McIntosh C108 - User manual

INSTRUCTIONMANUAL
MclNTOSHMODELC108
AUDIOCOMPENSATOR

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INSTRUCTIONMANUAL
McINTOSHMODELC-108
AUDIOCOMPENSATOR
TheMcIntoshAudioCompensatorisa completecontrolunitforprofessional
andhomeentertainmentsystems.Fiveinputchannelsareprovided;threewhich
produceconstantamplificationovertheaudiospectrumof20cyclesto20,000
cycles,andtwowhichareequalizedforusewithmagneticphonographcartridges.
TheC-108AudioCompensatorrequiresanexternalpowersource.A
McIntosh50W-2,20W-2,orA-116PowerAmplifier,orD-101powersupplymay
beusedforthispurpose.
PHYSICALSPECIFICATIONS
UNIT
C-108
C-108a
(C-108inwooden
enclosure)
C-108h
(C-108withcabinet
mountingpanel
11"x 4-1/4")
DIMENSIONS
10"x 3-1/2"x 7-1/2"
11-1/2"x 4-1/4"x 8"
10"x 3-1/2"x 7-1/2"
WEIGHT
6lbs.
7lbs.
6lbs.
INSTALLATIONWITHMcINTOSHAMPLIFIERS
1.Connectspeakertooutputofamplifier.
2.InsertPowerAmplifierlinecordintosocketlabeled
"PWRAMP"onC-108.
3.Insertinter-unitcableofC-108intosocketlabeled
"PRE-AMP"onpoweramplifier.

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4.Turnthepoweramplifiervolumecontrol(50W-2or
20W-2)tofullvolumesetting.Thevolumecontrolon
theA-116,30wattpoweramplifier,isinoperative
whenthepre-ampsocketisusedandthisstepmaybe
disregardedwhenusingthisamplifier.
5.TurnthevolumecontrolontheC-108to"OFF".
6.InsertthepowercordoftheC-108intoa 117V.A.C.
poweroutlet.
7.TurntheselectorswitchoftheC-108to"5"andbass
fullyclockwise.
8.TurnthevolumecontrolontheC-108clockwiseuntil
thepowerswitchisactivated.
9.Allowthirtysecondsforwarm-up,thenadvancethe
volumecontroltofullvolume.
10.Adjustthehumcenteringpotentiometeronthepower
amplifierforminimumhum.
11.TurnthevolumecontroloftheC-108toa minimum
andallothercontrolstothedesiredsettings.
12.Insertinputsintotheirproperjacksattherearof
theC-108.
INSTALLATIONWITHMcINTOSHD-101POWERSUPPLY
1.Connectspeakertopoweramplifier.
2.Insertpoweramplifierpowercordinsocketlabeled
"PWRAMP"onD-101.
3.InsertD-101powercordintosocketlabeled"PWR
AMP"oftheC-108.
4.Insertinter-unitcableofC-108intosocketlabeled
"PRE-AMP"oftheD-101.
5.Connect"OUTPUT"ofD-101totheinputofpower
amplifier(socketlabeled"PRE-AMP"onMcIntosh
PowerAmplifier).J-107seriescablesmaybeused
forthispurpose.

