthecablefromthe"right"taperecorder
headtothe"R"TAPEHEADinput.
CONNECTINGA STEREOTUNER
Connectthecablefromthe"left"channeltuneroutputto
the"L"tunerinputjack.
Connectthecablefromthe"right"channeltuneroutputto
the"R"TUNERjack.
AUX
Anyhighlevelprogramsourcesuchasanothertunerora TV
setcanbeconnectedtotheinputjacksmarked"AUX."
CONNECTINGA TAPERECORDER
ToRecord:
Connecta cablefromthe"L"TAPEOUTPUTjackmarkedTAPE1
tothe"left"highlevelinputofa taperecorder.
Connecta cablefromthe"R"TAPEOUTPUTjackmarkedTAPE1
tothe"right"highlevelinputofthetaperecorder.
Connecta secondtaperecorderinthesamefashiontothe
TAPE2 outputs.
ToPlayback/Monitor:
Connectthecablefromthe"left"channeloutputofa tape
recordertothehighlevelinputs. . . "L"TAPE1.
Connectthecablefromthe"right"channeloutputofa tape
recordertothehighlevelinput.."R"TAPE.
Connecta secondtaperecorderinthesamefashiontothe
TAPE2 inputjacks.5

HowToConnect
6

HowToConnect
CONNECTINGTHEC 28TOPOWERAMPLIFIERS
ConnecttheMAINoutputjackstotheinputofa
stereopoweramplifier.The"L"jackisconnectedtothe"left"
amplifierinputjack.The"Ft"jackisconnectedtothe"right"
amplifierinputjack.
TheoutputimpedanceattheMAINoutputis100ohms.Longer
cablesthanaresuppliedcanbeconnectedbetween
theC 28andtheamplifiers.Thelengthofthecableis
limitedbythecapacityofthecable.Thetotalcapacity
mustnotexceed1000pF.Forinstance:cableswitha
capacityof25pFperfootmaybe40feetlong.13.5pFper
footcablemaybe75feetlong.Theinputimpedanceof
theamplifiersshouldbe47,000ohmsorgreater.
CTROutput:
UsetheCTRoutputtofeedleftplusrightsignaltoa separate
poweramplifierformonophonicbackgroundmusicorfor
acenterchannelspeaker.
SPEAKERCONTROLRELAY
Tocontrolmainandremoteloudspeakersfromthefrontpanel
oftheC 28anaccessoryMclntoshSCRcontrolisneeded.
PlugthecablefromtheSCRcontrolintotheSPEAKERCONTROL
RELAYreceptacle.Thespeakersarethenconnectedtothe
SCRcontrol.(SeeDiagramp.8)
ACOUTLETS
Thereare4 blackACoutlets,2 greenACoutlets,andone
redACoutlet.ThepowertotheblackACoutletsiscontrolled
bythefrontpanelswitch.Usetheseoutletsfora tuner,
taperecorder,etc.Thegreenoutletsarecontrolledbythetop
panelswitchmarked"PowerAmplifier."Theredreceptacle
isonatalltimes.Usetheredoutletfora turntableor
recordchanger.Theturntableisprotectedbythisarrangement.
Itisnecessarytoturnofftheturntableorrecordchanger
withitsownACswitch.
GROUNDCONNECTION
Asinglegroundpostisprovided.Groundsforturntables,
recordchangers,tapedecks, etc.shouldbeconnectedtothis
post.Theleftandrightprogramcablesandthegroundwire
fromthatsourceshouldbewoundortwistedtogether.Toavoid
hum,makesurethegroundwiredoesnotmakeanyconnections
totheshieldsoftheleftandrightprogramcablesbetween
theprogramsourceandtheC 28.7

HowToConnect
8

AdjustingTheTopPanelControls
Youwillenjoythebestinstereoperformancemorewhenthe
stereosystemisproperlybalanced.Forproperbalanceeachchan-
nelmustbeequalinloudnessandsimilarinfrequencyresponse.
UsethetoppanelLEVELcontrolstobalancesystemloudnessand
thetoppanelBASSTRIMcontrolstobalanceforfrequencyre-
sponsedifferencesatlowfrequencies.
DonotusethefrontpanelBALANCEcontroltocorrectfor
systemunbalance.TheBALANCEcontrolisusedtoadjustfor
anyunbalanceinthesourcematerial,therecord,etc.
