Radio Shack MPA 31 User manual

Cat.No.32-2041

OWNER'SMANUAL

Pleasereadbeforeusingthisequipment

MPA31

20-WattAC/MobilePAAmplifier

RaAe/haek

FEATURES

YournewRatioShad<

N/PA-31

20-

WattAC/McAJtePAAmpfififfl-givesyou

20WattsofsofidpowerforyourPA

system.

ItswkJefrequencyresponse

easiyhandlesamplificationofvoiceand

music.Itopiatesoneither120volts

ACor12vdtsDCpowersoyoucan

useitinmeetinghallsandauditDriums,

atsportsevets,insdnools,intheoffice

forpagingsystems— ariywtTereyou

needtod^erspecialarvKXincemeits

withgreatsound.

ItinclLKJesVrsefolbwingfeatures:

N^a-opliotw\npuXJacks— letyoucon-

nectuptotwromiCTophones.

AuxifiarytnjaitJacks— letsyojcon^

necta varietyofaucfoinputsouroKfor

musicandspecialeffects.

70-VoHLireOutput— letsyou

con-

nectlinetransformersfora multipte-

speakerPAsystem.

MasterVottmreContrDi— letsyouad-

justtheoverallsoundlevel.

TOhECkHttrd—letsyoucustomize

thetoneofthesoundtosuityourper-

sonal preferencesdependingonthe

acoustics,speakers,andsoundsource.

Readthismanualcarefully.Itdescrit)es

variousspeakercormectlorstohelpyou

setectthebestan-angementforyour

systemandatoexplainshowtouse

ttieampfflCT.

TheserialnuntierisontheampSfier's

backpanel.Foryourpenmaientrec-

ords,

vwerecomrrffindyoirecorditbe-

low.

V«AflNW&TOREDUCETVCRS<OFFWEOfi

aECTFSC

SHOCK,

DONOT

EXPOSE.

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CAUTION:

PHXKETI-EHEKOFFffCOR

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C0VB1(OHBACK).NOU^SfflVlCEABLE

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INSCE.

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dartyefcjusinnsutslBdvottagBwithnthe.

product'serdosLMOmightbeofsuffcivit

iTiaynitudetocorstitLdsa risK ofelectric

shock.Donotop^theproduct'scase.

TtiB'syrrtertisintendedto nformyouofim-

portantoperafingSFtimaintenance(servi-

ng)nstructionsinthepapersaccompany-

ingttiisproc&jct.

RightsReserved.

RacfioShockisaregisteredtractemiarkusedbyTandyCorporation.

PREPARATION

PLACINGTHEAMPUFCR

Beforeyouuseyouamftffier,beaireyouchoosea kxationwithadequateventila-

tion.

Donotptebcetheampfifieronthickcarpeting(wtiichcanrestrictttisairfkiw)or

n^a heatsouce,ajchasa heatventorradiator(wtvchcancauseVheampfifierto

overheat).

PRESETTMGTHECONTROLS

SettingtheAmplifier

Warrang:Asuddenhighoutputfrom

theampliftercoukjdamageyotrhearing

orthespeakersconnectedtotheampH-

fia-'soutput.

Toavoid

accidentaftyoverdrivinga chan-

nelorprenatur^annplifyinganaucfio

inpuL,setVneamfifier'scontrolstotfie

levels^lovmbetowbeforeyouconnect

ttreACpowercord ortumonpovwer.

Control

PO\NER

MIC1,MC2,PHOISHD/AUX.CX

TONE

MASTERVOLUME

Skiing

Off

MIN

MID

nilIIIIPIIIIIIl

MikSTCBVnUiME

MXeXMtCaPMDHOL/AUX.CSTONE•.<''''l«

:()::

MU>MMIMXWMMKIMMM>LOUMXOM•'X.^./*^*

MP*~atP.A.AMm.TT'teB.t«av..^ev

SettingtheInputSource

Toavoidsuddenaudiofromtheinput

sources,setthercontrolstotfielevels

^tovimbetowbeforeyouconnecttheir

outputjackstotheannplifier'sinput

jad(S.

AucfioDevkw

Turntable

TapeDeck

CDPlayer

Amplifier/Receiver

Power

Tone

Selling

Off

Flat

CONNECTINGAUDIO

COMPONENTS

TOTHEAMPUFIER

Youcanconnectoptionalcomporents

(suchasmiCTophones,tuners,turnta-

bles,

orCDplayers)toyouramplifierto

expandyoursystem.Yourtocal Radio

Shackstorecaniesa wideselectionof

audiocomponents,adapters,micro-

phones,andspeakers.

