music, recording music and building recording studios

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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