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    ModelLA-2A

    LevelingAmplifier

    UniversalAudio,Inc.www.uaudio.comPOBox3818

    SantaCruz,CA95063-3818

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    ii

    TeletronixLA-2AbyUniversalAudio

    Thank you for purchasing this reproduction of the Teletronix LA-2A. The LA-2A was

    originally

    produced

    inthe

    early1960s

    by

    Teletronix,

    which

    was

    later

    acquired

    byBabcockElectronicsCorporation. My fatherpurchased theproductrightsand thenameTeletronix from Babcock Engineering in 1967, folding it into his Studio ElectronicsCorporation, shortly before he changed the name to UREI. There were three differentvariations of the LA-2A during this period before productionwas discontinued around1969.

    Straightforward initsdesign,and initially intendedforbroadcastapplications, theLA-2Aquicklybecamestandardequipmentinstudiosworldwide.Manyhavebeenpainstakinglymaintainedfor the30yearsthat theyhaveremained inusesinceproductionstopped.Atube-based compressor, the LA-2A features hand-wired components and two simplecontrols.Atthetime,itselectro-luminescentopticalgainreductionwasquiterevolutionary:applying

    the

    audio

    signal

    to

    an

    electro-luminescent

    light

    panel

    which

    shines

    on

    aphoto-

    electriccellwhichinturncontrolsthegain. Incontrasttotheelectro-opticaldeviceswhichpreceded it, the electro-luminescent light source provided the fast attack necessary forbroadcast applications. Additionally, the cadmium-sulfide photo-cells provided a verynatural two-stage release which resulted in a compression characteristic more

    transparent than the other compressors of its day. To this day the LA-2A delivers atrademarksoundtreasuredbyengineersworldwide.

    Here at Universal Audio, we have gone to great lengths to recreate the LA-2A withcompleteauthenticity. Itsbeennosmall feat to locateobscureparts,putqualitycontrolprograms in place that didnt exist 30 years ago and find personnel capable of the

    handworkthat

    goes

    into

    eachunit

    .

    Every

    stepwas

    necessary

    to

    ensurethat

    each

    LA-2Adeliversthesoundyouexpect.

    As for the future,we areworking on additional reproductions beyond the LA-2A and1176LN. To thatend,weare interested inyouropinionsaboutyour favoritepiecesofvintagegear. Whatcantyoulivewithout? Whatwouldyoulovetoown,butcantfindany longer? Inaddition,UniversalAudio isworkingonnewproductsdesigned tomeetthedemandsofthemoderndigitalrecordingstudio,yetretainingthecharacterofclassicvintageequipment.

    Developing theseproducts hasbeenquiteanadventure,enjoyedbyall involved. Wethankyouforyoursupportandwethankmyfather,BillPutnam.

    Thankyou,

    BillPutnam

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    iv

    LA-2A!!!!UsersGuide

    UniversalAudio,Inc.

    PO

    Box3818

    SantaCruz,CA95063-3818(831)454-0630voice

    (831)454-0689faxwww.uaudio.com

    UniversalAudioPartNumberLA2A-M01.Revision1.3

    Notice

    Thismanualprovidesgeneralinformation,preparationforuse,installationandoperatinginstructionsfortheUniversalAudioLA-2ALevelingAmplifier.

    Theinformationcontainedinthismanualissubjecttochangewithoutnotice.UniversalAudio,Inc.makesnowarrantiesofany kindwith regard to thismanual, including,butnot limited to, the impliedwarrantiesofmerchantability and fitness for a particular purpose. Universal Audio, Inc. shall not be liable for errorscontained hereinordirect, indirect, special, incidental,or consequentialdamages in connectionwith thefurnishing,performance,oruseofthismaterial.

    Copyright

    "2000UniversalAudio,Inc.Allrightsreserved.

    Thismanual

    and

    any

    associated

    software,

    artwork,

    product

    designs,

    and

    design

    concepts

    are

    subject

    to

    copyright protection.No part of this document may be reproduced, in any form, without prior writtenpermissionofUniversalAudio,Inc.

