Api 3124mb+ User manual

3124mb+

All‐Discrete

4‐ChannelMic/InstrumentPreamplifier

withStereoMixer

Operator’sManual

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WrittenbyCarlJHoude

2015

2

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TableofContents

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1.0 Introduction......................................................................................................................................................3

2.0 Overview..........................................................................................................................................................4

2.1 3124mb+FeaturesandIntroduction............................................................................................................4

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3.0 SignalFlowandBlockDiagrams........................................................................................................................5

3.1 3124mb+SignalFlow....................................................................................................................................5

3.2 AdditionalRouting........................................................................................................................................5

3.2.1 Insert................................................................................................................................................5

3.2.2 AuxiliarySend/Return......................................................................................................................5

3.3 PreamplifierBlockDiagram..........................................................................................................................6

3.4 StereoMixerBlockDiagram.........................................................................................................................7

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4.0 InputSection:Mic/Instrument/LinePreamplifier..............................................................................................8

4.1 PreamplifierOverviewandFeatures............................................................................................................8

4.2 PreamplifierControls....................................................................................................................................8

4.3 InputSelection..............................................................................................................................................9

4.3.1 MICSwitch.......................................................................................................................................9

4.3.2 MicrophoneInput............................................................................................................................9

4.3.3 InstrumentInput............................................................................................................................10

4.4 PolarityInverter..........................................................................................................................................10

4.5 VUMeter.....................................................................................................................................................10

4.6 DirectOutput..............................................................................................................................................10

4.7 PreamplifierBlockDiagram........................................................................................................................11

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5.0 OutputSection:StereoMixer..........................................................................................................................12

5.1 StereoMixerOverviewandFeatures.........................................................................................................12

5.2 StereoMixerControls.................................................................................................................................12

5.2.1 Masters..........................................................................................................................................12

5.2.2 AuxiliaryLevel................................................................................................................................12

5.2.3 AuxiliaryReturnPan......................................................................................................................13

5.3 StereoMixerBlockDiagram.......................................................................................................................13

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6.0 PanelInterfaces..............................................................................................................................................14

6.1 AudioPathInputs.......................................................................................................................................14

6.1.1 FrontPanel.....................................................................................................................................14

6.1.2 RearPanel......................................................................................................................................14

6.2 AudioPathOutputs.....................................................................................................................................14

6.2.1 RearPanel......................................................................................................................................14

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7.0 ACPower........................................................................................................................................................15

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8.0 CustomerSupport...........................................................................................................................................15

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Appendix....................................................................................................................................................................16

i. Specifications..............................................................................................................................................16

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3

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1.0 Introduction

ThankyouforpurchasingAPI’s3124mb+!Thisisthe3124mb+operator’smanual.Thepurposeoftheoperator’s

manualistoguideyou,theaudioengineer,throughthe3124mb+featuresandfunctions.Whatfollowsisa

comprehensiveguidethatwillexplainhowandwhyeachfeaturecanbeusedinaprofessional,project,orhome

studio.Eachofthe3124mb+preamplifierandstereomixerparametersiscovered.Includedaresignalflow

schematicsandblockdiagramsthatmayhelptroubleshootanyissuesthatarisewhenusingthe3124mb+.After

readingthisoperator’smanual,youwillbearmedwithallthenecessaryknowledgetoefficientlyusethe

3124mb+sothatyoucanspendmoretimemakingmusic.

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2.0 Overview

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Boththe3124+andthe3124mb+(seeFigure1)aredesignedwiththeprofessionalengineerinmind.Bothunits

givethehighestpossiblequality4channelmicpreamp.However,the3124mb+providesanadditionalaudio

mixerwithatransformerbalancedoutput,keepingtheunitsizeandpriceatareasonablelevel.Bothmodelsare

equallyathomeinthecontrolroom,studio,andrecordingtruckoronstage.

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2.1 3124mb+FeaturesandIntroduction

Features

UsesAPI2520Op‐Amp

ClassicConsoleCircuit

FourXLRMicInputs

Four¼”UnbalancedInputs

FrontPanelPolaritySwitch

FrontPanel20dBPadSwitch

FrontPanelMicSwitch

Frontpanel48VPhantomPowerSwitch

OutputClipsat+30dBm

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The3124mb+utilizesthesamemicrophonepreampcircuitthatisusedinallAPIconsoles.Itusesa115Ktype

micinputtransformeralongwiththesameAPIproprietaryoutputtransformerthatisusedacrossAPI’sproduct

line.Theunithasaninternal48voltphantompowersupply,whichisfrontpanelswitchableforeachchannel.

