McIntosh MPI 4 User manual

THEMclNTOSHMPI4 MAXIMUMPERFORMANCEINDICATOR
ReadingTime40Minutes
Price$1.25

YourMPI4 MaximumPerformance
Indicatorwillgiveyoumanyyearsof
pleasantandsatisfactoryperformance.
Ifyouhaveanyquestionsconcerningthe
operationormaintenanceofthis
instrument,pleasecontact:
CUSTOMERSERVICE
MclntoshLaboratoryInc.
2ChambersStreet
Binghamton,NewYork13903
Phone:[phone]
TakeAdvantageof3 years
ofFREEFactoryService. . .
FillintheApplicationNOW.
contents
GUARANTEE...1
GENERAL...2
INSTALLATION...2,3
HOWTOCONNECT. . . 3-5
FRONTPANELINFORMATION...6-8
LEVELSETPANELINFORMATION...8
REARPANELINFORMATION...9
INITIALSETUP...9,10
HOWTOUSETHEMPI4 ... 10-18
PERFORMANCELIMITS...18,19
TECHNICALDESCRIPTION...19,20
BLOCKDIAGRAM...21
Guarantee
MclntoshLaboratoryIncorporatedguaranteesthisinstrument
tobecapableofperformanceasadvertised.Wealsoguarantee
themechanicalandelectricalworkmanshipandcomponentsto
befreeofdefectsfora periodof90daysfromdateofpurchase.
Ifsuchdefectsoccur,MclntoshLaboratoryoroneofitsauthorized
agencieswillrepairthedefectatnocosttothepurchaser.This
guaranteedoesnot extendtocomponentsdamagedbyimproper
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orserviceagency.
THREEYEARFACTORYSERVICECONTRACT
Anapplicationfora FREETHREEYEARFACTORYSERVICE
CONTRACTisincludedwiththismanual.Thetermsofthecontract
are:
ForThreeYearsfromdateofpurchase—
1.Mclntoshwillprovideallparts,materialsandlaborneeded
toreturnthemeasuredperformanceoftheinstrumenttothe
originalperformancelimitsfreeofanycharge.TheSERVICE
CONTRACTdoesnotcoveranyshippingcoststoandfrom
theauthorizedserviceagencyorthefactory.
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lntoshinstrumentsatnormalservicerates.Toreceivethefree
serviceunderthetermsoftheSERVICECONTRACT,the
SERVICECONTRACTCERTIFICATEmustaccompanythein-
strumentwhentakentotheserviceagency.
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agency.Iftheinstrumentismodifiedordamaged,asa result
ofunauthorizedrepairtheSERVICECONTRACTwillbecan-
celled.Damagebyimproperuseormishandlingisnot covered
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purchaser.Toprotectyoufrommisrepresentationthiscontract
cannotbetransferredtoa secondowner.
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inthe50UnitedStatesorCanadaonly.
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madefroma Mclntoshfranchiseddealer.
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TRACTmustbepostmarkedwithin30daysofthedateof
purchaseoftheinstrument.
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applicationmustbefilledin.TheSERVICECONTRACTwill
beissuedwhenthecompletelyfilledinapplicationisre-
ceivedatMclntoshLaboratoryIncorporatedinBinghamton,
NewYork,IftheapplicationisnotreceivedatMclntosh
Laboratory,onlytheserviceofferedunderthe90-dayguar-
anteewillapply.
Copyright© 1973ByMclntoshLaboratoryInc.
1

General
installation
TheMPI4 isa laboratory-gradeinstrument.Itprovides
thefacilitytocontinuouslymonitorthequalityoftheper-
formanceofa stereosystem.TheMPI4 cansampleanddis-
playsignalsfromthetuner,preamplifierandpowerampli-
fierwithoutreconnectingcables.Signalsaredisplayesonan
oscilloscopescreencalibratedwithscalesfortuning,
measuringandtesting.
Asa tuningaid,theinstrumentisa guidetoexactFM
stationselectionandprecisetuning.Thescreendisplays
FMsignalstrength,modulationpercentageandmulitpath
interference.Audiosignalsmaybeviewedforstereobal-
ance,strength,phaseandchannelseparation.Outputpower
ofthepoweramplifiercanbeseenatanyinstantduring
programperformance,orstoredtodevelopa trendover
severalminutes.
Withtheadditionoftestrecords,theMPI4 canshow
complianceandtrackabilityofa phonopickup,frequency
responseofthepreamplifierandpoweramplifier,audio
distortionandstereospeakerbalance.
Inoneofitsoperationalmodes,theMPI4 becomesa
"dualtrace"oscilloscope.Whenoperatedinthedualtrace
modetheleftandrightstereochannelsappearsimul-
taneouslyandseparatelyonthescreenfordirectcompari-
son.Theinstrumentalsohas"triggeredsweep."Itpermits
theviewertochoosea singletoneandlockitonthescreen
forcarefulinspection.
Ina searchforconvenientequipment-mountingtech-
nique,MclntoshdevelopedthePANLOCsystem.Pressing
thetwoPANLOCbuttonsonthefrontpaneloftheMPI4
releasestheunittoslideinoroutofitsmounting.This
allowseasyaccesstocableconnectionsattherear.It
bringstoppanelcontrolsintoviewforeasyadjustments,
adjustments.
Ventilationextendsthetrouble-freelifeofaninstru-
mentbypreventingexcessiveinternaltemperatureand
insulationbreakdown.Toaccomplishthis,allowcoolair
toenteratthebottomoftheinstrumentandwarmairto
escapeatthetop.TheMPI4 MaximumPerformanceIn-
dicatormaybemountedinanyposition.Itrequiresa
mountingspace15inchesdeep(38.1cm),17½inches
wide(44.45cm),and6 incheshigh(15.24cm).
TomountintheMclntoshcabinetfollowtheinstruc-
tionsenclosedwiththecabinet.Foranyotherinstallation,
removetheinstrument,PANLOCbrackets,partsbagand
mountingtemplatefromthecarton.RemovetheMPI4
fromtheplasticbagandplaceitupsidedownonthe
shippingpallet.Thenremovethefourplasticfeetfastened
tothebottomofthechassis.
1.POSITIONTEMPLATEANDMARK
Positiontheplasticmountingtemplateovertheareaof
thecabinetpanelwheretheMPI4 istobeinstalled.
Besurethattheedgesoftheequipmentmarkedonthe
templateclearsanyshelves,partitionsorexisting
equipmentlocatedbehindthepanel.Withthetemplate
inplacemarkthesix"A"and"B"holesandfoursmalt
holeslocatingthecornersofthecutout.Next,jointhe
fourcornermarkswithpencillines.Theedgeofthe
templateisusedasa straightedge.
2.DRILLHOLES
Withthedrillperpendiculartothepanel,drillthe
six"A"and"B"holesusinga 3/16inchdrill.THE
SIXHOLESMUSTBEDRILLEDBEFOREMAKING
THECUTOUT.
2