BeforeattemptingtobalancetheoutputoftheC 28makecertain
thefrontpanelcontrolsaresetproperly.
TurntheVOLUMEcontroltotheOFF(totallycounter-clockwise)
position.
SettheMODESELECTORtoSTEREOandtheBALANCE
controlatthecenteror12o'clockposition.Turnthetonecontrols
tothecenteror12o'clockposition.TheHFandLFpushbuttons
shouldbeintheoutpositionandtheCOMPensationcontrolinthe
flatposition.TurntheINPUTSELECTORtoTUNER.
DepressthePANLOCbuttonsandpullthepreamplifieroutto
theadjustposition.Thecontrolsonthetoppanel arenoweasily
adjusted.
OnthetoppanelturntheBASSTRIMcontrolscounter-clock-
wise.Turnallthelevelcontrolstotheclockwiseposition.Turn
thePOWERAMPLIFIERswitchon.
Withthetunerturnedon,turnuptheVOLUMEcontrolonthe
frontpaneluntila comfortableroomloudnessisreached.
ThenswitchtheINPUTSELECTORtoPHONO1,theMODE
SELECTORtoL TOL & R,usea monophonicrecordandturndown
thetoppanelLEFTPHONO1 LEVELcontroltomatchtheloudness
ofthetuner.RepeattheprocedurewiththeRIGHTPHONO1 LEVEL
control.Whenthechannelsareequallyloudthesystemisbalanced
forloudness.
RepeatthesamestepsforPHONO2.
BassTrim:
Acontrolhasbeenprovidedineachchannelthatadjuststhe
bassloudness.Thesecontrolsareusedtocompensateforthedif-
ferencesinloudspeakerresponseatlowfrequenciesorforthe
roominwhichtheyareused.Theyarevariablecontrolsthatpro-
videupto6 dBofboostbelow100Hz.Withthecontrolinthe
counter-clockwisepositiontheresponseisflat.Clockwiserotation
increasesthebassloudness.Adjustonechannelata time.
HeadphoneLevel:
Acontrolhasbeenprovidedineachchanneltoadjustthe
loudnessoftheprogramwhenusingheadphones.Thecontrols
adjusttheoutputineachchanneltotheHEADPHONEjackonly
anddonotaffecttheprogramloudnessfromtheloudspeakers.
Toadjustforcomfortableheadphonelisteningfirstadjustthe
VOLUMEcontrolonthefrontpaneltonormalroomloudness.Then,
whilewearingtheheadphones,adjusttheHEADPHONELEVELcon-
troltothedesiredloudnesslevel.
OutputLevel:
Acontrolhasbeenprovidedineachchannelthatadjuststhe
outputofthepreamplifier.Usethesecontrolstocompensatefor
minordifferencesinloudspeakerefficiencyoramplifiergain.These
controlsadjusttheleveltotheMAINOUTPUTSonly.
WiththeMODESELECTORintheMONO(L+ R)positionsetthe
BALANCEcontrolto12o'clock.AdjustthetoppanelOUTPUT
LEVELcontrolsuntiltheloudnessfromeachloudspeakerisequal.
CenterChannelLevel:
Acontrolhasbeenprovidedthatadjuststhecombinedleft
plusrightprogramleveltotheCTRoutputjacks.
PowerAmplifierOn/Off:
AswitchhasbeenprovidedthatwillcontroltheACpowerto
thegreenPOWERAMPLIFIERreceptaclesindependentlyoftheC 28
frontpanelcontrol.Usethisswitchtoturnofftheamplifierwhen
listeningtotheheadphones,etc.
IMPORTANT:TOHEARTHEPROGRAMFROMTHELOUD-
SPEAKERSTHISSWITCHMUSTBEINTHEONPOSITION.
C28 9

UsingTheFrontPanelControls
10
Intheupperleftofthefrontpanelisa concentriccontrol.The
largeouterknobistheBALANCEcontrol.Thesmallcenterknob
istheCOMPENSATIONcontrol.
BALANCE:
TheBALANCEcontroladjustsforunequalloudnessineither
theleftorrightchannels.Theloudnessofthechannelscan
bevariedrelativetoeachotherwithoutaffectingtheircom-
binedloudness.
Left. . . turningthecontroltotheleftaccentstheleftchannel
byreducingtherightchanneloutput.
