McIntosh MA 230 - SERVICS BULLETINS User manual

STEREO
PREAMP-AMPLIFIER
MA230
TABLEOFCONTENTS
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3
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5
9
11
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12
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14
20
20
GENERALDESCRIPTION
TECHNICALDESCRIPTION
MechanicalSpecifications
ElectricalSpecifications
FRONTPANELINFORMATION
INSTALLATION
CONNECTIONS
ACConnections
GroundConnection
TapeOutputConnections
LoudspeakerConnections
ACPower
InputConnections
OPERATINGINSTRUCTIONS
GUARANTEE
3-YEARFACTORYSERVICECONTRACT
MA230

MA230PREAMP-AMPLIFIER
GENERALDESCRIPTION
ThenewMclntoshMA230presentstwo
outstanding"FIRSTS"foryourhomestereo
listeningenjoyment.
.. . TheMA230istheFIRSTstereopre-
amp-amplifierononechassisthatmeetsthe
traditionalrigorousMclntoshengineering
performancestandards.
.. . TheMA230istheFIRSTstereoinstru-
menttocombinea solidstatepreamplifier
witha tubeandtransformerpoweramplifier
onthesamechassis.
TheMclntoshMA230haseliminated all
previouslimitationsofsinglechassispreamp-
poweramplifiers.Thecompactdesignofthe
MA230preamplifierallowsadequatespace
onthesamechassisfora coolrunning30
wattperchanneltubepoweramplifier.You
cannowenjoyMclntoshperformanceand
reliabilitywiththeconvenienceofa complete
singlechassisstereoinstrument.
Thedramaticdifferenceinthequalityof
musicreproductionthroughMclntoshinstru-
mentsisduedirectlytolowdistortionper-
formance.MclntoshLaboratoryistheonly
manufacturerintheentireindustrytoguar-
anteeanddeliverthelowestdistortionatall
audiofrequencies.
Longlife,flexibility,andhighestquality
constructionarecharacteristicdesignsin
everyMclntoshinstrument.Wideelectrical
andthermalmarginsofsafetyforallcom-
ponents,transistorsandtubesaddtothe
longlifebuiltintoeveryMclntoshproduct.
Advancedengineeringandcooloperatingde-
signinsurereliabilityandlowmaintenance
costs.A Mclntoshinstrumentis without
doubtthemosteconomicalandworthwhile
longterminvestmentinthehighfidelity
industry.
Onceyouhaveenjoyedtheoutstanding
performanceoftheMA230,youwillunder-
standwhyMclntoshproductshaveearned
theirreputationas"THEBEST."YourMc-
lntoshMA230stereopreamp-amplifierwill
giveyouyearsofthefinestpossibleper-
formanceandwillbecomea highlyvalued
partofyourhomemusicsystem.
TECHNICALDESCRIPTION
ThenewMclntoshMA230combines,for
thefirsttime,a Mclntoshengineeredstereo
solidstatepreamplifierandtubepoweram-
plifieronthesamechassis.Longmonthsof
diligentresearchbytheMclntoshengineer-
ingstaffhaveproduceda compactsolidstate
preamplifierwhichmeetsallthetraditional
Mclntoshperformancestandards.TheMA-
230solidstatepreamplifiereliminatesthe
drawbacksandlimitationsofallprevious
solidstatecircuits.Thecompactdesignof
thispreamplifierhasallowedsufficientspace
toproperlypositiona 30wattperchannel
stereotubepoweramplifieronthesame
chassis.
TheMA230continuestheMclntoshrepu-
tationforcoolandefficientoperation.Careful
chassisplanninghaspermittedtheoutput
tubestobespacedwellapart.Thiswide
spacingallowsmoreaircirculationaround
thetubes.Betteraircirculationmeanscooler
operation.Cooleroperationmeanslonger
troublefreelife.ThelargeMclntoshoutput
andpowertransformersarepositionedacross
thecenterofthechassisformechanical
stabilityandstrength.
TheMA230preamplifiersectionisde-
signedaroundthelatesttypeSilicon-Planar
transistors.Silicon-Planartransistorswere
selectedbecauseoftheirhighthermalsta-
bility,lowleakage,lownoise,andsuperior
highfrequencyresponse.A totalof12tran-
sistorsareused.Threetransistorsareused
ineachchannelofthephonopreamplifier
section.Threetransistorsarealsousedin
1