3.SAWCUTOUT
Carefullycuttherectangularopeningontheinsideof
thepencilledrectangle.
4.SECUREMOUNTINGSTRIPS
Installthemountingstrips(suppliedinthehardware
package)ontheinsideofthecabinetpanel.Insert
twoscrews(suppliedinthehardwarepackage)into
thecenterholes("B"holesonthetemplate).Usethe
¾-inchlongscrewsforpanelsunder½-inchthickor
1¼-inchscrewsforpanels½-inchthickorover.Place
amountingstriponthebackofthecabinetpanel.
Alignitwiththethreeholesinthepanelandtighten
thescrew.Thescrewheadshouldpullslightlyintothe
woodpanel.Attachtheothermountingstripbyrepeat-
ingtheprocedure.
5.MOUNTTHEPANLOCBRACKETS
AttachthePANLOCbracketstothecabinetpanel
usingfourscrewsoftheproperlength.Placethetem-
plateoverthemountingscrews.Thescrewsshould
becenteredonthe"A"and"B"holesinthetemplate.
Ifnecessary,loosenthescrewsandpushthemounting
bracketsintoalignmentthenretighten.
6.INSTALLTHEUNIT
Threadthepowercordthroughtheopeninginthe
cabinetpanel.Carefullyslidetheinstrumentintothe
openingsotherailsonthebottomoftheinstrument
engagethetrackonthemountingbrackets.Slidethe
instrumentinuntilitstopsatthead|ustposition
latches.Pressthelatchesinandcontinuetoslidethe
instrumentuntilitsfrontpanelisflushwiththecabi-
netpanel.AtthebottomfrontcornersarethePANLOC
buttons.DepressingthePANLOCbuttonswilllockthe
instrumentfirmlyinthecabinetpanel.Pressingthe
PANLOCbuttonsa secondtimewillreleasetheinstru-
mentYoucanthenslidetheinstrumentforwardtothe
adjustposition.Pressingtheadjustpositionlatches
willallowtheinstrumenttoberemovedfromthe
cabinet.
Howtoconnect
TheMPI4 maybeconnectedtoa stereoreceiver(Fig.
1)ortoa componentsystemwitha separatepreampli-
fierandpoweramplifier(Fig.2).Choosewhichmost
closelyresemblesyoursystem.
AUDIOINPUTS
LowLevelAudioInput
Useoneofthe6-footshieldedcablessupplied,tocon-
necttheleftchanneloutputonyourpreamplifiertothe
LEFTAUDIOINPUTontheMPI4 backpanel.Similarly,
connecttherightchannelpreamplifieroutputtothe
RIGHTAUDIOINPUT.
SPEAKERINPUT
Therearefourcolor-codedpushconnectorsontheback
paneloftheMPI4.Connectthesewithtwopairsofspeaker
cablestotheleftandrightoutputonthepowerampli-
fier.
BlackLeftspeakercommonterminal
GreenLeftspeakerhighterminal
WhiteRightspeakercommonterminal
RedRightspeakerhighterminal
SettheSPEAKERIMPEDANCEswitchontheMPI4 back
paneltoagreewiththespeakersystemimpedance:4W,
8W,or 16W.
TUNERINPUTS
SignalStrengthInput
Mclntoshtunersandreceiversprovidesignalforthe
SIGNALSTRENGTHINPUTata connectormarkedTP1
onthebackofeachtuner.Usingthe3-footlow-capacity
shieldedcablesupplied,connecttheTP1 outputtothe
SIGNALSTRENGTHINPUT.
TOPREVENTHIGHFREQUENCYLOSSES,THESPECIAL
3-FOOTCABLESSUPPLIEDMUSTBEUSED.DONOT
SUBSTITUTEORDINARYAUDIOCABLE.
Forothertunersorreceiverswhichdonotprovidea
signalstrengthoutput,consultthemanufacturerortheir
authorizedserviceagency.
DeviationInput
Mclntoshtunersandreceiversprovidesignalforthe
DEVIATIONINPUTata connectormarkedTP2 ontheback
ofeachtuner.Usingthe3-footlow-capacityshielded
cablesupplied,connecttheTP2 outputtotheDEVIA-
TIONINPUT.
TOPREVENTHIGHFREQUENCYLOSSES,THESPECIAL
3-FOOTCABLESSUPPLIEDMUSTBEUSED.DONOT
SUBSTITUTEORDINARYAUDIOCABLE.
Fortunersorreceiverswhichdonotprovidea devia-
tionoutput,consultthemanufactureortheirauthorized
serviceagency.
3

HOWtoConnect
FIG.1 CONNECTINGTHEMPI4 TOSTEREORECEIVER
(TYPICALCONNECTIONS)
STEREORECEIVER
ACCORD
ENVIRONMENTAL
EQUALIZER.IF
USED
BLACK
GREEN
RED
WHITE
4

FIG.2.CONNECTINGMPI4 TOCOMPONENTSYSTEM
(TYPICALCONNECTIONS)
STEREOFMTUNER
LEFT
SPEAKER
5
RIGHT
SPEAKER
ENVIRON-
MENTAL
EQUALIZER
(OPTIONAL)