Right. . . turningthecontroltotherightaccentstherightchan-
nelbyreducingtheleftchanneloutput,
COMPENSATION:
TheCOMPENSATIONcontrolisa threepositionswitch.
Pres:IntheleftofcenterpositiontheresponseoftheC 28is
shapedtoemphasizetheuppermid-frequencies.
Flat:InthecenterpositiontheresponseoftheC 28isunmodi-
fied.
Loud:Whenthevolumeisreduced,themusicwillseemtolose
muchofitsbassandsomeofitstreble.Thiseffectisdueto
thesensitivitycharacteristicofhumanhearing.Theresponse
ofthehuman eartobassandtreblepitchdecreasesmore
rapidlythanitsresponsetonotescenteredinthemid-tonal
rangeassoundintensityisreduced.TheLOUDcontrolauto-
maticallyprovidesthecorrectamountofequalizationrequired
tocompensateforthechangeinresponseofthehuman ear
atlowloudnesslevels.WhentheswitchisintheLOUDposition,
itconvertsthevolumecontroltoa loudnesscompensatedcon-
trol.UsetheLOUDpositiontolistenatlowvolumeandstillhear
full-frequencyrange.
INPUTSELECTOR:
Aux:Connectstheoutputfromanyhighlevelprogramsource
requiringflatamplificationtothehighlevelinputstage.Such
asourcecouldbea televisionset.IntheAUXpositionthegain
is20dBtotheMAINoutputs,0 dBtotheTAPEoutputs,and
17.5dBtotheLINEoutputs.Theinputimpedanceis250,000
ohms.
Tuner:ConnectstheoutputfromanyAM,FMorMPXFMtuner
tothehighlevelinputstage.IntheTUNERpositiontheC 28has
flatamplification.Thereis20dBofgaintotheMAINoutputs,
0dBtotheTAPEoutputsand17.5dBtotheLINEoutputs.The
inputimpedanceis250,000ohms.
Phono1:Connectstheoutputofanymagneticphonocartridge
tothelowlevelinputstage.Theresponsehasbeenshapedto
compensateforthecharacteristicsofthemagneticphonocart-
ridge.Thegainat1 kHzis62dBtotheMAINoutputs,42dB
totheTAPEoutputsand59.5dBtotheLINEoutputs.Theinput
impedanceis47,000ohms.
Phono2:SameasPHONO1.
Mic:Connectstheoutputofanyhighimpedancemicrophoneto
thelowlevelinputstage.IntheMICpositiontheC 28hasflat
amplification.Thegainis60dBtotheMAINoutputs,40dB
totheTAPEoutputsand57.5dBtotheLINEoutputs.Theinput
impedanceis500,000ohms.
TapeHd:Connectstheoutputofanytapehead(atapedeck
withoutitsownelectronics)tothelowlevelinputstages.The
responsehasbeenshapedtocompensateforthecharacteristics
ofthetapehead.Thegainat500Hzis64dBtotheMAIN
outputs,44dBtotheTAPEoutputsand61.5dBtotheLINE
outputs.Theinputimpedanceis500,000ohms.
MODESELECTOR:Connectstheprogramtotheloudspeakerinthe
followingsevenways:
LtoL & R:Connectsthe"left"inputtobothloudspeakers.
RtoL & R:Connectsthe"right"inputtobothloudspeakers.
StereoRev:Connectsthe"left"inputtothe"right"loudspeaker
andthe"right"inputtothe"left"loudspeaker.
Stereo:Connectsthe"left"inputtothe"left"loudspeakerand
the"right"inputtothe"right"loudspeaker.
Mono(L+ R):addsthe"left"inputandthe"right"inputand
thenconnectstheL + R programtobothamplifiersandloud-
speakers.
L+RtoL:Connectsthe"leftplusright"programtothe
"left"loudspeakeronly.
L+ R toR:Connectsthe"leftplusright"programtothe
"right"loudspeakeronly.

VOLUMEON/OFF:
TurningtheVOLUMEtotallycounter-clockwiseturnstheC 28
OFF.TheVOLUMEcontrolregulatestheloudnessinbothchan-
nels.TheVOLUMEcontrolhasbeenprecisiontrackedthrough-
outthelisteningrange(0to-65dB)foraccuratestereo
balance.
