McIntosh C20 - User manual

STEREO
PREAMPLIFIER
C20
TABLEOFCONTENTS
GENERALDESCRIPTION
TECHNICALDESCRIPTION
MechanicalSpecifications
ElectricalSpecifications
FRONTPANELFACILITIES
INSTALLATION
CONNECTING
A-CConnections
InputConnections
OutputConnections
GroundConnections(ProgramSources)
OPERATINGINSTRUCTIONS
Balancinga StereoSystem
ToAdjustforBalanceintheTreble
Range
ToAdjustforAmplitudeBalancein
theBassRange
AdjustingPhase
Listeningtoa StereoRecord
ToAdjusttheBalanceControlAfterthe
SystemhasbeenBalanced
AdjustingforSpecialEffects
UsingtheC20witha StereoTuner
UsingtheC20witha StereoTapeMachine_
UsingtheC20FrontPanelTapeJacks
UsingtheC20withTapeDecks
UsingtheC20withMicrophonesforStereo.
MonophonicRecordSettings
OperatingCurves
GUARANTEE
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C20

C20STEREOPHONICPREAMPLIFIER
GENERALDESCRIPTION
TheMclntoshC20StereophonicPre-amplifierisa
controlcenterforanystereophonicsoundsystem.This
controlcenterisnecessarytoaccuratelyperformfour
specificfunctionstoincreasetheenjoymentofstereo.
First,thecontrolcenteramplifiesweakelectrical
impulses.Astherecordrotatesontheturntable,un-
dulationsinthegroovesmovethepick-upstylusap-
proximatelyone-thousandthofaninch,inanydirection,
fromtherestposition.Fromthisslightmechanical
movement,thepick-upstylusgeneratesa weakelec-
tricalimpulseontheorderofa fewthousandthsofa
volt.Toamplifyandpreservethecharacterofsuchan
electricalimpulse,thefinestamplifierperformanceis
required.
Second,everysoundsystemisusedina different
acousticalenvironment.Thetonebalanceofthemusic
isaffectedbyvariationsinenvironment.Also,people
listeningtothemusichavevaryingideasofcorrect
tonebalance.Toadequatelycompensateforthesecon-
ditions,a high-qualitycontrolcenteris needed.
Third,thereisa greatvarietyofstereophonicand
monophonicrecordsmanufacturedtoday,bothdomestic
andforeign.Thecontrolcentermustproviderecord
compensationfora greatvarietyofrecordings.
Fourth,withprogramsoriginatingfroma varietyof
sourcessuchastuners,records,tapemachines,micro-
phones,etc.,a controlcenterisneededtoselectand
switchthesesourcesseparatelyorincombination.
Allofthesejobsareperformedwithexcellence
bytheC20andyetthisinstrumentiseasytomount,
simpletooperate,andisthefinestinappearance.
TECHNICALDESCRIPTION
Younowownthefinestexpressionofstereocrafts-
manship. . . designedandbuilttofulfillyourneeds.
Throughdirectconsumercontact,a uniqueMclntosh
marketingresearchprogramdeterminestheapplication
ofelectronicandmechanicalengineeringtofityour
needs.RelentlessresearchbyMclntoshengineersim-
provestheselectionofmaterialsandthecircuitsin
whichtheyareused.Itisthistotalconceptofcrafts-
manshipdirectedtoconsumersatisfactionthathas
maintainedtheMclntoshreputationforexcellencein
performance,quality,andreliability.
Perhapsyouwouldliketoknowa fewofthe
featuresdevelopedthroughresearchbasedoncon-
sumerneedsthatplaceyourC20Pre-amplifierabove
allotherpre-amplifiers.
Anexampleoftheuniquemechanicalconstruction
throughoutisemphasizedonthebackpanelwherelow-
voltageprogramsourcesareconnectedtotheC20.This
portionofthepaneliscutoutandmountedonsmall
electricalinsulators.Thegroundcircuitisconnected
tothemainchassisatonlyonepoint.Bybreakingthe
pathforcirculatinghumcurrentsinthismanner,the
humandunwantednoisesinducedinotherstereo
systemswhenusedwithvariousprogramsourcesand
combinationsofprogramsourcesareeliminated.
Humnoisesarealsointroducedintostereosys-
temsbythemagneticfieldsproducedbythepower
transformerwindings.Thegreatestcarewentintothe
designandconstructionofthepowertransformerin
yourC20.Itiswoundinsucha waythatthemagnetic
fieldsproducedbythewindingstendtocancel.Thisis
accomplishedbysplittingthewindingsintotwoseg-
ments.Furtherreductionofthemagneticfieldintensity
isachievedthroughtheuseofadditionalmagneticand
electricalshielding.Withtheseconstructionimprove-
mentsthehumnoisesintroducedbyordinarypre-
amplifiersareeliminatedbytheC20.
Nearlyallofthesmallresistorandcapacitorcom-
ponentpartsintheC20aremountedonmilitary-type
terminalboards.Thisspecializedconstructionprevents
damagingmechanicalstrains.In additionit makes
servicing,ifeverrequired,mucheasierandmore
effective.
ThemechanicallayoutoftheC20allowsmaximum
separationoftheleftandrightchannels.Theterminal
boardattherearoftheC20isassociatedwiththeright
channelandtheterminalboardatthefrontwiththe
leftchannel.C20terminalboardsareconstructedof
naturalbakelitebecauseofitslow-volumeresistivity.
Thispreventsthegradualincreaseofelectricalnoise
commontootherterminalboardmaterialsaftercon-
tinueduseofthecontrolcenter.
TheC20istheonlycontrolcenterthathasan
illuminatedfrontpaneltoprovideconvenientreading
underlow-levellightingconditions.Thisfeatureisof
particularimportancewhena closetisadaptedtohouse
stereoequipment.
Frontpaneltapeinputjacksareanotherexclu-
sivefeatureprovidedbytheC20.Withthestartof
stereoFMbroadcastingitwillbeimportanttotape
andpreservethosespecialprogramsthatwillother-
wiseneverbeheardagain.Thisfeaturewillbegreatly
appreciatedbyyouandyourfriendswhenrecording
onportabletapemachines.
Onlyextensiveresearchandplanningcombined
withskilledengineeringandmanufacturingknowhow,
directedtowardconsumerneeds,canproducesucha
fineelectronicinstrument.
1