FrontPanelinformation
FIG.3 FRONTPANEL
MODESELECTOR
TheMODESELECTORpushbuttonsselectthetypeof
displayseenonthescreenoftheMPI4.Eachofthefive
pushbuttonsselectsa trace—aglowinglineofgreenlight—
whichshowsa varietyofinformationaboutsignalsfrom
thetuner,preamplifierorpoweramplifier.Toassistthe
evaluationofeachdisplay,thereticleinfrontofthe
screenismarkedwithcalibrationpointswhichareusedto
measuresignalcharacteristics.AsMODESELECTOR
buttonsarepressed,thescreenreticleisilluminatedin
thesecolors:
ModeColor
MultipathBlue
StereoRed
LevelAmber
SweepGreen
MULTIPATH
WhenproperlyconnectedtoanFMtunertheMPI4
willdetectanddisplaymultipartreception.Multipart
receptionistheresultofa reflectedsignalarrivingatthe
tunerantennaslightlylaterthanthedirectsignal.By
rotatingor repositioningtheFM antennait is possibleto
reducemultipathreception.TheMPI4 makesiteasyto
knowwhentheFMantennaisorientedforthebestrecep-
tionofanystation.
ToshowmultipartreceptiontheMPI4 displaysin-
stantaneoussignalstrengthversusfrequencydeviation.
Signalstrengthisshownasverticaldeflectionofthein-
dicatordisplaybeam.Frequencydeviationisshownas
horizontaldeflection.Multipathreceptionappearsasa
peakorvalleyinthedisplay.
MultipathreceptiondegradesFMtunerperformancein
severalways:
1.Usuallythereisanincreaseinbackgroundnoise
level.
2.Distortionisoftenheardintheprogramsignal
3.Stereoseparationmaybereduced.
4.Thestereoeffectmaybecompletelylost.
5.Stereoindicatorsmayfailtofunction,orfunction
erratically.
Toovercomemultipartreceptionitisusuallynecessary
toturntheantennatoreceivetheFMsignalbyonepre-
dominantpath.Rotatinga directionalantennaiseffective
atcorrectingmultipathreception.Inareaswherea simple
antennasuchasa dipoleisusedrepositioningtheantenna
canachievesimilarresults.
IntheMULTIPATHmodetheMPI4 isa veryeffective
tuningindicator:
1.Signalstrengthisshownbytheverticalpositionof
thedisplaytrace.Thehigherthepositionofthe
tracethegreaterthesignalstrength.
2.Correcttuningoccurswhenthedisplaytraceis
centeredhorizontallyonthescreen.Sincethedis-
playtraceeffectivelyfollowsthetunerIFresponse
curve,centeringthetracetunesthedetectorto
thecenteroftheIFcurve.
Thedisplayofthesignal,whenthereisnomultipath
receptionaffectingtheprogram,appearsasa smooth
curvingline,(Fig.4).Thecalibrationpointsarethetwo
100%marksatthebottomofthescreen.Astheprogram
materialgrowslouderorsofter,thetraceexpandsand
contracts.The100%pointsindicatethehighestmodula-
tionpercentagenormallytransmittedbyanFMstation.
(Amoredetaileddescriptionappearsinthe"HowtoUse
Section.")
STEREO
Astereoprogramcausesa complexdisplaywhich
variesbetweena circularshapeandanellipticalshape.
Amonoprogramcausesthedisplaytobea slantedline.
Withanin-phasemonoprogram,thesignalfallsbetween
theL + R boundaries;inout-of-phasemonoprogramthe
tracefallsalongtheL — R boundaries.
6

FIG.4 MULTIPATHDISPLAY
LEVEL
TheaudioLEVELofstereosignalsisdisplayedastwo
verticalcolumnsonthescreen( Fig.5).Theheightof
eachcolumnisdeterminedbythepoweroramplitudeof
theinputsignal.Thecalibrationscalebetweenthetwo
columnsandthepositionofthePOWERLEVELknob
indicatetheactualpowerofthesignal.Thenomenclature
ontherecticleisshownindecibels(dB).
FIG.5 LEVELDISPLAYOFL & R CHANNEL
DUALTRACE
WhentheDUALTRACEbuttonsarepressed,theL
(Left)programandtheR (Right)programsareseenas
separatetracesonthescreen.Theleftchannelisthe
uppertrace;therightchannelisthelower.
IfonlyonebuttonunderDUALTRACEispressed(L
orR),thescreendisplaysonlythesignalselected.
SWEEPandSWEEPFREQUENCY
Musicalprogrammaterialhasmanyfrequenciesandit
maybedisplayedasa complexjumbleofwavesthatare
difficulttoview.Bychangingthetiming,orsweep,ofthe
trace,theMPI4 canlockontoanyportionoftheaudio
spectrum.Theresultisa clear,easy-to-viewwavethat
remainsstableonthescreen.UsetheSWEEPFREQUENCY
pushbuttonstoprovidea choiceoflowrangefrequencies
(20-200Hz),mid-rangefrequencies(200-2000Hz)and
high-rangefrequencies(2000-20,000Hz).UsetheSWEEP
controlforfinetuningofthesweepwithinanyrange.
GAIN
TheGAINcontroloperatesonlywhenpreamplifier
signalsarebeingdisplayed.TheGAINcontrolvariesthe
verticalsizeoftheimageinallaudiomodesofoperation.
Whena signalofunknownstrengthistobeviewed,start
withtheGAINfullycounterclockwise,thenturnthecon-
troluntilthedisplayreachescomfortableviewingsize.
WhentheGAINcontrolissettoOFF,ACpowerisremoved
fromtheMPI4.
POWERLEVEL
ThePOWERLEVELswitchdeterminesthefull-scale
calibrationinwattsofsignalsdisplayedonthescreen.
Whentheswitchisturned,a redindicatorilluminates
theselectedpowerrangeoftheWATTScolumnalong
therightsideofthescreen( Fig.6).Theserangesmeas-
uretheactualpowerlevelofthepoweramplifier.(How
tousetheserangeswillbedescribedinthenextsection.)
Whentheredindicatorisoppositethetopmostmarking,
PREAMP,thescreendisplaystheamplitudeofthepre-
amplifiersignal.
FIG. 6
INTENSITY
TheINTENSITYcontroladjustsbrightnessofthetrace
onthescreen.Forlongestscreenlife,usetheminimum,
comfortableviewinglevel.
Thetracewilldisappearwhenthereisnoinputsignal
present.Forextendedcathoderaytubelifea built-inauto-
maticintensitycontrolextinguishesthetraceduring
non-signalperiodstopreventa stationaryspotfrom
burninga permanentmarkinthescreensurface.
VERTICAL
TheVERTICALcontroladjuststheupanddownlocation
ofthetraceonthescreen.
HORIZONTAL
TheHORIZONTALcontroladjuststhelefttorightloca-
tionofthetraceonthescreen.
7