    Trademarks

    LA-2A,1176and theUniversalAudio, Inc. logoare trademarksofUniversalAudio, Inc.Othercompanyandproductnamesmentionedhereinaretrademarksoftheirrespectivecompanies.

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    v

    TableofContents

    TeletronixLA-2AbyUniversalAudio................................................................................... ii

    Specifications ....................................................................................................................... 1

    OperationoftheLA-2A .......................................................................................................2

    InputandOutputConnections ............................................................................... 2

    PeakReductionControl ........................................................................................ 2

    GainControl ....................................................................................................... 2

    VUMeterOperation ............................................................................................ 3

    Limit

    /

    Compress

    Switch........................................................................................ 3Calibration ........................................................................................................................... 4

    MeterZeroAdjust............................................................................................... 4

    Side-ChainPre-Emphasis(R37).............................................................................. 4

    StereoBalanceAdjust(R3) ................................................................................... 4

    TheoryofOperation ............................................................................................................ 5

    CompressorBasics ............................................................................................... 5

    GainReductionCircuit.......................................................................................... 8

    Side-ChainCircuit .............................................................................................. 11

    OutputCircuit.................................................................................................... 11

    MeteringCircuit................................................................................................. 11

    Appendix .......................................................................................................................... 12

    CreativeClassics:The1176SolidStateLimitingAmplifierandtheLA-2A

    LevelingAmplifier .............................................................................................. 12

    TheLA-2A ..................................................................................................... 12

    Developing

    the

    1176..................................................................................... 13

    MoreThanaVintageFad:ClassicSound.......................................................... 13

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    1

    Specifications

    ! Gain

    Reduction:up

    to

    40

    dB

    ! Distortion:lessthan0.35%totalharmonicsat+10dBm,andlessthan0.75%totalharmonicsat+16dBmoutput

    ! Response:+/-0.1dB,30cyclesto15kilocycles

    ! Noise:75dBbelow+10dBmoutputlevel

    ! Gain:40+/-1dB

    ! OutputLevel:+10dBmnominal,+16dBmpeaks

    ! InputLevel:+16dBmmaximum

    ! Very

    fast

    attacktime

    ! ReleaseTime:approximately0.06secondsfor50%release,0.5to5secondsforcompletereleasedependingupontheamountofpreviousreduction

    ! InputImpedance:600ohmsbalanced

    ! OutputImpedance:600ohmsbalanced

    ! PanelSize:19x5

    ! DepthBehindPanel:7

    ! PanelControls:Gain(Outputlevel),PeakReduction,andMeterSelectorSwitch

    ! Meter:

    dB

    Gain

    Reduction

    and

    dB

    Output

    ! TubeComplement:(2)12AX7A,(1)12BH7A,(1)6AQ5

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    2

    OperationoftheLA-2A

    InputandOutputConnections

    Input

    and

    Output

    connections

    are

    made

    using

    standardXL

    R

    style

    connectors. T

    erminalstripsarealsoprovided.

    Outputconnections Inputconnections

    6) StereoLink 1) +600ohms7) Ground 2) +250ohms8) +600ohms 3) Centertap9) Centertap 4) -250ohms

    10) -600ohms 5) -600ohms

    BarrierStripConnections

    IfyouwishtousethebarrierstripinsteadoftheXLRconnectors,connectasfollows:INPUT: Connect +600(1)toHOTand600(5)toNEUTRAL.OUTPUT:Connect+600(8)toHOTand600(10)toNEUTRAL.

    ConnectGround(7)tothecableshield.

    PeakReductionControl

    OperationoftheLA-2Aisverystraightforward. Thereareonlytwocontrolsthatonemustdealwith. The first is thePeakReductioncontrol. Thiscontrolshouldbesetso that the

    compressor

    exhibitsthe

    desired

    amount

    ofcompression

    .

    Thiscontrol

    should

    be

    setindependentlyoftheGainControl.

    GainControl

    This controldoes not affect the compression. The gain control should be set after thedesiredamountofcompressionisdeterminedusingthePeakReductioncontrol. OncethePeakReductioncontrolisset,adjusttheGainControltoachievethedesiredoutputlevel.

    PowerTransformer

    12AX7

    6AQ5

    12AX712BH7

    R3