eachchannelofthetonecontrolsection.The
entirepreamplifierhaslownoise,lowdistor-
tion,andisnotaffectedbynormalroom
temperaturevariations.
TypicalMclntoshcareindesignprotects
againstinputsignaloverload.Boththehigh
levelinputs(Tuner,TapeandAux)andthe
lowlevelphonoandtapeheadinputscan
acceptmuchhigherthanaverageinputsig-
nalswithoutoverload.
Forexample,at2000cyclesthephono
inputscan-accept150millivoltsofsignalbe-
foreoverload.Nomagneticphonocartridge
nowavailableiscapableofevenonehalfthis
outputvoltage.
PREAMPLIFIER
EachchannelofthePhonopreamplifier
sectionuses3 transistors.Thefirstinput
stageisa highgainamplifier.Theoutputof
thistransistorfeedsa pairoftransistorscon-
nectedina Darlingtonconfiguration.A nega-
tivefeedbackloopconnectsfromtheoutput
oftheDarlingtonpairbacktotheemitterof
thefirststagetransistor.Thisfeedbackloop
reducesnoiseanddistortionandalsopro-
videsaccuratefrequencycompensationfor
phonorecordsandtapeheadplayback.Neg-
ativefeedbackremainsineffectevenat20
cycleswheregainishighest,toinsurelow
distortionovertheentirefrequencyrange.
Thephonoinputimpedanceis47,000
ohmstomatchmostmagneticphonocar-
tridges.Otherresistorsmaybeaddedto
matchtheoccasionalcartridgewhichre-
quiresa differentinputimpedance.
TheTapeHeadinputimpedanceisslightly
over1 megohmforuniformhighfrequency
responsewithtypicaltapeplaybackheads.
TheTapeOutputscomedirectlyfromthe
SelectorSwitchandprovidesignallevelsuffi-
cientforfeedinga taperecorder.Forex-
ample,10millivoltsofsignalatthephono
inputresultsin1.6voltsattheTapeOutput.
Thehighlevelinputsfeedthroughthe
BalanceandVolumecontrolsintoa transistor
connectedasanEmitter-Follower.Thistran-
sistoristhefirststageoftheToneControl
section.Theimpedanceofthehighlevel
inputsis250,000ohms.Anyconventional
tunerortaperecordermaybeconnectedto
theMA230withoutlossoflowfrequencies.
Theemitter-followerprovidestherequired
highinputimpedanceandlowoutputim-
pedanceforfeedingthetonecontrolnegative
feedbackcircuits.Thelasttwostagesofthe
tonecontrolsectionaretwotransistorsina
Darlingtonconfigurationsimilartothephono
preamplifier.Thehighgainofthesestages
isusedtoadvantageforthetonecontrol
negativefeedbackcircuits.Thistypeofcir-
cuitassureslowdistortionandthecorrect
shapeforthetonecontrolresponsecurves.
Negativefeedbackismaintainedatallfre-
quencies,evenwiththetonecontrolsturned
tofullboost.Distortionis,therefore,kept
verylow,evenatthefrequencieswhere
maximumboostoccurs.Thetotaldistortion
oftheentireMA230preamplifiercircuitis
actuallyonlya fewhundredthsof1 percent.
POWERAMPLIFIER
Theoutputofthesolidstatepreamplifier
feedsintoonehalfofa 12AX7dualtriode
tube.Thetwotriodesectionsofthe12AX7
arethefirststagevoltageamplifiersineach
channelofthepoweramplifier.Theoutputof
each12AX7isdirect-coupledtoa 12AU7
tubeusedasa grounded-gridinverter-driver.
Thebalancedoutputvoltagesofthegrounded-
gridinverterarepreciselymaintainedin
amplitudeovertheentireaudiofrequency
range.Theinverteroutputbalanceiscon-
trolledbypreciseplateloadresistors.An
adjustingcontrolisalsoincludedinthein-
verterplatecircuittoinsureexactsignalbal-
anceandminimumlowfrequencydistortion.
Thiscontrolisfactorysetusinga distortion
analyzer.Normally,themidpointsettingof
thiscontrolisadequatetokeepoveralldis-
tortionlessthan½ of1%atfulloutput.
Theoutputsofthe12AU7tubesarecou-
pledthroughmylar-insulatedcapacitorsto
theoutputtubegrids.Thesecapacitorsare
theonlycouplingcapacitorsusedinthe
poweramplifiercircuit,whichkeepsphase
shiftverylowatlowfrequencies.
The7591outputtubeplatesarecoupled
tothespeakerthrougha specialMclntosh
engineeredoutputtransformer.A separate
tertiarywindingonthetransformeralso
2