MECHANICALSPECIFICATIONS
DIMENSIONS
Chassis:14-1/2incheswide;4-1/2incheshigh;12
inchesdeep
FrontPanel:15-5/8incheswide;4-7/8incheshigh
FrontPanelMountingSpaceRequired:16-3/8inches
wide;5 incheshigh
ELECTRICALSPECIFICATIONS
WEIGHT
Chassis:18pounds
ShippingWeight:28.5pounds
FINISH
Anodizedgoldandblack(frontpanel)
POWERREQUIREMENTS
117volts,50/60cycles,ac,35watts
INPUTSENSITIVITYANDINPUTIMPEDANCE
Auxiliary:0.25volt;470,000ohms
Tape:0.25volt;470,000ohms
Tuner1:0.25volt;470,000ohms
Tuner2:0.25volt;470,000ohms
Phono1:2 to10millivolts;47,000ohmsforlow-output
cartridge
10to70millivolts;47,000ohmsforhigh-output
cartridge
0.1volt;220mmfinserieswith47,000ohmsfor
Xtalorceramiccartridge
Phono2:Sameasphono1
TapeHead1:2 to10millivolts;47,000ohmsforlow-
outputhead
10to70millivolts;267,000ohmsforhigh-output
head
TapeHead2:Sameastapehead1
TapeCompare(Monitor):0.25volt;115,000ohms
FREQUENCYRESPONSE
±0.5db;20to20,000cycles
DISTORTION
Lessthan0.2%atratedoutput,20to20,000cycles
HUMANDNOISE
High-levelinputs:85dbbelowratedoutput
Low-levelinputs:lessthan2 microvoltsatinputter-
minals
MAINOUTPUT
2.5voltswithratedinput
2output jacksinparallelforeachchannel
TAPEOUTPUT
0.25voltwithratedinput
1output jackforeachchannel
LEFTPLUSRIGHTOUTPUT
2.5voltsfromgeneratorimpedanceof23,000ohms
VOLTAGEAMPLIFICATION
Low-levelinputstoMainOutput:1,000to1 (60db)at
1000cycles
Low-levelinputstoTapeOutput:100to1 (40db)at
1000cycles
High-levelinputstoMain Output:10to1 (20db)
High-levelinputstoTapeOutput:1 to1 (0db)
TapeCompare(Monitor)inputto
MainOutput:10to1 (20db)
A-CAUXILIARYOUTLETS
1unswitchedfortapemachineorturntable,
coloredRed
4switched,coloredBlack
FRONTPANELFACILITIES
Figure1.C20FrontPanel
2

INPUTSELECTOR
INPUTSELECTOR
PHONO1
2S M S
TUNER
1
TAPE
AUX
PHONO2
M
1
TAPEHD
L. . . leftchanneltoleftspeaker,noprogramto
rightspeaker.
R. . . rightchanneltorightspeaker,noprogram
toleftspeaker.
MLEFT. . . leftchannelonlytobothspeakers.
MRIGHT. ..rightchannelonlytobothspeakers.
RECORDCOMPENSATOR
Thisten-positionprogramswitchconnectsthe
C20asfollows:
AUX...anyauxiliaryservice,suchasa television
set,anextratuner,oranyotherprogramsource
requiringflatamplification.
TAPE. . . anyself-containedtapemachine(tape
machinehavingitsownplaybackpreamplifier).
TUNER1 & 2 ...AMandFMoutputsfroma
stereotunerora pairofstereotuners.
PHONO1 & 2 — S & M ...stereoormonophonic
operationwiththefollowingtypesofphonocar-
tridges.
a.Constantamplitudecartridgessuchascrystal,
ceramic,orfrequency-modulateddevices.
b.Magneticcartridgeshavinganoutput of10mv
ormore.Maximuminputvoltageforthisoutput
is70mv.
c.Magneticcartridgeshavinganoutputofless
than10mv.
TAPEHEAD—1& 2 ...a tapedeckora pairof
tapedecksthatdonotcontaintheirownplayback
preamplifiers.Twotypesoftapeheadoutputscan
beusedinthisposition.
a.Tapeheadshavinganoutput oflessthan10mv.
b.Tapeheadshavinganoutput of10mvormore.
Maximuminputvoltageforthisoutput is70mv.
MODESELECTOR
MODESELECTOR
REV
MRIGHT
RECORDCOMPENSATOR
BASSTREBLE
400RIAA-10-12
Thesecontrolsareusedtocorrectforprogram
equalizationintroducedbytherecordingprocess.
Table3 givestherecommendedsettingsoftheRECORD
COMPENSATORcontrolsoftheC20formonophonic
recordings.
BASSANDTREBLE
TherearetwotonecontrolsontheC20—BASS
andTREBLE.
BASS. . . clockwiserotationincreasesbassloud-
ness;counterclockwiserotationdecreasesbass
loudness.
TREBLE. . . clockwiserotationincreasestreble
loudness;counterclockwiserotationdecreases
trebleloudness.
PHASE
Thissix-positionswitchconnectstheC20for
properleft-rightdistributionofsoundfortheprogram
sourceselected.Itspositionsareasfollows:
REV. . . connectsleftchanneltorightspeaker,
rightchanneltoleftspeaker,correctsforleft-
rightreversalofprogram.
STEREO. . . thisisthenormalstereoMODE
SELECTORposition;leftchanneltoleftspeaker,
rightchanneltorightspeaker.Thistwo-positionswitchreversesthephaseinthe
leftchanneltocorrectforspeakerorprogramphasing.
2
300
0
TAPETAPE
UP
-5
RIAA
LP
BASS
TREBLE
PHASE
0° 180°
MLEFT
LR
STEREO
-° + -° +
3

