4.Theheatersofthe12AX7tubesusedintheC-4arereturnedto
groundthrougha humreducingpotentiometerinthepoweramplifier.
HeatersoftubesusedintheC-4Parereturnedtogroundthrougha hum
reducingpotentiometerinthepowersupply.Thiscontrolrequiresan
initialadjustmentforminimumhum,andshouldbereadjustedeach
timeoneormoretubesarereplaced.
5.GroundingtheturntablemotorframetotheAudioCompensator
chassisneartheinputjacksmayreducethehumlevelonthephono-
graphchannels.
OUTPUTCONNECTIONS
Threeoutputsareprovided:onetapeandtwomainoutputs.
Thetapeoutputmaybeusedforrecordingtapefromanysourceconnected
totheAudioCompensator.TheSelectorSwitch,andCompensationSwitchare
effectiveatthisoutput.AdjustmentoftheBassandTrebletonecontrolsand
Volumecontrolmaybemadewithoutaffectingtherecordedsignal.Thetape
outputdeliversa signalofonevolt.
Allcontrolsareeffectiveatthemainoutputs,whichareavailableatthe
octalsocketlabeled"INTER-UNITCABLE"betweenpins#1and#2(pin#1is
ground),andattheRETMApinjacklabeled"MAINOUTPUT".Theinter-unit
cableconnectingtheC-4toanyMcIntoshpoweramplifierusestheoctalsocket
output.Thepinjackoutputmaybeusedfordrivinga secondpoweramplifier
ifsodesired.
Themainandtapeoutputsarefedfromcathodefollowers.Theinputim-
pedanceofdevicesconnectedtotheseoutputsshouldbe50,000ohmsor
greater,andthecapacitivereactanceofaudiocablesconnectingthesedevices
shouldnotbelessthan8,000ohmsat20,000cycles.Thisisthereactanceof
acapacityof1000mf.Audiocablehavinga capacityof25mmfperfootmay
be40feetlong.
TAPEandTUNERChannels:Thesechannelsareeachterminatedbya
potentiometermountedonthebackpanelwhichshouldbeusedtoreducesignal
inputifinexcessof. 1 volts.Highimpedancesources,suchascrystal
microphonesandthedetectoroutputoftuners,maybeconnecteddirectlyto
thesechannelssincetheyhaveaninputimpedanceof660,000ohms.
MICChannel:Thischannelisterminatedbya 100,000ohmpotentiometer
mountedonthebackpanelwhichshouldbeusedtoreducesignalinputifin
excessof10MV.Lowimpedancemicrophonesinconjunctionwithaninput
transformer,suchasMcIntoshM-107,maybeusedonthischannel.
TheTAPE,TUNERandMICchannelsprovideflatamplificationfrom20
to20,000cycles.TheBassandTrebletonecontrolsmaybeusedtoalterthe
responseasdesired.
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