McIntosh C8 - SCHEMATICS User manual

INSTRUCTIONMANUAL
MclNTOSHMODELC-8andC-8P
AUDIOCOMPENSATORS
McINTOSHLABORATORY,INC.
320WaterSt.Binghamton,N.Y.
U.S.A.

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INSTRUCTIONMANUAL
McINTOSHMODELC-8andC-8P
AUDIOCOMPENSATORS
TheMcIntoshAudioCompensatorisa completecontrolunitforprofessional
orhomeentertainmentsystems.TheModelC-8derivesitspowerfromany
McIntoshpoweramplifier:theModelC-8Pisself-powered.
Fiveinputchannelsareprovided:threewhichproduceconstantamplifica-
tionovertheaudiospectrumof20-20,000cycles,andtwowhichareequalizedfor
magneticphonographcartridges.
THEAUDIOCOMPENSATORISA COMPLETEPRE-AMPLIFIERAND
RECORDCOMPENSATOR:THEREFORE,THEUSEOFANAUXILIARYEQUAL-
IZERORPRE-AMPLIFIERWITHTHISUNITISNOTRECOMMENDED.
INSTALLATIONOFMODELC-8andC-8P,
AUDIOCOMPENSATORS
TheC-8andC-8PAudioCompensatormaybemountedinanytypeequip-
mentcabinet,relayrackpanel,door,wall,etc.,orinitsowncabinetforchair
sideoperation.ItisnotnecessarytodisassembletheAudioCompensatorfor
mounting.Cuta rectangularholeinthepaneltobeusedformounting,insertthe
AudioCompensator,andsecurewithwoodormachinescrews.Mountingtem-
platesareprovidedwiththismanualfortheC-8andC-8P.
WheninstallingtheC-8P,thepowersupplysectionshouldbemountedat
leasttwofeetfromtheAudioCompensator.
Aftertheseunitshavebeensecuredintheirdesiredlocation,proceedas
follows:
1.Connectspeakertooutputofpoweramplifier.
2.InsertpoweramplifierlinecordintooneoftheAuxiliaryA.C.
receptaclesprovidedattherearchassisoftheAudioCompensator.

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3.C-8:Connectinter-unitcabletosocketlabeled"PRE-AMP.
INPUT"onMcIntoshpoweramplifiers.
CAUTION:THEINTER-UNITCABLEMUSTNOTBEREMOVED
FROMTHEC-8.
C-8P:InsertcableofD-8powersupplyintosocketlabeled"INTER-
UNITCABLE"onC-8P.Connectaudiocableprovidedbetween
RETMApinjacklabeled"MAINOUTPUT"onC-8Pand2.5Vinput
ofpoweramplifier.(Socketlabeled"PRE-AMPINPUT"onMcIntosh
poweramplifiers.)
4.TheAudioCompensatordelivers2.5voltsofaudiosignalatfull
output.Thegaincontrolofthepoweramplifiershouldbe
adjustedasoutlinedintheamplifierinstructionmanualforthis
sensitivity.
5.TurnthevolumecontrolontheAudioCompensatorto"OFF".
6.InsertpowercordoftheAudioCompensatorintoa 117V.A.C.
poweroutlet.
7.TurntheSelectorswitchontheAudioCompensatorto"5"and
Basscontrolfullyclockwise.
8.TurnthevolumecontrolontheAudioCompensatorclockwise
untilthepowerswitchisactivated.Allowthirtysecondsfor
warm-up,thenadvancethevolumecontrolto"10".
9.C-8:Adjustthehumreducingpotentiometeronthepower
amplifierforminimumhum.
C-8P:Adjustthehumreducingpotentiometeronthepower
supplyforminimumhum.
10.TurnthevolumecontrolontheAudioCompensatortooff.
11.InsertinputsintotheirproperjacksatthebackoftheAudio
Compensator,andallA.C.powercordsintotheA.C.outlets
provided.