BALANCE
LEFT
RIGHT
ThiscontrolbalancestheC20forunequalpro-
gramsources.
LEFT. . . turningthecontroltotheleftslowly
reducestherightchanneltonooutputand
accentstheleftchannel.
RIGHT. . . turningthecontroltotherightslowly
reducestheleftchanneltonooutputandaccents
therightchannel.
HFCUTOFFFILTER
HFCUTOFFFILTER
9KC
FLAT5KC
Thisthree-positionswitchminimizessurfacenoise
whenreproducingold,badlywornrecordings.Itsposi-
tionsareasfollows:
FLAT...filterdisconnected.
9KC... rollsoffresponsesharplystartingat9KC.
5KC. . . rollsoffresponsesharplystartingat5KC.
LOUDNESS
L0UDNESS
23
FLAT
Musicreproducedatverylowvolumelosesits
bassandtrebleduetoa selectiveshiftinsensitivity
ofhumanhearing.ThiseffectisknownastheFletcher-
Munsonhearingcharacteristics.(Seepage15,Figure
13.)TheLOUDNESScontrolcorrectsforthiseffect.
WiththeRUMBLEFILTERbuttonpushedtothe
IN position,low-frequencyrumblenoisebelow60 cps
createdbya turntableorchangerandundesirable
acousticallycoupledfeedbackarereduced.
TAPEJACK
TAPE
JACK
Thispushbuttoncontrolsthesignaldirectionto
orfromthefrontpaneltelephonejacks.
IN-PLAYBACK. . . TAPEinputisswitchedfrom
reartapejackstofrontpaneltelephonejacks.
Anyprogramoriginatingfroma portablemachine
connectedtotheC20canbeheardbyrotating
theINPUTselectortotheTAPEposition.
OUT-RECORD. . . connectsignalsfromtherear
tapejackstotheINPUTSELECTORTAPEposi-
tion.AnyprogrampickedupbytheC20iscon-
nectedtotheportablemachineforrecording,
TAPECOMPARE
TAPE
COMPARE
IN-TAPE
Thispushbuttonmakesitpossibletoinstantane-
ouslycomparetherecordedmaterialwiththesource
signal.TAPECOMPAREjacksareprovidedontheback
paneltoaccepta signal-froma taperecorderwitha
monitorheadandpreamplifier.WhentheTAPECOM-
PAREpushbuttonisintheoutposition,theprogram
sourceisfedthroughthepoweramplifiersandthe
loudspeakers.WhentheTAPECOMPAREpushbutton
isintheINposition(depressed),thesignalsource
becomesthemonitoredprogramfromtherecordedtape
andisfedthroughthepoweramplifiersandloud-
speakers.
RUMBLEFILTER
IMPORTANT
WhentheTAPECOMPAREpushbuttonisde-
pressed,signalfromanyothersourcewill
notbeheardfromtheloudspeakers.When
notinuse,makesurethepushbuttonisin
theoutposition.
BALANCE
0
4
I
5
RUMBLE
FILTER
IN-ON
IN-PLAYBACK
OUT-RECORD
4

VOLUME
LOWFREQUENCYTRIM
VOLUME
OFF
ThecombinedVOLUMEcontrolandOFF-on
switchcontrolsthevolumeforbothchannelsand
switcheslinepowertofourblackreceptaclesonthe
backpanel.
LOWFREQUENCYTRIM
LEFTRIGHT
Thesecontrols,locatedonthebackpanel,com-
pensateforunequalspeakerresponseatlowfrequen-
ciesduetolocationofspeakersina roomordiffer-
encesinspeakerefficiency.Itprovides6dbboostat
50cyclesstartingfrom500cyclesor8dbcutat20
cyclesstartingfrom200cycles.
INSTALLATION
TheC20canbeinstalledinconventionalcabinets,
custombuilt-ins,orprofessionalequipmentracks.If
theunitistobeplacedona shelfortable-top,itis
recommendedthatitbehousedina MclntoshModel
L-66cabinet.InstalltheC20fromthefrontofthe
cabinet;notfromtherear.
WhenmountingtheC20theminimumthickness
ofwoodpanelshouldbe1/4"inordertosupport the
weight.Panelsupto1"thicknessmaybeused.Ifthe
frontpanelofa cabinetismadeofwood,toprevent
warpinga shelfisrequiredtosupporttherearofthe
chassis.Whenmountedona metalrackpanel,a shelf
isnotneeded.
TheC20installationshouldallowatleast13-3/4"
behindthefrontpaneltoallowabout1-1/2"forcon-
nectors.Thedesireablewidthandheightare,16-1/2"
and5-1/2",respectively,sothere*willbesufficient
spaceforcirculationofair.Theseareinsidedimensions.
Thefrontpanelmountingspacewidthandheight
are16-3/8"and5",respectively.
MAKINGTHEFRONTPANELCUTOUT
Thepaneliscutoutusingthe"FRONTPANEL
CUTOUTTEMPLATE."Topositionthetemplateonthe
frontofthepanel,maketwolocatingholesfromthe
back(inside)ofthepanelusingoneofthemounting
strips(1/2"by3-1/2")asa measuringtool.Proceedas
follows:
Determinetheexactcenteroftheproposedcutout
area.Scribea verticalcenterlinefromthetopofthe
paneltothetopsurfaceoftheshelfasillustratedin
"A",Figure2.Usingoneofthemountingstripsasa
measuringtool,drawa horizontalline3-1/2"abovethe
shelf.(See"B",Figure2.)Placea mountingstripalong
thehorizontallinetotheleftoftheverticalcenterline
andmarka point3-1/2"leftfromtheverticalcenter
line.Repeatthisprocedureandmarka point3-1/2"to
therightoftheverticalcenterline.Thesepointsshould
nowbe3-1/2"upfromthetopoftheshelfand7"
apart,one3-1/2"totheleftandone3-1/2"totheright
oftheverticalcenterline.(See"C",Figure2.)Drilla
3/16" hole at each point. Hold the drill perpendicular
tothepanelsothattheholewillbelocatedaccurately
onthefrontofthepanel.
Positionthetemplateonthefrontofthepanel
usingthetwolocatingholestolineitupcorrectly.
Scribetherectangularopeningonthefrontpaneland
markthepositionofthesixmountingholes.Drillthe
six3/16"mountingholesbeforecuttingthepanel
opening.Thencutouttheopening.Itisimportantthat
thecutoutbejustwithinthelines.
SHELFMOUNTING
Iftheinstallationrequiresa shelf,proceedas
AVERTICALCENTERLINE
Positions"A"to"C"showthelocationofthe
verticalcenterline,theuseofthemeasuring
tool(mountingstrip)tolocatethehorizontal
centerline,andhowtomeasureoffthetwo
pointstotherightandleftofthevertical
centerline.
Figure2.CutoutMeasurements
5