couplestheoutputtubecathodesintothe
transformer.Sixdbofnegativefeedbackis
producedintheoutputstagewiththiscircuit.
Twentydbofnegativefeedbackaround
theentirepoweramplifiercircuitisachieved
bycouplinga specialsecondarywindingon
theoutputtransformerbacktothefirststage
12AX7cathode.
Thefixedbiasonthe7591outputtubes
isadjustableovera smallrangewithindi-
vidualcontrols.Theseadjustmentsarefac-
torysetto0.7voltsDCatthetestpoints.
Convenienttestpointjacksareprovidednext
toeachoutputtube.Thesettingofthesecon-
trolsisnotcriticalandneednotbetouched
innormaluse.Toassurebestpossibleper-
formanceoftheMA230overlongperiodsof
operation,orwheneveroutputtubesare
changed,thebiascanbecheckedandreset
ifnecessary.
Apairofstereoheadphonejacksispro-
videdonthefrontpanel.Thejacksarecon-
nectedtotheamplifieroutputsthrough100
ohmresistorsforlowimpedanceheadphones.
Thespeakerswitchturnsoffthespeakers
forheadphonelistening.
POWERSUPPLY
Asiliconrectifiervoltagedoublerpower
supplyassuresstablevoltagesandcooloper-
ation.A zenerdiodeholdsthetransistorpre-
amplifieroperatingvoltagesatexactvalues
andeliminatesalltracesofhum.
AthermistorisusedintheprimaryAC
circuitofthepowertransformertoprotect
againstlinevoltagesurgesandextendtube
andtransistorlife.Thethermistorplaces
slightlymorethan25ohmsintheACcircuit
whencold.Astheamplifierwarmsupthe
thermistoralsowarmsanditsresistance
thendropstolessthan0.7ohm.Theampli-
fierthenoperatesatnormallinevoltagesbut
isprotectedduringtheinitialwarmupperiod.
Again,Mclntoshcareinengineeringprotects
yourinvestmentinlisteningpleasure.
Thecombinationofthesefeaturesresults
inperformanceavailableonlyfroma Mc-
lntoshamplifier.TheMA230delivers30
wattsRMScontinuouspowerfromboth
channelsatthesametime,20cyclesthrough
20,000cycleswithharmonicdistortionless
than½ of1%.Thissuperiorlevelofper-
formanceisunequaledbyanyotherpreamp-
amplifier.A listeningtestquicklyprovesthe
superiorityoftheMclntoshMA230.
MECHANICALSPECIFICATIONS
Size
Frontpanel,16incheswideby57/16inches
high;chassis,15incheswideby4½inches
highby14½inchesdeep,includingconnec-
tors.Clearanceinfrontofmountingpanel
includingknobs,1½inches.
Weight
43poundsnet,57poundsinshippingcarton.
Finish
Anodizedgoldandblack(FrontPanel).
ELECTRICALSPECIFICATIONS
PowerOutput
30wattscontinuousperchannelwithboth
channelsoperatingsimultaneously.60watts
continuous,monophonic.
HarmonicDistortion
Lessthan0.5%at30wattsoutput,20cycles
through20,000cycles.Distortiondecreases
aspoweroutputisreduced.
IntermodulationDistortion
Lessthan0.5%foranycombinationoffre-
quenciesfrom20 cyclesthrough20,000
cyclesifinstantaneouspeakpoweris60
wattsperchannelorless.
PhaseShift,PowerAmplifier-
Lessthan± 5°20to20,000cycles.
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FrequencyRange
At30wattsoutputbothchannels.
+0,-0.5db20cyclesthrough20,000
cycles.
+0,-3db15cyclesthrough70,000
cycles.
OutputImpedance
4ohms,8 ohms,16ohms.
InternalImpedance/Damping
Lessthan10%ofratedloadimpedance;
dampingfactoryof10.
InputSensitivityandImpedance
Auxiliary,Tape,Tuner,andTapeMonitor:
.25volts,250Kohms.
Phono1 andPhono2:1.5millivolts,47,000
ohms.
TapeHead:1.5millivolts,1 Megohm.
TotalNoise(includingPowerAmplifier)
Highlevelinputs:75dbbelowratedoutput.
Lowlevelinputs:60dbbelowratedoutput;
lessthan4.0microvoltsatinputterminals.
TapeOutput
.25voltsinto25,000ohmswithratedinput;
1.6voltswith10millivoltsatPhonoinput.
LeftPlusRightOutput
10voltsfromgeneratorimpedanceof5,000
ohms.
BassControls
±18dbat20cycles,withfrictionclutchfor
independentadjustmentofeachchannel.
TrebleControls
±18dbat20,000cycles,withfrictionclutch
forindependentadjustmentofeachchannel.
Comp(Compensator)Switch
RIAAorLPphonoequalization.
TapeSwitch
NormalorTapeMonitor.
PhaseSwitch
Normal(0°)orreverse(180°).
SpeakerSwitch
SpeakersON,orOFFforheadphonelistening.
HFFilter
Flat,or5,000cyclecutoff,12dbperoctave.
LFFilter
Flat,or50cyclecutoff,12dbperoctave.
LoudnessSwitch
Normalorcompensatedbassandtreble.
HeadphoneJacks
Two,fortwopairsofheadphones.
InputSelector
6positions:AUX,TAPE,TUNER,PHONO1,
PHONO2,TAPEHD.
ModeSelector
7positions:L toL andR,R toL andR,
STEREOREVERSE,STEREO,MONO(L+R),
L+RtoL,L+RtoR.
TransistorComplement(Preamplifier)
8-2N2926SiliconPlanar
4-11BQ101SiliconPlanar
TubeComplement(PowerAmplifier)
4-7591PowerOutput
2-12AU7Driver/PhaseInverter
1-12AX71stAudioVoltageAmplifier
PowerRequirements
120-125voltsAC,60cycles.150wattsat
zerosignaloutput;210wattsatratedoutput.
.
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FRONTPANELINFORMATION
INPUTSELECTOR
Figure1.MA230FrontPanel.
Selectanyofsixprogramsourceswiththe
MA230INPUTSELECTORswitch.
1.AUX:UsetheAUXpositionforany
auxiliaryprogramsourcerequiringflatampli-
fication,suchasa tunerortelevisionsound,
connectedtothebackpanelAUXinputjacks.
2.TAPE:UsetheTAPEpositionfora self-
containedtaperecorder(taperecorderhav-
ingitsownplaybackpreamplifier),connected
tothebackpanelTAPEinputjacks.
3.TUNER:UsetheTUNERpositionfor
anyAM,FM,orFMstereotunerconnectedto
thebackpanelTUNERinputjacks.
4.PHONO1:UsethePHONO1 position
foranymagneticphonocartridgeconnected
tothebackpanelPHONO1 inputjacks.
5.PHONO2:SameasPHONO1.(Forex-
ample,PHONO1 canbeconnectedtoa
recordchangerwhilePHONO2 isconnected
toa manualturntable.)
6.TAPEHD:UsetheTAPEHD(Tape
Head)positionfora tapedeckthatdoesnot
haveitsownplaybackpreamplifier.TheTape
Headleadsareconnectedtothebackpanel
TAPEHDinputjacks.
MODESELECTOR
UsetheMODESELECTORto:
Listentonormalstereo(see4 following
andpage15);
Reversetheleftandrightarrangementof
musicalinstruments(see3 followingand
page15).
Balancetheamplifiersandloudspeakers
ina stereosystem(see6 and7 followingand
page15).
Listentomonophonicsound(see1 and2
followingandpage15).
Listenthroughbothloudspeakersto
eitherchannelofa stereoprogramsource
(see1 and2 followingandpage15).
5
Figure2.INPUTSELECTORSwitch.
Figure3.MODESELECTORSwitch.