INPUTAUDIO
Amicrophone,taperecorder,FMtunerorotherequip-
mentnotnormallyconnectedtotherearpanelconnec-
tionoftheMPI4 maybepluggedintotheINPUTAUDIO
jackonthefrontpanel.Signalsaredisplayedonthescreen
forobservationortesting.Duringthistime,thePOWER
LEVELselectormustbesettothePREAMPposition.The
sizeofthedisplayisadjustedbytheGAINcontroland
TRIMcontrols.
Somemicrophonesmaynotgenerateenoughsignalto
drivethedisplaytocomfortableviewinglevels.This
canbecorrectedbyaddinga microphonepreamplifier
betweenthemicrophoneandAUDIOINPUTjack.
LevelsetPanel
information
AUDIOTRIMLEFT
Adjuststraceheightfora leftchannelpreamplifieraudio
signal.
AUDIOTRIMRIGHT
Adjuststracewidthforstereodisplayortraceheight
forsweeporleveldisplayfroma rightchannelpreampli-
fieraudiosignal.
SIGNALSTRENGTH
Adjuststraceheightabovethebottomorbaselineof
themultipathdisplay.
DEVIATION
Adjuststracewidthofthemultipathdisplay.
MULTIPATHPOLARITY
TheMULITPATHPOLARITYswitchcontrolspolarityof
thesignal-strengthsignal.Theminuspositionisusedwith
mosttuners.
TRACESEPARATION
TheTRACESEPARATIONcontroladjuststhedistance
betweenthetwotracesintheDUALTRACEmodeof
operation.
SWEEPEXPANSION
TheSWEEPEXPANSIONcontroladjustsmaximumwidth
ofthetracedisplay.SWEEPEXPANSIONoperatesonly
whenoneorbothoftheDUALTRACEpushbuttonsare
pressed.
TRIGGERSOURCE
TheTRIGGERSOURCEswitchselectsthesignalused
totriggerthedisplaysweep.IntheDUALTRACEmode
thesweepmaybetriggeredfromtheleftorrightchannel,
orfromthe60hertzlinefrequency.
FOCUS
TheFOCUScontroladjustssharpnessofthetrace.
LOWPASSFILTER
TheLOWPASSFILTERswitchinsertsorremovesa filter
thateliminates19,000and38,000Hzstereoreference
signals.Theseunwantedsignalsproducefuzzyandin-
distincttracesonthescreen.Themostusefulpositionis
theINposition.Onlyinspecialtestproceduresisitneces-
sarytoswitchthefilterOUT,
RETICLEILLUMINATION
TheRETICLEILLUMINATIONswitchturnsillumination
ofthescreenscalesonoroff.
LEVELMODE
IntheNORMALpositionthetwocolumnsriseandfall
likeVUmeters.InthePEAKpositionthecolumnsindicate
the"average"peaklevelforsignalsthatchangecon-
tinuouslyinamplitude.TheResetpositionresetsthe
Peakcircuitryandfreezesthehighestlevelachievedby
theaudio.
FIG.7 LEVELSETPANEL
8

RearPanelinformation
FIG.8 REARPANEL
TUNER-SIGNALSTRENGTH(TP1)
Usethe3 footlowcapacitycablesprovidedtoconnect
TestPointNo.1 (TP1)ona Mclntoshtunertothisinput.
TOPREVENTHIGHFREQUENCYLOSSES,THESPE-
CIAL3-FOOTCABLESSUPPLIEDMUSTBEUSED.DO
NOTSUBSTITUTEORDINARYAUDIOCABLE.
TP1 suppliestheMPI4 witha voltagewhichispropor-
tionaltothestrengthofa receivedFMstation.Thetrace
onthescreenwillmoveverticallytoindicaterelative
signalstrength.
TUNER-DEVIATIONINPUT(TP2)
Usethe3 footlowcapacitycableprovidedtoconnect
TestPointNo.2 (TP2)ona Mclntoshtunertothisinput.
TOPREVENTHIGHFREQUENCYLOSSES,THESPE-
CIAL3-FOOTCABLESSUPPLIEDMUSTBEUSED.DO
NOTSUBSTITUTEORDINARYAUDIOCABLE.
TP2 suppliesa voltageproportionaltothemodulation
(deviation)oftheFMsignal.Thetraceonthescreenwill
expandina horizontaldirectionproportionaltoa station's
modulation.
PREAMP-LEFTAUDIOINPUT
Theleftoutputofa preamplifierconnectstothisinput.
InsomemodesofMPI4 operation,theleftchannelaudio
signalcausesverticalmovementofthetraceonthescreen.
PREAMP-RIGHTAUDIOINPUT
Therightoutputofa preamplifierconnectstothisinput.
InthestereomodeofMPI4 operation,therightchannel
causesthetraceonthescreentomovehorizontally,in
thesweeporlevelmodestherightchannelcausesthe
tracetomovevertically.
PREAMP-LEFTAUDIOOUTPUT
TheLEFTAUDIOOUTPUT|ackisdirectlyconnected
totheLEFTAUDIOINPUTjackoftheMPI4.Usethe
LEFTAUDIOOUTPUTjacktoconnectthepreamplifier
outputtotheleftpoweramplifierinput.
PREAMP-RIGHTAUDIOOUTPUT
TheRIGHTAUDIOOUTPUTjackisdirectlyconnected
totheRIGHTAUDIOINPUTjackoftheMPI4.Usethe
RIGHTAUDIOOUTPUTjacktoconnectthepreamplifier
outputtotherightpoweramplifierinput.
POWERAMP-SPEAKERIMPEDANCE
ThePOWERAMP-SPEAKERIMPEDANCEselectorcali-
bratestheMPI4 tothespeakerimpedanceinuse:4W,
8Wor 16W.
POWERAMPCONNECTIONS
ThePOWERAMPLIFIERpushconnectionsare:
BlackLeftAmplifierCommon
GreenLeftAmplifierHigh
WhiteRightAmplifierCommon
RedRightAmplifierHigh
ACPOWEROUTLET
TheACpoweroutletmaybeusedtoprovideACto
additionalequipmentdrawingupto350watts.Theoutlet
isnotfusedandisonwhenevertheMPI4 powercordis
connectedtoanACpoweroutlet.
FUSE
The0.5AmperefuseprotectsonlytheMPI4.Itdoes
notprotectadditionalequipmentpluggedintotheadjacent
ACpoweroutlet.Forcontinuedprotectionreplacethefuse
withlikevalueonly.
InitialSetup
AfterconnectingtheMPI4 asdescribedintheprevious
section,turnonallequipment.ReleasethePANLOCbut-
tonsandslidetheMPI4 outtotheadjustposition.This
allowsaccesstothelevelset(toppanel)controls.Next:
1.SettoppanelLEFTAUDIOTRIMandRIGHTAUDIO
TRIMfullycounterclockwise,theSIGNALSTRENGTH
andDEVIATIONfullycounterclockwise,theMULTI-
PATHPOLARITYtominus,theFOCUScontroltomid
position,theLOWPASSFILTERto"in",andthe
LEVELMODEswitchtoNORMAL.
9

