McIntosh MR80 User manual

ReadingTime:32Minutes
Price:$2.00
THEMclNTOSHMR80DIGITALFMTUNER

VARIOUSREGULATORYAGENCIESREQUIRETHATWEBRINGTHEFOLLOWING
INFORMATIONTOYOURATTENTION.PLEASEREADITCAREFULLY.
WARNING:TOPREVENTFIREORSHOCK
HAZARD,DONOTEXPOSETHISUNITTO
RAINORMOISTURE.
TheMclntoshyouhavepurchasedisa Model
MR80.Ithasa serialnumberlocatedontherear
panelofthechassis.Recordthatserialnumber
here:
SerialNumber
Themodel,serialnumberandpurchasedateare
importanttoyouforanyfutureservice.Recordthe
purchasedatehere:
Purchasedate
Uponapplication,MclntoshLaboratoryprovidesa
Three-YearServiceContract.YourMclntoshauthor-
izedserviceagencycanexpediterepairswhenyou
providetheServiceContractwiththeinstrumentfor
repair.Toassist,recordyourServiceContract
numberhere:
ServiceContractNumber

YourMR80DigitalFMTuner
cangiveyoumanyyearsof
satisfactoryperformance.Ifyou
haveanyquestions,pleasecontact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903-9990
Phone:[phone]
TakeAdvantageof3 years
ofContractService...
FillintheApplicationNOW.
Contents
SERVICECONTRACTINFORMATION. ..1
INSTALLATION..2
HOWTOCONNECTAND
BACKPANELINFORMATION...4
FRONTPANELINFORMATION
ANDUSEOFCONTROLS.. .6
TOPPANELINFORMATION
ANDSECONDARYCONTROLS...8
PERFORMANCELIMITS. . .9
PERFORMANCECHARTS.-10
TECHNICALDESCRIPTION.14
BLOCKDIAGRAM..20
MclNTOSHTHREEYEARSERVICECONTRACT
AnapplicationforA THREEYEARSERVICECONTRACTisincludedwiththismanual.
Thetermsofthecontractare:
1.Mclntoshwillprovideallparts,materials
andlaborneededtoreturnthemeasured
performanceoftheinstrumenttothe
originalperformancelimits.TheSER-
VICECONTRACTdoesnotcoverany
shippingcoststoandfromtheauthoriz-
edserviceagencyorthefactory.
2.AnyMclntoshauthorizedserviceagency
willrepairMclntoshinstrumentsatnor-
malservicerates.Toreceiveservice
underthetermsoftheSERVICECON-
TRACT,theSERVICECONTRACTCER-
TIFICATEmustbepresentedwhenthe
instrumentistakentotheserviceagency.
3.Alwayshaveservicedonebya
Mclntoshauthorizedserviceagency.If
theinstrumentismodifiedordamaged
asa resultofunauthorizedrepair,the
SERVICECONTRACTwillbecancelled.
Damagebyimproperuseormishandl-
ingisnotcoveredbytheSERVICE
CONTRACT.
4.TheSERVICECONTRACTisissuedto
youastheoriginalpurchaser.Topro-
tectyoufrommisrepresentation,this
contractcannotbetransferredtoa se-
condowner.
5.ToreceivetheSERVICECONTRACT,
yourpurchasemustbemadefroma
Mclntoshfranchiseddealer.
6.Yourcompletelyfilledinapplicationfor
theSERVICECONTRACTmustbepost-
markedwithin30daysofthedateof
purchaseoftheinstrument.
7.ToreceivetheSERVICECONTRACT,all
informationontheapplicationmustbe
filledin.TheSERVICECONTRACTwill
beissuedwhenthecompletelyfilledin
applicationisreceivedbyMclntosh
LaboratoryIncorporatedinBinghamton,
NewYork.
8.UnitsinoperationoutsidetheUnited
StatesandCanadaarenotcoveredby
theMclntoshFactoryServiceContract,
irrespectiveoftheplaceofpurchase.
Norareunitsacquiredoutsidethe
U.S.A.andCanada,thepurchasersof
whichshouldconsultwiththeirdealer
toascertainwhat,ifany,servicecon-
tractorwarrantymaybeavailablelocally.
Copyright1980© byMclntoshLaboratoryInc.
1