TurntheMODESELECTORto:
1.LTOL & R:connectsthe"left"inputto
bothloudspeakers.
2.R TOL & R:connectsthe"right"input
tobothloudspeakers.
3.STEREOREV:connectsthe"left"input
tothe"right"loudspeakerandthe"right"
inputtothe"left"loudspeaker.
4.STEREO:connectsthe"left"inputto
the"left"loudspeakerandthe"right"input
tothe"right"loudspeaker.
5.MONO(L+R):addsthe"left"input
andthe"right"inputandthenconnectsthe
L+ R programtobothamplifiersandloud-
speakers.
6.L + R TOL:connectsbothleftandright
inputstothe"left"loudspeakeronly.
7.L+R TOR:connectsbothleftandright
inputstothe"right"loudspeakeronly.
VOLUME
UsetheMA230VOLUMEcontroltoregu-
latethevolumelevelofbothchannels.Turn-
ingtheVOLUMEcontrolclockwiseincreases
volumelevel.
BALANCE
UsetheMA230BALANCEcontroltobal-
anceunequalvolumeintheleftandright
channelsofa programsource.Thevolume
ofeachspeakersystemrelativetotheother
canbevaried,atthesametimethecombined
roomvolumelevelisnotchanged.
LEFT. . . turningthecontroltotheleft
accentstheleftchannelbyreducingtheright
channeloutput.
RIGHT. . . turningthecontroltotheright
accentstherightchannelbyreducingthe
leftchanneloutput.
BASS
Figure5.BALANCEControl.
TheBASScontrolisa dual-concentric
control.Thetwoarefrictioncoupled.The
centerknobcontrolstheleftchannel.The
outerringcontrolstherightchannel.Withthe
BASScontrolitispossibletovarythebass
loudnessrelationship existingbetweenthe
leftandrightspeakers.Bothcontrolscanbe,
turnedtogetherasa singleadjustmentorone
maybeheldastheotheristurned.Clockwise
rotationincreasesbassloudness;counter-
clockwiserotationdecreasesbassloudness.
TREBLE
TheTREBLEcontrolisdual-concentric
control.Thetwoarefriction-coupled.The
centerknobcontrolstheleftchannel.The
outerringcontrolstherightchannel.With
thiscontrolitispossibletovarythetreble
relationship existingbetweenleftandright
speakers.Bothcontrolscanbeturnedto-
getherasa singleadjustmentoronemaybe
heldastheotheristurned.Clockwiserota-
tionincreasestrebleloudness;counterclock-
wiserotationdecreasestrebleloudness.
Figure6.BASSControl.
Figure4.VOLUMEControl.
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Figure7.TREBLEControl.
COMP(Compensation)
UsetheCOMPswitchtocorrectforphono
equalizationintroducedbytherecording
process.Therecordingindustryhasagreed
torecordallcurrentLPandstereorecordings
withRIAAequalization.Onearlierstereoand
onmonorecordingsusethepositionthat
soundsbesttoyou.
TheMA230TAPEswitchmakesitpossible
toinstantaneouslycomparerecordedma-
terialwiththesourcesignal.UsetheMA230
TAPEswitchtoknowinstantaneously,asyou
arerecording,thatthemusiconthetapeis
acceptable.Tapemonitorjacksontheback
panelaccepta signalfroma taperecorder
witha monitorheadandpreamplifier.
NORMAL. . . theoriginalprogramsource
isfedthroughthepoweramplifiersandthe
loudspeakers.
MONITOR. . . therecordedsoundonthe
tapeisfedthroughthepoweramplifiersand
speakers.
ThePHASEswitchcorrectsforloud-
speakerorprogramphasing.Whenthis
switchisinthe180°positionthephaseinthe
leftchannelisreversed.
Figure9.TAPESwitch.
Theloudspeakersareturnedoffwhenthe
SPEAKERswitchisintheOFFposition,to
allowlisteningthroughheadphones.The
headphonejacksareonatalltimes.
Figure8.COMP(Compensation)Switch.
TAPE
7
Figure11.SPEAKERSwitch.
SPEAKER
Figure10.PHASESwitch.
PHASE

LF(LowFrequencyFilter)
LOUDNESS
UsetheLFfiltertoreducelowfrequency
noisescreatedbyaturntable,recordchanger,
orvibrationacousticallycoupledtothephono
playerfromthespeakers.
FLAT...filterdisconnected;flatresponse.
FILTER. . . lowfrequenciesreduced
sharplybelow50cycles.
Whenyouturndownthevolume,music
seemstolosemuchofitsbassandsomeof
itstreble.Thiseffectis dueto thesensitivity
characteristicsofhumanhearing.There-
sponseofthehumaneartobassandtreble
pitchdecreasesmorerapidlythanitsre-
sponsetothemid-tonalrange.TheLOUD-
NESSswitchautomaticallyprovidesthecor-
rectamountofbassandtrebleboostre-
quiredtocompensateforthischangein
responseofthehumanearatlowloudness
levels.UsetheLOUDNESSswitchinthe
COMPENSATEDpositiontolistenatlow
volumeandstillhearfullfrequencyrange.
HEADPHONE
SPEAKER
ON
POWER
ON
HEADPHONEHEADPHONE
OFFOFF
UsetheHFfiltertominimizesurfacenoise
whenreproducingoldorbadlywornrecord-
ings.
FLAT...filterdisconnected;flatresponse.
FILTER. . . highfrequenciesreduced
sharplyabove5000cycles.
Twopairsoflowimpedancestereohead-
phonescanbeconnectedtotheMA230.
Bothfrontpanelheadphonejacksarecon-
nectedtotheMA230outputthrough100
ohmresistors.Theseresistorsprovidethe
correctoutputvolumelevelforheadphone
operation.
8
HF(HighFrequencyFilter)