BASS:
TheC 28hasseparate11positiontonecontrolswitchesin
eachchannelforbassandtreble.
Left:Adjuststhebassloudnessfromtheleftloudspeaker.Clock-
wiserotationincreasesthebassloudnesswhilecounter-clock-
wiserotationdecreasesthebassloudness.Eachstepofthe
tonecontroladjuststhebassloudness4 dB.
Right:Hasthesameeffectonthesoundfromtherightloud-
speaker.
TREBLE:
Left:Adjuststhetrebleloudnessfromtheleftloudspeaker.
Clockwiserotationincreasesthetrebleloudnesswhilecounter-
clockwiserotationdecreasesthetrebleloudness.Eachstep
ofthetonecontroladjuststhetrebleloudnessabout4 dB.
Right:Hasthesameeffectonthesoundfromtherightloud-
speaker.
PANLOC:
MclntoshdevelopedPANLOCmountingbringsprofessional
installationtechniquetostereo.DepressingthePANLOCbut-
tons(aswitha ballpointpen)willreleasetheinstrument.It
canthenbepulledtowardyoutothe"adjustment"position.
Inthispositionthetoppanelcontrolscanbeadjusted.11

UsingThePushbuttons
TheC 28isdesignedtobeusedwithone,twoorthreetape
recorders,forexample— tapeplaybackfroma tapedeck(onewith-
outit'sownelectronics)and,inaddition,twocompletetapere-
corders.Thefrontpanelpushbuttonscontrolthelatter.Thepush-
buttonspermitnormalplaybackofeitherrecorder,monitorofeither
recorderasrecordingsarebeingmade,orcopyingtapesfromone
recordertoanotherwhilelisteningtoa separateprogram.
TAPE1
PUSHBUTTONOUT. . . Theprogramsourceisfedtothepower
amplifiersandheardthroughtheloudspeakers.
IN...Theprogramsourcebecomestherecordedtapeonthe
taperecorderconnectedtoTAPEINPUT1.Therecordedprogram
fromtaperecorder1 isfedtothepoweramplifiersandheardfrom
theloudspeakers.
Withthepushbuttonsinthemonitorpositiona rectangleis
lightedinREDabovethepushbutton.WhentheREDlightison
onlythetapecanbeheard.Tolistentoothersourcesthepush-
buttonmustbeoutandthelightoff.
TAPE2
Thesecondcompletetaperecordercanbeoperatedinthe
samefashion.
TAPE2 pushbuttonalsocontrolstheprogramfroma tapere-
corderpluggedintothefrontpaneljacksmarkedTAPEINPUTand
TAPEOUTPUT.Whena taperecorderispluggedintothefront
paneljacksallthefacilitiesforTAPE2 areautomaticallyswitched
tothefrontpaneljacks.A taperecorderpluggedintotheTAPE2
INPUTSandOUTPUTSonthebackpanelisautomaticallydis-
connected.
UsethefrontpanelbushbuttonTAPE2 torecordonorplayback
froma taperecorderpluggedintothefrontpaneljacks.
TAPECOPY1 - 2
Thispushbutton,whenpushedIN,connectstheTAPE1 INPUT
jackstotheTAPE2 OUTPUTjackswithoutaffectingtheprogram
beingheardfromthespeakers.Inthispositiona copyofthepro-
gramontaperecorder1 canbemadeontaperecorder2.Withthe
pushbuttonINa rectangleislightedinORANGEabovethepush-
button.
TomonitorthetapecopyproceduresusetheTAPE1 MONITOR
pushbutton.
TAPECOPY2 - 1
Thispushbutton,whenpushedIN,connectstheTAPE2 INPUT
jackstotheTAPE1 OUTPUTjackswithoutaffectingtheprogram
heardfromthespeakers.Inthispositiona copyoftheprogramon
taperecorder2 canbemadeontaperecorder1.Withthepush-
buttonintheINpositiona rectangleislightedinORANGEabove
thepushbutton.
TomonitorthetapecopyproceduresusetheTAPE2 MONITOR
pushbutton.
L.F.(LOWFREQUENCYFILTER)
UsetheL.F.filterswitchtoreduceobjectionablelow-frequency
noisecreatedbya turntableorrecordchangeroracoustically
coupledfeedback.