2.SetfrontpanelGAINcontrolfullycounterclockwise
(butnottoOff),theINTENSITYcontrolfullyclock-
wise, andthePOWERLEVELswitchtoPREAMP
(fullyclockwise).
3-DepressfrontpanelSTEREOpushbutton.
4.UsingthefrontpanelHORIZONTALandVERTICAL
controls,movethespotoflighttothecenterofthe
screen,directlybehindthe3 intheLEVELcolumn.
5.Selecta monosignalsource.
6.AdjusttoppanelLEFTAUDIOTRIMandRIGHTAUDIO
TRIMtothemidpointintheirclockwisetravel.
7.AdjustfrontpanelGAINtoobtaina 1-to2-inch
pattern,andre-adjustbothtoppanelAUDIOTRIM
controlstoobtaina patternsimilartoFig.9.
FIG.9 STEREODISPLAYOFA MONOSIGNAL
ByadjustingthedisplaywithintheL + R guide,
thedisplayisbalancedforequalamplitudeleftand
rightchannels.
8.Adjustintensitycontrolfora comfortablebrightness.
9,AdjusttoppanelFOCUScontrolforclearesttrace.
10-SetthetoppanelTRIGGERSOURCEswitchtoLEFT.
11.DepressthefrontpanelL button.
12.DepressthefrontpanelSWEEPFREQUENCY20-200
button.
13.AdjustthefrontpanelSWEEPcontroltotheapproxi-
matemidpointofitsrange.
14.AdjustthetoppanelSWEEPEXPANSIONcontrolto
obtainthepatternshowninFigure10.Thecontrol
shouldpositionnearthe1 marking.
15.DepressthefrontpanelR button.Determinethatthe
patternissimilartothatobtainedinFig.10.
16.Depressboth frontpanelL andR buttons.
17.AdjusttoppanelTRACESEPARATIONtoobtainthe
patternshowninFigure11.
FIG.11DUALTRACEDISPLAY
18.DepressthefrontpanelLEVELbutton.
19.AdjustthefrontpanelPOWERLEVELknobtoobtain
thepatternshowninFigure12.
FIG.12LEVELDISPLAYOFL & R CHANNEL
20.DepressthefrontpanelMULTIPATHbutton.
21.Observethatthespotoflightisatthebottomcenter
ofthescreen.
22.AdjusttoppanelSIGNALSTRENGTHcontroltoposi-
tionthespotabovethehorizontalcenterlineofthe
screen:(Ifthespotoflightmovesdownwardas
thetoppanelSIGNALSTRENGTHcontrolisadjusted,
setthetoppanelMULTIPATHPOLARITYswitchto
itsoppositesetting.)
23.AdjustthetoppanelDEVIATIONcontroltoobtain
thepatternshowninFigure13.
HOWtousetheMPI4
MULTIPATHMODE
MultipathiscausedbyanFMsignalarrivingatyouran-
tennabytwo(ormore)paths,a directonebetweenanFM
FIG.10SINGLETRACEDISPLAY
10

stationandyourantenna,anda reflectedpathwhichcauses
partofthesignaltoarriveslightlylaterintime.Such
signalsusuallydegradestereoreception.Typicalmulti-
pathsymptomsincludepoorchannelseparation,distortion,
noiseorbuzzingintheprogramanderraticoperation
ofa tuner'sstereoindicator.
MultipathfreereceptionisshowninFigure13.Thetrace
isformedbya combinationofsignalstrengthandmodula-
tion(orloudnessoftheprogrammaterial).Sincesignal
strengthraisesthepatternina verticaldirection,the
higherthetrace,thestrongerthestation.A powerful
localstationcanbeexpectedtobringthetracetoabout
½-or¾-inchesbelowthetopofthescreen.Weakstations
producelowerheightsonthescreen.
FIG.13MULTIPATHFREEDISPLAY
Programmodulationcausesthetracetoexpandina
horizontaldirection.Thepattern,therefore,widensin
stepwiththeaudiointensityoftheprogrammaterial.
Figure14showsa displayhavingmultipath.Thedips
andpeaksaretheresultofa reflectedsignalarrivingat
thetunerantennaslightlylaterthanthedirectsignal.
FIG.14MULTIPATHINTERFERENCE
Bycombiningdisplaysofstrengthandmodulation,
theMPI4 willnotonlyshowmultipath,butis,inaddition,
anaccuratetuningindicatorAdjusttheFMtuningdial
untilthetracereachesitshighestpoint,whilealsobeing
centeredhorizontallyonthescreen.Centeringthetrace
placesthesignalatthecenterofthetuner'sIFresponse
curve,themostdesirablepoint.Anexampleofa detuned
stationisshowninFig.15:notehowthecurveisshifted
totheleftonthescreen.Correctthetuningbyadjusting
thetunerstuningknobtocenterthetrace.
FIG.15DETUNEDSTATION
Multipathproducesseveralvisiblesymptonsonthe
screen.Peaksorvalleysmayappearonthecurve,asshown
inFig.16.Note,too,howtheentiredisplayisshifted
FIG.16MULTIPATH& DETUNED
totheleftwhichindicatesa combinationofbothdetuning
andmultipathreception.Ingeneral,a tracethatisnot
smoothsuffersfrommultipathcontamination.Insevere
cases,multipathcausesconsiderablefuzzinessorblurring
oftheoveralldisplay.
Multipathismostoftenovercomebychangesinantenna
direction.Foroutdoorantennaswitha rotator,aiming
theantennaina differentdirectionusuallyhelps.Indoor
dipolesorsimilarantennamayalsoberepositioned.In
allcases,bestresultsareclearlyindicatedontheMPI4
screen.
MakesurethattheMPI4 ispropertysetup.
1.TurnthePOWERLEVELswitchtothePREAMP
position.
2.SettheGAINcontrolfullycounterclockwise(but
not toOFF),andtheINTENSITYcontrolfullyclock-
wise.
11