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INPUTCONNECTINGPROCEDURE
TheinherenthumandnoisevoltagesappliedtotheinputoftheAudio
Compensatorare-110DBM,orlessthan3 microvolts.Toavoidloweringthesig-
naltohumratiooftheAudioCompensator,byaddinghumvoltagestotheinput,
extremecaremustbetakeninitsinstallation.Weofferthefollowingrecommenda-
tionsasa guidetoinstallation:
1.ConnectinputsofAudioCompensatorasoutlinedonthetablebelow.
CHANNEL
1& 2
3
4
5
FORUSEWITH
AM-FMTuners
WireReproducers
TapeReproducers
CrystalorCeramic
cartridges
CrystalMicrophones
LowImpedance
Microphone
HighlevelMagnetic
cartridges.(Termi-
natedforPickering
cartridge)
Lowlevelmagnetic
cartridgesorampli-
tuderesponsive
cartridgessuchas
FMorceramic
INPUT
(FOR2.5V.OUTPUT)
MIN.MAX.
70MV.20V.
10MV.1 V.
30MV.150MV.
10MV.50MV.
GAIN
32db
50db
40db
50db
REMARKS
Inputlevelsinexcess
of.07Vshouldbere-
ducedbypotentiometers
onbackpanel.
Inputlevelsinexcess
of10MVshouldbe
reducedbypotentiom-
eteronbackpanel.
Seetextforoperation
ofthesechannels.
TheAudioCompensatorandmagneticphonographcartridgesshould
bemountedatleasttwofeetfrompowertransformers.
Inter-unitcablesprovidea completegroundsystem.Alternate
groundwirescreategroundloopswhichwillusuallyincreasehum
level.

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4.Theheatersofthe12AX7tubesusedintheC-8arereturnedto
groundthrougha humreducingpotentiometerinthepower
amplifier.HeatersoftubesusedintheC-8Parereturnedto
groundthrougha humreducingpotentiometerinthepower
supply.Thiscontrolrequiresaninitialadjustmentformini-
mumhum,andshouldbereadjustedeachtimeoneormore
tubesarereplaced.
5.GroundingtheturntablemotorframetotheAudioCompensator
chassisneartheinputjacksmayreducethehumlevelonthe
phonographchannels.
OUTPUTCONNECTIONS
Threeoutputsareprovided:oneauxiliaryandtwomainoutputs.
Theauxiliaryoutputmaybeusedforrecordingtapefromanysourcecon-
nectedtotheAudioCompensator.TheSelectorswitch,BassandTreble
compensationswitches,andRumbleFilterareeffectiveatthisoutput.Adjust-
mentoftheBassandTrebletonecontrols,AuralCompensatorandVolume
controlmaybemadeformonitoringpurposeandwillnotaffecttherecorded
signal.Theauxiliaryoutputdeliversa signalofonevolt.
Allcontrolsareeffectiveatthemainoutputs,whichareavailableatthe
octalsocketlabeled"INTER-UNITCABLE"betweenpins#1and#2(pin#1is
ground),andattheRETMApinjacklabeled"MAINOUTPUT".Theinter-unit
cableconnectingtheC-8toanyMcIntoshpoweramplifierusestheoctalsocket
output.Thepinjackoutputmaybeusedfordrivinga secondpoweramplifier
ifsodesired.
Themainandauxiliaryoutputjacksarefedfromcathodefollowers.The
inputimpedanceofdevicesconnectedtotheseoutputsshouldbe50,000ohms
orgreater,andthecapacitivereactanceofaudiocablesconnectingthese
devicesshouldnotbelessthan8,000ohmsat20,000cycles.Thisisthe
reactanceofa capacityof1000mmf.Audiocablehavinga capacityof25mmf
perfootmaybe40feetlong.