follows:Locatethecenteroftheshelfandscribea
linefromfronttoback.The"SHELFCUTOUTTEM-
PLATE"ismarkedforpanelthicknessesfrom1/4"to1".
Foldthetemplateonthelinethatcorrespondstothe
thicknessofthepanel.Placeitontheshelfsothatit
buttsagainsttheinsideofthepanel.Matchthecenter
linemarkonthetemplatetothescribedcenterlineon
theshelf.Markthepositionofthefourdrillholes.
Drillthefour1/4"holes.
INSTALLINGTHEC20
RemovethefourscrewsholdingtheC20tothe
shippingpallet.(Savethesescrews,youwillneedthem
ifyourcabinethasa 1/4"or3/8"shelf.)Removethe
fourplasticfeetfromthebottomoftheC20.
Inthemountinghardwarepackagearefour6-32
flatheadscrewsandeight6-32roundheadscrews.Two
oftheflatheadscrewsoftheproperlengthareusedto
attachthemountingstripstothecabinet.Fourofthe
roundheadscrewsoftheproperlengthareusedto
attachtheC20tothecabinetandmountingstrips.
The6-32x 1/2"screwsaretobeusedwithpanels
under3/8"inthickness.The6-32x 1-1/4"screwsare
tobeusedwithpanels1/2"to1"inthickness.
Selecttheproperlength6-32flatheadscrewsand
usethemtoinstallthetwomountingstripsbehindthe
frontpanel.Besurethattheedgeofthestripwiththe
clipsistowardthepanelopening.Lineupthemount-
ingstripsoneachsideofthefrontpanelcutoutsothe
threeholesinthestripareinlinewiththethreeholes
inthepanel.(SeeFigure3.)Installtheproperlength
flatheadscrewsinthecenterholeofeachstrip.Drive
theminsotheflatheadsareflushwiththepanel;if
necessary,countersinkthetwocenterholes.
CarefullyinserttheC20throughthefrontofthe
panelopeningsothatitrestsontheshelf.Insertthe
properlength6-32roundheadscrewsintothefour
holesinthemountingflangesoneachendofthetuner
frontpanel.Drivethemin,butdonottighten.
Ifthecabinetisfixedandwillnotbemoved
about,itisnotnecessarytosecuretheC20chassisto
theshelf.Ifthecabinetistobemovedabout,itis
recommendedthattheC20chassisbesecuredtothe
shelfinthefollowingmanner.Tightenthefourscrews
holdingthefrontpanel.Thefour10-32x 1/2"screws
usedinshippingaresuppliedforuseiftheshelfis
under3/8".Usethe10-32x 3/4"screwsiftheshelfis
1/2"or5/8"andthe10-32x 1"screwsiftheshelf
is3/4"or7/8".Securethechassiswiththeproper
length10-32machinescrews,insertingthemfrombe-
neaththeshelf.Donottightenthe10-32screwsuntil
youhavetightenedthefrontpanelscrews.
Attachthetwometalpanelendcaps(packedwith
mountinghardware)oneachendofthepanelbysliding
ontothepins.(SeeFigure4.)Theendcapsareheld
byspringtensionandcaneasilyberemovedifthe
chassisistobetakenoutofthecabinet.
Useofthewronglength10-32screwsmay
causeelectricalshortinginthecircuit.
Figure3.SecuringtheMountingStriptothe
FrontPanel
Figure4.FittingofPanelEndCapstoPanel
MOUNTINGINTHEL-66CABINET
TheMclntoshL-66cabinetissuppliedwithcom-
pleteinstructionsandallnecessaryhardwareforin-
stallingtheC20.ThedimensionsoftheL-66are
16-9/16"wideby6-11/16"high,includingmounting
feet,by13-3/4"deep,includingthefrontpaneland
controlknobs.
CONNECTING
A-CCONNECTIONS
Therearefivea-creceptaclesinthelowerleft-
handcorneroftherearpanel.(SeeFigure5.)These
receptacleshavea maximumratingof600-watttotal.
ThefourblackreceptaclesarecontrolledbytheOFF-
onswitchontheVOLUMEcontrol.Theredreceptacle
isnotswitched.Theredreceptacleisusedforpower-
inga turntableorrecordchanger.Thereceptacleis
notswitchedsothattheturntablepowerwillnotbe
turnedoffwhiletheturntableidlerwheelisengaged.
Withthisarrangementitisnecessarytoturnoffthe
turntablewithitsowncontrolswitchsothatnodamage
willresulttotheturntabledrivesystem.
6

Figure5.C20BackPanel
INPUTCONNECTIONS
TheC20provideseightseparateprograminputs
controlledbytheINPUTSELECTORswitch,oneinput
fortapecomparisonormonitorcontrolledbytheTAPE
COMPAREpushbutton,anda pairoftelephonejack
inputslocatedonthefrontpanelandcontrolledby
theTAPEJACKpushbutton.
Theinputprogramconnectionshouldbemadein
accordancewithTables1 and2.
Figure6.C20InputConnections(BackPanel)
7

Table1.High-LevelInputConnections
TAPECOMPAREThetapecompareinputacceptsa signal
froma taperecorderwitha monitorhead
andpre-amplifier.
AUXTheauxiliaryinputacceptsanyauxiliary
servicerequiringflatfrequencyresponse,
suchasa T.V.set,tuner,taperecorder
withitsownplaybackpre-amplifier,etc.
TAPEThetapeinputoperateswithtapemachines
containingtheirownplaybackpre-ampli-
fier.
TUNER1 & ThetunerinputsacceptAMandFMoutputs
TUNER2 froma stereotunerora pairofstereo
tuners.
0.25V
0.25V
0.25V
0.25V
115K
470K
470K
470K
TAPEHEAD1 & 2
2-10 MV
TAPEHEAD1 & 2
10-70 MV
PHONO1 & 2
XTAL
CERAMIC
PHONO1 & 2
MAGNETIC
2-10 MV
PHONO1 & 2
MAGNETIC
10-70 MV
Thesejacksaretobeusedwitha tapedeck
ora pairoftapedecksthatdonotcon-
taintheirownplaybackpre-amplifiersand
haveanoutputoflessthan10MV.
Thesejacksaretobeusedwitha tapedeck
ora pairoftapedecksthatdonotcon-
taintheirownplaybackpre-amplifiersand
haveanoutputofmorethan10MV.
Thesejacksaretobeusedwitha constant
amplitudecartridgesuchasa crystal,
ceramic,orfrequency-modulateddevice.
Thesejacksaretobeusedwithmagnetic
cartridgeshavinganoutputlessthan
10MV.
Thesejacksaretobeusedwithmagnetic
cartridgeshavinga relativelyhighoutput.
Maximuminputvoltageforthisinputis
70MV.
2MV
10MV
0.1V
2MV
10MV
47K
267K
220mmf
inseries
with47K
47K
47K
Ifa cartridgerequireslessthan47,000ohms
loadimpedance,a resistorcanbeaddedacrosstheterminalsofthecartridgetoachievethecorrectter-
mination.Thefollowingchartmaybeusedasa guide:
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)
INPUTINPUT
CONNECTIONFUNCTIONSENSITIVITYIMPEDANCE
Table2.Low-LevelInputConnections
CONNECTIONFUNCTIONSENSITIVITYIMPEDANCE
8