HowtoConnectand
BackPanelInformation
Refertopage5.
AUDIOOUTPUTS
UsetheFIXEDOUTPUTjacksontherearpanelto
feedprogramtoa stereocontrolpreamplifieror
otherequipmentwhichhasitsownvolumecontrol.
ThefrontpanelVOLUMEcontroldoesnotaffectthe
loudnessofthetunerattheFIXEDOUTPUTjacks.
Theoutputlevelisa nominal1 voltfor100%FM
modulation.
UsetheVARIABLEOUTPUTjackstoconnectto
equipmentsuchasa poweramplifierora tape
recorderwherecontrolofthevolumeatthetuneris
desired.TheoutputattheVARIABLEOUTPUTjacks
isa nominal2.5voltsfor100%FMmodulation.
Thereisnodifferenceinthesignalqualityateither
pairofoutputjacks.
BothpairsofOUTPUTjacksmaybeusedsimul-
taneously.Theoutputimpedanceatbothoutputsis
verylowsothatlongaudiocablescanbeused
withouta lossofhighfrequenciesduetocable
capacity.
RFINPUTS—ANTENNACONNECTIONS
Twooffourdifferentantennasystemscanbe
usedwithyourMR80.1)anoutdoorFMantenna,2)
anallchannel(UHF-VHF-FM)antenna,3)a cablein-
putfromyourlocalcablecompany,or4)theindoor
dipolesuppliedwiththeMR80.A switchisprovided
onthetoplevelsetpaneltoselectbetweentwoof
thefoursystemsmentioned.
Anoutdoorantennaisrecommendedforoptimum
performanceinallareas.Infringeareas,bestresults
willbeobtainedwitha highlydirectionalFMan-
tennausedinconnectionwitha rotator.Rotatethe
antennauntilthebestreceptionisobtained.Con-
necta 300ohmoutdoorantennatothe300WAN-
TENNA(red)terminals.Connecta 75ohmantenna
and/or75ohmcablesystemtothecoaxialantenna
jack.
Aflexiblefoldeddipoleantennasuppliedwith
yourMR80maybeusedinurbanorinhighsignal
strengthareas.Theflexibilityofthethinflatwire
assemblypermitsittobeplacedundera rug.tacked
behindthestereoorplacedinanyotherconvenient
location.Insomecasesitmaybenecessarytoposi-
tiontheantennaforbestsignalreception.This
shouldbedonebeforeitispermanentlylocated.
Avoidlocatingthisantennanexttootherwiresor
metalobjects.Thisantennamaynotproveeffective
inhouseshavingmetalsidingormetalcladinsula-
tion.
Thecablesignalfroma localcablecompanyora
secondFMantennawith75ohmsimpedancemay
beconnectedtothecoaxialcablejack.
REMOTESCAN
TheREMOTESCANCONTROLSIGNALjackisto
beconnectedtothecablepushbuttonassembly
suppliedwiththeMR80forremotetuning.Plugthe
cableintotheCONTROLSIGNALjack.Pressingthe
pushbuttonattheendofthecablecausestheMR
80toscantothenextstation.Themodeofscancan
beselectedbytheSTATION'Sslideswitch.Inthe
PRESETpositioneverytimethepushbuttonis
depressedtheMR80willscantothenextpresetsta-
tion.IntheALLpositiondepressingthebuttonwill
causetheMR80toscantothenextstation.
IfREMOTEtuningisnotused,leavethejackfree
ofanyconnection.
SCOPE
Theverticalandhorizontalscopejacksarepro-
videdtoconnecttoa maximumperformancein-
dicatororanoscilloscopeforindicationofFM
multipathandsignalstrength.Connectthevertical
jacktotheverticalinputoftheindicatorandthe
horizontaljacktothehorizontalinput.
UNSWITCHEDACPOWEROUTLET
Thisoutletmaybeusedtopowerauxiliaryequip-
mentsuchasanantennarotatorora maximumper-
formanceindicator.Powerisavailablewheneverthe
MR80isconnectedtoa powersource.
4

FMCABLE
INPUTOR
2ND75WANTENNA
LEAD-IN
FMANTENNA
OPTIONAL
75W ANTENNA
LEAD-IN
REMOTECONTROL
PUSHBUTTON
POWERAMPLIFIER
PREAMPLIFIER
LEFTSPEAKERRIGHTSPEAKER
5
MAXIMUMPERFORMANCE
INDICATOR
OR
OSCILLOSCOPE
TOAC
POWER
SOURCE

FrontPanelInformationand
UseofControls
TheMR80Tunerhasthemostflexiblecontrol
systemeverdesignedina stereoFMtuner.Correct
useofthesecontrolswillyielda higherlevelofper-
formancethanpreviouslypossiblewithconven-
tionaltuners.
VOLUMECONTROLANDACPOWERSWITCH
TheVOLUMEcontrolhasbeenprecisiontracked
throughoutthelisteningrange(0to- 65dB)forac-
curatestereobalance.
ItsetstheoutputleveloftheVARIABLEOUTPUT
jacksandthefrontpanelHEADPHONEjack.The
FIXEDOUTPUTjacksarenotaffectedbytheposi-
tionoftheVOLUMEcontrol.TheACpowerswitchis
partoftheVOLUMEcontrol.TurningtheVOLUME
controlfullycounterclockwiseturnstheACpower
off.
TUNINGCONTROLSANDFREQUENCYDISPLAY
FrequencyDisplay
TheFrequencyDisplayindicatesthereceivedfre-
quencytothenearest100kHz.
Tuning
TherearefourmethodsoftuningyourMR80.
Automaticselectionofthetuningmethodispro-
videdbytouchsensorsassociatedwitheachofthe
tuningcontrols.
ManualTuning
WhenpowerisappliedtotheMR80,thecircuitry
automaticallyselectsthemanualorknobtuning
controlmode.Turningthetuningknobclockwise
willincreasethereceivedfrequency.Counterclock-
wisedecreasesthereceivedfrequency.
Note:WhentheMR80isoperatedbutisnotcon-
nectedtoanyotherdevice(preamp,poweramp,
antenna,testequipment,etc.),thereisa chancethe
frequencydisplaywillblankoutwhentuningwith
themaintuningknob.Thisisnormalandcaneasily
becorrectedbyreversingthe120VAClineplugorby
connectingtheMR80toanyotherequipment.
AutoScan
AUTOSCANisprovidedbytwotouchpadsim-
mediatelytotheleftofthetuningknob.Thesetwo
touchpadsstartthetunersearchingfora newsta-
tion.Thesmallarrowwilllightnexttothepad
touchedandindicatethedirectionofscanning.It
willscaninthedirectionchosenuntilitstopsata
stationorreachestheendoftheband.Attheband
endthetunerwillreverseitsscandirection.
Preset1,2,3 & 4
Thesetouchpadslocatedtotheleftofthefre-
quencydisplayselectoneofthefourpresetsta-
tions.Justtouchtooperate.A smallrectanglewill
lightabovethepadindicatingwhichpresethasbeen
selected.
RemoteSCAN
RemoteSCANofeitherthepresetsorallstations
isprovidedforasdescribedunderbackpanelinfor-
mation.
INDICATORLIGHTS
Threeindicatorlightsareprovidedimmediatelyto
theleftofthepresettouchpads.Theuppermost
STEREOindicateswhena stereobroadcastisbeing
received.Thesecond,LOCK,indicateswhenthe
tunerislockedtothestation.Thelockcircuitinthe
MR80isuniqueinthattunedfrequencyislockedto
thestation,nottoaninternalstandardasinthecase
ofmanydigitaltuners.ThisallowstheMR80tobe
tunedtoanyfrequencywithintheFMbandandlock
onthatfrequency.Otherdigitaltunerscanonlylock
onspecificchannelassignments.Thislockcircuitis
sopowerfulthatitmustbedisabledinordertotune
thetuner.Youwillnoticethatthemomentthatyou
touchanyoneofthetuningcontrolsthelocklight
extinguishesandonlycomesonwhenthestationis
properlytuned.Oncelockhasbeenestablishedit
willremainonevenifthestationbeingreceived
shoulddriftupto2 megacycleseithersideofthe
centerofthecarrier.Thus,perfecttuningisalways
assured.Thethirdindicatorlight,FILTER,indicates
whenthestereonoisefilterisinoperation.Thein-
dicatorlightsareinthreedifferentcolors:redfor
STEREO,amberforLOCK,andgreenforFILTER.
SELECTIVITYSWITCH
TwodegreesofIFselectivityareselectablebythe
SELECTIVITYswitch.TheNARROWornormalposi-
tionprovidesadequateselectivityforstereorecep-
tionevenunderseverereceivingconditions.Five
linearphasepiezoelectricIFfiltersprovidelow
distortionreceptionwiththishighdegreeofselec-
tivity.SettingtheSELECTIVITYswitchtoSUPER
NARROWaddsanadditional4-pole4-zeroquartz
crystalfiltertothefivepreviouslymentionedfilters.
UsetheSUPERNARROWpositiontoreceivesta-
tionsfromdistantcitieswhichareonchannelsadja-
centtolocalstations.Theremaybeuseablesignals
whichwereneverheardbeforewithordinaryFM
tuners.
6