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6.Followsteps4 through9 above.
7.AdjustthehumcenteringpotentiometerontheD-101
forminimumhum.
8.Followsteps11and12above.
INPUTCONNECTINGPROCEDURE
TheinherenthumandnoisevoltagesappliedtotheinputoftheC-108is
-110DBM,orlessthan3 microvolts.Toavoidloweringthesignaltohumratio
oftheC-108byaddinghumvoltagestotheinput,extremecaremustbetakenin
itsinstallation.Weofferthefollowingrecommendationsasa guidetoinstalla-
tion:
1.ConnectinputtoC -108asoutlinedonthetable
below.
CHANNEL
1&2
3
4
5
FORUSEWITH
AM-FMTuner
WireReproducer
TapeReproducer
CrystalPickup
CrystalMicrophone
LowImpedance
Microphone
HighLevelMagnetic
cartridges.(Ter-
minatedfor
PickeringCartridge)
LowLevelmagnetic
cartridges.
(Terminatedfor
Audaxpolyphase
cartridgeand
WeathersFM
cartridge.)
INPUT
(For3 v.output)
Min.Max.
.1V20V.
12MV.60MV.
30MV..15 V.
12MV.60MV.
GAIN
30db
48db
40dbfrom
Turn-overto
20,000cps.
48dbfrom
Turn-overto
20,000cps.
FREQUENCY
RESPONSE
(20-20,000cps.)
+.25db
+.25db
Risesatthe
rateof6 db
peroctavebe-
lowturn-over
frequencyto
20cps.
REMARKS
Inputlevelsinex-
cessof. 1Vshould
bereducedby
potentiometeron
backpanel.
Inputnottoexceed
60MV.
Cartridgeofother
manufacturersmay
beusedbutinput
mustbeterminated
asrecommendedby
manufacturer.Alter
R6&R7orR8.

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2.TheC-108andmagneticphonographcartridgesshould
bemountedatleasttwofeetfrompowertransformers.
3.Inter-unitcablesprovidea completegroundsystem.
Alternategroundwirescreategroundloopswhichwill
usuallyincreasehumlevel.
4.Theheatersofthe12AX7tubesusedintheC-108are
returnedtogroundthrougha humbalancingpotentiom-
eterinthepoweramplifier(orD-101powersupplyif
used).Thiscontrolrequiresaninitialadjustmentfor
minimumhum,andshouldbereadjustedeachtimeone
ormoretubesarereplaced.
5.GroundingtheturntablemotorframetotheC-108
chassisneartheinputjacksmayreducethehumlevel
onthephonographchannels.
TheoutputstageoftheC-108isa cathodefollower.Thegeneratorresis-
tanceofthistubeis600ohms,butshouldnotbeloadedwitha capacitivereactance
oflessthan10,000ohmsat20,000cycles.Thisisthereactancepresentedby
750micromicrofarads,andisequaltothatofa cable30feetlongandhavinga
capacityof25mmfperfoot.UnderspecialcircumstanceswheretheC-108must
beconnectedtothepoweramplifierbya longercable,eitherlowercapacity
mustbeemployed,ortheoutputmustbereduced.
OPERATION
REDUCETURNTABLERUMBLE,
ORLOWFREQUENCYDISTURB-
ANCESONALLCHANNELS.
SELECTDESIREDBASS
COMPENSATIONON
CHANNELS4 AND5.
SELECTDESIREDTREBLE
ROLL-OFFONALLCHANNELS.COMPENSATEFOREAR
CHARACTERISTICAT
REDUCEDVOLUMEON
ALLCHANNELS.
SELECTANYONEOFFIVE
INPUTCHANNELS.UNUSED
CHANNELSAREGROUNDED
TOPREVENTCROSSTALK.CONTROLBASSRESPONSE ONALLCHANNELS.CONTROLTREBLERESPONSE ONALLCHANNELS.
CONTROLVOLUMEON
ALLCHANNELS.ON-OFF
CONTROLFORC-108
ANDITSPOWERSUPPLY.