INSTALLATION
TheMA230canbeinstalledinfurniture
cabinets,custombuiltinstallationsorpro-
fessionalrelayracks.Iftheunitistobeused
ona shelfortabletop,itcanbehousedinan
attractiveMclntoshcabinet.
Allowsufficientcabinetspaceforaircircu-
lation.Minimuminternalcabinetdimensions
shouldbeatleast16incheswide,14inches
deep,and6 incheshigh.Thebackofthe
cabinetshouldbeleftasopenaspossiblefor
ventilation.Properventilationwillinsureyour
amplifiera longandtrouble-freelife,
TheMA230installsconvenientlyfromthe
frontofthecabinetintothepanelcutout.
Twoamplifiermountingbracketsarepro-
videdforeachsideofthecabinetpanelopen-
ingsotheMA230canslideeasilyintoposi-
tion.Themountingbracketsareattachedto
thecabinetpanelbytwomountingstrips.
Themountingstripsareattachedtotheback
ofthecabinetpaneloneachsideofthepanel
cutout.Withthescrewssupplied,frontcabi-
netmountingpanelsuptooneinchthickness
maybeused.Twoknurledscrewsplacedinto
theMA230backpanel,throughthemounting
brackets,holdtheunitfirmlyinplace.Dueto
theweightoftheMA230,itisrecommended
thatthemountingbracketsrestona wooden
shelfinthecabinetforaddedsupport.
Thedesignofthemountingtemplate
allowsthecutouttobelocatedeitherfrom
thefrontorthebackofthecabinetpanel.
SincetheMA230shouldrestona shelf,lo-
catethecutoutfromthebackofthepanel.
1A.PositiontheMA230mountingtem-
plateonthecabinetpanelareatobecutout
fortheinstallation.
1B.Onthebackofthecabinetpanel,
scribea verticallinethroughtheexactcenter
ofthecutoutarea.
Placethetemplateagainstthebackofthe
panel.Matchthetemplatecenterlinewiththe
scribedcutoutcenterline.Thebottomofthe
templatemustrestontheshelf.
1C.Oneachsideofthecenterlineofthe
templatetherearetwoholesmarked"C."
Thesmallerdiameterholeisbelowthelarger
diameterhole.Thesearethe"LOCATING
HOLES."Theseholesareusedtolocatethe
frontpaneloftheMA230withreferenceto
theshelfbehindthecabinetpanel.Sothat
theMA230willrestonthecabinetshelf,fol-
lowtheseinstructionscarefully.
Markthebackofthecabinetpanelwitha
pointedinstrumentthroughthetwosmall
diameter"LOCATINGC"holes.Drillthese
twoholesthroughthecabinetpanelwitha
3/16"diameterdrill.Becertainthedrillisper-
pendiculartothepanel.
Nowpositionthetemplateonthefrontof
thepanel.Alignthelarger3/16"diameter
upper"LOCATINGC"holesinthetemplate
withthedrilledholesinthecabinetpanel.
2.Markthe"A"and"B"drillholesand
alsothefourcornercutoutsinthetemplate.
Jointhecornermarkers.Theedgeofthe
templatecanbeusedasa straightedge.
Figure17.PositioningtheMountingTemplate
overproposedareatobecutout.Figure18.MarkingtheCutoutIndications.
3.Firstdrillthemountingholes.
9

4.Cutouttherectangularopening.
5.Securethemountingstripstothein-
sideofthepanel.
Inthehardwarepackageare4 flathead
screwsand8 fillisterheadscrews.Twoofthe
flatheadscrewsoftheproperlengthare
usedtoattachthemountingstripstothe
cabinetpanel.Fourofthefillisterhead
screwsareusedtoattachtheMA230mount-
ingbracketstothecabinetpanelandthe
mountingstripsbehindthepanel.The¼ inch
screwsareusedforpanelthicknesslessthan
3/8inch.The1¼inchscrewsareusedwith
panelsfrom3/8inchto1 inchinthickness.
Inserttheproperlengthflatheadscrew
throughthecenter"B"holesofthecabinet
panel("B"holesmarkedonmountingtem-
plate).Positionthemountingstripbehind
thecabinetpanel.Theedgeofthemounting
stripthathastheclipsmustbefacingthe
rectangularcutout.Alignthethreeholesin
themountingstripwiththeholesinthecabi-
netpanel.
Tightentheflatheadscrewsothatthe
screwheadpullsinthewoodpanellevelwith
thepanelsurface.Repeatthiswiththesec-
ondmountingstripontheothersideofthe
rectangularcutout.
6.Leftandrightmetalmountingbrackets
arepackedwiththeMA230.Fastenthesetwo
mountingbracketstothecabinetpanelusing
fourofthefillisterheadscrews.Thesescrews
shouldpassthroughthemountingshelf
flange,throughthecabinetpanelandthen
intothemountingstripattachedtotheinside
ofthepanel.Tightenthescrewsfirmly,but
donotover-tighten.
7.PreparetheMA230formountingby
removingthefourplasticfeetfastenedunder
thechassis.
8.TheMA230isinstalledfromtheFRONT
ofthecabinet.InserttheMA230powercord
throughtherectangularopeningofthecabi-
netpanel.CarefullyslidetheMA230intothe
openingsotheplasticrailsonthebottomof
thechassisengagethegroovesinthemetal
mountingbrackets.SlidetheMA230inuntil
itsfrontpanelisagainstthecabinetmount-
ingpanel.
9.SecuretheMA230tothemounting
bracketsbyinsertingthetwoknurledscrews
intothebackoftheMA230chassis,through
thebackflangesofthemountingbrackets.
Figure21.MountingBracketsinstalledincabinetpanel.Figure22.SecuringMA230toMountingBrackets.
10
Figure20.SecuringMountingStrips
toInstallationCutout.
Figure19.InstallationCutout.