SIGNALCOLUMN
AcolumnofLEDlampsrespondtothesignal
strengthofthestationbeingreceived.Thestronger
thesignalthehigherthecolumnreaches.Thereisa
controlonthetunertoppaneltoadjustthecolumn
heightforfullscalewhenreceivingthestrongest
signalinyourlisteningarea.
FILTERSWITCHANDFUNCTIONINDICATOR
TheMR80FILTERswitchprovidesautomatic
stereonoisereductiononweakstereostations.With
theswitchintheAUTOpositionthefilterwillbeon
onlywhenthestationisbroadcastinga stereopilot
toneandthesignalstrengthisbelow100microvolts.
WiththeswitchintheINpositionthefilteriscon-
nectedatalltimes.Thefilterhasnoaffectonmono
stations.Thefilterfunctionindicatorlightglows
greenwhenthefilterison.
MODESWITCH
AtwopositionMODEswitchisprovidedsothat
youmayselecteitherautomaticstereoormono
reception.IntheSTEREOpositionthetuner
automaticallyswitchesfrommonotostereomode
whena pre-determinedsignaltonoiseratiohas
beenreached.IntheMONOpositionallstationswill
bereceivedmonophonicallybuttheSTEREOindicator
willlightifthestationisbroadcastinginstereo.
HEADPHONEJACK
AHEADPHONEjackisprovidedtodrivelowim-
pedancedynamicheadphonesfromaninternal
poweramplfier.
SCANCONTROL
TheSCANcontroladjuststhespeedatwhichthe
tunersearchesforthenextstation,whenusingthe
AUTOSCANmodeoftuning.Ifthedialiscrowded
withstationsusea slowscanspeed.Iftherearefew
stationsfastscanningcanbeused.
MUTINGCONTROL
MUTINGsuppressesthebackgroundnoiseand
hissnormallyheardbetweenstations.Turningthe
controlcounterclockwisetotheOUTpositiondis-
ablesthemutingcircuits.Turningthecontrolclock-
wiseincreasesthesignallevelrequiredtounmute.
ThiscontrolalsoadjuststhesensitivityoftheAUTO
SCANtuningcircuitsandthenumberofstations
youwillreceivewhenusingthistuningmode.
7

TopPanelInformationand
SecondaryControls
Onthetopofthechassisbehindthefrontpanela
recessedpanelcontainsthesecondarycontrols.
WhentheMR80isinstalledinthecabinetaccessto
thispanelmaybegainedbydepressingthetwo
PANLOCbuttonsandslippingtheunitpartiallyfor-
ward.
Preset1 thru4
ThePRESETtuningadjustmentsareusedtoset
thereceivedfrequencyforeachpreset.Toseta
presettothedesiredstation,touchthecorrespond-
ingpresetpadandatthesametimeadjustthe
presetcontrolonthetoppanelforthedesiredfre-
quencyindication.Youmusttouchthepadwhile
tuningtoholdthefrequencylockcircuitinactive,
otherwiseerroneoustuningwillresult.
Preselect
TheRFPRESELECTswitchswitchesanaddi-
tionaltunedcircuitbetweentheantennaandthe
firstRFstagetoimmunizeagainstoverload.Usethe
preselectorinverystrongsignalareas.
Input
TheINPUTswitchselectseitheranantennaor
cableastheRFinputsource.TheCABLEinputmay
alsobeusedasa secondantennainput.
Lock
Thisswitchwilldisablethelockcircuitsonly
whenthemaintuningknobisinuse.UsetheON
positionforallnormalreception.SwitchtotheOFF
positionwhenthereceivedstationhasa deepfade.
Thispreventsthefrequencylockcircuitfromchang-
ingtuningtolocktoanadjacentstrongerstation.
De-emphasis
The50/75msbuttonselectsthecorrectde-
emphasisforyourcountry.75msisusedontheNorth
Americancontinentand50msisusedinWestern
EuropeandtheFarEast.25msde-emphasisisalso
availablebydepressingthebuttonmarked
Note:Thenormaloperatingpositionofthefive
pushbuttonswitchesisfortheswitchestobeinthe
outorupposition.
SignalStrength
Usethiscontroltosetthesignalstrengthcolumn
tofullscaleforthestrongeststationinyourarea.
Thiscontrolisa sensitivityadjustmentforthesolid
statesignalstrengthindicator.Itmerelyadjuststhe
heightofthecolumn.Itdoesnotaffectthesensitiv-
ityofthetuner.
8