Alsoprovidedisafrontpanel‐20dBpadswitchthataffectsboththerearmicinandfrontHi‐Zin.A¼”phone

jackisavailableontherearpanelforeachchannelasaninserttip‐send/ring‐returnplacedbetweenthemic

preampoutputandthemixerinput.

Likethe3124+,the3124mb+providesupto65dBofgaintoanoutputcliplevelof+28dBu.TheHi‐Zfrontpanel

inputgoesdirectlytotheop‐amp,allowingalowlevelinputsuchasaguitarorbasstobeamplifiedwithouta

matchingtransformerordirectbox.ThisHi‐Zinputcanacceptinputlevelsashighas+20dBu,makingitperfect

forkeyboardsandotherhighleveldevices.TherearoutputisanXLRconnector.

Additionally,the3124mb+addsastereopannerwithalevelcontrol,andapost“fader”auxsend.Thestereo

pannersandtheauxsendsarebussedtomasteroutputcontrolsandthentotherearpaneljacks.Astereoaux

returnisprovidedtoreturneffectsorcascadeadditionalmixersformoreinputs.Theuniquestereoauxreturn

controlactstobalancetheleftandrightsignal,yetstayingstereo.Itcanalsobeusedasamonoreturn.

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Figure1:3124mb+FrontPane

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3.0 SignalFlowandBlockDiagram

3.1 3124mb+SignalFlow

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3.2 AdditionalRouting

3.2.1 Insert

EngagingtheINSERT,byconnectingaTRScabletotheINSERTjack,willaddtheINSERTrouting

toachannel’ssignalflow.TheTRScable’s“tip”carriesthesignaloutfromthe3124mb+channel

andthecable’s“ring”carriesthereturningsignalfromtheinsertdevice.Thiscanbeusefulfor

addingsignalprocessingtoanindividualchannel.

3.2.2 AuxiliarySend/Return

AUXILIARYfunctionsarecontrolledfromthe3124mb+frontpanel.Eachchannelhasits

respectiveAUXknobwhichcontrolhowmuchofachannel’ssignalisbeingsenttotheAUXbus.

ThesummedAUXsignalcanthenbesentandreturnedtoanexternalsignalprocessorvia

independentTRSconnections.AUXlevelandAUXreturnpancanbeadjustedbyusingthe

respectiveknobslocatedonthe3124mb+frontpanel.

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Figure2:SignalFlow

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3.3 PreamplifierBlockDiagram

Figure3showsablockdiagramthatillustratessignalflowthrougheachpreamplifierchannelofthe

3124mb+.Understandingthesignalflowthrougheachpreamplifierchannelwillhelpdevelopabetter

understandingofhowandwheneachchannel’sparameterscanbeused.

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Figure3:PreamplifierSignalFlow

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3.4 StereoMixerBlockDiagram

Figure4showsablockdiagramthatillustratessignalflowthroughthestereomixersectionofthe

3124mb+.Understandingthesignalflowthrougheachpreamplifierchannelwillhelpdevelopabetter

understandingofhowandwheneachchannel’sparameterscanbeused.

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Figure4:StereoMixerSignalFlow

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4.0 InputSection:Mic/Line/InstrumentPreamplifier

4.1 PreamplifierOverviewandFeatures

Eachofthefour3124mb+preamplifiers(seeFigure5)

isanall‐discretemicrophone/instrument/linepre‐

amplifierdesignedtoprovideanunusuallygood

soundingfront‐endforalltypesofaudiorecording

applications.Sonically,itoffersthedistinctAPIsound,

highqualityperformance,andlownoise.

Eachpreamplifierremainsfaithfultothecircuit

designsofAPI’sfounder,SaulWalker.Fullyfeatured,

eachcarefullypreservestheoriginalsoundcharacter

thatmadeitsomuchapartoftheearlydaysof

recording.