Cautton:

Makesureyoumakeallttie

connectionstottieanrtplifierand^aeak-

ersbeforeconnectingandtumingon

power.

ConnectingMicrophones

Youcanconnecta microphonetoone

orbothoftheamplifier'sMIC1 and

MIC2 inputjacks.Themcrophone(s)

canbe

high-

orlow-impedanceand

musthavea

-inch

plug.

Connectinga Turntable

Youcanconnectanaudioinputsource,

suchasa magneticcartridgetumtatJle

totheamplifier'sPHONOjack.

Cautton:

Donotconnecta highlevel

audioinputsource,suchasa ceramic

cartridgeturntable,tothePHONO

inputjack.Doingsocouldcausesound

distortion.

QROUNDWRE

Notes

•Toavoida lowfrequencyhum,

con-

nectyourturntable'sgproundwire

(usuallyblad<orgreen)totheampli-

fier'sGNDscrew.

»Topreventa tjeatorhowingsairKJ

duringmonauraloperationinthe

PHONOmode,s^iaratethePHONO

inputlinefromthe^Deaka-wire.

ConnectinganAuxifrary

AudioSource

Youcanconnectanauxiaryaudo

inputsource(suchasa tapedeck,CD

player,cerarrriccartridgeturntableor

tuner)totheamp6fier'sAUX.COjack.

mr["mum'

^ ^

^JSSHJO

Note:

Toconnecta stereoaudto

sourcetotheAUX.COjack,usea

shiekledY-adapter,su*asCat.No.

42-2438(notsuppled).

PUCINGTHESPEAKERS

Sf»akerptecanaitdepencteonyour

room'ssizeandanrangerr^itWere-

commaxJyoupiaya wide-rangere-

corcfingandexperimentwithspeaker

placementuntilyoufirto thelocations

ttratresultinthebest

sound.

ThefoBow-

ingdrawings^x)wrecommerxjed

qjeakerplacementsfortypical,nanow,

aixlwkJesoundcoverage.

lyptealCovofsge

*^oo9-

•$oo9-

-Q009.

.QooQ-

Usethe^tortestlatgthofwirepossitde

toconnecttheqaeakers.Afterplacing

thespeakers,detemninethevinrelength

andchoosetfieapfiv'opriategaugesize

asfoUows:

WireLength

25feetorless

Over25feet

WireGauge

18-gauge

16-gauge

SngiaSpsaksr(NanowCcwsrsse)

Note:

Ifyouconnectspeakerswithout

transfomners,thespeakerwireshouto

benolongerthan50feet

CONNECTINGTHE

SPEAKERS

Youcanconnectoneormore4-,8-or

16-ohmspeakers,withorwittrauttrans-

formers,betweentheamplifier'soutput

andthespeakers'inputToensure

equalvolumefromeachspeaker,allttre

connectedspeakersshouldhavethe

sameimpedancerating.

Removeabout1 inchofinsulationfrom

theendofeachwire.Thentwisttfieex-

posedwiretosecureallitsstrands.

I#l't\

b0 0 0^

b0 c_o3-

)0 c_o5-

>0 d 0^

0 j^oS-

IW0Speakers(WMeAreaCoverase)

•

W///C

Connecttfiespeakerwiretotheampli-

fierandthespeaker(s)bypressing

downontheappropriatepushterminal

leverandinsertingtheendofttietwist-

edwireintoHieterminal's

hole.

Thenre-

leasethelevertosecurethevwre.

PhasingtheSpe^ricers

Properptia^gisimportantwhenyou

usemorettianonespeakerinttiesame

roomorarea.Out-of-phasespeakers

canloseuptoone-halfofttieirpotential

volume,andcanhavea significanttyde-

creasedbasseffect.

Mostspeakerterminalsarecotor-coded

orhavea markthatindicatettieter-

minal'spotenty.Usually,terminalswith

positivepolarityareredorhavea plus

symbol(+),andterminatevwthnegative

polarityareblackorhavea minussym-

bol(-).

Ptiasingiscon-ectv^rtienyouconnect-F

to-Fand- to-.

DetemiiningTotalSpeaker

Impedance

Caution:

A totalspeakerimpedance

thatishigherthan16ohmsortower

than4 ohmscandamageyouramplifier

orspeakers.