PerformanceLimits
PerformanceGuarantee
Performancelimitsarethemaximumdeviationfrom
perfectionpermittedfora Mclntoshinstrument.We
promiseyouthattheMR80,atthetimeofitspur-
chase,iscapableofperformanceatorexceeding
theselimitsoryougetyourmoneyback.Mclntoshis
theonlymanufacturerthatmakesthisguarantee.
Tuning:
88to108MHz
AntennaInputs:
One300Wbalancedandtwo75Wunbalanced.
IntermediateFrequency:
10.7MHz
Sensitivity:
9.3dBf(1.6mV)for35dBofquieting
14.7dBf(3mV)for50dBofquieting
13.2dBf(2.5mV)for3%totalnoiseandharmonicdis-
tortion
SignaltoNoiseRatio:
75dBbelow100%modulation
HarmonicDistortion:
0.2%20Hzto15kHz,monoorstereo
Typically,0.08%at1000Hz
IntermodulationDistortion:
0.15%monoorstereoforanycombinationoffre-
quenciesfrom20Hzto15,000Hzwithpeakmodula-
tionequalto100%orless.Typically0.1%
FrequencyResponse:
MonoandStereo± 1dB20Hzto15kHzwith75,50
or25mSdeemphasis
CaptureRatio:
1.5dB
Selectivity:
Adjacentchannel
Alternatechannel
SpuriousRejection:
110dB
Narrow
8dB
90dB
SuperNarrow
60dB
110dB
TunerIM(RF):
-23dBmfor2 signals1MHzapart
TunerInterceptPoint:
-10dBm75W
ImageRejection:
90dB
MaximumSignalInput:
8voltsacross75W(1W)antennaterminalwillnot
increaseharmonicorintermodulationdistortion.
AudioHum:
75dBdownfrom100%modulation
Muting:
70dBnoisereductionbetweenstations
MutingThreshold:
2mVto1000mV
SCARejection:
60dBminimum
StereoSeparation:
50dBto1000Hz
StereoFilter:
10dBnoisereduction
AudioOutput:
Variable:
2.5Vinto47k
Fixed:
1Vinto47k
GeneralInformation
PowerRequirements:
120volts50/60Hz.25watts
SemiconductorComplement:
57Transistors
68IntegratedCircuits
81Diodes
4LEDDisplays
18LED's
7NeonLamps
MechanicalInformation
SIZE:Frontpanelmeasures16incheswide(40.6cm)
by5 7/16incheshigh(13.8cm).Chassismeasures
143/4incheswide(37.5cm)by4 13/16incheshigh
(12.2cm)by13inchesdeep(33cm),includingcon-
nectors.Knobclearancerequiredis1 1/4inches(3.2
cm)infrontofmountingpanel.
FINISH:Frontpanelisanodizedgoldandblackwith
specialgold/tealnomenclatureillumination.
Chassisisblack.
MOUNTING:ExclusiveMclntoshdevelopedprofes-
sionalPANLOC
WEIGHT:27pounds(12.2kg)net,39pounds(17.7kg)
inshippingcarton
9

PerformanceCharts
SIGNALINPUT
10
SIGNALINPUT

11
FREQUENCYINHERTZ
FREQUENCYINHERTZ
FREQUENCYINHERTZ

12
FREQUENCYINHERTZ
FREQUENCYINHERTZ
FREQUENCYINHERTZ

13
FREQUENCYINHERTZ
FREQUENCYINHERTZ
FREQUENCYINHERTZ

TechnicalDescription
Engineeringdirectiondictateda tunerdesign
governedbyinsistenceongreatflexibilityandease
ofuse.ThishadtobedonewhiledesigninganRF
sectionwithgreatsensitivityandtheworld'sbest
selectivityinkeepingwiththeneedsoflowdistor-
tion.Thesevalueswereachievedandtheyretainthe
Mclntoshreputationofoutstandingperformance,
longlifeandreliability.
RF-IFSECTION
IntheANTSWITCHsixRFPINdiodesarecon-
nectedasa singlepoledoublethrowswitch.This
allowstheuseoftwoantennasortheuseofan
antennaanda cable.Inputtooutputisolationofthis
switchisgreaterthan75dB.
FollowingtheANTSWITCHisanRFtunerofex-
ceptionalperformance.Thisperformanceisachiev-
edbytheuseofa lownoisejunctionFETanda high
powerbipolartransistor(aheatsinkisused)con-
nectedasa cascodeamplifier.Thisconnection
allowshighgain,lownoise,andhighoutputlevels
withouttheneedforneutralization.Twoadditional
PINdiodesareusedtoinserta secondtunedanten-
naPreselectorcircuitduringstrongsignalrecep-
tion.Forlowerintermodulationdistortionthetuned
circuitsaretunedbya seriesparallelconnectionof
fourmatchedvaractordiodes.Thiscircuitandthe
hightuningvoltage(5-26volts)eliminatestheRFin-
termodulationdistortioncausedbydiodenon-
linearities.
AftertheRFamplifiertwoparalleltunedcircuits
areusedtoprovidetheproperloadimpedancefor
thebipolartransistor.Theuseoftwotunedcircuits
atthislocationgreatlyimprovestheimagerejection
andoverloadperformanceofthetuner,aswellasin-
creasingtheRFselectivity.
Thefollowingbalancedmixerisa matcheddual
J-FETandbipolartransistorcircuit.A lowloss
toroidalphasesplittingtransformerisusedasan
impedancematchingnetworkinthegatecircuitof
themixer.Attheoutputa balanceddoubletuned
transformerisusedasthedrainload.Thisarrange-
mentgivesgreatimmunitytomixeroverloadinthe
presenceofa verystrongsignal.A bipolartransistor
isusedasanoscillatorbuffertopreventoscillator
pullingonstrongsignals,andastheconstantcur-
rentsourceforthedualJ-FETmixer.
TheMR80hasthenarrowestIFbandwidthever
usedina stereotuner.Itisthecorrectwidthtolet
justoneFMstationthrough.Theexcellentselectivi-
tyoftheMR80(210kHzwideat60dBdown)permits
tuningtostationsthatareimpossibletoreceiveon
ordinarytuners.
Constantdelaydesigntechniquesareusedinthe
4-pole4-zerocrystalfilterusedintheSUPERNAR-
ROWposition.However,duetotheextremeselec-
tivity,delaydistortionisveryslightlyincreasedover
theNARROWselectivityposition.
Fourdifferentialamplifiers,coupledwithPHASE-
LINEARmonolithicfilters,comprisetheNARROW
selectivityandsignalstrengthsectionsoftheIF
amplifier.Onehalfofeachdifferentialamplifierout-
putdrivesa filterandthesecondoutputdrivesa full
waverectifiercircuit.Theoutputsofthesefour
rectifiercircuitsaresummedattheinvertinginputof
anoperationalamplifier.A fifthrectifiercircuitthat
isdrivenfromthelimiterisalsosummedattheinput
totheoperationalamplifier.Theoutputoftheopera-
tionalamplifierisa voltagethatisproportionalto
thelogoftheRFinputlevel.Dynamicrangeisfrom
2mVtoover2V,thatis,greaterthan120dB.A solid
statesignalstrengthmeterisusedasa frontpanel
indicationoftheincomingRFsignallevel.Twelve
LED'sareusedinplaceoftheconventionalmeter
movement.TheLED'shavean almostunlimitedlife.
ThefastresponseoftheLED'splainlyshows
multipathsignalsandantennamisorientation.To
betterusethewidedynamicrangeofthefivesignal
strengthdetectors,anadjustmentisprovidedto
reducethefullscalesignalfrom100,000mVtoany
valuebelowthat.Thismetercanbesettogivea full
scaleindicationona signalaslowas2mV.This
allowssettingthesignalmetertoindicatefullscale
onthestrongeststationintheusersarea.Thenthe
signalstrengthmeterindicatestheRFlevelofall
stationsreceivedrelativetothestrongestinthe
listener'sarea.
Thesignalstrengthvoltageisalsousedtocontrol
mono/stereoswitching,stereofilterinsertion,
muting,andautomaticscanstop.Becauseofit's
widerangeandhighrepeatabilitythiscontrol
voltageisalsousedtoadjustthestereoseparation
atlowRFsignallevels.Thisproducesthemaximum
signaltonoiseratiopossibleforallsignallevels.
FollowingtheselectivitysectionoftheIFampli-
fieristheLIMITER.A totalgainof80dBisusedin
thiscircuit.Theuseofveryhighgaininthelimiter
circuitproduceshardlimitingwithverygoodim-
pulsenoiserejection.Limiterbandwidthisgreater
than50MHz,producingexcellentdetectorcapture
characteristics.
AbroadbandFoster-Seeleydiscriminatorisused
asthedetector.Thisdetectorcoupledwiththe
broadbandlimiterproducesunmeasurablenoise
anddistortion.A highspeedbufferamplifierfollow-
ingthedetectorisolatesthedetectorfromallvaria-
14