Figure7.TurntablesFeedingLowLevelInput.
OUTPUTCONNECTIONS
Twosetsofoutputs,locatedintheupperleft-hand
cornerofthebackpanel,areprovided.(SeeFigure8.)
TheMAINoutputconnectstopoweramplifiers
(Figure9)andtheTAPEoutputtofeeda taperecorder.
LEFTAMPLIFIER
RIGHTAMPLIFIER
Figure8.OutputConnections
Figure9.MAINOutputConnectedtoPowerAmplifiers
TheMAINandTAPEoutputjacksarefedfrom
cathodefollowers.Theinputimpedanceofdevices
connectedtotheseoutputsshouldbe50,000ohmsor
greater,andthecapacitivereactanceofaudiocables
connectingthesedevicesshouldnotbelessthan8,000
ohmsat20,000cycles.Thisisthereactanceofa
capacityof1,000mmf.Audiocablehavinga capacity
of25mmfperfootmaybe40feetlong;13.5mmfper
footcablemaybe75feetlong.
TheTAPEOUTPUTisunaffectedbyanyadjust-
mentsmadewiththefollowingcontrols:MODESELEC-
TOR,BALANCE,PHASE,LOUDNESS,BASS,TREBLE,
RUMBLEFILTERandVOLUME.Anyadjustmentsmade
intheINPUTSELECTOR,RECORDCOMPENSATOR,
andtheHFCUTOFFFILTERwillaffectthesignalat
theTAPEOUTPUTjacksifthesignaloriginatesinthe
phonoortapeheadsinputs.
C20Preamplifiers,SerialNo.6L700andlater,
haveanadditionalleftplusrightoutputjack.A mono-
phonicsignalcanbedistributedtootherroomsbycon-
nectingthisjacktoa poweramplifiertodrivethe
monophonicloudspeakers.Thecableconnectingto
thisoutputshouldnothavea capacityofmorethan
30mmf.Theinputimpedanceofthepoweramplifier
connectingtothisoutputshouldnotbelessthan
150,000ohms(150K).Thegeneratorimpedanceat
thisoutputisapproximately23,000ohms(23K).
GROUNDCONNECTION(PROGRAMSOURCES)
Asinglegroundpostisprovided.Thechassis
groundfromturntable,recordchangers(motorsused
witheach),tapedecks,etc.,shouldbereturnedtothis
post.Donotduplicatethisgroundcircuit.Unde-
sirablehumislikelytobeheardinthesystemifdupli-
categroundreturnsareused.
Theleftandrightprogramcablesfromeach
sourceshouldbetwistedtogetherandthegroundwire
fromeachsourcecanbewoundortwistedinwiththese
cables.Toavoidhum.makesurethegroundwiredoes
notmakeany connectionstoshieldsoftheleftand
rightchannelcablesexceptfortheconnectionpro-
videdwiththeC20groundpost.
9

OPERATINGINSTRUCTIONS
BALANCINGA STEREOSYSTEM
Theultimateinstereoperformanceandlistening
enjoymentisobtainedthroughtheproperbalancingof
thestereosystem.A properlybalancedstereosystem
mustbeinphase.Eachchannelmustbeequalinloud-
nessandsimilarinfrequencyresponse.Whenthe
properbalancingoftheMclntoshModelC20Stereo-
phonicPre-amplifierisaccomplished,thestereosystem
willremainbalancedthroughoutallmodesofoperation.
ToproperlybalancetheMclntoshC20proceedas
follows:A familiarrecording,eitherstereoormono-
phonic,shouldbeusedinbalancingthestereosystem.
1.TurntheINPUTSELECTORtoPHONO1 M.
2.TurneachRECORDCOMPENSATORcontrolto
RIAA.
3.TurntheBASSandTREBLEcontrolsto0.
4.TurntheMODESELECTORtoSTEREO.
5.TurntheBALANCEandPHASEcontrolstoO.
6.TurntheHFCUTOFFFILTERtotheFLATposi-
tion.
7.TurntheLOUDNESScontroltoFLAT.
8.Withthecontrolssetinthismanner,a mono-
phonicsignalofequalamplitudewillbefedtoeach
sideofthepre-amplifier.
TOADJUSTFORAMPLITUDEBALANCEIN
THETREBLERANGE
DonotusetheC20BALANCEcontrolforthispro-
cedure.TheC20BALANCEcontrolisusedtoadjust
foranyunbalanceinthesourcematerial,thephono
cartridge,andthetapemachine.
1.AdjusttheBASStonecontroltoitsfullcounter-
clockwiseposition.
2.Whiletherecordingisplaying,alternatethe
MODESELECTORbetweenL andR positions.Adjust
thegaincontrolontheinputtothepoweramplifier
untiltheloudspeakersareofequalloudness.
WhenusingtheMclntoshMC240Twin40Wattor
MC275Twin75WattDualStereoPowerAmplifierand
connectingtheC20tothestereoinputjacks,merely
rotatetheBALANCEcontrolontheMC240orMC275
untiltheloudspeakersareofequalloudness.
TOADJUSTFORBALANCEINTHEBASSRANGE
1.AdjusttheTREBLEtonecontroltoitsextreme
counterclockwiseposition.
2.AdjusttheBASStonecontroltoitsextreme
clockwiseposition.Foranadditionalboost,ifdesired,
rotateRECORDCOMPENSATORcontrolmarkedBASS
totheTAPEposition.
Themusicwillhaveanunnaturaltonebalancedur-
ingthisprocedure.Thebasssoundwillpredominate.
Insomeinstallationsitmaybenecessarytoreducethe
volumetopreventacousticalfeedback.
3.SwitchtheMODESELECTORbetweenL andR
andlistencarefullytothelow-frequencyresponse.
4.AdjusttheLOWFREQUENCYTRIMcontrolson
thebackpanelandestablishbalancebyadvancingthe
controls,onemorethantheother.
TheLOWFREQUENCYTRIMcontrolsareinde-
pendentofthefrontpaneltonecontrolsandwilladjust
onlythelow-frequencybalance.Thisarrangement
leavesthefrontpanelcontrolsfreetocorrectover-all
tonebalanceintheprogram,correctingforrecording
orplaybackenvironment.
Ifyourloudspeakersproducemorethanadequate
bassresponsewhentheC20isadjustedfornormal
playback,turnbothLOWFREQUENCYTRIMcontrols
fullycounterclockwise.Thenbringthesysteminto
balancebyadvancingonlythetrimcontrolcorrespond-
ingtotheloudspeakerproducinglessbassresponse.
Ifyourloudspeakersystemsproducelessbass
responsethanyoudesire,theLOWFREQUENCYTRIM
controlsmaybeturnedfullyclockwise.Thesystemis
thenbroughtintobalancebyreducingthebassre-
sponse ontheloudspeakerproducingthegreaterbass
amplitude.
ADJUSTINGPHASE
1.RotatebothRECORDCOMPENSATORcontrolsto
RIAA.SettheMODESELECTORtoSTEREO.
2.AdjustBASSandTREBLEtonecontrolsto0.
3.Standapproximately10feetinfrontofandmid-
waybetweentheloudspeakers.
Thesourceofsoundshouldappeartobedirectly
infrontofyou.RotatethePHASEcontrolfrom0°to180°.
Ifthesourceofsoundisnotdirectlyinfrontofyouin
0°positionreversetheleadstooneloudspeaker.The
PHASEcontrolcorrectsphaseinsourcematerialwhen-
evernecessary.
Ifafterhavingmadethissystemphaseadjustment,
thestereosoundseemstocomefrombothsidesof
theroominsteadofbeingdistributedbetweenthe
loudspeakers,adjustthePHASEcontrolto180°.This
listeningeffectisduetoreproducingsoundthatisout
ofphasefromonechanneltotheother.Youwillfind
somerecordsdifferfromothersinthisrespectand
sometapesdifferfromothers.
LISTENINGTOA STEREORECORD
Uponcompletionoftheconnectingandbalancing
instructions,theC20isreadyforuse.Tolistento
stereorecords,proceedasfollows:
1.SettheMODESELECTORtoSTEREO.
2.SetthePHASEswitchto0°.
10