OUT...filterdisconnected
IN...low-frequencyrumbleandnoisebelow50Hzarere-
ducedwhentheswitchispushedtotheINposition.
WiththeLFpushbuttonintheINpositiona rectangleislighted
inGREENabovethepushbutton.WhentheGREENlightisonthe
lowfrequencyfilterisinoperation.
H.F (HIGHFREQUENCYFILTER)
UsetheH.F.filterswitchtoreduceobjectionablehigh-fre-
quencynoisesuchasrecordscratch.
OUT. . . filterdisconnect
IN...rollsoffresponsesharplyat7 kHz.
WiththeH.F.pushbuttonintheINpositiona rectangleislighted
inGREENabovethepushbutton.WhentheGREENlightisonthe
highfrequencyfilterisinoperation.
SPEAKERPUSHBUTTONS
Speakerscanbeturnedonandoffwhenproperlyconnected
withtheaccessoryMclntoshSCRcontrol.(SeediagramPg.8)
Iftheprogramistobeheardfromthemainspeakersonly,the
REMOTEpushbuttonispushedIN.Thisturnsofftheremote
speakersandlightsa rectangleinBLUEabovethepushbutton.The
BLUElightindicatesthattheremotespeakersareoffandnopro-
gramcanbeheardfromthem.
12

Iftheprogramistobeheardfromtheremotespeakersonly
theMAINpushbuttonispushedIN.Thisturnsoffthemainspeakers
andlightsa rectangleinBLUEabovethepushbutton.TheBLUE
lightindicatesthatthemainspeakersareoffandnoprogramcan
beheardfromthem.
Tohearprogramfrombothmainandremotespeakers,boththe
MAINandREMOTEpushbuttonsmustbeoutandtheBLUElights
mustbeoff.
FRONTPANELJACKS:
TAPEINPUT- TAPEOUTPUT
Whena taperecorderispluggedintothefrontpaneljacksall
thefacilitiesforTAPE2 areautomaticallyswitchedtothefront
paneljacks.A taperecorderpluggedintotheTAPE2 INPUTSand
OUTPUTSonthebackpanelisautomaticallydisconnected.
UsethefrontpanelpushbuttonTAPE2 torecordororplayback
froma taperecorderpluggedintothefrontpaneljacks.
HEADPHONES:
PlugheadphonesintothefrontpanelHEADPHONEjack.Adjust
thefrontpanelVOLUMEcontrolforcomfortableheadphonelisten-
ing.{SeePg.9 )
AnamplifierintheC 28providesthepowerthatfeedsboththe
HEADPHONEjackonthefrontpanelandtheLINEOUTPUTjacks
ontherearpanel.Ifyouchoosetolistentoheadphonesonlyit
isnotnecessarytooperatethepoweramplifiersthatfeedthe
loudspeakers
Toturnthepoweramplifiersoffusetheswitchonthetoppanel
oftheC28markedPOWERAMPLIFIER.Thisswitchcontrolsthe
ACtothegreenPOWERAMPreceptaclesonthebackpanel.With
thisswitchintheOFFpositionnothingwillbeheardfromthe
speakers.
13

Specifications
FREQUENCYRESPONSE:
+0,-0.5dB20Hzto20,000Hz.
DISTORTION
Lessthan0.1%atratedoutputlevel,20Hz
to20,000Hz.
INPUTSENSITIVITYANDIMPEDANCE:
Auxiliary,Tuner,Tape1,Tape2 0.25voltsat250,000ohms.
Phono1 andPhono2 2 millivoltsat47,000ohms{1,000Hz).
Microphone2.5millivoltsat500,000ohms.
TapeHead2 millivoltsat500,000ohms(500Hz).
HUMANDNOISE
Auxiliary,Tuner,Tape1,andTape2 90dBbelowrated
output.
Phono1,Phono2 andTapeHead78dBbelow10millivolts
input,equivalenttolessthan1.2microvoltsattheinputter-
minals.
Microphonelessthan1.5microvoltsattheinputterminals.
OUTPUTLEVELANDIMPEDANCE:
MainOutput2.5voltswithratedinput,lessthan100ohms
sourceimpedance,tooperateinto47,000ohmsorgreater.
TapeOutput0.25voltswithratedinput,lessthan150ohms
sourceimpedance,tooperateinto47,000ohmsorgreater.