3.DepresstheSTEREObuttonandcheckifthespot
oflightisinthecenterofthescreen.Ifnot,use
theHORIZONTALandVERTICALcontrolstocenter
thespot.
TooperatetheMPI4 intheMULTIPATHmode:
4.DepresstheMULTIPATHbuttonandsettheFM
tunertothedesiredstation.AdjusttheINTENSITY
controlfordesiredbrightness.
5.AlternatelyadjustantennadirectionandFM
tuningtoobtainthehighestsignalstrengthand
leastmultipath,asshownintheillustrations.
STEREO
Inthismode,theMPI4 displayssignalssampledfrom
thepreamplifierorpoweramplifieroutput.TheLeftchan-
nelsignalscausethetracetodeflectina verticaldirection.
Rightchannelsignalsextendthetracealonga horizontal
line.Randomlyphasedstereosignalswillproducea pat-
ternonthescreenappearinglike"aballoftwine."(Fig.
23)Ifleftandrightsignalsarepresentinequalamounts
andequalphase,thedisplayisa diagonallinealongthe
screen'sL + R line(Fig.17).
FIG.17INPHASE& BALANCED
ThisdisplayalsoappearswhentheFMtunerorother
programsourceisdeliveringa monoprogramsinceright
andleftchannelsareequal.
Ifonlya leftchannelispresent,thetracewillextend
onlyintheverticaldirection.Ifonlya rightchannelis
presentthetracewillextendonlyinthehorizontaldirec-
tion.Withtheseindications,youcansettheprecisebalance
ofa stereosystem.
BALANCEANDPHASECHECK
Makesurethespotisproperlycentered(Steps1,2
and3 onpages11,12).Then:
1.DepresstheSTEREOpushbutton.
2.Setthepreamplifierorotherprogramsourceto
delivera monosignal.
3.AdjusttheGAINcontroltoobtainapproximately
a2-inchdisplay.
4.Balancetheprogramsourcebymakingthetrace
onthescreenfallpreciselyalongtheL + R line.
Thisisdonebyadjustingtheleftandrightgain(or
balance)controlsonthepreamplifier.Ifthescreen
producesa tracelikethatofFigure17,electrical
balanceandphasearecorrect.Ifthetraceisre-
versed,(Figure18)thechannelsareelectrically
balanced,butoutofphase.
FIG.18BALANCEDBUTOUTOFPHASE
Considerotherpossibletracesandvariationswhich
mayappearduringthistest.InFigs.19and20forex-
ample,bothtracesaretiltedtowardtherightwhichin-
dicatesthetwochannelsarecorrectlyinphase.Butsince
thetracesfailtolineupwiththediagonalscreenL + R
calibrationtheyarenotequalinelectricalstrength.In
Fig.19therightchannelhasgreateramplitudethanthe
leftchannel,andcausesthetracetotilttowardthehori-
zontal.InFig.20,thehighverticaltiltofthetracein-
dicatesexcessiveleftchannelstrength.ThecorrectL + R
angleappearswhentheamplifiergaincontrolsaread-
justedforproperbalance.Figs.21and22showthesame
effectsofelectricalunbalance,aswellasanout-of-phase
condition.
FIG19 PHASEBUTUNBALANCED
Theacousticalbalanceofthestereosystemisaffected
bymanythingsincludingroomacoustics,furnitureplace-
ment,roomshape,smalldifferencesinloudspeakers,etc.
Electricalbalanceandacousticalbalancemaynotagree.
12

FIG.20INPHASEBUTUNBALANCED
FIG.21OUTOFPHASE& UNBALANCED
FIG.22OUTOFPHASEANDUNBALANCED
SEPARATIONCHECK
Astereoprogramcreatesanimageonthescreenwhich
vanesbetweenanellipticalandcircularpattern.Although
thepatternisirregularandchanging,itispossibleto
judgetheapproximateamountofseparationbetween
channels.Tomakethischeckmakesurethespotisproperly
centered,then:
1.DepresstheSTEREObutton.
2.Setthepreamplifierorotherprogramsourceto
thestereomode.
3.AdjusttheGAINcontroltoobtainapproximatelya
2-inchdisplay.
Stereoseparationisusuallydictatedbytheprogram
source.Asyouviewthescreenandlistentoa stereopro-
gramthepatternmayfollowseveraltrends.Whenitex-
tendsoutwardineverydirectionandapproximatesa circle,
itisindicatingexcellentstereoseparationbetweenchan-
nels.AnexampleisshowninFig.23.
FIG.23STEREODISPLAY
Ifthepatterntendstowardanellipticalshape,asin
Fig.24,stereoseparationislessthanoptimum.
FIG.24REDUCEDSEPARATION
Apatternwhichtiltstowardtheleft,asinFig.25not
onlysuggestsreducedstereoseparation,butindicatesan
out-of-phaseconditionintheprogrammaterialInjudging
anyofthepatternsjustdescribed,allowtheprogram
materialtoplayforenoughtimefora trendtodevelopin
thedisplay.
LEVELMODE
IntheLEVELmodeofoperationtheleftchannelappears
asa leftverticalcolumnonthescreen,whiletherightchan-
nelappearsasa rightverticalcolumn.DepresstheLEVEL
pushbuttonandthedisplayshouldagreewiththeone
showninFig.26duringa stereoprogram.
SignalstobeviewedareselectedbythePOWERLEVEL
switch.IftheswitchisinthePREAMPposition,thepre-
L3