3.SettheHFCUTOFFFILTERtoFLAT.
4.SettheLOUDNESScontroltoFLAT.
5.RotatetheINPUTSELECTORtoPHONO1Sor
PHONO2Swhicheverisconnectedtothecartridge
youwishtohear.
6.SettheRECORDCOMPENSATORcontrolsto
RIAA.
7.SettheBASSandTREBLEcontrolsto0.
8.PlacetheRUMBLEFILTERpushbuttoninthe
outposition.
9.PlacetheTAPECOMPAREpushbuttonintheout
position.
10.RotatetheVOLUME(OFF-on)controltoonand
adjusttothedesiredvolume.
TOADJUSTTHEBALANCECONTROLAFTER
THE SYSTEMHASBEENBALANCED
Thebalancesettingofsomerecordswilldiffer
fromothers.Ifthesoundislouderontheleftthanon
theright,adjusttheBALANCEcontrolto.therightto
bringthesoundinto"left-to-right"balance.Ifthe
soundislouderontheright,adjusttheBALANCE
controltotheleft.
If afterbalancingyourstereosystem,youfindthat
nearlyallrecordsrequireanadjustmentoftheBAL-
ANCEcontrol,anunbalancedstereocartridgeis
probablythesourceofthiscondition.Thisisnogreat
disadvantageasitcanbecorrectedbyoffsettingoneof
thepoweramplifierinputgainsettings.Whenswitching
fromSTEREOtoREV,youwillheara changeinvolume
asa resultofthiscorrection.
ADJUSTINGFORSPECIALEFFECTS
HFCUTOFFFILTER.Ifyouwishtoreproduceold,
badlywornrecords,youcanminimizethesurfacenoise
byswitchingtheHFCUTOFFFILTERto9KCor5KC.
(Seesectionentitled"FrontPanelFacilities.")
RUMBLEFILTER.Ifyouareusinga turntableor
changerwhichhaslow-frequencyrumblenoise,you
mayreduceitbypushingtheRUMBLEFILTERpush-
buttontotheINposition.Undesirableacoustic
couplingintheverylow-frequencybassrangemayalso
bereducedinthismanner.
BASSANDTREBLE.Thetonebalancewhichyou
hearwhenlisteningtoanorchestraisaffectedbythe
conductor'sinstructionstohismusicians,theacousti-
calenvironmentinwhichyouarelistening,andyour
ownsubjectivehearinginterpretation.Eventonebal-
ancewillvarywithintheroomorhallwhereyoulisten
tothemusic.Consideringtheseconditions,itiseasyto
seewhytonebalancecontrolsplaya majorrolein
correctingthefollowingfactors:
1.Eachperson'ssubjectiveideaoftonebalance.
2.Loudspeakerfrequencyresponsecharacteristics.
3.Loudspeakerplacementinthelisteningroom.
4.Theconductor'sideaoftonebalanceatthetime
therecordingwasmade.
5.Themicrophonefrequencyresponsecharacter-
istics.
6.Therecordingprocessinfluences.
Thesefactorscanbeconsideredasenvironmental
influences.TheBASSandTREBLEcontrolsarede-
signedtoprovidea degreeofcompensationforthe
effectsofenvironment.Listentoyoursystemwitheach
controlsetatzero.Ifyouwishtoreducetreblein
relationtobass,rotatetheTREBLEcontrolcounter-
clockwiseuntilthetonebalancesoundscorrectto you.
Donotbesurprisedifyoufindyourpreferenceintone
changingfromtimetotime.Thesecontrolswillmodify
tonebalancewithoutintroducinganyundesirable
effects.
Tonebalancemaybeaccentedinthetreblerange
byrotatingtheTREBLEcontrolclockwise.Similarly
tonebalanceinthebassrangemaybemodifiedupor
downbyuseoftheBASScontrol.
RECORDCOMPENSATOR.TheRECORDCOM-
PENSATORcontrolsareusedtocorrectfortheneces-
saryprogramequalizationwhichtherecordingprocess
introduces.Recordingrequiresa changeinthedis-
tributionofintensitywithfrequency.Withoutcom-
pensationa magneticcartridgewouldsounddeficient
inthebassrangeandoverlybrightorshrillinthetreble
range.RecommendedsettingsoftheRECORDCOM-
PENSATORcontrolsoftheC20formonophonicrecords
aregiveninTable3,page12.
LOUDNESSCONTROL.Duetoa selectiveshiftin
sensitivityofthehumanhearing,musicreproduced
atverylowvolumelosesitsbassandtreble.Thefamily
ofcurvesshowingthiseffectareknownasFletcher-
Munsoncurves.(SeeFigure13.)TheLOUDNESScon-
trolontheC20correctsforthiseffect.Whenyouwish
tolistentomusicata greatlyreducedloudnesslevel
andyethearbaseandtreble,turntheLOUDNESS
controlto reduceintensity.Someusersof theC20
leavetheLOUDNESScontrolatpositions1 or2 to
correctforenvironmentalconditionssuchasloud-
speakercharacteristics,roomplacement,etc.
USINGTHEC20WITHA STEREOTUNER
AstereotunermaybeusedwiththeC20byplug-
gingtheleftandrightchannelsintoTUNERINPUT
1or2.WhentheINPUTSELECTORswitchisturnedto
theTUNERpositions,therecordcompensatorpre-
amplifierisdisconnectedandtheRECORDCOMPEN-
SATORcontrolswillnotrequireadjustment.TheMODE
SELECTORswitch,BALANCEcontrol,PHASEswitch,
LOUDNESScontrol,BASSandTREBLEcontrols,the
RUMBLEFILTER,TAPEJACKswitch,andVOLUME
(OFF-on)controlalloperateunderthisconditionand
shouldbeusedinthesamewayaswithanyother
program.
USINGTHE C20WITHA STEREOTAPEMACHINE
Astereotapemachinewithitsownplaybackpre-
amplifiersshouldbepluggedintotheTAPEINPUTS—
nottheTAPEHEADinputs.Theinformationonadjust-
ingtheC20forlisteningtoa stereotunerwillalso
applywhenlisteningtoa tapemachine.
11

