McIntosh C11 - SERVICE User manual

STEREO
PREAMPLIFIER
C11
TABLEOFCONTENTS
GENERALDESCRIPTION1
TECHNICALDESCRIPTION1
MechanicalSpecifications2
ElectricalSpecifications2
FRONTPANELFACILITIES2
BACKPANELFACILITIES5
INSTALLATION6
CONNECTING8
A-CConnections8
InputConnections9
OutputConnections10
LoudspeakerPhasingConnections11
GroundConnection11
OPERATINGINSTRUCTIONS11
Balancinga StereoSystem11
AdjustingPhase12
Listeningtoa StereoRecord12
AdjustingtheBalanceControlAfterthe
SystemhasbeenBalanced12
AdjustingforSpecialEffects12
UsingtheC11witha StereoTuner13
UsingtheC11witha StereoTapeMachine_13
UsingtheC11withTapeDeck13
UsingtheC11withMicrophonesforStereo.13
ListeningtoMonophonicRecords13
GUARANTEE16

C11STEREOPHONICPREAMPLIFIER
GENERALDESCRIPTION
TheMcintoshC11StereophonicPre-
amplifierisa controlcenterforanystereo-
phonicsoundsystem.Toincreasethe
enjoymentofstereo,thiscontrolcenterdoes
fourjobswithprecisecontrol.
First,thecontrolcenteramplifiesweak
electricalimpulses.Astherecordrotateson
theturntable,undulationsinthegrooves
movethepick-upstylusapproximatelyone-
thousandthofaninch,inanydirection,from
therestposition.Fromthisslightmechanical
movement,thepick-upstylusgeneratesa
weakelectricalimpulseontheorderofa few
thousandthsofa volt.Toamplifyandpre-
servetheinformationinsuchanelectrical
impulse,thefinestamplifierperformanceis
required.
Second,everysoundsystemisusedina
differentacousticalenvironment.Thetone
balanceofthemusicisaffectedbyvariations
TheC11StereophonicPreamplifiercom-
binesexcellenceinperformancewitheaseof
operation.Thecontrolsusedthemosthave
largediameterknobs.A newtypeofrocker
switchindicatesthosecontrolswithsimple
off-onfunctions.TheC11hasanilluminated
frontpanelwithlightintensitycontrolto
provideconvenientreadingunderlow-level
lightingconditions.
TheC11circuitconsistsofthreeamplify-
ingsectionsinduplicatefortheleftandright
stereochannelsanda powersupply.The
firstsectionistheinputpreamplifierusedto
amplifyandequalizetheinputsignalscom-
ingfromphonographpickups,microphones,
ortapeheads.Skillfullayout,grounding,and
shieldingforlowhumpickups,metalfilmand
wirewoundresistors,terminalboardswith
highspecificresistivity,lownoisetubesand
extremecareinmanufacturingcombineto
achievea newlowinnoiseandhum.
Thesecondamplifyingsectionfollowsthe
volumecontrol,andthusitisimpossibleto
overloadthecircuitoranyfollowingcircuits.
Thesametechniquesaswereusedinthe
preamplifierstageassurelowhumandnoise.
Thebassandtrebletonecontrolsarefeed-
backtypecircuitsandoperateinconnection
inenvironment.Also,peoplelisteningtothe
musichavevaryingideasofcorrecttonebal-
ance.Tocompensatefortheseconditions,a
high-qualitycontrolcenterisneeded.
Third,thereisa greatvarietyofstereo-
phonicandmonophonicrecordsmanufac-
turedtoday,bothdomesticandforeign.The
controlcentermustaccuratelycompensate
fortheequalizationintroducedinthere-
cordingprocess.
Fourth,withprogramsoriginatingfrom
severalsourcessuchastuners,records,tape
machines,microphones,etc.,a controlcen-
terisneededtoselectandswitchthese
sourcesseparatelyorincombination.
Allofthesejobsareperformedwithex-
cellencebytheC11andyetthisinstrument
issimpletooperate,easytomount,andis
thefinestinappearance.
withthissection.Exceedinglylowdistortion
andcorrectfrequencyresponseareassured
usingthisarrangement.
Thethirdsectionisthecathodefollower
output.Thesharpcut-off(18dbperoctave)
rumbleandhighfrequencyfiltersareasso-
ciatedwiththissection.Outputlevelsetcon-
trolsarelocatedattheinputofthecathode
followertoallowsimplebalanceoftheentire
amplifyingandspeakersystem.Thesecon-
trolsareconvenientlyaccessibleateachside
ofthefrontpanelundertheendcaps.
Thepowersupplydeservesspecialmen-
tion.Thepowertransformerisconstructed
with"core"typegrainorientedlaminations
andmagneticshieldingforlowhumfield.
Longliferectifiers,fullwaverectification,
filtercondensersectionalizingandcareful
groundingaddtothehumfreeandlonglife
characteristicsoftheC11.
Specialattentionhasbeengiventothe
mechanicaldesignalso.TheC11maycon-
venientlybeinstalledinfurniturecabinets,
custombuiltinstallations,orprofessional
relayracks.Thetubesandtheelectricalcon-
nectionsareconvenientlylocatedonthe
backpaneloftheC11forreadyaccess.
1
TECHNICALDESCRIPTION