Headphone/LineOutputmaximum0.75voltsinto8 ohm
loador2..5voltsintointo600ohmline,lessthan0.2ohm
sourceimpedance,levelcontrolsprovided.
CenterChannelOutput1.25voltswithratedinputtoboth
channels,tooperateinto47,000ohmsorgreater,levelcontrol
provided.
VOLTAGEAMPLIFICATIONINDECIBELS:
Auxiliary,Tuner,Tape1 andTape2
toMainOutput20dB
toTapeOutput0 dB
toHeadphone/LineOutput17.5dB
Phone1 andPhone2 at1 kHz
toMainOutput62dB
toTapeOutput42dB
ToHeadphone/LineOutput59.5dB
Microphone
toMainOutput60dB
toTapeOutput40dB
toHeadphone/LineOutput57.5dB
TapeHeadat500Hz
toMainOutput64dB
toTapeOutput44dB
toHeadphone/LineOutput61.5dB
POWERREQUIREMENT:
117volts,50/60Hz,45watts.
FACILITIES& FEATURES
BASSCONTROLS:
Separate11positionrotaryswitchesforeachchannel,+20dB
to-20dBat20Hz.
TREBLECONTROLS:
Separate11positionrotaryswitchesforeachchannel,+18dB
to-18dBat20kHz.
COMPENSATIONSWITCH:
ThreepositionswitchforFlat,Loudness,orPresence.Loud-
nesspositionboostslowfrequenciesforlowlevellistening.
Presencepositionboostsmidfrequencies4 dBtoincrease
"presence"effect.Thiscontroloperatesasa functionofvol-
umecontrolpositionsofullcompensationisobtainedatlower
volumelevelsandflatresponseisobtainedatfullvolume.
BALANCECONTROL:
Naturalbalanceatcenterposition,attenuationofleftorright
channelbyrotatingcontrol.
VOLUMECONTROL:
Precision"trackedatalllisteninglevels.(0to—65db).Does
notchangestereobalanceasloudnessischanged.Thepower
ON/OFFswitchiscoupledwiththiscontrol.
INPUTSELECTOR:
SixpositionsAuxiliary,Tuner,Phono1,Phono2,Micro-
phone,andTapeHead.
MODESELECTOR:
SevenpositionsLeftchannelonlytobothspeakers,Right
14

channelonlytobothspeakers,StereoReverse,Stereo,Mono,
L+ R toleftspeakeronly,andL + R torightspeakeronly.
TAPEMONITORSWITCHES:
Twopushbuttonswitches.Eitheroftwotaperecordercanbe
monitoredbyselectingtheTAPE1 pushbuttonorTAPE2 push
button.Theyaremechanicallyinterlockedtoacceptonlyone
pushbuttonattheINpositionatonetime.
TAPECOPYSWITCH:
Twopushbuttonswitches.Eitheroftwotaperecorderscanbe
connectedtocopyfromtapemachine1 totapemachine2 or
viceversa.Theyaremechanicallyinterlockedtoacceptonly
onepushbuttonattheINpositionatonetime.
LFFILTERSWITCH(RumbleFilter):
Flatorroll-off12dBperoctavebelow50Hz,downto18dBat
20Hz.
HFFILTERSWITCH(ScratchFilter):
Flatorroll-off12dBperoctaveabove7 kHz,down18dBat
20kHz.
SPEAKERSWITCHES:(Operateswithaccessoryspeakercontrol
relay)
MainSwitchtheMAINloudspeakersystemONorOFFwith-
outaffectingtheperformanceofREMOTEspeakers.
RemoteSwitchtheREMOTEloudspeakersystemONorOFF
withoutaffectingtheperformanceofMAINspeakers.
FRONTPANELTAPEJACKS:
Allowsconnectiontoinputandoutputofa taperecorderfrom
thefrontpaneloftheC 28.Insertingplugsintotheirjacks
disconnectstheTAPE2 circuitsfromtherearpanel oftheC 28
andusestheTAPE2 facilitiesforthefrontpaneljacks.
HEADPHONEJACK:
Forlisteningwitheitherloworhighimpedancestereohead-
phones.Powertothisjackissuppliedbyanamplifierprovided
intheC 28.Headphonelisteningcanbeaccomplishedwithout
theuseofanexternalpoweramplifier.