Channels1 and2:
Channels1 and2 areeachterminatedbya potentiometer.Thesepotentiom-
etersarescrewdriveradjustmentsonthebackpanelandshouldbeusedtoreduce
signalinputtothesechannelsifinexcessof. 1 volts.Correctadjustmentoccurs
whenthesoundlevelofchannels1 and2 isequivalenttothatofchannels4 or5.
Highimpedancesources,suchascrystalmicrophonesandthedetectoroutputof
tuners,maybeconnecteddirectlytothesechannelssincetheyhaveaninput
impedanceof660,000ohms.
Channel3:
Channel3 isa highgainmicrophonechannelhavinganinputimpedanceof
100,000ohms.Theinputtothischannelshouldnotexceed60MV.Lowimpedance
microphonesinconjunctionwithaninputtransformer,suchastheMcIntoshM-107
(ATI-1),maybeusedonthischannel.
Channels1,2 and3 provideflatamplificationfrom20cyclesto20,000
cycleswiththebassandtreblecontrolsintheircentralposition,andthetreble
compensationswitchesintheupposition.Thesecontrolsmaybeusedtoalterthe
responseofthesechannelsasshownonpage9.
Channels4 and5:
Channels4 and5 areequalizedforusewithmagneticphonographcartridges.
Thedegreeofequalizationmaybevariedwiththebassandtreblecompensation
switchesasshownonpages8 and9.Thebassandtrebletonecontrolsmaybe
usedto supplementthesecompensationswitches.
Theinputsofchannels4 and5 havebeenterminatedtogiveflatresponsefrom
thePickeringandAudaxPolyphasecartridgesrespectively.Ifcartridgesofother
manufacturersareused,theterminatingresistorsshouldbereplacedbyvalues
recommendedbythemanufacturer.Forexample,the47,000ohmterminating
resistanceofchannel5 shouldbereplacedby12,000ohmsiftheG.E.reluctance
cartridgeisused.IfitisdesirablenottoaltertheC-108an18,000ohmresistor
maybeconnectedacrosstheG.E.cartridgeinthelinetothecartridge.
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TheAuralCompensatormaybeusedtocompensatefortheresponsecharac-
teristicoftheearasloudnessisadjusted.Theresponseofthiscontrolis
plottedonpage9.Thiscontrolshouldnotbeuseduntilallotheradjustments
havebeenmade.
TheRumbleFiltermaybeusedtoeliminateturntablerumbleandotherlow
frequencydisturbances.Theresponseofthiscontrolisplottedonpage9.
AnadditionaloutputjackhasbeenprovidedattherearoftheC-108.This
jackmaybeusedforrecordingtapewhilethesignalisbeingmonitoredbythe
poweramplifier.Theselectorswitch,rumblefilter,andbasscompensation
switchesareeffectiveattheauxiliaryoutput.
GUARANTEE
WeguaranteetheperformanceoftheC-108andthemechanicalandelec-
tricalworkmanshiptobefreeofseriousdefectsfora periodof90dayswiththe
exceptionthatwedonotguaranteethetubesandfiltercapacitorbeyondthatof
theirmanufacturers.
McINTOSHLABORATORY,INC
320WaterStreet
Binghamton,NewYork
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Forconvenienceofinstallation,wehavemadethefollowingconnectorsand
cablesavailablefromyourdealer.
J-100OutputPlug
J-101Inputplug
*J-102J-100Outputplugfittedwith6 footlengthoftwo
conductorcable,connectedfor4 ohmoutputof
McIntosh50W-2or20W-2.
*J-103SameasJ-102,butconnectedfor8 ohms.
*J-104SameasJ-102,butconnectedfor16ohms.
*J-105SameasJ-102,butconnectedfor32ohms.
*Forusewith20W-2or50W-2Amplifiersonly.
J-109J-100outputplugfittedwith6 footlengthoftwo
conductorcableconnectedfor4 ohmoutputof
McIntoshA-116.
J-110SameasJ-109,butconnectedfor8 ohms.
J-111SameasJ-109,butconnectedfor16ohms.
J-106SameasJ-102,butconnectedfor600ohms,for
usewith50W-2,20W-2orA-116.
J-107J-101inputplugfittedwith6 feetof25MMF
capacityperfootcableandphonopinjack.For
2.5Vinputof50W-2,20W-2,orA-116.
J-107aSameasJ-107,but12ft.long.
J-107bSameasJ-107,but18ft.long.
J-107cSameasJ-107,but24ft.long.
J-107dSameasJ-107,but30ft.long.
J-108Phonopinjackfittedwith6 feetof25MMFcapa-
cityperfootcable,withshieldandcenter
conductorstrippedandtinned.
J-112Inputplugfittedwith6 feetof25MMFcapacity
perfootcableandphonopinjack.For. 5Vinput
ofA-116.
J-101
J-103
J-104
J-105
J-106
J-107
J-107a
J-107b
J-107c
J-107d
J-108
J-101
J-100

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