MECHANICALSPECIFICATIONS
Dimensions
Chassis:14½incheswide;4¾incheshigh;
12inchesdeepincludingconnectors.
FrontPanel:15¾incheswide;51/8inches
high
FrontPanelMountingSpaceRequired:163/8
incheswide;5¼incheshigh
Weight
Chassis:15pounds
ShippingWeight:25pounds
Finish
Anodizedgoldandblack(frontpanel)
ELECTRICALSPECIFICATIONS
PowerRequirements
117volts,ac,50/60cycles,30watts
InputSensitivityandInputImpedance
Auxiliary:0.25volt;250,000ohms
Tape:0.25volt;250,000ohms
Tuner1:0.25volt;250,000ohms
Tuner2:0.25volt;250,000ohms
Phono1:2 millivolts;47,000ohms
Phono2:Sameasphono1
TapeHead:2 millivolts;1 megohm
TapeCompare(Monitor):0.25volt;250,000
ohms
Microphone:2.5millivolts;1 megohm
FrequencyResponse
±0.5db;20to20,000cycles
Distortion
Lessthan0.2%atratedoutput,20to20,000
cycles
HumandNoise
High-levelinputs:85dbbelowratedoutput
Low-levelinputs:lessthan2 microvoltsat
inputterminals
MainOutput
2.5voltswithratedinput
2outputjacksinparallelforeachchannel
TapeOutput
0.25voltwithratedinput
1outputjackforeachchannel
LeftPlusRightOutput
1voltfromgeneratorimpedanceof25,000
ohms
VoltageAmplification
Low-levelinputstoMainOutput:1,000to1
(60db)at1000cycles
Low-levelinputstoTapeOutput:100to1
(40db)at1000cycles
High-levelinputstoMainOutput:10to1
(20db)
High-levelinputstoTapeOutput:1 to1 (0db)
TapeCompare(Monitor)inputto
MainOutput:10to1 (20db)
A-CAuxiliaryOutlets
1unswitchedfortapemachineorturntable,
coloredRed
4switched,coloredBlack
FRONTPANELFACILITIES
Figure1.C11FrontPanel
2

UsetheMODESELECTORto:
Listentonormalstereo(4followingand
page16).
Reversetheleftandrightarrangementof
musicalinstruments(3followingandpage
12).
Balancetheamplifiersandloudspeakers
ina stereosystem(6and7 followingand
page11).
Listentomonphonicsound(1and2
followingandpage13).
Listenthrubothloudspeakerstoeither
trackofa stereoprogramsource.
TurntheMODESELECTORto:
1.L TOL & R:connectsthe"left"inputto
bothloudspeakers.
2.R TOL & R:connectsthe"right"inputto
bothloudspeakers.
3.STEREOREV:connectsthe"left"inputto
the"right"loudspeakerandthe"right"
inputtothe"left"loudspeaker.
4.STEREO:connectsthe"left"inputtothe
"left"loudspeakerandthe"right"input
tothe"right"loudspeaker.
5.MONO(L+R):addsthe"left"inputand
the"right"inputandthenconnectsthe
L+Rprogramtobothamplifiersandloud-
speakers.
6.L+RTOL:connectsthe"leftplusright"
programstothe"left"loudspeakeronly.
7.L+RTOR:connectsthe"leftplusright"
programstothe"right"loudspeakeronly.
BASSCONTROLS
RIGHT
TheLEFTandRIGHTBASSCONTROLS
regulatebassloudnesstotheleftandright
speakers,respectively.Clockwiserotationin-
creasesbassloudness;counterclockwise
rotationdecreasesbassloudness.
TREBLECONTROLS
LEFT RIGHT
TheLEFTandRIGHTTREBLECONTROLS
regulatetrebleloudnesstotheleftandright
speakers,respectively.Clockwiserotation
increasestrebleloudness;counterclockwise
rotationdecreasestrebleloudness.
3
Selectanyoneofeightprogramsources
withthisswitch:
1.AUX:anyauxiliaryservicerequiringflat
amplification,suchasa televisionset,is
connectedtotheC11throughthisposi-
tion.
2.TAPE:anyself-containedtapemachine
(tapemachinehavingitsownplayback
preamplifier)isconnectedtotheC11
throughthisposition.
3.TUNER1:AMandFMoutputsfroma
stereotunerorMPXFMprogramarecon-
nectedtotheC11throughthisposition.
4.TUNER2:sameasTUNER1.
5.PHONO1:connectstheC11forstereo
andmonophonicoperationforrecords.
6.PHONO2:sameasPHONO1.
7.MIC:stereomicrophonesareconnected
totheC11throughthisposition.
8.TAPEHD:a tapedeckthatdoesnotcon-
tainitsownplaybackpreamplifieriscon-
nectedtotheC11throughthisposition.
INPUTSELECTOR
INPUTSELECTOR
MODESELECTOR
MODESELECTOR
TREBLECONTROLS
0
0
BASSCONTROLS
LEFT
0 0
STEREOREV
STEREO
MONO(L+R)
L+RTOL
L+R TOR
RTOL&R
L TOL&R
TUNER2
TUNER1
TAPE
AUX
PHONO1
PHONO 2
MIC
TAPEHD