SECONDARYCONTROLS:
Thefollowingcontrolsarelocatedbehindthefrontpanelon
topoftheC 28chassis.Thesecontrolsarereadilyaccessible
bydepressingthePANLOCbuttonsandslidingtheC 28for-
wardfromthemountingpanel.
LOWFREQUENCYTRIMCONTROLS
Permitstheincreaseinoutputoffrequenciesbelow100Hz
ofupto6 dBtocompensateforunequalspeakerresponseor
theunequalinfluenceofroomacoustics.
PHONO1 ANDPHONO2 LEVELCONTROLS
Permitsvariationsinthephonoinputsensitivityofupto10dB.
Providesforoptimumsignaltonoiseratioandproperbalance
ofthechannelsofthephonocartridge.
OUTPUTLEVELCONTROLS
Permitsthebalanceoftheentiresystemtobeconveniently
preset.
HEADPHONELEVELCONTROLS
Adjuststhelevelandbalanceoftheheadphone/lineoutput.
POWERAMPLIFIERON-OFFSWITCH:
Controlspowertothegreen117voltPowerAmplifierrecep-
tacles.Allowsthepoweramplifierstobeturnedoffwhennot
neededforheadphonelistening,etc.
TRANSISTORCOMPLEMENT:
26silicon-planartransistors,4 silicondiodes,2 siliconbridge
rectifiers.
MECHANICALSPECIFICATIONS
SIZE:
Frontpanelmeasures16incheswideby5-7/16incheshigh.
Chassismeasures15incheswideby5 incheshighby13inches
deepincludingPANLOCmountingbracketsandbackpane!
connectors.Knobclearancerequiredis1½inchesinfrontof
themountingpanel.
FINISH:
FrontpanelisanodizedgoldandblackwithspecialMclntosh
gold/tealpanelnomenclatureillumination.Chassisisblack.
MOUNTING:
ExclusiveMclntoshdevelopedprofessionalPANLOC.
WEIGHT:
25poundsnet,35poundsinshippingcarton.
15

TechnicalDescription
Basically,eachchannelofyourC 28consistsoffourmain
parts:lowlevelamplifier,highlevelamplifier,activefiltersand
headphoneamplifier.Commonregulatedpowersuppliesfurnish
powertobothchannels.
LOWLEVELAMPLIFIER
Eachchannelofthelowlevelamplifierisa fourtransistordif-
ferentialamplifierinputcircuit.Preciseequalizationismaintained
bytheuseofnegativefeedbackandappropriatecomponents
speciallydesignedforlownoise.Particularattentionhasbeen
exercisedintheuseoftransistorshavingexceptionallownoise
characteristics.Thedifferentialamplifierstageisthebasisforthe
highopen-loopgainofthisportionofthecircuit.Witha higher
open-loopgainthereisamplenegativefeedbackavailableunder
allequalizationconditionstoensureanextremelylowlevelof
harmonicdistortion.Becauseequalizationhasbeendesignedfor
minimumerrortheresponsefrombothtapeandrecordsisaccurate.
Oneoftheimportantfeaturesofthissectionistheuseofset
levelpotentiometersinthephonocircuit.Thegainofthephono
preamplifierstagescanbeadjustedfrom32dBto42dBtocor-
respondtothesensitivityofyourphonocartridge.
ThephonosetlevelcontrolsinyourC 28aredesignedintothe
negativefeedbackloop.Theyarenotpotentiometersattheinput
oroutputofthelowlevelamplifier.Thisimportantdesignconsidera-
tionallowsthegaintobereducedfrom42dBto32dBwithout
adverselyaffectingthenoiselevel.Becausethecontrolisinthe
feedbackloopthelevelofnoiseanddistortionisreduced10dB
butthemaximuminputvoltagethatthissectioncanhandleis
increasedby10dB.With42dBofgaininthephonosectionthe
maximuminputvoltagethatthelowlevelamplifiercanacceptwith-
outoverloadingis150mVat1 kHz.Whenthegainisreducedto
32dBthissectioncanacceptover0.5voltwithoutoverloadingat
1kHz.
HIGHLEVELAMPLIFIER
Thelinearhighlevelamplifierhasa gainof20dB.Thesame
carefuldesignconsiderationsapplywithrespecttonoiseandthe
reductioninnon-lineardistortion.Eachchannelofthehighlevel
18