Offeringhighheadroomandawidevarietyofinputsandinputaccesspoints,eachpreamplifieris

equallyathomeinthecommercialrecordingstudioasitisinthehomeprojectstudio.

Features

UsesAPI2520Op‐Amp

XLRMicInput

¼”UnbalancedInput

FrontPanelPolaritySwitch

FrontPanel20dBPadSwitch

FrontPanelMicSwitch

FrontPanel48VPhantomPowerSwitch

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4.2 PreamplifierControls

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 

Eachpreamplifierprovidesacomprehensivesuiteofcontrols:

GAIN:Preampgain

POL:Preampinputpolarityinverter

48V:PhantomPower

PAD:‐20dBmicrophonepad/‐6dBinstrumentpad

MIC:Mic‐Instrumentinputselector

Figure

:Channel1Controls

Figure5:Channel1PreamplifierSection

9

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HI‐ZIN:¼”high‐impedanceinstrumentinput

LEVEL:Stereomixersendlevel

PAN:Stereomixersendpan

AUX:Auxiliarybussendlevel

VUMETER:7LEDVUmeter

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4.3 InputSelection

Eachpreamplifiercanreceivethree(3)inputsources:

MIC(Microphone):RearpanelfemaleXLRmicrophoneinputwithswitchable48Vphantom

power

INST(Instrument):Frontpanel¼”unbalanced‐10dBuinstrumentlevelinput

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4.3.1 MICSwitch

TheMICswitchisusedtoselecttheinputsource.WhenthegreenLEDabovetheswitch

isilluminated,therearpanelXLRinputistheactivesource.WhenthegreenLEDabove

theswitchisnotilluminated,thefrontpanel¼”inputistheactivesource.

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4.3.2 MicrophoneInput

SelectthemicrophoneinputbypressingtheMICswitchandagreenLEDshouldturnon

abovetheMICswitch.TheMICinputconnectionontherearpanelwillbetheactive

input.

FemaleXLRmicrophoneinput

48Vphantompower

‐20dBpad

GreenLEDilluminateswhenMICswitchengaged

VUmeterindicateslevelofpreamplifieroutput

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48V:Provides48voltphantompowertotheMICinputfemaleXLRconnector

RedLEDaboveswitchilluminateswhenengaged

IMPORTANT: Cautionshouldbeexercisedwhenengagingphantompower!Damage

canoccurifphantompowerisappliedtosomeaudiodevices,including

mostribbonmicrophones.The3124mb+outputshouldalsobefully

loweredwhenengagingthe48Vswitch.

‐20dBPAD:Insertsa‐20dBattenuatorafterthemicrophoneinput

YellowLEDaboveswitchilluminateswhenengaged

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GAIN:microphonepreamplifierlevelcontrol

10dBminimumgain(includingPAD)

65dBmaximumgain(includingPAD)

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10

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4.3.3 InstrumentInput

The¼”jackonthefrontpanelistheactiveinputwhentheMICswitchisnot

engaged.

‐10dBinstrumentlevelinput

Unbalanced,high‐impedanceinput(¼”tip‐sleeve)

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GAIN:Instrumentpreamplevelcontrol

14dBminimumgain

50dBmaximumgain

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4.4 PolarityInverter

Apolarityinverter(sometimesreferredtoasa“phasereverse”)isavailableattheinputofthe

preamplifier.

POL(Polarity):Invertsthepolarityofthesignalattheinputofthepreamplifier.

YellowLEDaboveswitchilluminateswhenengaged

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4.5 VUMeter

ThepreamplifieroutputscanbemonitoredviatheVUmeterineachinputsection.

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4.6 DirectOutput

Eachpreamplifier’soutputisavailableatitsrespectiveOUTPUTconnectionontherearpanel.

XLRconnection

PluggingintotheOUTPUTjackdoesnotbreaktheconnectiontotheINSERTjack

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4.7 PreamplifierBlockDiagram

Figure7showsablockdiagramthatillustratessignalflowthrougheachpreamplifierchannelofthe

3124mb+.Understandingthesignalflowthrougheachpreamplifierchannelwillhelpdevelopabetter

understandingofhowandwheneachchannel’sparameterscanbeused.