BALANCE
RIGHT
TheC11isbalancedforunequalprogram
sourcesbythiscontrol.
LEFT. . . turningthecontroltotheleftac-
centstheleftchannelbyreducingtheright
channeloutput.
RIGHT. . . turningthecontroltotherightac-
centstherightchannelbyreducingthe
leftchanneloutput.
Thiscontrolcorrectsforprogramequali-
zationintroducedbytherecordingprocess.
TAPE
TAPE
NORMAL
MONITOR
Thiscontrolmakesitpossibletoinstan-
taneouslycomparetherecordedmaterial
withthesourcesignal.Tapejacksontheback
panelaccepta signalfroma taperecorder
witha monitorheadandpreamplifier.
NORMAL. . . theprogramsourceisfed
throughthepoweramplifiersandtheloud-
speakers.
MONITOR. . . thesignalsourcebecomesthe
monitoredprogramfromtherecordedtape
andisfedthroughthepoweramplifiersand
loudspeakers.
PHASE
REVERSE
Thistwo-positionedswitchreversesthe
phaseintheleftchanneltocorrectforloud-
speakerorprogramphasing.
POWER
POWER
ON
OFF
TheC11andthefourblackreceptacleson
thebackpanelareturnedonbythisswitch.
Low-frequencyrumblenoisebelow50cps
createdbya turntableorrecordchangerand
acousticallycoupledfeedbackarereduced
whentheRUMBLEfilterbuttonispushedto
theFILTERposition.
H.F.
H.F.
FLAT
FILTER
Thisswitchminimizessurfacenoisewhen
reproducingold,badlywornrecordings.Its
positionsare:
FLAT. . . filterdisconnected.
FILTER. . . rollsoffresponsesharplyat5KC.
LOUDNESS
LOUDNESS
ThisswitchconvertstheVOLUMEcontrol
toa loudnesscompensatedcontrolwhenin
theCOMPENSATEDposition.
0
COMPENSATOR
COMPENSATOR
RIAA
LP
PHASE
NORMAL
4
NORMAL
COMPENSATED
FILTER
FLAT
RUMBLE
RUMBLE
BALANCE
LEFT

VOLUME
VOLUME
Thiscontinuouslyvariablecontrolregu-
latesthevolumeforbothchannels.
OUTPUTLEVELCONTROLS
Underthepanelendcapsarethethumb
wheelOUTPUTLEVELCONTROLS.TheL
OUTPUTisontheleft-handside.TheR
OUTPUTisontheright-handside.
BACKPANELFACILITIES
Figure2.C11BackPanel
ACOUTLETS
TherearefiveACoutletsontheleft-hand
sideoftherearpanel.(SeeFigure2.)These
outletshavea maximumratingof660watt
total.Thefourblackoutletsarecontrolledby
thePOWERON-OFFswitchonthefront
panel.Theredoutletisusedforpoweringa
turntableorrecordchanger.Thisoutletis
notswitchedsothattheturntablepowerwill
notbeturnedoffwhiletheturntableidler
wheelisengaged.Withthisarrangementitis
necessarytoturnofftheturntablewithits
owncontrolswitchsothattheturntabledrive
systemwillnotbedamaged.
PANELLIGHT
ThePANELLIGHTswitch,locatedinthe
lowerleft-handcornerofthebackpanel,
providesa choiceofbrightordimfrontpanel
lighting.
OUTPUTCONNECTIONS
TheMAINoutputconnectstopoweram-
plifiers(Figure2);theTAPEoutputconnects
toa taperecorder.
TheMAINandTAPEoutputjacksarefed
fromcathodefollowers.Theinputimpedance
ofdevicesconnectedtotheseoutputsshould
be50,000ohmsorgreater.Thecapacitive
reactanceofconnectingaudiocablesshould
notbelessthan8,000ohmsat20,000
cycles.Longercablesthanarenormallysup-
pliedcanbeconnectedbetweentheC11
andtheamplifiersorloudspeakers.The
lengthofthecableislimitedbythecapacity
ofthecableperfoot.Thetotalcapacitymust
notexceed1000mmf.Forinstance;cables
witha capacityof25mmfperfootmaybe
40feetlong;13.5mmfperfootcablemaybe
75feetlong.
5