CONNECTING
ACCONNECTIONS
TherearethreeACoutletsontheback
paneloftheMA230.Theblackreceptacles
havea maximumpowerratingof350watts
total.Thepowertothetwoblackreceptacles
iscontrolledbythefrontpanelpowerswitch.
Usethesereceptaclesforaccessoriessuch
asa tunerandtaperecorder.Theredrecep-
tacleisnotswitched.Usetheredrecep-
tacleforpoweringa turntableorrecord
changer.Theredreceptacleisnotswitched
topreventturningoffthepowertotheturn-
tablewhileitsidlerdriveisstillengaged.The
turntableisprotectedbythisarrangement
becauseitisnecessarytoturnofftheturn-
tablewithitsowncontrolswitch.Theturn-
tabledriveswillthenbeproperlydisengaged
toavoidpossibledamage.
Figure23.ACCONNECTIONS
L+ROUTPUT
Bothleftandrightchannelamplifierout-
putsarecombinedintoa monophonicsignal
attheL+Routputjack.Connectthisjackto
anexternalamplifierformonophonicrepro-
ductionthroughanotherspeakersystem.
Monophonicsignalscanthenbedistributed
tootherroomswithoutaffectingthenormal
stereoperformanceoftheMA230.
GROUNDCONNECTIONS
Asinglegroundpostisprovidedonthe
MA230.Thechassisgroundfromturntables,
recordchangers,tapedecks,etc.,shouldbe
connectedtothispost.Donotconnectother
groundwirestothesameunits.Humis
likelytobeheardinthesystemifmorethan
onegroundcircuitisused.
Theleftandrightcablesfromeachpro-
11

gramsourceshouldbetwistedtogetherand
thegroundwirefromeachsourcecanbe
woundortwistedinwiththesecables.To
avoidhum,makesurethegroundwiredoes
notmakeanyconnectionstoshieldsofthe
leftandrightchannelcablesexceptforthe
connectionprovidedwiththeMA230ground
post.
TAPEOUTPUTCONNECTIONS
TheTAPEOUTPUTSonthebackpanel
providetheprogrammaterialwithsufficient
levelforfeedinga tapedeckorrecorder.The
TAPEOUTPUTsignalisnotaffectedby
thesefrontpanelcontrols:VOLUME,BASS,
TREBLE,BALANCE,LOUDNESS,PHASE,
TAPE,MODESELECTOR,SPEAKER,LFand
HFFILTERS.TheINPUTSELECTORandthe
COMPswitch(inPhono1 andPhono2)affect
theTAPEOUTPUTS.Allrecordingvolume
adjustmentsaremadeatthetaperecorder.
TheroomlisteningvolumeoftheMA230can
thenbesetatanydesiredlevelwithout
affectingrecordingvolume.
LEFTandRIGHTSPEAKEROUTPUT
Speakersystemsof4,8,or16ohmsim-
pedanceconnecttotheSPEAKERterminals
onthebackpaneloftheMA230.
Selecttheoutputimpedancedesiredby
placingthewirepigtailwiththelugunderthe
appropriateimpedancescrewoneachchan-
nel.Tightenthescrewsfirmly.Connectthe
leftspeakerleadstothetwoscrewsunder
theletteringmarkedLEFTSPEAKER.Con-
necttherightspeakerleadstothetwoscrews
undertheletteringmarkedRIGHTSPEAKER.
Thecommonorchassisgroundtaponeach
channelismarkedC.Connecteachspeaker
inanidenticalmanner.
ACPOWER
PlugtheACpowercordintoa 120-125
volt,50or60cyclepowerline.
INPUTCONNECTIONS
TheMA230providessevenseparatepro-
graminputscontrolledbytheINPUTSELEC-TORswitch.Theinputfortapemonitoris
controlledbytheTAPEswitch.
12
CONNECTION
TAPEMONITOR
AUX
TAPE
TUNER
CONNECTION
PHONO1 & 2
TAPEHEAD
FUNCTION
Thetapemonitorinputacceptsa signalfroma tape
recorderwitha monitorheadandpreamplifier
Theauxiliaryinputacceptsanyauxiliaryservicerequir-
ingflatfrequencyresponse,suchasa T.V.set,tuner,
taperecorderwithitsownplaybackpreamplifier,etc.
Thetapeinputoperateswithtapemachinescontaining
theirownplaybackpreamplifier
ThetunerinputsacceptAMandFMoutputsfroma
stereotunerora pairofstereotunersorthemultiplex
outputofanadapterofmultiplextuner
FUNCTION
Thesejacksaretobeusedwithmagneticcartridges,..
Thesejacksaretobeusedwitha tapedeckthatdoes
notcontainitsownplaybackpreamplifier
INPUT
SENSITIVITY
0.25V
0.25V
0.25V
0.25V
INPUT
SENSITIVITY
1.5MV
1.5MV
INPUT
IMPEDANCE
250K
250K
250K
250K
INPUT
IMPEDANCE
47K
1megohm