Figure7:PreamplifierSignalFlow

12



5.0 OutputSection:StereoMixer

5.1 StereoMixerOverviewandFeatures

The3124mb+outputsection(seeFigure8)

offersabuilt‐insummingstereomixerwith

independentleftandrightmasterlevel

controls.Thestereomixeralsoincludesan

auxiliarybuswhoselevelandreturnpancan

becontrolledfromthefrontpanel.



Features

Fullattenuationto+10dBofgain

Highheadroom+28dBcliplevel

TraditionalAPIfullydiscretecircuitdesign

API2520discreteop‐ampwithtransformeroutput



5.2 StereoMixerControls



 

TheStereoMixerprovidesacomprehensivesuiteofcontrols:

LEFT:Masterlevelforleftchannel

RIGHT:Masterlevelforrightchannel

AUX:Auxiliaryreturnlevel

RETPAN:Auxiliaryreturnpan



5.2.1 Masters

LEFT,RIGHT:Mainoutputfaders

Fullattenuation(‐∞)to+10dBofgain

Detentedrotarypotsforeasyrecall



5.2.2 AuxiliaryLevel

AUX:Auxiliaryreturnlevel

Figure9:StereoMixerControls

Figure8:StereoMixerSection

13



Controlsamountofauxiliaryreturnsignalmixedwithmainoutput



5.2.3 AuxiliaryReturnPan

RETPAN:Auxiliaryreturnpan

Controlspanofauxiliaryreturnsignalmixedwithmainoutput



5.3 StereoMixerBlockDiagram

Figure10showsablockdiagramthatillustratessignalflowthroughthestereomixersectionofthe

3124mb+.Understandingthesignalflowthrougheachpreamplifierchannelwillhelpdevelopabetter

understandingofhowandwheneachchannel’sparameterscanbeused.





Figure1

:StereoMixerSignalFlow

14



6.0 PanelInterfaces

6.1 AudioPathInputs

6.1.1 Frontpanel



6.1.2 RearPanel



6.2 AudioPathOutputs

6.2.1 RearPanel





Figure11:FrontPanelInputConnections

Figure12:RearPanelInputConnections

Figure13:RearPanelOutputConnections

15



7.0 ACPower

The3124mb+canoperateoneither115voltsor230volts50‐60HzACpower.

TheACpowerissuppliedviatheIECconnectorontherearpanel.

OperatingvoltageisdeterminedbytheVoltageSelectorswitch.

VoltageSelectorSwitch:Selectsoperatingvoltage

115volts

230volts



Thefuseholderislocatedontherearpanel.

0.5A/0.25A250V



TheACpowerswitchforthe3124mb+islocatedatthelowerrightoftheAPIlogoonthe

frontpanel.

AblueLEDindicatorilluminateswhentheunitison.



8.0 CustomerSupport

Forfurtherinformationandinquires,pleasecontactAPI’scustomersupport:

Callusat301‐776‐7879

Faxusat301‐776‐8117

Emailusat[email protected]





16



Appendix

i. Specifications

InputImpedance:Mic:1500Ω

Unbalanced:470kΩ

Hi‐Z

OutputImpedance:Lessthan75ΩChannelOutputs

NominalLevels:XLRChannelOutput+4dBu

StereoOutputLevel:Balanced:+4

Unbalanced:Nominal‐2

ClippingLevel:XLRChannelOutputbetterthan+28dBm

FrequencyResponse:+0,‐5,10Hzto20kHz(‐0.5at10Hz)

NoiseEIN:Mic:‐129

UnbalancedActual:‐129

MeasuredNoise:Betterthan‐91dBm/BelowNominal+4

Distortion:AllOutputsat+4Out, 0.03%

AllOutputsat+22Out,0.09%

GainRange:150ΩInput: 10dBMin,65dBMax(Incl.PAD)

UnbalancedInput:14dBMin,50dBMax

VUMeter:CalibratedforXLROutputs,OVU=+4dBu

(‐12,‐6,‐3,0,+3,+6,+18)

Controls:GAIN,PAD(20dB),48V(Volts),POL(Polarity),

MIC(Mic/Unbalanced),VU,AC

PowerConsumption,Quiescent:19.2Watts

Size:19”×1.75”(1U)×10.5”Deep

Size(BoxedforShipping):23.25”×6.5”×16”

ActualWeight:11.54lbs.

ShippingWeight:15.3lbs.

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