FIG.25OUTOFPHASE
FIG.26LEVELDISPLAY
amplifieroutputsaredisplayed,andtheirheightscanbe
adjustedbytheGAINcontrol.Forotherpositionsofthe
POWERLEVELselector,theGAINcontrolisdisabledand
poweroutputfromthepoweramplifierisindicatedon
thescaleinrangesfrom100wattsto0.1watt.The
levelcolumnsrespondtothepeakvoltagepresentin
thesuppliedpoweramplifiersignal.Thepowercalibra-
tionisinaveragewattsforsinewavesignals.Eachstep
ofthePOWERLEVELswitchindicatesa differenceof
5dBinpoweroutput.TurnthePOWERLEVELswitchuntil
youdiscovera positionwhichcompletelycontainsthe
peaksoftheprogrammaterial.Toconvertthedisplay
readingstoactualpoweramplifieroutputinwatts,usethe
PowerTable,Fig.31.
Example:AssumethePOWERLEVELcontrolissetso
theredindicatorisopposite"10"ontheWATTSscale.
Whileplayingprogrammaterial,assumethetracereaches
aheightof"+1"ontheLEVELSCALE(centerofthescreen).
ConsultthePOWERTABLEandfind"+1"intheLEVEL
SCALEcolumnatleft.Next,readtotherightuntilyou
reachthe"10"columnheadedundertheWATTSheading.
Thefiguregiventhereistheexactwattageoutputofthe
poweramplifier.Inthisexample6.3watts.
LEVELMODE
ThetoppanelLEVELmodeisactivatedwhentheMPI-4
LEVELbuttonispressed.WiththeLEVELmodeswitchin
theNORMALpositiontheheightofthetwocolumns,as
readonthecenterdBscale,isanindicationoftheaudio
level.Theverticallinesonthescreenriseandfallinstep
withtheprogrammaterial.Thecolumnsriseveryquickly,
(250msrisetime)butdecaysomewhatslowly(½sec.
decayrate).
WiththeLEVELmodeswitchinthePEAKmodethe
twocolumnsindicatethe"average"peakvalueofthe
audiowaveform.Thetwocolumnsriseslower(approx.
½sec.)thanintheNORMALmodeandtheyalsofall
slower(25sec.decayrate).Forsoundthatcontinuously
changesinamplitudethismodewillgiveanindication
ofthe"average"peaklevel.Fora sinewave(acontinuous
tone)theNORMALandthePEAKwillgivethesamedB
reading.
TheRESETpositionoftheLEVELmodeswitchquickly
dischargesthe"average"Peaktimingcircuitformaking
another"average"Peakmeasurement.
Insomeinstances,itisdesirabletostoptheaction
andobservethehighestpointachievedbytheaudio
signalovera periodoftime.Thispermitsclosecompari-
sonbetweenthehighestlevelsattainedbyleftandright
channelsandsimplifiestheirmeasurementagainstthe
scalesonthescreen.Thismaybedonebyplacingthe
LEVELMODEswitchintheRESETposition.Thisallows
thechangingsignaltobuildupanddisplayitshighest,
orpeakindication.Ifa higherpeakcomesalong,while
theswitchisstillheld,thetwocolumnswillgouptothe
highervalue.Ifthepowerlevelswitchisina wattposition
thetwocolumnswillindicatethe"equivalentpeakaverage
power"beingdeliveredtotheloudspeakers.
Thedecaytimefor"Peak"readingswhileintheRESET
positionis100seconds.(Fora sinewavethepeakvalue
asreadintheRESETpositionwillbeslightlygreaterthan
intheNORMALandPEAKpositions.)
ReturntheswitchtoNORMALforconventionaldisplay.
SWEEPMODE
IntheSWEEPmodetheMPI4 operatesasa standard
audiooscilloscope.Inthismodeitispossibletoviewin-
dividualaudiocyclesintheprogram.Sincemostprogram
materialconsistsofmanytones,theMPI4 maybead-
justedto"trigger"atnearlyanyfrequencyintheaudio
spectrum.Thisprovidesa cleardisplayoftherangeof
interest.Ifyouwishtoviewtonesinthelowerendofthe
audiorange,pressthe20-200pushbuttononthefront
panel.AlsopresstheL orR buttonundertheMODESELEC-
TOR.Astheprogramplays,youshouldbeabletofreeze
oneormorecyclesonthescreenbyfurtheradjustment
oftheSWEEPcontrol(whichactsasa finetuningcontrol).
AsingletracedisplayisshowninFig.27.
Itisalsopossibletoroughlyestimatethefrequencyof
theaudiotonedisplayedonthescreen.AssumetheSWEEP
FREQUENCYbuttonissetto20-200andtheSWEEP
controlisturnedfullycounterclockwise.Atthistime,the
screenis"sweeping"20timespersecond.Ifoneaudio
14

FIG.27SINGLETRACESWEEP
cycleappearsstationaryonthescreen,itisa 20Hztone.
If10cyclesappearonthescreenatthesamesettings,the
toneis200Hz.
Toexamineaudiotonesinthemid-range,pressthe200-
2,000button.FurtheradjustmentoftheSWEEPcontrol
shouldlockthewaveformonthescreen.Again,anesti-
mateoffrequencymaybemade.IftheSWEEPissetfully
counterclockwise,thetraceissweepingattherateof
200Hz.Countthenumberofcyclesonthescreen,multiply
by200,andtheresultistheaudiofrequency.
TonesinthehighestrangeareobservedwiththeSWEEP
FREQUENCYbuttoninthe2,000-20,000band.Ifthe
SWEEPcontrolissetfullycounterclockwise,(a2000Hz
sweep),twocyclesonthescreenrepresenta 4000Hz
tone;threecyclesarea 6000Hztone,etc.
Thescreencansimultaneouslydisplayleftandright
stereochannelsasa dualtrace,asshowninFig.28.To
viewbothsignals,depressL andR pushbuttonsofthe
DUALTRACEMODESELECTOR.
FIG.28DUALTRACEDISPLAY
Itispossibletomagnifythedisplayforcloserviewingby
adjustingtheSWEEPEXPANSIONcontrolonthetoppanel
asdesired.
PHONOPICKUPCOMPLIANCEANDTRACKINGCHECK
Withtheaidofa testrecord,complianceandtrackingof
apickupmaybechecked.Followtheinstructionsonthe
testrecordjacketandmakecertainthespotontheMPI4
isproperlycentered,then:
1.DepresstheSTEREObutton.
2.Startthephonoturntableandsetthepickuponthe
appropriatetestband.
3.Ad|usttheGAINcontroltoobtainapproximatelya
2-inchdisplay.Figure29showsgoodcomplianceand
tracking,whileFigure30showsdistortiondueto
impropertracking.
FIG.29GOODTRACKING
FIG.30IMPROPERTRACKING
FREQUENCYRESPONSECHECK
Checkthefrequencyresponseofyoursystemwiththeaid
ofa testrecord.ThegraphinFig.31showsanidealRIAA
curveusingtheCBSSTR100testrecord.Makethistest
andallsinglefrequencytestsatlowacousticlevelsto
preventpotentialloudspeakerdamage.Toperforma
frequencyresponsecheck:
1.Playthe1000Hztesttoneonthephonograph.
2.Adjustthepreamplifiervolumecontrolforanade-
quatesoundlevel.Becautious.Theuseofloudsingle
frequencyprogrammaterialcanoverloadloudspeaker
systems.
3.SetthePOWERLEVELselectortoa settingwhichpro-
videscolumnheightsclosesttothe0 dBmarkonthe
levelscale.
4.Adjustyourpreamplifiervolumecontrolstoobtain
precise0 dBreadingsforbothcolumnsusingthe
15