USINGTHEC20FRONTPANELTAPEINPUTJACKSUSINGTHEC20WITHTAPEDECKS
TwotapemachinescanbeusedwiththeC20
StereophonicPreamplifier.Afteryouhaveconnected
yourtapemachinetotherearpanelofthepreamplifier
youmayhavesomeonebringina portablemachineto
makea copyofoneofyourtapesortolistentooneof
histapesonyoursystem.WiththeC20younolonger
havetounplugyourpermanentmachine.TheC20is
suppliedwithtwocables.Thecableshavephoneplugs
ononeendtoplugintothefrontpaneloftheC20and
pinjacksontheotherendtoplugintoany tapema-
chine.(AdaptersareavailableatanyHi-Firetailerto
permitpinplugstoconnectwithphonejacks.)
Tolistentotheportableorsecondtapemachine
plugthepinjackendofthetwoC20cables,mentioned
above,intothetapemachineoutput.Connectthetele-
phoneplugsintothetelephonejacksontheC20front
panel.Theleftjacksuppliestheleftchannel.Theright
jacksuppliestherightchannel.RotatetheINPUT
SELECTORswitchtoTAPE.Whenthetapejackswitch
isdepressedtotheIN-PLAYBACKposition,theperma-
nenttapemachineoutputisdisconnectedfromthe
rearpanel.Theportabletapemachineisnowconnected
andanyprogramoriginatinginthismachinewillbe
heardthroughtheC20,andwillalsobeavailablefrom
theC20-TAPEOUTPUTtodrivethepermanenttape
machineinput.Thisfeatureallowsyoutocopya tape
fromtheportablemachineintoyourpermanentma-
chine,providedyourpermanentmachinehasitsown
recordingpre-amplifier.
Torecordontheportablemachineplugthetwo
phonopinplugsofthetwoC20cablesintotheinput
oftheportablemachine.Leavethetelephoneplugs
connectedtotheC20telephonejacksonthefront
panel.OperatethetapejackswitchtotheOUTposi-
tion.Thepermanenttapemachinewillbereconnected.
NowanyprogrampickedupbytheINPUTSELECTOR
switchwillbeavailabletodrivetheportablemachine.
Youcannowmakea copyontheportablemachine
ofanytapeplayedonthepermanentmachine.Youcan
copyanyotherprogramsourceontobothtapemachines
atthesametime.
Whenrecordingfromonetapemachinetothe
othertheonlycontrolsthatareeffectivearetheHF
CUTOFFFILTERandtheTAPEJACKswitch.(Note:Some
portabletapemachineswilldrivetheC20eventhough
theTAPEJACKswitchisintheOUTposition.Thisis
nota normalcircuituseanda distortedsignalusually
results.Forlow-distortionoperationfollowtherec-
ommendedprocedure.
TheC20StereoPreamplifiermaybeusedwith
tapedeckswhichdonothaveplaybackpreamplifiers.
Tapeheadsrequirea formofplaybackcompensation.
SettingtheRECORDCOMPENSATORcontrolstothe
TAPEpositionsprovidescorrectplaybackfortape
headsandeliminatestheneedforusingplaybackpre-
amplifierswithtapedecks.(Note,however,thatthe
C20cannotconvenientlybeusedtorecordontape.If
youneedrecordingfacilitiesina tapemachine,a re-
cordingpreamplifierwillberequired.Inmanytape
machinesthispreamplifierservesbothplaybackand
recordfunctions.)
USINGTHEC20WITHMICROPHONESFORSTEREO
MicrophonesinstereomaybeusedwiththeC20.
Ifthemicrophonesarelowlevel(lowoutput— 2 to
10MV)thentheymaybepluggedintoeitheranun-
usedpairoflowlevelPHONO2-10MVjacksoranun-
usedpairoflowlevelTAPEHEAD2-10MVjacks.
Ifthemicrophonesaremedium-level(10to70
MV),thentheymaybepluggedintoeitheranunused
pairofhigh-levelPHONO10-70MVjacksoranunused
pairorhigh-levelTAPEHEAD10-70MVjacks.
Whenreproducingfrommicrophonesinphonoor
tapeheadchannelssettheBASSRECORDCOMPENSA-
TORcontrolto0 andtheTREBLERECORDCOM-
PENSATORcontroltoTAPE.Thisadjustmentgivesa
flatresponseforthemicrophones.
Ifhigh-outputmicrophones(100MVandup)are
used,plugthemintotheauxiliarychannel.Inthis
channeltheRECORDCOMPENSATORcontrolsdonot
operateanditwillbenecessarytoadjustthemicro-
phones.Allpreviousinformationgivenonmicrophones
applies.
MONOPHONICRECORDSETTINGS
Forseveralyearsrecordcompaniesusedmany
differentrecordingmethodsinanefforttogivemaxi-
mumentertainmentvaluewhenlisteningtotheir
records.
Ifyouwishtolistentomonophonicrecords,switch
theINPUTSELECTORtoPHONO1 M orPHONO2 M.
Verticaloutputfromthestereocartridgesiscancelled
byoperatingtheINPUTSELECTORtotheM (mono-
phonic)positions.Whenlisteningtomonophonicrec-
ordsverticaloutputconsistsonlyofundesirablesounds
suchasrecordscratch.Therecommendedsettingsare
asfollows:
Table3.RecommendedSettingsoftheRECORDCOMPENSATORControlsoftheC20forMonophonicRecords
Manufacturer
Allegro
American
Recording
Society
Angel
Speed
33
33
33
RECORDCOMPENSATOR
BASS
(Turnover)
LP
RIAA
RIAA
TREBLE
(Roll-Off)
LP
-12
-12
RECORDCOMPENSATOR
Manufacturer
Atlantic
Audiophile
BachGuild
Banner
Speed
33
78
33
BASS
(Turnover)
RIAA
300
LP
TREBLE
(Roll-Off)
LP
-10
LP
12