HIGHLEVELINPUTS
Thesereceptaclesaccepthigh-levelpro-
gramsourceconnectionsasfollows:
TAPEMONITOR(COMPARE). . . acceptsa
signalfroma taperecorderwitha monitor
headandpreamplifier.
AUX. . . acceptsanyauxiliaryservicere-
quiringflatfrequencyresponse,suchasa
T.V.set,tuner,taperecorderwithitsown
playbackpreamplifier,etc.
TAPE. . . acceptsconnectionfroma tape
machinewithitsownplaybackpreamplifier.
TUNER1 & TUNER2 . . . acceptAMandFM
outputsfroma stereotunerora pairof
stereotuners.
LOWLEVELINPUTS
Thesereceptaclesacceptlow-levelpro-
gramsourceconnectionsasfollows:
PHONO1 & 2 . . . acceptsconnectionfor
normalstereoandnormalmonophonic
operation.
MIC. . . acceptsconnectionfromstereo
microphones.
TAPEHEAD. . . acceptsconnectionfroma
TheC11canbeinstalledinconventional
furniturecabinets,custombuiltinstallations
orprofessionalrelayracks.Iftheunitisto
beplacedona shelfortable-top,itisrecom-
mendedthatitbehousedina McintoshL66
cabinet.InstalltheC11fromthefrontofthe
cabinet,notfromtherear.
TosupporttheweightoftheC11,the
woodpanelusedtomountit,shouldbeat
least¼ inchthick.Ifthefrontpanelofa cabi-
netismadeofwood,a shelfmaybeneeded
tosupporttherearofthechassistoprevent
tapedeckthatdoesnotcontainitsown
playbackpreamplifier.
TAPEEQUALIZATION
Onthebackpaneltherearetwotape
equalizingcontrols.Thesecontrolsshouldbe
settoNABfornormal7.5inchtapespeed
machines.TurningtheTAPEEQUALIZATION
controlsclockwiseincreasesthetreblere-
sponse,turningitcounterclockwisede-
creasesthetrebleresponse.Usethecontrols
tocompensatefor3%tapespeedforindi-
vidualtapeheadcharacteristics.
LOUDSPEAKERPHASINGCONNECTIONS
Twopairsofscrewterminalsarelocated
onthelowerleftsectionoftheC11back
panel.Thespeakerleadsfromthe"left"
poweramplifiershouldbeconnectedtothe
screwterminalsmarkedFROMAMPLIFIER.
ThepairofterminalsmarkedTOSPEAKER
shouldbeconnectedtothe"left"loud-
speaker.
Theseconnectionsallowthefrontpanel
PHASEswitchtoreversethephaseonthe
leftloudspeaker.Thisarrangementiscon-
venientwhensettingupa stereosystem.
warping.WhentheC11ismountedona
metalrackpanel,a shelfisnotneeded.
TheC11installationshouldallow12
inchesbehindthefrontpanelsothatthere
isatleast1½inchesforconnectors.Thede-
sirablewidthandheightare16½inchesand
5½inches,respectively,sothatsufficient
spaceisallowedforthecirculationofair.
Theseareinsidedimensions.Thefrontpanel
mountingspacewidthandheightare163/8
inchesand53/8inches,respectively.
6
Figure3.CutoutMeasurements
Positions"A"to"C"showthelocationofthe
verticalcenterline,theuseofthemeasuring
tool(mountingstrip)tolocatethehorizontal
centerline,andhowtomeasureoffthetwo
pointstotherightandleftofthevertical
centerline.

MAKINGTHEFRONTPANELCUTOUT
Thepaneliscutoutusingthe"FRONT
PANELCUTOUTTEMPLATE."Toposition
thetemplateonthefrontofthepanel,make
twolocatingholesfromtheback(inside)of
thepanelusingoneofthemountingstrips
(½inchby3½inches)asa measuringtool.
Proceedasfollows:
Scribea verticalcenterlinethroughthe
exactcenteroftheproposedcutoutarea
fromthetopofthepaneltothetopsurface
oftheshelfasillustratedin"A,"Figure3.
Usingoneofthemountingstripsasa meas-
uringtool,drawa horizontalline3½inches
abovetheshelf.(See"B,"Figure3.)Placea
mountingstripalongthehorizontallinetothe
leftoftheverticalcenterlineandmarka
point3½inchesleftfromtheverticalcenter
line.Repeatthisprocedureandmarka point
3½inchestotherightoftheverticalcenter
line.Thesepointsshouldnowbe3½inches
upfromthetopoftheshelfand7 inches
apart,one3½inchestotheleftandone
3½inchestotherightoftheverticalcenter
line.(See"C,"Figure3.)Drilla3/16inchhole
ateachpoint.Holdthedrillperpendicularto
thefrontpanelsothattheholewillbelocated
accuratelyonthefrontofthepanel.
Positionthetemplateonthefrontofthe
panelusingthetwolocatingholestolineit
upcorrectly.Scribetherectangularopening
onthefrontpanelandmarkthepositionof
thesixmountingholes.Drillthesix3/16inch
mountingholesbeforecuttingthepanel
opening.Thencutouttheopening.Itisim-
portantthatthecutoutbejustwithinthelines.
SHELFMOUNTING
Iftheinstallationrequiresa shelf,proceed
asfollows:Locatethecenteroftheshelfand
scribea linefromfronttoback.The"SHELF
CUTOUTPLATE"ismarkedforpanelthick-
nessesfrom¼ inchto1 inch.Foldthetem-
plateonthelinethatcorrespondstothe
thicknessofthepanel.Placeitontheshelf
sothatitbuttsagainsttheinsideofthepanel.
Matchthecenterlinemarkonthetemplate
tothescribedcenterlineontheshelf.Mark
thepositionofthefourdrillholes.Drillthe
four¼ inchholes.
INSTALLINGTHEC11
RemovethefourscrewsholdingtheC11
totheshippingpallet.(Savethesescrews,
youwillneedthemifyourcabinethasa ¼
inchor3/8inchshelf.)Removethefourplastic
feetfromthebottomoftheC11.
Inthemountinghardwarepackageare
four6-32flatheadscrewsandeight6-32
roundheadscrews.Twooftheflathead
screwsoftheproperlengthareusedtoat-
tachthemountingstripstothecabinet.Four
oftheroundheadscrewsoftheproperlength
areusedtoattachtheC11tothecabinetand
mountingstrips.The6-32x ½ inchscrews
aretobeusedwithpanels½ inchto1 inch
inthickness.
Selecttheproperlength6-32flathead
screwsandusethemtoinstallthetwomount-
ingstripsbehindthefrontpanel.Besure
thattheedgeofthestripwiththeclipsis
towardthepanelopening.Lineupthemount-
ingstripsoneachsideofthefrontpanel
cutoutsothethreeholesinthestriparein
linewiththethreeholesinthepanel.(See
Figure4.)Installtheproperlengthflathead
screwsinthecenterholeofeachstrip.Drive
theminsotheflatheadsareflushwiththe
panel;ifnecessary,countersinkthetwo
centerholes.
Figure4.SecuringtheMountingStriptotheFrontPanel
CarefullyinserttheC11throughthefront
ofthepanelopeningsothatitrestsonthe
shelf.Inserttheproperlength6-32round-
headscrewsintothefourholesinthemount-
ingflangesoneachendofthetunerfront
panel.Drivethemin,butdonottighten.
Ifthecabinetisfixedandwillnotbe
movedabout,itisnotnecessarytosecure
theC11chassistotheshelf.Ifthecabinetis
tobemovedabout,itisrecommendedthat
theC11chassisbesecuredtotheshelf.The
four10-32x ½ inchscrewsusedinshipping
aresuppliedforuseiftheshelfisunder3/8
inch.Usethe10-32x ¾ inchscrewsifthis
shelfisV2inchor5/8inchthickandthe10-32
x1 inchscrewsiftheshelfis¾ inchor7/8
7

