API 3124mb+ - Overview; 3124 mb+ Features and Introduction

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2.0 Overview 
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Inpu ts
 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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