Table3.RecommendedSettingsoftheRECORDCOMPENSATORControlsoftheC20forMonophonicRecords(Cont)
Manufacturer
Bartok
Boston
BlueNote
Caedmon
Capital
Capital
Canyon
Capital-Cetra
Colosseum
Cetra-Soria
Columbia
Columbia
Columbia
Contemporary
ConcertHall
Coral
Cook
Decca
Dial
Electra
Ems
Epic
Esoteric
European
Festival
Folkways
Good
TimeJazz
HandelSoc.
HaydnSoc.
London
Speed
33
33
33
45
33
78
33
33
45
78
33
33
33
45
78
33
33
33
33
33
78
33
33
33
33
33
RECORDCOMPENSATOR
BASSTREBLE
(Turnover)(Roll-Off)
LPLP
400-12
LP-12
RIAA-12
400-12
400-12
LPLP
RIAALP
300LP
400-12
RIAA-12
LPLP
LPLP
400-12
LPLP
RIAA-12
300-5
LPLP
LPLP
400-12
LPLP
LP-10
ManufacturerSpeed
London78
Lyricord33
Mercury33
45
78
MGM33
45
78
Montilla33
NewRecords33
Oceanic
Oxford
Period33
Philharmonia33
Rachmaninoff33
Society
RCAVictor(Old)33
45
78
RCAVictor33
(H.M.V.)45
(NewRIAACurve)78
Remington33
Renaissance33
Stradivari33
Technicord78
Telefunken78
Urania(Old)33
Urania(New)33
Vanguard33
Vox
Westminster
RIAA,ORTHO,New
NARTB,NewAES
usedonrecordings
madesince1955
RECORDCOMPENSATOR
BASSTREBLE
(Turnover)(Roll-Off)
300
LP
400
RIAA
RIAA
LP
RIAA
400
LP
RIAA
RIAA
RIAA
LP
LP
RIAA
400
LP
400
LP
RIAA
-5
LP
-12
-12
-12
LP
LP
-12
LP
-10
-12
LP
-12
LP
-12
-5
LP
-12
LP
RIAA
13

OPERATINGCURVES
25
20
15
10
5
0
-5
-10
-15
-20
-25
20
Figure10.RECORDCOMPENSATORControls
10KC20KC
Figure11.BASSandTREBLEControls
10KC 20KC
14
RESPONSE
INOB
100
FREQUENCY
1KC
FREQUENCY
1KC 100 20
-5
-10
-15
-20
RESPONSE
IND8
20
15
10
5
0
BASS,MAX.ANDMIN.RANGE
TREBLE,MAX.ANDMIN.RANGE
=TAPE
=RIAA
=LP
=300/-5
= 400/-I0
=0/TAPE
ATOTALOF25EQUALIZATIONCOMBINATIONS
AREPOSSIBLE,THEABOVESHOWSSEVERAL
OFTHEMOSTUSEDCURVES.

-5
-10
-15
-20
-25
20 100
1KC
10KC
20KC
FREQUENCY
Figure12.RUMBLEFILTERandHFCUTOFFFILTER
0
-5
-10
-15
-20
-25
20
100 1KC
FREQUENCY
Figure13.LOUDNESSControl
10KC 20 KC
Figure14.BASETRIMControls—separatecontrolsare
providedforR andL outputs.
15
RESPONSE
INOB
RESPONSE
INOB
10
5
0
-5
-10
RESPONSE
INDB
0

YourC20willgiveyoumanyyearsofpleasantandsatisfactory
performance.Ifyouhaveanyquestionsconcerningtheoperation
ormaintenanceofthispre-amplifierpleasecontact:
CustomerService
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork
Ourtelephonenumberis723-5491.
Thedirectdialareacodeis607.
GUARANTEE
MclntoshLaboratoryIncorporatedguaranteesthis
equipmenttoperformasadvertised.Wealsoguarantee
themechanicalandelectricalworkmanshipandcom-
ponentsofthisequipmenttobefreeofdefectsfora
periodof90daysfromdateofpurchase.Thisguaran-
teedoesnotextendtocomponentsdamagedbyim-
properusenordoesitextendtotransportationtoand
fromthefactory.
3-YEARFACTORYSERVICECONTRACT
Anapplicationfora FREE3-YEARFACTORY
SERVICECONTRACTisincludedinthepocketinthe
backcoverofthismanual.TheFREE3-YEARFACTORY
SERVICECONTRACTwillbeissued byMclntoshLab-
oratoryuponreceiptofthecompletelyfilledoutappli-
cationform.Thetermofthiscontractisdefinedinthe
3-yearfactoryservicecontract.Iftheapplicationisnot
mailedtoMclntoshLaboratory,onlytheservicesoffered
underthestandard90-dayguaranteewillapplyonthis
equipment.TAKEADVANTAGEOF3 YEARSOFFREE
FACTORYSERVICEBYFILLINGINTHEAPPLICATION
NOW.
InCanada:manufacturedunderlicenseby:
McCurdyRadioIndustries,Ltd.
22FrontStreetWest
Toronto,Canada
16
Designsubjecttochangewithoutnotice.

LABORATORYINC.
2CHAMBERSSTREET,BINGHAMTON,N.Y.
MadeinU.S.A.
Phone—AreaCode607-723-5491
2M-AA117-185BE102002PrintedinU.S.A.