DIRECTIONAL
FMANTENNA
ROTATOR
8OHMSPEAKERSSHOWN
TO12OV
ACOUTLET
13
GROUND

Ifa phonocartridgerequireslessthan
47,000ohmsloadimpedance,a resistorcan
beaddedacrosstheterminalsofthecar-
tridgetoachievethecorrecttermination.
Thefollowingchartmaybeusedasa guide:
DesiredImpedance
47,000ohms(47K)
37,000ohms(37K)
27,000ohms(27K)
15,000ohms(15K)
6,800ohms(6.8K)
ResistorAcrossInput
NoResistor
180,000ohms(180K)
62,000ohms(62K)
22,000ohms(22K)
8,200ohms(8.2K)
OPERATINGINSTRUCTIONS
BALANCINGA STEREOSYSTEM
Theperformanceandenjoymentofa
stereosystemisgreatlyincreasedwhenthe
systemisproperlybalanced.Thebalanceof
astereosystemisaffectedbymanythings
includingroomacoustics,furnitureplace-
ment,roomshape,smalldifferencesinloud-
speakers,andunequalprogramloudness.
ThecontrolmarkedBALANCEonthe
MA230canbeusedtoperfectlybalanceall
factorsforbestlistening.
1.Playa familiarrecordingontherecord
player.
2.TurntheINPUTSELECTORtothe
PHONOpositionintowhichtherecordplayer
isconnected.
3.TurntheBASSandTREBLEcontrols
sothattheknobindicatorsarecenteredbe-
tweenthepanelmarkingsL andR.
4.TurntheBALANCEcontroltothecen-
teror12o'clockposition.
5.PlacetheLOUDNESSswitchinthe
NORMALposition.
6.PlacetheTAPEswitchintheNORMAL
position.
7.PlacethePHASEswitchinthe0°
position.
8.PlacetheLFfilterswitchintheFLAT
position.
9.PlacetheHFfilterswitchintheFLAT
position.
10.TurntheMODESELECTORtothe
L+RtoL position.
11.Whiletheprogramisplaying,alter-
natetheMODESELECTORbetweentheL+R
toR andtheL+RtoL positions.Adjustthe
MA230BALANCEcontroluntiltheloud-
speakervolumesareequal.
Thestereosystemwillnowbebalanced.
Differentprogrammaterialsuchasrecords,
tapesorFMbroadcastsmayrequiredifferent
BALANCEcontrolsettings.Itisnotatallun-
usualfortheBALANCEcontroltoremainoff
centeronewayortheotherforcorrectbal-
ance.ThismeanstheBALANCEcontrolis
performingthefunctionitwasdesignedfor.
ADJUSTINGPHASE
1.SettheMODESELECTORtoSTEREO.
2.TurntheBASScontrolsandTREBLE
controlstostraightuppositionwiththedial
indicatorscenteredbetweenthepanelmark-
ingsL andR.
3.Standapproximately10feetinfrontof
andmidwaybetweentheloudspeakers.The
14

sourceofsoundshouldappeartobedirectly
infrontofyou.AlternatethePHASEswitch
between0°and180°.Ifthesoundisnotdi-
rectlyinfrontofyouinthe0°position,re-
versetheleadstooneloudspeaker.The
PHASEswitchisusedtocorrectphaseinthe
sourcematerialwhenevernecessary.
ADJUSTINGFORSPECIALEFFECTS
HFFILTER
Ifyouwishtoreproducebadlyworn
records,youcanminimizethesurfacenoise
byswitchingtheHFfiltertotheFILTERposi-
tion.
LFFILTER
Ifyouareusinga turntableorchanger
whichhaslow-frequencyrumblenoise,you
mayreduceitbypushingtheLFfilterswitch
totheFILTERposition.
BASSCONTROLSANDTREBLECONTROLS
Thetonebalancewhichyouhearwhen
listeningtoanorchestraisaffectedbythe
conductor'sinstructionstohismusicians,
theacousticalenvironmentinwhichyouare
listening,andyourownsubjectivehearing
interpretation.Consideringtheseconditions,
itiseasytoseewhytonebalancecontrols
playa majorroleincorrectingforthefollow-
ingfactors:
1.Eachperson'ssubjectiveideaoftone
balance.
2.Loudspeakerfrequencyresponsechar-
acteristics.
3.Loudspeakerplacementinthelisten-
ingroom.
4.Theconductor'sideaoftonebalance
atthetimetherecordingwasmade.
5.Themicrophonefrequencyresponse
characteristics.
6.Therecordingprocessinfluences.
Thesefactorscanbeconsideredasen-
vironmentalinfluences.TheBASSCON-
TROLSandTREBLECONTROLSprovidea
degreeofcompensationforeffectsofen-
vironment.Listentoyoursystemwitheach
controlsetwiththeindicatorscenteredbe-
tweenthepanelmarkingsL andR.Ifyou
wishtoreducetrebleinrelationtobassfor
example,turntheTREBLECONTROLScoun-
terclockwiseuntilthetonebalancesounds
correcttoyou.Thesecontrolswillmodify
tonebalancewithoutintroducinganyunde-
sirableeffects.Donotbesurprisedifyou
findyourpreferenceintonechangingfrom
timetotime.
PHASE
Ifthestereosoundseemstocomefrom
eithersideoftheroominsteadofbeingdis-
tributedbetweentheloudspeakers,turnthe
PHASEswitchto180°.Thislisteningeffect
isduetoreproducingsoundthatisoutof
phasefromonechanneltotheother.You
willfindsomerecordsandtapesmaydiffer
fromothersinthisrespect.
LISTENINGTOA STEREOTUNER
1.TurntheINPUTSELECTORtoTUNER.
2.TurntheMODESELECTORtoSTEREO.
3.SetthePHASEswitchto0°.
4.SettheHFcutofffilterswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
5.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEFFECTS.)
6.SettheLOUDNESSswitchtoNORMAL.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
7.TurntheBASSCONTROLSandTREBLE
CONTROLSsothattheindicatorsarecen-
teredbetweenthepanelmarkingsL andR.
(Seepage15BASSANDTREBLECON-
TROLS.)
8.SettheTAPEswitchtoNORMAL.
9.AdjusttheVOLUMEcontroltothede-
siredvolume.
10.AdjusttheBALANCEcontrolifneces-
sary.
Aftera warmupofabout30seconds,turn
thetuningknobonyourtunertofindthe
stationofyourchoice.
LISTENINGTOA STEREORECORD
Tolistentostereorecords,proceedas
follows:
1.TurntheINPUTSELECTORtoPHONO
1orPHONO2,whicheverisconnectedtothe
cartridgeyouwishtohear.
2.SettheMODESELECTORtoSTEREO.
3.SetthePHASEswitchto0°.
4.SettheHFcutofffilterswitchtoFLAT.
15