•Speakersareconnectedinseries

whenthefirst^Deaker'spoativeter-

mrialiscorBiectedtothenextspeak-

er'snegativeterminal.Determinethe

totalspeakerimpedanceofspeakers

connectedinseriesbyadcBngupthe

individualimpedancesofaflthe

con-

nectedspeakers.

Forexampte,ifyouwanttoconnect

two8-ohm^leakersinseries,add8

(ttieimpedanceofcmespeaker)plus

8(ttieimpedanceoftheotherspeak-

er)fora totalspeakerimpedanceof

16dims.

COM4 0 8CJISO70V

•Sprakerserecomectedinparallel

v^rtienaflthernegativetaminalsare

connectedto^tfierandafltheir

posi-

tiveterrrwiateareconnectedtogether.

Determinethetotalspeakerimped-

anceofspeakersconnectedinparal-

lelbydividingtheinipedanceofone

speakerbythenumberofspeakers.

Beforeyouconnectspeakerstothe

amplifier,youmustdeterminethetotal

speakerimpedance.Indeterminingthe

totalspeakerimpedance,youmustfirst

detemnineifyourspeakersareconnect-

edinseries,paraUel,ora series/parallel

combinatton.

Forexam|:te,ifyouplantoconnect

two8-ohmspeakersinparaUel,di-

vide8 (theimpedanceofonespeak-

er)by2 (thersjmberofspeakers)fa

atotalspeakerimpec^ceof4

ohms.

COM4 0 8016070V

8Q^

•

Ifyouconnectmorethantwospeak-

asusngonly

seri^

oronlyparaBel

comecttons,thetotalimpedance

mightexceedtheamplifier'smaximum

impedance(16ohnrs)orfaflbelowits

mininrHjnimpedance(4ohms).

Forexample,ifyouconnectfour8-

ofvnspeakers:

-Inseries,ttietotalimpedanceis

32ohms(8-F8 -f8 -F8 = 32).

Thisexceedsthemaximumrating.

-Inparaflel,thetotalimpedance

is2 ohms(8dividedby4 = 2).

Thisfaflsbdowtheminimumrating.

Youcananiveata propertotalim-

pedancebycombiningseriesand

parallelccmriections.

ConnectingOrriyOne

Speaker

Connectthespeaker'snegative(-)ter-

minaltotheamplifier'sCOMtenrrwial.

Thenconnectthe^leaker'spositive

(-F)terminaltotheterminalthatmatch-

esthespeaker'simpedance(4Q,8Q,

or16Q).

isn70V

ConnectingSg;»aker8in

Series

Followthesestepstoconnectspeakers

inseries. COM4 0 8016070V

CannecAthefirstspeaker'spositive

(-F)terminal tothesecondspeak-

er'snegative(-)termirral.

Connectthefirstspeaker'snegative

(-)terminaltotheamplifier'sCOM

tenninal.

3.Connectthesecondspeaker's

posi-

tive(-F)terminaltotheamplifier's

4Q,

8Q,or16Q temninalthat

matchesthetoalspeakerimpectence.

ConnectingSpeakersin

Parallel

Fdtowthesestepstoconnectspeakers

inparallel. CDM408016070V

Connectthespeakers'negative(-)

tenninalstogether.

Connectthespeakers'positive(-F)

tenninalstogether.

3.Connectthespeakers'negative(-)

terminalstottieamplifier'sCOMter-

minal.

Connectthespeakers'positive(-F)

terminalstotheamplifier's4£2,82,

or16Qtenninalthatmatchesthe

totalspeakerimpedance.

ConnectingFourSpeakers

inSeries/ParallelCombination

Followthesestepstoconnectfour

speakersinseries/parallelcombrtation.

COM4(1snisnTOV

KI<IIQK3l>Za)E<|

LjiSllSIJiill:?^

^^y^^

160

Groupthefourspeakersintotwo

pairs.

Connecteadipairofspeakersin

series.Thetotalimpedanceofeach

pairis16ohms(8+ 8 = 16).

3.Connectthetwopairsofspeakersin

parallel.

Thetotalimpedanceofboth

pairsis8 ohms(16/ 2 = 8).

Connectbothspeakers'negative(-)

terminatetotheampfifier'sCOMter-

minal.

5.(Connectboth^jeakers'positive(-F)

terminatetotheampfifier's4Q,8Q,

or16Qterminalthatmatctwsthe

totalspeakerimpedance.

ConnectingSpeakerswith

Transformers

Forthebestresultswhenyouconnect

twoormorespeakerstoyoursystem,

werecommendyouusea linetrans-for-

mer(suchas(^tNo.