inchthick.Securethechassiswiththeproper
length10-32machinescrews,insertingthem
frombeneaththeshelf.Donottightenthe
10-32screwsuntilyouhavetightenedthe
frontpanelscrews.
IMPORTANT:
USEOFTHEWRONGLENGTH10-32
SCREWSMAYCAUSEELECTRICAL
SHORTINGINTHECIRCUIT.
Attachthetwometalpanelendcaps
(packedwithmountinghardware)oneach
endofthepanelbyslidingontothepins.
(SeeFigure5.)Theendcapsareheldby
springtensionandcaneasilyberemovedif
thechassisistobetakenoutofthecabinet.
MOUNTINGINTHEL66CABINET
TheMcintoshL66cabinetissupplied
withcompleteinstructionsandallnecessary
hardwareforinstallingtheC11.Thedimen-
ENDCAP
PUSHON
Figure5.FittingofPanelEndCapstoPanel
sionsoftheL66are169/16incheswideby
611/16incheshigh,includingmountingfeet,
by13¾inchesdeep,includingthefront
panelandcontrolknobs.
CONNECTING
A-CCONNECTIONS
Therearefivea-creceptaclesontherear
panel.(SeeFigure6.)Thesereceptacles
havea maximumratingof660-watttotal.The
fourblackreceptaclesarecontrolledbythe
POWERON-OFFswitchonthefrontpanel.
Theredreceptacleisnotswitched.Thered
receptacleisusedforpoweringa turntable
orrecordchanger.Thereceptacleisnot
switchedsothattheturntablepowerwillnot
beturnedoffwhiletheturntableidlerwheel
isengaged.Theturntableisprotectedby
thisarrangementbecauseitisnecessaryto
turnofftheturntablewithitsowncontrol
switchsothatnodamagewillresulttothe
drivesystem.
Figure6.A-CConnections
8

TheC11provideseightseparateprogrammonitor.
inputscontrolledbytheINPUTSELECTORTheinputprogramconnectionshouldbe
switchandoneinputfortapecomparisonormadeinaccordancewithTables1 and2.
Figure7.C11InputConnections(BackPanel)
DesiredImpedance
47,000ohms(47K)
37,000ohms(37K)
27,000ohms(27K)
15,000ohms(15K)
6,800ohms(6.8K)
ResistorAcrossInput
NoResistor
180,000ohms(180K)
62,000ohms(62K)
22,000ohms(22K)
8,200ohms(8.2K)
CONNECTION
TAPEMONITOR
(COMPARE)
AUX
TAPE
TUNER1 &
TUNER2
CONNECTION
PHONO1 & 2
MAGNETIC
TAPEHEAD1 &2
2-10MV
FUNCTION
Thetapemonitorinputacceptsa signalfroma tape
recorderwitha monitorheadandpreamplifier.
Theauxiliaryinputacceptsanyauxiliaryservicerequiring
flatfrequencyresponse,suchasa T.V.set,tuner,tape
recorderwithitsownplaybackpreamplifier,etc.
Thetapeinputoperateswithtapemachinescontaining
theirownplaybackpreamplifier.
ThetunerinputsacceptAMandFMoutputsfroma stereo
tunerora pairofstereotunersorthemultiplexoutput
ofanadapterormultiplextuner.
FUNCTION
Thesejacksaretobeusedwithmagneticcartridges.
Thesejacksaretobeusedwitha tapedeckthatdoesnot
containitsownplaybackpreamplifier.
INPUT
SENSITIVITY
0.25V
0.25V
0.25V
0.25V
INPUT
SENSITIVITY
2MV
2MV
INPUT
IMPEDANCE
250K
250K
250K
250K
INPUT
IMPEDANCE
47K
1megohm
9
tridgetoachievethecorrecttermination.
Thefollowingchartmaybeusedasa guide:
Ifa phonocartridgerequireslessthan
47,000ohmsloadimpedance,a resistorcan
beaddedacrosstheterminalsofthecar-