tionsinloadimpedance.Thispreventschangesin
audiocablelengthsoutsidethetunerfromaffecting
thedetectorperformance.
FMSTEREOMULTIPLEX
Theheartofthemultiplexsectionisa newthird
generationphaselockedloop(PLL)stereodecoder
integratedcircuit(IC).ThisPLLICincorporatestwo
specialsystems,anautomaticvariableseparation
controlcircuittoreducebackgroundnoisewhen
receivingweakstereostations,andtri-leveldigital
waveformgenerationwhicheliminatesinterference
fromSCAsignalsandfromthesidebandsofadja-
centchannelFMsignals.
Thevariableseparationcontrolisoperatedfrom
theIFamplifier'ssignalstrengthdetector.A smooth
transitionisprovidedfrommonotostereoorfrom
stereotomonoatweaksignallevelstoprovidethe
optimumsignaltonoiseratioandbeststereo
separationfortheprevailingsignalconditions.The
circuitoperatesonlyduringstereoreception.Itswit-
chesautomaticallytomonophonicifthe19kHzpilot
toneisabsent.
InthePLLtheinternaloscillatoroperatesat
228kHz,lockedontothe19kHzpilottone.The
228kHzfeedsa 3 stageJohnsoncounterviaa binary
dividertogeneratea seriesofsquarewaves.
SuitablyconnectedNANDgatesandexclusiveOR
gatesproducethetri-leveldrivewaveformforthe
variousdemodulatorsinthecircuit.Theusual
squarewaveformshavebeenreplacedinthePLL
anddecodersectionsbytri-levelwaveforms.These
tri-levelformscontainnoharmonicswhichare
multiplesof2 or3.Thiseliminatesfrequency
translationanddetectionofinterferencefromthe
side-bandsofadjacentstationssincethethirdhar-
monicofthesub-carrier(114kHz)isexcluded.Italso
eliminatesinterferencefromSCAbroadcastssince
thethirdharmonicofthepilottone(57kHz)isexclud-
ed.Unwantedspuriousaudiblecomponentsand
phasejitterinthePLLareinherentlyeliminatedby
thistechnique.
Additionaladvantagesofthephaselockedloop
stereodemodulationaretheeliminationofinduc-
torstominimizedrift,integrallampdrivingcapabili-
tytoindicatethepresenceofthe19kHzpilotcarrier,
excellentchannelseparationovertheentireaudio
frequencyrange,extremelylowdistortion,lowout-
putimpedance,andtransient-freemono/stereo
switching.
AUDIOCIRCUITS
FollowingtheMPXdecoderisthethreeposition
deemphasisswitch.Thethreedifferentpositions
allowtheMR80tobeusedinNorthAmericawith
standard75msdeemphasisandinWesternEurope
andtheFarEastwith50msdeemphasis.The25ms
positionisforusewithanexternalnoisereduction
adapter.
Anelectronicallyswitchedfiltercircuit,im-
plementedwithtwoJ-FETsofa quadJ-FET
package,isusedtoreduceoutofphasenoisewhen
inthestereomodeandtunedtoa weakstation.This
filterisactuallya twin-Tbandpassthatblendsthe
highandlowfrequencies,leavingseparationunaf-
fectedatmid-frequencies.Thisresultsina greatly
improvedstereoimagewhenthefilterisrequired.
Acombinationofthreeinputsareusedtocontrol
theswitchpointofthefilter.Thefirstisthefront
panelswitch.Thefilterisonlyactivewhenthis
switchisintheAUTOorONposition.IntheONposi-
tionthefilterisinthecircuitforallstationsmonoor
stereo.IntheAUTOpositionthefilterwillswitchin
whenthestationistransmittinga stereopilotsignal
andthesignalstrengthisbelow100mV.
InthesamequadJ-FETpackagearethetwoFETs
thatareusedforthemutingcircuit.TheseFETsare
controlledbythelogicalANDingofthreesignals.
Thefirstsignalisthedeviationorcentertune,this
detectswhenthetuneriscorrectlytunedtothe
centeroftheFMchannel.Thesecondsignalisthe
signaltonoiseratio.Onlywhenthereissufficient
signalwillthetunerbeallowedtounmute.Signalto
noiseratioismeasuredbya specialbandpass
amplifiercenteredaround138kHz.Thisfrequencyis
usedtopreventfalsetriggeringduetoadjacent
channelandovermodulationproducts.Thethird
signalistheRFsignallevelthatisderivedfromthe
fivesignaldetectorcircuits.A frontpanelcontrol
(MUTINGLEVEL)adjuststhereferenceleveltoa
voltagecomparator.Theotherinputtothecom-
paratoristhesignalstrengthvoltage.WhentheRF
levelexceedsthepresetreferencelevel,a signalis
senttothemutinglogictobeANDedwiththeother
twosignals.Thisadjustmentallowstheunmute
leveltobesettoanyvaluefrom2mVtogreaterthan
1000mV.
Thiswiderangeisnecessaryforthetunertoscan
properlyinallsignalconditionsandprovidethebest
combinationofeaseofusewithmaximumintersta-
tionnoisesuppression.
19AND38kHzFILTER
AnLCtunednotchfilterisusedtoeliminateany
beatnoteinterferencewiththebiasoscillatorina
userstaperecorder.Thisfilterisdrivenfroma filter
bufferamplifierandterminatedbytheoutputopera-
tionalamplifier.Theseamplifiersprovidethe
necessaryinputandoutputimpedancesforproper
phaseresponse.Theoutputamplifierisalsousedas
anaudiobandpassfiltertopreventunwantednoise
andtransientsfrombeingpassedontothehead-
phoneamplifier.
HEADPHONEAMPLIFIER
Theheadphoneamplifieriscapableofdrivinga
pairofdynamicheadphoneswithlessthan.02%
15