1000Hztesttone.
5.Playtheothertonesonthetestrecordandwrite
downthecolumnindicationsforeachfrequency
playedonthetestrecord.
6.TransferthereadingsobtainedinStep5 tothe
graphinFigure33.Compareyourcurvewiththe
curveonthegraph.A deviationof3 dBisacceptable.
FIG.31POWERTABLE
PHONOCHANNELSEPARATIONCHECK
Checkchannelseparationofyoursystemwiththeaid
ofa testrecord(suchastheCBSSTR100).
Makethistestandallsinglefrequencytestsatlow
acousticlevelstopreventpotentialloudspeakerdamage.
Toobservetheresultsfollowtheinstructionsfurnished
withthetestrecordand:
1.DepresstheLEVELbutton.
2.Playtheleftchannelspotfrequencybandonthe
record.
3.SetthePOWERLEVELselectortoa positionthat
yieldsapproximately0 dBdeflectionontheleft
column.
4.Youshouldobtaina displaylikethatshowninFigure
32.Thedifferenceinheightbetweenleftcolumnand
rightcolumnindicateslefttorightchannelseparation
indB.ThePOWERLEVELswitchmaybeadvancedto
increasetheleveloftherightvolumeifnecessary.
EachstepofthePOWERLEVELswitchadds5 dB.
(20dBisgenerallyconsideredfair,30dBgoodand
40dBexcellent.
Repeatsteps2,3 and4 butplaytherightchannelfor
righttoleftchannelseparationmeasurements.
FIG.32CHANNELSEPARATION(Approx15dB)
AMPLIFIERLINEARITYCHECK
Withtheaidofa testrecordyoumayperformanampli-
fierlinearitycheck.
Makethistestandallsinglefrequencytestsatlow
acousticlevelstopreventpotentialloudspeakerdamage.
Highintensitysinglefrequencyprogrammaterialcan
overheattheloudspeakersvoicecoilandcauseburnout.
Toperformthischeck:
1.DepresstheL button.
2.Playthe1000Hztesttoneontherecord.
3.SetthePOWERLEVELselectorswitchtoa settingthat
producesanadequatedisplaybetween1000and0.1
watt.
4.Depressthe200-2,000SWEEPFREQUENCYbutton
andadjusttheSWEEPcontroltoobtaina fewcycle
waveform.
5.ReferringtoFigure34:waveformA issinusoidaland
16
LEVEL
SCALE
POWERLEVELSWITCHSETTING(WATTS)
(dB)
+3
+2
+1
0
-1
-3
-5
-7
-10
-20
1000
1000
800
630
500
312
250
126
100
50
5
300
300
240
190
150
93
75
38
30
15
1.5
100
100
80
63
50
31.2
25
12.6
10
5
0.5
30
30
24
19
15
9.3
7.5
3.8
3.0
1.5
.15
10
10
8
6.3
5
3.12
2.5
1.26
1.0
.5
.05
3
3
2.4
1.9
1.5
.93
.75
.38
.3
.15
.015
1
1.0
.8
.63
.5
.312
.25
.126
.1
.05
.005
3
.3
.24
.19
.15
.093
.075
.038
.030
.015
.0015
.1
.1
.08
.063
.05
0312
.025
0126
.01
.005
.0005

IDEALRIAASYSTEMRESPONSEUSINGCBSSTR100TESTRECORD
FREQUENCYINHz
FIG.33
17
20
I00
1,000
10,000
20,000
-20
-18
-16
-14
-12
-10
-8
6
-4
-2
0
2
4
4
2
0
2
4
-6
-8
10
12
-14
-16
-18
20
20,00010,000
1,000
100 20

indicatestheamplifierhasloworlittledistortion:
waveformB indicatespoorlinearityandclipping:
whilewaveformC indicatescrossoverdistortion.
6.DepressbuttonR andobservetherightchannel
waveform.
FIG.34(a)NORMAL
(b)CLIPPING
(c)CROSSOVERDISTORTION
PerformanceLimits
Allratingsarenominal
MULTIPATHMODEOFOPERATION
Sensitivity:l00mV/cm
FrequencyResponse:DCto50kHz(-3dB)
InputImpedance:250,000W
SignalStrengthPolarity:Selectablepositiveornegative
STEREOMODEOFOPERATION
Sensitivity- L (VerticalAmp.):1.75mVrms/cm(5mV
P-P/cm)
Sensitivity- R (HorizontalAmp.):1 75mVrms/cm(5mV
P-P/cm)
FrequencyResponse:5Hzto50kHz(-3dB)
InputImpedance:250,000W
POWERLEVELMODEOFOPERATION
Sensitivity 0.1to 1000 average watts for lull scale
indication(+3dB)in9 calibratedsteps.
FrequencyResponse:5Hzto100kHz( -3dB)
InputImpedance:75,000W
Calibration:Forbridging4,8or16ohmspeakerloads
PREAMPLEVELMODEOFOPERATION
Sensitivity:15mVrmsfor+3dBindication
FrequencyResponse:5Hzto50kHz
InputImpedance:250,000W
SWEEPMODEOFOPERATION
Displaymodes:Left,right,orboth(dualtrace)
Sensitivity:1.6mVrms/cm(45mVP-P/cm)
FrequencyResponse:5Hzto50kHz( - 3dB)
InputImpedance.250,000W
SweepFrequency:20Hzto20,000Hzin3 Decade
ranges
SweepExpansion:0.25Xto5X
SweepI rigger:Thesweepistriggeredonlyinthepres-
enceofaninputsignal.
Inthesingletracemodeitistriggered
bythedisplayedwaveform.
Inthedualtracemodethetriggeris
selectable:leftchannel,rightchannel,
orlinefrequency.
LEVELINDICATIONMODE
Normal250m s risetime
500msfalltime
Peak:500msrisetime
25secfalltime
Reset.250m s risetime
l00secfalltime
18