Figure8.TurntablesFeedingLowLevelInput
OUTPUTCONNECTIONS
Twosetsofoutputs,locatedintheupper
left-handcornerofthebackpanel,arepro-
vided.(SeeFigure2.)
TheMAINoutputconnectstopoweram-
plifiers(Figure9)andtheTAPEoutputto
feeda taperecorder.
TheMAINandTAPEoutputjacksarefed
fromcathodefollowers.Theinputimpedance
ofdevicesconnectedtotheseoutputsshould
be50,000ohmsorgreater,andthecapaci-
tivereactanceofaudiocablesconnecting
thesedevicesshouldnotbelessthan8,000
ohmsat20,000cycles.Thisisthereactance
ofa capacityof1,000mmf.Audiocable
havinga capacityof25mmfperfootmaybe
40feetlong;13.5mmfperfootcablemaybe
75feetlong.
Thetapeoutputisaffectedonlybythe
INPUTSELECTORintheAUX,TAPE,TUNER
1,TUNER,orMICpositions.
WhentheINPUTSELECTORisturnedto
PHONO1 orPHONO2 inputsthentherecord
compensatorisincluded.WhentheINPUT
SELECTORisturnedtoTAPEHDthenthe
recordcompensatorswitchshouldbesetat
RIAA.
OnthebackpaneltherearetwoTAPE
EQUALIZATIONcontrols.Thesecontrols
shouldbesettoNABfornormal7.5inchtape
speedmachines.TurningtheTAPEEQUAL-
IZATIONcontrolsclockwiseincreasesthe
Figure9.MAINOutputConnectedtoPowerAmplifiers
10

11
trebleresponse,turningitcounterclockwise
decreasesthetrebleresponse.Usethecon-
trolstocompensatefor3%tapespeedfor
individualtapeheadcharacteristics.
Aleftplusrightoutputjackisnexttothe
MAINoutput.ItismarkedL+R.A mono-
phonicsignalcanbedistributedtoother
roomsbyconnectinga thirdpoweramplifier
tothejackmarkedL+R.Thisamplifieris
usedtodrivethemonophonicloudspeakers.
Thecableconnectingtothisoutputshould
nothavea capacityofmorethan200mmf.
Theinputimpedanceofthepoweramplifier
connectingtothisoutputshouldnotbeless
than150,000ohms(150K).Thegenerator
impedanceatthisoutputisapproximately
25,000ohms(25K).
LOUDSPEAKERPHASINGCONNECTIONS
Twopairsofscrewterminalsarelocated
onthelowerleftsectionoftheC11back
panel.Thespeakerleadsfromthe"left"
poweramplifiershouldbeconnectedtothe
screwterminalsmarkedFROMAMPLIFIER.
ThepairofterminalsmarkedTOSPEAKER
Theultimateinstereoperformanceand
listeningenjoymentisobtainedthroughthe
properbalancingofthestereosystem.A
properlybalancedstereosystemmustbein
phase.Eachchannelmustbeequalinloud-
nessandsimilarinfrequencyresponse.
DonotusetheC11BALANCEcontrolfor
thisprocedure.TheC11BALANCEcontrol
isusedtoadjustforanyunbalanceinthe
sourcematerial,thephonocartridge,and
tapemachine.
Beforeattemptingthebalancingofthe
C11makesurethecontrolsontheamplifiers
aresetproperly.OntheMC240andMC275
turnthecontrolmarkedBALANCEtoits
centerposition.OntheMC225settheinput
levelcontrolsforeachchanneltotheblack
dotabovethecontrol.
ToproperlybalancetheC11,proceedas
follows:A familiarrecording,eitherstereo-
phonicormonophonic,shouldbeusedin
balancingtheC11.
1.TurntheINPUTSELECTORtotheposi-
tioncorrespondingtotheprogramselected.
2.TurntheBASSCONTROLSandTREBLE
CONTROLStotheir0 positions.
3.TurntheMODESELECTORtotheL+R
TOL position.
4.PlacetheCOMPENSATORswitchinthe
RIAAposition.
5.PlacetheTAPEswitchintheNORMAL
position.
6.PlacethePHASEswitchintheNORMAL
position.
7.PlacethePOWERswitchintheON
position.
8.PlacetheRUMBLEswitchintheFLAT
position.
9.PlacetheH.F.cutofffilterswitchinthe
FLATposition.
10.PlacetheLOUDNESSswitchinthe
NORMALposition.
11.TurntheBALANCEcontroltothe0
position.
12.Whiletheprogramisplaying,alternate
theMODESELECTORbetweentheL+RTO
LpositionandtheL+RTOR position.Adjust
thethumbwheellevelcontrolsunderthe
endcapsuntiltheloudspeakersareofequal
loudness.
WhentheproperbalancingoftheMcin-
toshC11isaccomplished,thestereosystem
willremainbalancedthroughoutallmodes
ofoperation.
OPERATINGINSTRUCTIONS
BALANCINGA STEREOSYSTEM
shouldbeconnectedtothe"left"loud-
speaker.
Theseconnectionsallowthefrontpanel
PHASEswitchtoreversethephaseonthe
leftloudspeaker.Thisarrangementiscon-
venientwhensettingupa stereosystem.
GROUNDCONNECTION
Asinglegroundpostisprovided.The
chassisgroundfromturntable,recordchang-
ers(motorsusedwitheach),tapedecks,etc.,
shouldbereturnedtothispost.Donotdupli-
catethisgroundcircuit.Humislikelytobe
heardinthesystemifduplicategroundre-
turnsareused.
Theleftandrightprogramcablesfrom
eachsourceshouldbetwistedtogetherand
thegroundwirefromeachsourcecanbe
woundortwistedinwiththesecables.To
avoidhum,makesurethegroundwiredoes
notmakeanyconnectionstoshieldsofthe
leftandrightchannelcablesexceptforthe
connectionprovidedwiththeC11ground
post.