harmonicdistortion.Becauseofitsextremelylow
THDandpowercapability,itisalsothemainoutput
amplifier.
TOUCHSENSOR
Thetouchsensorconsistsofthreefunctional
elements:1)Inputbuffersandstaticprotectioncir-
cuits.2)Latches,and3)Encoder.Thesevensensors:
KNOB,PRESET1 to4,UPandDOWNSCANarein-
putstotheseveninputbufferamplifiers.Theseper-
forma dualfunction.Firsttheinputsarebiasedtoa
highlevelbya veryhighresistance.Secondthebuf-
fersaredesignedtodetecta negativetransition
froma referencelevel.Whena sensoristouched,
thestraycapacityofthehumanbodyshuntssome
ofthisreferencesignaltoground.Thisreference
signalisderivedfromthe228kHzoscillatoronthe
multiplexcircuitboard.Thismeansaltnoisecom-
ponentsofthereferencesignalarea multipleof
19kHz,andwillbefilteredoutbythe19and38kHz
filters.Thesecondphaseofthisreferencesignalis
usedtotransfertheoutputofthebufferamplifiers
intothelatches.Thelatchesareusedastemporary
storagetopreventfalsetriggeringduetostaticand
voltagetransients.
Theoutputfromthelatchedinputsaresuppliedto
theencoder,whichperformstwofunctions.First,it
putsinordertheinputs,assigninghighestpriorityto
thetuningknobandthelowesttothedownscan
sensor.Second,itencodestheinputwiththe
highestpriorityintoa binarycodeddecimalword
andoutputsthistothedecodercircuit.Thisdecoder
reconvertstheBCDwordbackintoa 1 ofsevenline
code,indicatingthesensorthatistouched.Anaddi-
tionalinputtothedecoderisthereferencephasein-
putthatinhibitsthedecoderduringclockedgetran-
sitions.Thisisdonetopreventfalsetriggeringdue
tonoiseglitchesandpartialcontactwiththetouch
sensor.
PRESETSCAN
Thesevenoutputsfromthetouchcontroland
decodergotothepresetscancircuits.Inthepreset
scanisanelectronicswitchanda counter.A switch
ontherearpanelselectswhetherthetunerscansall
stationsoronlythepresetstations.Thecircuit
operatesinthepresetscanmodeasfollows:Whena
pulseisreceivedattherearpanelconnectorthe
counterisindexedbyone,thenthesevenpoledou-
blethrowswitchconnectstheinputtothetuning
controllogictotheoutputofthecounter.Thecon-
trollogicthenselectsthepresetthatisrepresented
bythecounteroutput.Attheendofthepulsethe
counterisdisconnectedandthelockcircuitauto-
maticallyfinetunesthetunertothecenterofthe
channel.
Wheninthescanallstationsmode,theinput
pulseisroutedtothescancircuitryonthetuning
controllogicboard.Thelogiccircuitrywillthen
selecttheautoscancircuitandstartsearchingfor
thenextacceptablestation.Thedirectionofscan
willbethelastselectedscandirectionandwill
changewhenthebandlimitisreached.
Theremoteinputtothetunerisa groundasserted
logiclevelthatisnormallyat+ 15volts.Whenthis
lineisgroundedthetunerwillstartscanning.The
useofthislogicpermitsanynumberofremote
cablestobeconnectedtotheMR80.
CONTROLLOGIC
Thecontrollogicportionofthetunerismadeup
ofverylowpowercomplementaryMOSintegrated
circuits.Byusingthislogicfamilya verysignificant
powerreductionwasrealizedinthedesign.Withthe
lowerpowerconsumption,a veryrealreductionin
theoperatingtemperatureandanimprovementin
theoperatinglifeisachieved.
Averyimportantconsiderationinthedesignofa
digitaltuneristheamountofradiatednoisefromthe
digitalintegratedcircuits.Toachievelownoisethe
controllogicwasmadetooperateina staticmode
toentirelyeliminateanyinterference.Thisallows
thecontrollogicboardtobebuiltwithoutthe
shieldingnecessarytoreduceinterference.
Theseventouchsensorinputsfromthepreset
scanboardarestoredineightC-MOSflip-flop's.The
stateoftheflip-flop'sindicatewhichinputwasac-
tivelast.Onebitisusedforthemaintuningknob,4
bitsareusedtorepresentthe4 presets.Thescancir-
cuitryuses3 bitstotellifthescanisonoroff,setto
scanupordown,andthethirdissettoa zerowhen
thetunerreachesanacceptablestation.Thiscom-
plexgroupofcircuitsprovidesa levelofsophistica-
tionandeaseofoperationnotpossiblebeforeina
tuner.
Severaltimingcircuitsareusedtoprovidethe
varioustimesequencesanddelaysfortheproper
noisefreeoperationofthepresetandscancircuits.
Thefirstofthesemonostablecircuitsisusedasa
poweronclearthatresetsthecircuitstothemain
tuningknobmode.Duringthefourseconddelaythe
lockcircuitisinhibitedandthehighspeedmuting
inputtothemultiplexisheldhightomutethetuner
andpreventanynoiseortransientfromaffectingthe
restoftheuserssystem.Atthecompletionofthis
fourseconddelaythelockcircuitisenabled,locking
thetunertotheincomingfrequencyandunmuting
thetuner.
Whenoneofthefourpresetsisactivated,the
displayandaudioareinhibitedfortwosecondsfrom
whenthesensoristouched.Thelockcircuitis
disabledduringthetimethesensoristouched,to
allowthepresetstobesettotheproperfrequency.
Whenthesensorisreleasedthelockcircuitthen
tunestothecenteroftheFMstation.Duringnormal
operation(notsettingofthepresets)thetouchsen-
16

