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.
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