ADJUSTINGPHASE
1.PlacetheCOMPENSATORswitchinthe
RIAAposition.
2.SettheMODESELECTORtoSTEREO.
3.TurntheBASSCONTROLSandTREBLE
CONTROLSto0.
Standapproximately10feetinfrontof
andmidwaybetweentheloudspeakers.The
sourceofsoundshouldappeartobedirectly
infrontofyou.AlternatethePHASEswitch
betweenNORMALandREVERSE.Ifthe
soundisnotdirectlyinfrontofyouinthe
NORMALposition,reversetheleadstoone
loudspeaker.ThePHASEcontrolisusedto
correctphaseinthesourcematerialwhen-
evernecessary.
LISTENINGTOA STEREORECORD
Uponcompletionoftheconnectingand
balancinginstructions,theC11isreadyfor
use.Tolistentostereorecords,proceedas
follows:
1.SettheMODESELECTORtoSTEREO.
2.SetthePHASEswitchtoNORMAL.
3.SettheH.F.cutofffiltertoFLAT.
4.SettheLOUDNESScontroltoNORMAL.
5.RotatetheINPUTSELECTORtoPHONO
1orPHONO2 whicheverisconnectedtothe
cartridgeyouwishtohear.
6.SettheCOMPENSATORcontrolto
RIAA.
7.SettheBASSCONTROLSandTREBLE
CONTROLSto0.
8.PlacetheRUMBLEcontrolintheFLAT
position.
9.PlacetheTAPEcontrolintheNORMAL
position.
10.AdjusttheVOLUMEcontroltothede-
siredvolume.
ADJUSTINGBALANCECONTROLAFTER
THESYSTEMHASBEENBALANCED
Ifafterbalancingyoursystemasoutlined
inthismanualyouthenfindthatnearlyall
recordsalwaysrequireanadjustmentofthe
BALANCEcontroltoonesideofthecenter,
theconditionindicatesanunbalancedstereo
cartridge.Whilethisisnogreatdisadvantage
assuch,youcancorrectforitbyoffsetting
oneofthepoweramplifierinputgainsettings.
WhenswitchingfromSTEREOtoSTEREO
REVyouwillnowexperiencea changein
volumeasa resultofthiscorrection.
Ifthestereosoundseemstocomefrom
eithersideoftheroominsteadofbeingdis-
tributedbetweentheloudspeakers,adjust
thePHASEcontrolto180°.Thislistening
effectisduetoreproducingsoundthatisout
ofphasefromonechanneltotheother.You
willfindsomerecordsdifferfromothersin
thisrespectandthatsometapesdifferfrom
records.
ADJUSTINGFORSPECIALEFFECTS
H.F.CutoffFilter.Ifyouwishtoreproduce
old,badlywornrecords,youcanminimize
thesurfacenoisebyswitchingtheH.F.cutoff
filtertotheFILTERposition.(Seesection
entitled"FrontPanelFacilities.")
RumbleFilter.Ifyouareusinga turntable
orchangerwhichhaslow-frequencyrumble
noise,youmayreduceitbypushingthe
RUMBLEfilterswitchtotheFILTERposition.
BassControlsandTrebleControls.The
tonebalancewhichyouhearwhenlistening
toanorchestraisaffectedbytheconductor's
instructionstohismusicians,theacoustical
environmentinwhichyouarelistening,and
yourownsubjectivehearinginterpretation.
Tonebalancewillevendependontheroom
orhallwhereyoulistentothemusic.Con-
sideringtheseconditions,itiseasytosee
whytonebalancecontrolsplaya majorrole
incorrectingforthefollowingfactors:
1.Eachperson'ssubjectiveideaoftone
balance.
2.Loudspeakerfrequencyresponsechar-
acteristics.
3.Loudspeakerplacementinthelisten-
ingroom.
12