sorreactsina smallfractionofa secondsothe
tunerappearstochangestationsinstantaneously,
withoutanyinterstationnoiseevenwiththemuting
turnedoff.
Wheneitherofthescansensorsistouchedthe
tunerismutedandthedisplayblankedfortwo
seconds,thisallowsthetunertoreachthenextsta-
tionundernormallisteningconditionswithoutany
interstationnoise.Ifthescanspeedissettoa slow
settingandthemutingisturnedoff,interstation
noiseandveryweakstationswillbeheardafterthe
twoseconddelay,whichisveryusefulwhenremote
tuningisused.
DrivenfromthetuningcontrollogicaresixLED
lamps.Fourareusedtoindicatewhichofthe
presetsareinuse.Theothertwolampsindicatethe
directionofscan.Thesesixlampsandthefrequency
displayindicateata glancehowthetuneris
operatingandwhatpresetorscandirectionhas
beenchosen.
LOCKCIRCUIT
Aninnovativenewcircuitwasdevelopedforusein
theMR80.Thisnewcircuitallowscorrecttuning
withouttheuseofa centertunemeter.TheMR80
willbecorrectlytunedevenifthestationorthe
cablecompanyisnotonitscorrectfrequency.This
isdonebytheuseoftwooperationalamplifiers,
Adeviationsignalfromthedetectorisfedintothe
firstamplifier.Thiscircuitisa logamplifierthatpro-
ducesanoutputvoltageproportionaltothelogof
theDCcomponentinthedetectoroutput.Because
theoutput voltagecontainsaudiosignals, a second
amplifier,connectedasa switchedgainlowpass
filter,removestheaudiosignals.Thisamplifierhas
averyhighgainwhenthelockcircuitisonandunity
gainwhenthelockcircuitisoff.AnN-channelJ-FET
isusedasthegainswitchingelementinthe
negativefeedbackpath.Thefilteroutput,nowcalled
thecorrectionvoltage,isfedintoa scalingcircuit
thatcompensatesforthetuningdiodesnonlinear
frequencytovoltageresponse.Bothofthe
amplifiersoperatewithgreaterthan50dBofgainat
DC.Witha closedloopgainofgreaterthan100dB
thetuningerrorwhenlockedislessthan1kHzat
100MHz,or1 partin100,000.Thiserroristhesame
asa crystalcontrolledsynthesizerwiththeaddi-
tionalbenefitofbeingcorrectlytunedevenifthe
stationorthecablesignalisnotontheproper
frequency.
Becausethelockcircuitwilltracka stationevenif
itdrifts1MHz,thelockcircuitmustbeturnedofffor
theoperatortobeabletotunetheMR80.Thisisthe
reasonforthetouchsensoronthemaintuning
knob.Topreventthetunerfromlockingontoa
strongsignalnexttoa weaksignal,a circuitisused
tosensethestrongadjacentchannelsignalandin-
hibitthelockcircuitundertheseconditions.Onthe
topcovercontrolpanelisa manuallockON/OFF
switchthatinhibitsthelockcircuitonlyifthetuner
isinthemaintuningknobmode.Thisprovisionis
madefortestingthetunerandforcaseswherethe
stationbeingreceivedhasa deepfadetothepoint
oflosinglock.Iftheswitchissettotheoffposition
thelockcircuitwillworknormallyforallthepresets
andthescancircuit,butnotforthetuningknob.
SCANCIRCUIT
WiththevoltagetunedRFsection,automatic
scanningisimplementedwithoutanymovingparts
suchasmotors,flywheels,orstrings.Bytheelimina-
tionofallmovingparts,a muchgreaterdegreeof
reliabilityisachievedandtuningconvenienceim-
proves.
TheMR80scancircuitconsistsoffivesections:
1)switchingcircuit;2)bipolarcurrentsource;3)in-
tegrator;4)bandlimitdetector;and5}theauto-track
circuit.Thescanswitchingcircuitcontrolsthescan
functionbyswitchingtwoflip-flops,thescanon/off
flip-flopandthescanrun/stopflip-flop.Wheneither
ofthescanbuttonsortheremotecontrolstartsa
scancycle,thepresetbuttonsandtuningknobcir-
cuitsareswitchedoff,thelockcircuitisinhibited,
thedisplayisblanked,theaudioismuted,andthe
scanon/offflip-flopturnson.Thedisplayisblanked
andtheaudioismutedfortwoseconds.Thescan
on/offflip-flopswitchestheRFtuningcontroltothe
scanrampvoltage.
Dependingonthescansensortouched,the
bipolarcurrentsourceissettothepropervalue
(negativeforscanup,positiveforscandown).This
currentisadjustedbythefrontpanelSCANSPEED
controlforthepropersearchspeed.Therun/stop
flip-flopstopsorstartsthescansequence.Thisflip-
flopissetwhenevera scanstopsignalissentfrom
themultiplex.Toresettheflip-floponeofthescan
sensorsmustbetouched.
Intheintegratorportionofthescancircuitthecur-
rentisconvertedintoa timedependentrampvoltage
untila stopsignalisreceivedfromthemultiplex.
Whenthetunerhasstoppedona stationthetuning
voltageisstoredona speciallowleakagecapacitor.
Topreventdriftduetoleakagecurrents,guard
trackswereemployedaroundthenegativeinputto
theintegratoroperationalamplifier.Thisamplifieris
aspecialtypewithMOS-FETinputtransistorsthat
haveaninputresistanceofgreaterthan100million
megohms.Withspecialcircuitcomponentsand
printedcircuitlayout,driftinthescancircuithas
beeneliminated.Thepositiveinputtotheopera-
tionalamplifierisusedastheinputforthelockcor-
rectionvoltage.Thecorrectionvoltageisonlyap-
pliedafterthetunerhasstoppedscanningandfine
tunesthetunertothecenterofthestation.
Twocomparatorsconnectedtothetuningvoltage
inputintheRFsectionareusedforbandlimitdetec-
17