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TYPICALINSTALLATION
AUDIOCOMPENSATOR,C-8
TYPICALINSTALLATION
AUDIOCOMPENSATOR,C-8P
(SELFPOWERED)

COMPENSATEFOREAR
CHARACTERISTICAT
REDUCEDVOLUMEON
ALLCHANNELS.
SELECTDESIREDTREBLE
ROLL-OFFONALLCHANNELS.
SELECTDESIREDBASS
COMPENSATIONON
CHANNELS4 AND5.
REDUCETURNTABLERUMBLE,
ORLOWFREQUENCYDISTURB-
ANGESONALLCHANNELS.
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SELECTANYONEOFFIVE
INPUTCHANNELS.UNUSED
CHANNELSAREGROUNDED
TOPREVENTCROSSTALK.CONTROLBASSRESPONSE
ONALLCHANNELSCONTROLTREBLERESPONSE
ONALLCHANNELS.
CONTROLVOLUMEON
ALLCHANNELS,ON-OFF
CONTROL.
Channels1 and2:
Channels1 and2 areeachterminatedbya potentiometermountedontheback
panelwhichshouldbeusedtoreducesignalinputtothesechannelsifinexcessof
.07volts.Correctadjustmentoccurswhenthesoundlevelofchannels1 and2 is
equivalenttothatofchannels4 or5.Highimpedancesources,suchascrystal
microphonesandthedetectoroutputoftuners,maybeconnecteddirectlytothese
channelssincetheyhaveaninputimpedanceof660,000ohms.
Channel3:
Channel3 isterminatedbya 100,000ohmpotentiometermountedontheback
panelwhichshouldbeusedtoreducesignalinputtothischannelifinexcessof
10MV.Lowimpedancemicrophonesinconjunctionwithaninputtransformer,
suchasMcIntoshM-107,maybeusedonthischannel.
Channels1,2 and3 provideflatamplificationfrom20to20,000cycles.All

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frontpanelcontrolsareeffective,withtheexceptionoftheBassCompensation
switches,andmaybeusedtoaltertheresponseasdesired.
Channel4:
Channel4 is equalizedforusewithhighlevelmagneticcartridgesdelivering
30MVofsignal.ItisterminatedforusewiththePickeringcartridge.
Channel4 maybemodifiedforusewithotherhighlevelmagneticcartridgesby
changingtheterminatingpadofR6andR7,ormaybeusedfora secondlowlevel
cartridgebyreplacingR6andR7witha singleterminatingresistorasrecommended
bythecartridgemanufacturer.
Channel5:
Channel5 isequalizedforusewithlowlevelmagneticcartridgessuchas
G.E.,Audax,orFairchildwithinputtransformer.A variableterminatingcon-
trolisprovided,anda switchforselectingeithermagneticcartridges(velocity
responsive),oramplituderesponsivecartridges,suchasa ceramicorF.M.type.
Whenusinga magneticcartridgethisswitchshouldbeinthe"MAG"position
andthecontrollabeled"LOAD"shouldbeadjustedtotheresistancerecommended
bythemanufacturer.Highfrequencyroll-offofthecartridgemaybeobtainedby
decreasingtherecommendedload. Theloadcontroliscalibratedfrom"0"to
"100"witheachcalibrationrepresentingthousandsofohms.
Amplituderesponsivecartridgesmaybeusedonchannel5 toallowfulluse
oftheextremelyflexiblecompensationavailable.Byplacingtheslideswitchin
position"F.M."andthe"LOAD"controlto"100",cartridgesofthistypemaybe
used.
Allcontrolsareeffectiveonchannels4 and5.
TheBassandTreblecompensationswitchesmaybeusedtocompensate
recordingsasrecommendedbythemanufacturerortoadjustthecompensationfora
morepleasingtonalbalanceforthelistener.TheBassandTrebletonecontrols
areindependentofthecompensationswitchesandmaybeusedasfineadjustments
inconjunctionwiththeseswitches.Inaddition,a rumblefilterisprovidedto
reduceturntable"wow"and"rumble".
•
ThefivepositionchannelSelectorswitchmaybeusedtoselectanyofthe
fiveinputchannelsavailable.
TheVolumecontrolselectsthedesiredlisteninglevelandsinceitislocated
attheoutputoftheAudioCompensator,thehighsignaltonoiseratiooftheunitis
maintainedatalllevels.Byproperlyadjustingtheinputpotentiometeronchannels