4.Theconductor'sidea oftonebalance
atthetimetherecordingwasmade.
5.Themicrophonefrequencyresponse
characteristics.
6.Therecordingprocessinfluences.
Thesefactorscanbeconsideredasen-
vironmentalinfluences.TheBASSCON-
TROLSandTREBLECONTROLSaredesigned
toprovidea degreeofcompensationfor
effectsofenvironment.Listentoyoursystem
witheachcontrolsettozero.Ifyouwishto
reducetrebleinrelationtobass,rotatethe
TREBLECONTROLScounterclockwiseuntil
thetonebalancesoundscorrecttoyou.
Thesecontrolswillmodifytonebalancewith-
outintroducinganyundesirableeffects.Do
notbesurprisedifyoufindyourpreference
intonechangingfromtimetotime.
Compensator.TheCOMPENSATORcon-
trolisusedtocorrectforthenecessarypro-
gramequalizationwhichtherecordingproc-
essintroduces.Recordingrequiresa change
inthedistributionofintensitywithfrequency.
Withoutcompensationa magneticcartridge
wouldsounddeficientinthebassrangeand
overlybrightorshrillinthetreblerange.
Loudness.Duetoa selectiveshiftinsensi-
tivityofhumanhearing,musicreproducedat
verylowvolumelosesitsbassandtreble.
TheLOUDNESSswitchontheC11changes
theVOLUMEcontroltoa loudnesscontrolto
correctforthiseffect.Whenyouwishtolisten
tomusicata greatlyreducedloudnesslevel
andyethearbassandtreble,settheLOUD-
NESSswitchtotheCOMPENSATEDposition.
USINGTHEC11WITHA STEREOTUNER
1.TurntheINPUTSELECTORtotheposi-
tioncorrespondingtotheprogramselected.
2.TurntheBASSCONTROLSandTREBLE
CONTROLStotheir0 positions.
3.TurntheMODESELECTORtoSTEREO,
4.PlacetheTAPEswitchintheNORMAL
position.
5.PlacethePHASEswitchintheNORMAL
position.
6.PlacethePOWERswitchintheON
position.
7.PlacetheRUMBLEswitchintheFLAT
position.
8.PlacetheH.F.cutofffilterswitchinthe
FLATposition.
9.PlacetheLOUDNESSswitchinthe
NORMALposition.
USINGTHEC11WITHA STEREOTAPE
MACHINE
Astereotapemachinewithitsownplay-
backpreamplifiersshouldbepluggedinto
theTAPEINPUTS—nottheTAPEHEADin-
puts.TheinformationonadjustingtheC11
forlisteningtoa stereotunerwillalsoapply
whenlisteningtoa tapemachine.
USINGTHEC11WITHTAPEDECKS
1.TurntheINPUTSELECTORtotheposi-
tioncorrespondingtotheprogramselected.
2.TurntheBASSCONTROLSandTREBLE
CONTROLStotheir0 positions.
3.TurntheMODESELECTORtoSTEREO,
4.PlacetheTAPEswitchintheNORMAL
position.
5.PlacethePHASEswitchintheNORMAL
position.
6.PlacethePOWERswitchintheON
position.
7.PlacetheRUMBLEswitchintheFLAT
position.
8.PlacetheH.F.cutofffilterswitchinthe
FLATposition.
9.PlacetheLOUDNESSswitchinthe
NORMALposition.
USINGTHEC11WITHMICROPHONES
FORSTEREO
Microphonesinstereomaybeusedwith
theC11.ThetwoMICchannelsamplifymi-
crophonesignals.Theyhavea sensitivityof
2millivoltsandaninputimpedanceof1
megohm.Forloweroutputmicrophonesin-
puttransformersshouldbeusedtoraisethe
voltageoutputtothe2 millivoltrange.
WhentheINPUTSELECTORisturnedto
theMICposition,theCOMPENSATORcon-
troldoesnotoperate.Alltheothercontrols
operateandmaybeusedthesameasfor
anyotherprogramsource.
LISTENINGTOMONOPHONICRECORDS
Ifyouwishtolistentomonophonicrec-
ords,switchtheINPUTSELECTORtoPHONO
1orPHONO2.TurntheMODESELECTORto
theL TOL+RorR TOL+Rposition.L TO
L+Rpositionconnectstheleftinputtoboth
loudspeakers.R TOL+Rpositionconnects
therightinputtobothloudspeakers. 13

EQUALIZATIONCURVES
RESPONSEINDB
20 100
FREQUENCY
Figure10.Equalizationcurves.
IOKC 20 KC
20
Figure11.Bassandtreblecontrols.
10KC 20
KC
14
100
FREQUENCY
1KC
-15
-20
-10
-5
RESPONSEINDB
0
5
10
15
20
BASSANDTREBLECONTROLS
1KC
-25
-20
-15
-10
0
-5
5
10
15
20
25

RUMBLEANDHIGHFREQUENCYFILTERS
RESPONSEINDB
20 100
FREQUENCY
10KC 20KC
Figure12.Rumblefilterandhighfrequencyfilter.
LOUDNESSCONTROL
20
15
10
0
RESPONSEINDB
-15
-20
20 100 1KC 10KC
Figure13.Loudnesscontrol.
15
20KC
FREQUENCY
-10
-5
5
1 KC
-30
-25
-20
-15
-10
-5
0

YourC11willgiveyoumanyyearsofpleasantandsatisfactory
performance.Ifyouhaveanyquestionsconcerningtheoper-
ationormaintenanceofthispreamplifierpleasecontact:
CustomerService
McintoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork
Ourtelephonenumberis723-5491.
Thedirectdialareacodeis607.
GUARANTEE
McintoshLaboratoryIncorporatedguar-
anteesthisequipmenttoperformasadver-
tised.Wealsoguaranteethemechanicaland
electricalworkmanshipandcomponentsof
thisequipmenttobefreeofdefectsfora
periodof90daysfromdateofpurchase.
Thisguaranteedoesnotextendtocompo-
nentsdamagedbyimproperusenordoesit
extendtotransportationtoandfromthe
factory.
3-YEARFACTORYSERVICECONTRACT
Anapplicationfora FREE3-YEARFAC-
TORYSERVICECONTRACTisincludedinthe
pocketinthebackcoverofthismanual.The
FREE3-YEARFACTORYSERVICECONTRACT
willbeissuedbyMcintoshLaboratoryupon
receiptofthecompletelyfilledoutapplica-
tionform.Thetermofthiscontractisde-
finedinthe3-yearfactoryservicecontract.
IftheapplicationisnotmailedtoMcintosh
Laboratory,onlytheservicesofferedunder
thestandard90-dayguaranteewillapplyon
thisequipment.TAKEADVANTAGEOF3
YEARSOFFREEFACTORYSERVICEBY
FILLINGINTHEAPPLICATIONNOW.
InCanada:manufacturedunderlicenseby:
McCurdyRadioIndustries,Ltd.
22FrontStreetWest
Toronto,Canada
Designsubjecttochangewithoutnotice.
16

LABORATORYINC.
2CHAMBERSSTREET,BINGHAMTON,N.Y.
MadeinU.S.A.
Phone-AreaCode607-723-5491
PrintedinU.S.A.