tion.Thecomparatorssensewhenthetuning
voltageexceedsthevalueneededfor87.5or
108.1MHzandgeneratesa pulsethattogglesthe
flip-flopcontrollingthebipolarcurrentsource,
changingthedirectionofscan.Ifa personattempts
toscanpastthebandends,bothscanindicatorswill
lightandthetunerwillhangatthebandlimituntil
thesensorisreleased.
Whenanyofthepresetsorthetuningknobareac-
tivetheautotrackcircuitisusedtoforcetheoutput
oftheintegratortoa valueequaltothecurrenttun-
ingvoltage.Duringtheturnondelaytheautotrack
ensuresthattheintegrator'soutputvoltageiswithin
thebandlimits.Thiscircuitallowsthetunertostart
searchingforthenextstationfromthecurrentloca-
tion.
FREQUENCYCOUNTER
Thecounteranddisplayformthedigital
equivalenttotheslideruledialandpointer,butwith
greateraccuracyandreadability.IntheRFsectiona
smallportionoftheoscillatorsignaliscoupledinto
thebufferamplifieronthecountercircuitboard.
Thisbufferamplifierismadewithemittercoupled
logiccircuitsandisusedtochangethesmall
oscillatorsignalintoa levelacceptablebythehigh
speedECLdivide-by-fourcircuit.Theoutputofthe
dividerislevelshiftedtolowpowerSchottkylevels
foruseintherestofthecountercircuit.Thedivided
localoscillatorsignalissampledfor40.96mSbya
synchronousgate,madefroma J-Kflip-flopto
eliminatethe± 1 counterror.Theactualcountingis
donebylowpowerSchottkyintegrateddecade
counters.IFfrequencyoffsetisaccomplishedby
presettingthecounterstothecomplementoftheIF
frequency,893.ThisallowssubtractingtheIFoffset
byaddingthenegativeoftheIFfrequency.
Thegatesignalisderivedfroma stable200kHz
crystaloscillatoranda binarydividermadefromLS
integratedcircuits.Twoothersignalsarederived
fromthedividerchain.Thefirstisusedtotransfer
theinformationinthedecadecounterstothe
displaybuffer.Thesecondisusedtoresetthe
countertothecomplementoftheIFfrequency.
Inthedisplayportion,threeTTLintegratedcir-
cuitsareusedasa latchtostorethefrequencyinfor-
mationandasconstantcurrentsourcestodrivethe
LEDfrequencydisplays.Byusingthelatches,a
flickerfreedisplayisassuredevenwhenthedisplay
ischanging.Theconstantcurrentsourcesimprove
reliabilitybyreducingthenumberofcomponents.
LEDdisplayswereusedbecauseoftheirvisibility,
characterfont,andverylonglife.
POWERSUPPLY
Specialdesignattentionhasbeengiventothe
powersupplysection.Nineseparatepowercircuits
areused.Sixoftheseareregulatedtopreventloss
ofperformanceduringa brownout.The- 15,- 5.2.
5,15and30vuseintegratedcircuit3 terminal
regulators,whilethe3macurrentsourceismade
withdiscretetransistorsbecauseofthehighvoltage
ontheinputterminal.Theremainingvoltagesareus-
edfortheheadphoneamplifierandthetouchcontrol
referencesignaldriver.
LAMPDRIVERS
Mclntosh,recognizingtheneedforimprovedrelia-
bility,hasdesigneda newcircuittodriveincande-
centlamps.Thisnewcircuitpreventsthefilaments
fromfailingduetonotchingwhenoperatedondirect
current.Thisfailuremodecanreducelamplifefrom
onehalftoonetenthofthedatasheetvalue.Inthe
MR80thethreelampsthatareusedforSTEREO,
LOCKandFILTERindicatorsareoperatedonACat
lowerthanratedvoltagetoextendtheusefullifeto
wellinexcessof15years.OnlyMclntoshbringsyou
thisfeature.
18

19

BlockDiagram
20
MclNTOSHMR80