32-1031,

not

suppfied)tareachspeaker.

Transfomiersofferttieseadvantages:

•Youcanconnectspeakerswithdiffer-

entimpedancewithoutcausrig

dif-

ferences

outputbetweenthespeak-

ers.

•Youcanaddorremovea speaker

fromtfiesystemwittxxithavingtore-

cateulatettieentiresystem'simped-

ance.

•Youcanreducesignallosswfienyou

usespeakerwireover50feettong.

Linetransformershaveseveralconnec-

torscafledtaps.Theprimarytaps(on

onesideofthetransfonnner)arethein-

puts

and

arerated

watts.

Thesecond-

arytaps(cff)theoppositesicteofthe

transformer)aretheoutputsandare

ratedinohms.

{SECONDARY)

Cauttons:

•Beforeyouconnectthespeakers,be

ajrethetotalwattageoftheprimary

tapsyouintendtousedoesnotex-

ceedtheampfifier'smaximum20-

wattoutputpowerrating.

•Avoidmultipleconnectionstotheamp-

lifier's70VandCOMterminals.

COM

0 an16070V

CDM4 0 8 0 16070V

(PRIMARY)(SECONDARY)

Connecta wirefromtheampliftor's

TOVtenninaltothetransfomner's

pri-

marytapthatmatchesyourspeak-

er'swattegeratFig.

Note:

Usually,eac*speaker

asys-

temusesthesamewattagetap.If

youwanta particularspeakerto

havea highervolumelevel,usea

higherwattagetaponitstransformer.

Connecta wirefromtheampfifier's

COM(common)tenninaltotheC

(common)tapsonthetransfomner's

primaryside.

3.Connecta wirefromthespeaker's

positive(-F)terminaltothetrans-

former'ssecondarytapthatmatches

thespeaker'stotalimpedance(4

ohms,

8 ohms,or16ohms).

Connecta wirefromthespeaker's

negative(-)tenninaltotheC (com-

mon)taponthetransformer'ssec-

ondaryside.

CONNECTINGPOWER

Youcanpoweryouramplifierfrom

stan-

dardACpowerorfroma 12-vdtDC

powersource(suchasyourvehide's

battery).

UsingACPower

TousestandardACpower,simplyplug

thesuppfiedACcorclintoanystandard

ACoutiet.

UsingVehicle

BatteryPower

Youcanpowertheamplifierfromyour

vehicle's12-voltbattery.

Cautinn:

•Yourvehidemusthavea negative-

grounddectricalsystem.Ifyouare

unsureaboutwhattypeofelectrical

systemyourvehide

has,

askyourve-

hidedealer.

•DisconnecttheACconjbeforeyou

connecttiie DCpowercable.

Touse12-vottDCpower,connectthe

suppliedDCpowercable'ssmallendto

theampfifier's12VNEGATIVEGND

jack.Thenconnectthecable'sother

endtoyourvehide'scigarette-lighter

socket.

ReplacingtheDCCable's

Fuse

Thecable's4A,125-voltin-linefuse

protectsyourampfifierfromvoltage

surges.Iftfieampfifier'spowerindicator

doesnotlightwhenyoupressPOWER,

checkthefuse.Ifitisbtown,replaceit

witha 4-amp,125-voltfuse(suchas

Cat.No.270-1010,notsupplied).

Toreplacettie fuse,unscrewttie tip of

tiie dgarette-lighter

plug.

Thenremove

theoldfuseandinserttfienewfuse.

Securetiie fusebyreattedwigthe

plug'stip.

ReplacingtheAmplifier's

Fuse

Thefuse(locatedonttie backofttie

ampfifier)protectsyourampfifierfrom

power(vottageorcunrent)surges.Ifttie

POWERHidicatordoesnotlightwfien

youpressPOWER,tiie fusemightbe

btovm.

CautfanuUseonlyanidentical5 x 20

mm,

fast-acting,2-amp,250-voltfuse

(suchasCat.No.270-1052).

Foflowthesestepstoreplacetiie ampfi-

fier's

fuse.

Unpfijgtheampfifier'spower

cord.

Usanga tiatislade saewdriver,push

andtijm tiie fuseholder'scapcoun-

terdockwiseuntfltfiefijse holder

popsout.

3.Removettie fuseholderandrepbce

ttie

fuse.

Usriga flatt}lade saewdriver,push

andtijm ttiefuseholder'scapfuOy

dockwisetoreplaceit.

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