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1,2 and3 thevolumelevelcanbeheldequalforallchannels;thesignalwill
remainata constantloudnesswhenswitchingfromonechanneltoanother.The
masteroff-onswitchisattachedtothevolumecontrol.Thisswitchcontrolsthe
threeauxiliaryA.C.outletsontherearpaneloftheAudioCompensatoraswellas
thethreeauxiliaryA.C.outletsonthepowersupplyoftheC-8P.
Theauralcompensatormaybeusedtocompensatefortheresponsecharac-
teristicoftheearatreducedvolume.Thiscontroldecreasesthemid-range
frequencieswhileleavingthelowandhighfrequenciesatrelativelyconstant
intensity.Byreducingvolumelevelwiththiscontrolproperbalanceofthepro-
grammaterialcanbemaintained.
GUARANTEE
Weguaranteetheperformanceofthisequipmentandthemechanicalandelec-
tricalworkmanshiptobefreeofseriousdefectsfora periodof90days.This
guaranteedoesnotextendtocomponentsdamagedbyimproperusenordoesit
extendtotransportationtoandfromthefactory.
McINTOSHLABORATORYINC.
320WaterStreet
Binghamton,N.Y.,U.S.A.
ELECTRICALANDMECHANICALSPECIFICATIONS
PowerSourceC-8:AnyMcIntoshPowerAmplifier
C-8P:Self-powered
OutputMain:2.5 volts
Auxiliary:1 volt
InputlevelChannels1 & 2:70MV-20volts
Channel3:10MV
Channel4:30MV(MagneticCartridge)
Channel5:10MV(Magneticorconstant
amplitudecartridge)
FrequencyResponseSeeGraphs
HarmonicDistortionLessthan. 3%at2.5 voltsoutput,20-20,000cycles
HumandNoise-110db(2.5 microvolts)orlower,(referredtoinput)
0db=.775volts
SizeC-8:10"x 3-1/2"x 7-1/211
FrontPanel11"x 4-1/4"
C-8P:Same
D-8(PowersupplysectionofC-8P):5-l/2"x4-3/4"x2-3/8"
WeightC-8:6 lbs.
C-8P:8 lbs.

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-10-
VOLTAGEANDRESISTANCECHART
Resistancesmeasuredtogroundwithpin#4ofinter-unitcablesocketshortedtopin#1
D.C.VoltagesmeasuredwithVTVMtogroundusingD-8powersupply.
Signalvoltagemeasuredwithallcontrolsinflatposition,1000cyclesignalof
10MVinchannel3,volumecontrolfullyon,andwitha VTVM.
Tube
Input
Tube
Center
Tube
Output
Tube
PinNo.
1
2
3
4& 5
6
7
8
9
1
2
3
4& 5
6
7
8
9
1
2
3
4& 5
6
7
8
9
Resistance
430K
1M
4.1K
*0-65ohms
440K
1M
1.8K
*0-65ohms
110K
440K
330K
*0-65ohms
110K
200K
102K
*0-65ohms
340K
**0-lmeg
1.8K
*0-65ohms
12K
1.1M
102K
*0-65ohms
D.C.Voltage
110V
0
1.2V
*0-4.8V.A.C.
108V
0
1.2V
*0-6.3V.A.C.
195V
108V
110V
*0-4.8V.A.C.
195V
45V
55V
#0-6.3V.A.C.
160V
0
1.2V
*0-4.8V.A.C.
95V
25V
350V
*0-6.3V.A.C.
SignalVoltage
17MV
10MV
9.5MV
--
1.25V
17MV
0--
0
1.25V
1.2V
__
0
1.0V
1.1V
--
2.7V
95MV
14MV
--
0
2.65
2.85
--
*Dependsonpositionofhumreducingpotentiometer.
**DependsonpositionofBasspotentiometer.100K,Bassat"0"

C-l1.345
MCINTOSHLABORATORY,INC.
320WaterStreet,Binghamton ,NewYork
MODELC-8P,AUDIOCOMPENSATO R
7-7-54
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