(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
5.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEF-
FECTS.)
6.SettheLOUDNESSswitchtoNORMAL.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
7.SettheTAPEswitchtoNORMAL.
8.SettheBASSCONTROLSandTREBLE
CONTROLSsothattheindicatorsarecen-
teredbetweenthepanelmarkingsL andR.
(Seepage15BASSandTREBLECON-
TROLS.)
9.AdjusttheVOLUMEcontroltothede-
siredvolume.
10.AdjusttheBALANCEcontrolifneces-
sary.
LISTENINGTOMONOPHONICRECORDS
Tolistentomonophonicrecords,proceed
asfollows:
1.TurntheINPUTSELECTORtoPHONO
1orPHONO2,whicheverisconnectedtothe
cartridgeyouwishtohear.
2.TurntheMODESELECTORtoMONO
(L+R).
3.SetthePHASEswitchto0°.
4.SettheHFcutofffilterswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
5.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEF-
FECTS.)
6.SettheLOUDNESSswitchtoNORMAL.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
7.SettheBASSCONTROLSandTREBLE
CONTROLSsothattheindicatorsarecen-
teredbetweenthepanelmarkingsL andR.
(Seepage15BASSANDTREBLECON-
TROLS.)
8.AdjusttheVOLUMEcontroltothede-
siredvolume.
9.AdjusttheBALANCEcontrolifneces-
sary.
LISTENINGTOTAPEDECKS
Tolistentotapefroma tapedeck,proceed
asfollows:
1.TurntheINPUTSELECTORtoTAPE
HEAD.
2.TurntheMODESELECTORtoMONO
(L+R)orSTEREO,dependingonthepro-
gramonthetape.
3.SetthePHASEswitchto0°.
4.SettheHFcutofffilterswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
5.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEF-
FECTS.)
6.SettheLOUDNESSswitchtoNORMAL.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
7.SettheBASSCONTROLSandTREBLE
CONTROLSsothatthedialindicatorsare
centeredbetweenthepanelmarkingsLandR.
8.AdjusttheVOLUMEcontroltothe
desiredvolume.
9.AdjusttheBALANCEcontrolifneces-
sary.
LISTENINGTOA STEREOTAPEMACHINE
Astereotapemachinewithitsownplay-
backpreamplifiersshouldbepluggedinto
theAUXinputortheTAPEMONITORinput-
nottheTAPEHEADinput.
IftheTAPEinputisused,proceedas
follows:
1.TurntheINPUTSELECTORtoTAPE.
2.TurntheMODESELECTORtoMONO,
(L+R)orSTEREOdependingontheprogram
onthetape.
3.SetthePHASEswitchto0°.
4.SettheHFcutofffilterswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
5.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEF-
FECTS.)
6.SettheLOUDNESSswitchtoNORMAL.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
7.SettheBASSCONTROLSandTREBLE
CONTROLSsothatthedialindicatorsare
centeredbetweenthepanelmarkingsLandR.
8.AdjusttheVOLUMEcontroltothede-
siredvolume.
9.AdjusttheBALANCEcontrolifneces-
sary.
IftheAUXinputisused,turntheINPUT
SELECTORtoAUX;then,proceedthesame
16

asforTAPEinput.
1.SettheTAPEMONITORswitchto
MONITOR.
2.TurntheMODESELECTORswitchto
MONO(L+R).
3.SettheHFcutofffilterswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
4.SettheLFfilterswitchtoFLAT.(See
page15ADJUSTINGFORSPECIALEF-
FECTS.)
5.SettheLOUDNESSswitchtoFLAT.
(Seepage15ADJUSTINGFORSPECIAL
EFFECTS.)
6.SettheBASSCONTROLSandTREBLE
CONTROLSsothatthedialindicatorsare
centeredbetweenthepanelmarkingsLandR.
7.AdjusttheVOLUMEcontroltothede-
siredvolume.
8.AdjusttheBALANCEcontrolifneces-
sary.
POWER
ThePOWERON-OFFswitchcontrolsthe
ACpowertotheMA230andthetwoblackAC
receptaclesonthebackpanel.TheredAC
receptacleisnotswitched,andisonatall
times.
HEADPHONE
Twopairsoflowimpedancestereohead-
phonescanbeconnectedtotheMA230.
Bothfrontpanelheadphonejacksarecon-
nectedtotheMA230outputthrough100
ohmresistors.Theseresistorsprovidethe
correctoutputvolumelevelforheadphone
operation.
ADJUSTMENTS
Twosimplecircuitadjustmentsarein-
cludedintheMA230.Afterextensiveuseor
whentubeshavebeenreplaced,thesead-
justmentswillinsuretopperformancefrom
yourMA230.
TheDCbiasofeach7591outputtubecan
beindividuallyset.TestPointjacksandbias
adjustcontrolsareconvenientlymountedon
thechassisnexttoeachoutputtube.The
outputtubes,TestPointjacks,andbiascon-
trolsaremarkedV,TP,andR,respectively.
Thebiasadjustcontrolcanbereachedfrom
thetopofthechassiswitha smallscrew-
driver.SettheBiascontrolsfora DCvoltage
of0.7voltsfromeachTestPointjackto
chassisground.Usea VTVMorsensitiveDC
voltmeter.Checkallvoltagesa secondtime
andreadjustthecontrolsifnecessary.
AphaseinverterACsignalbalancecontrol
isprovidedoneachamplifierchannel.These
controlsarefactorysetwitha harmonicdis-
tortionanalyzerforminimumdistortionat 20
cyclesat30wattsoutput.Normallyjusta
midpointsettingofthesecontrolsisade-
quatetokeepoveralldistortiontolessthan
0.5%atfulloutput.Ifthenecessarydistor-
tionmeasuringequipmentisavailable,set
eachcontrolforminimumharmonicdistor-
tionat20cyclesat30wattsoutput.Balance
controlR4adjuststheleftchannelsignal
balance,andR5therightchannelbalance.
17

RESPONSEINDB
20
10
0
-10
-20
201001KC10KC20KC
0
-5
-10
-15
-20
-25
-30
18
BASSANDTREBLECONTROLRESPONSE
FREQUENCY
RUMBLEANDHIGHFREQUENCYFILTERS
RESPONSEINOB
201001KC10KC20KC
FREQUENCY