GRAS 12AA Manual de usuario

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Instruction Manual





Revision 20 05 2019

Power Module

Type 12AA

G.R.A.S. Sound & Vibration

CONTENTS

1. Introduction and Description ......................................4

1.1 Polarization Voltage ................................................4

1.2 PreamplierVoltageSupplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 SignalConditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

FrequencyResponse ......................................................6

Gain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Direct-modeCoupling ......................................................6

1.4 SysCheck(SystemCheck) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.5 PowerSupplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.6 Input/Output ......................................................6

2. External Features ................................................7

2.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Rear Panel .......................................................8

3. Internal Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 BatteryPack ......................................................9

3.2 User-servicableSwitches ............................................9

4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1 BatteriesandExternalPower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.2 PolarizationVoltageandPreamplierVoltage ........................... 11

4.3 FilterSettingsandDirectMode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.4 SysCheck(SystemCheck) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5. Service and Repair ..............................................12

6. Specications ..................................................13

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 4

1. Introduction and Description

TheG.R.A.S.PowerModuleType12AA(Fig.1.1)isadual-channelpowersupplyforpreampli-

ersusedwithcondensermicrophones.Itisforgeneraluseinacousticmeasurementsaswell

asforintensitymeasurements;bothinthelaboratoryandintheeld.

Itprovides:

• apolarizationvoltagefortwocondensermicrophones

• avoltagesupplyforpoweringuptotwomicrophonepreampliers.

• achoiceofsignalconditioning.

AblockdiagramofitsmaincomponentsisshowninFig.1.2.

1.1 Polarization Voltage

Thepolarizationvoltagecanbesettoeither0Vor200Vviaaninternalswitch(seesection3.2).

Use:

• 0Vforprepolarizedmicrophones,and

• 200Vforexternally-polarizedmicrophones(defaultsetting)

1.2 PreamplierVoltageSupplies

Thepreampliervoltagesupplycanbesettoeither28VDCor120VDCviaaninternalswitch

(seesection3.2).Use:

• 28Vforminimumpowerconsumption(defaultsetting),and

• 120Vformaximumdynamicrange

Fig. 1.1 Power Module Type 12AA

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 5

Fig. 1.2 Block diagram of the Type 12AA

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 6

1.3 Signal Conditioning

1.3.1 Frequency Response

Thefrequencyresponsecanbesettooneofthefollowingviainternalswitches(seesec-

tion3.2):

• Linear

• A-weighted

viastandardA-weightingltersfulllingtherequirementsofIECStandard60651“Sound

LevelMeters”Type0.

• High-pass

via3-poleButterworthhigh-passlterswitha–1dBcutoffatafrequencyof20Hz

Whicheveroneisselectedisappliedtobothchannels.

1.3.2 Gain

Thegainofeachchannelcanbesetindependentlytooneofthefollowing:

• –20dB

•   0 d B

•   20dB

•   40dB

1.3.3 Direct-mode Coupling

Finally,themicrophonesignalfromeachpreampliercanbecoupleddirectlywithitsBNC

outputsocketviaindependentinternalswitches(seesection3.2),thusby-passingallsignal

conditioning.Forintensitymeasurements,whereextremelygoodphasematchingisrequired,

useDirectmodeinbothchannels.Also,tofullyusethedynamicrangepossiblewith120Vpre-

ampliersupply,useDirectmode,seealsoSection4.2.

1.4 SysCheck (System Check)

TheType12AAhasabuilt-in1000HzSysCheckgeneratorforverifyingthestabilityofthecom-

pletemeasuringsystemincludingthemicrophone.

Thesignallevelfromthegeneratorcanbepre-adjustedbeforeitisappliedtothemeasurement

set-up.Asystemcheckcanbeactivatedlocallyviaapushbuttononthefrontpanel,orremotely

viaaMiniJacksocketontherearpanel.

SysCheck(orsimilartechnique)canbeusedwithpreamplierssupportingthisfeature,e.g.the

G.R.A.S.preampliersType26AJandType26AL.

1.5 Power Supplies

TheType12AAcanrunoninternalbatterieswithabatterylifeofapproximately10hoursusing

G.R.A.S.preampliers,orfromanexternalpowersupplyof12-18VDC,e.g.themains/line

adapterincludedwiththeType12AA.

1.6 Input/Output

TheType12AAhastwo7-pinLEMOinputconnectors(AandB)formicrophonepreampliers

suchastheG.R.A.S.PreampliersTypes26AM,26ACand26AK.Fig.2.2showsthewiringdia-

gramoftheseinputconnectorswhicharealsocompatiblewitharangeofmicrophonepreampli-

ersfromothersupplierssuchasNorsonic,L&DandBrüel&Kjær.

Thecorrespondingoutputsforthetwo7-pinLEMOinputconnectorsareavailableviastandard

BNCsockets(AandB)fordirectusewithanalyzers,voltmeters,oscilloscopesetc.

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 7

2. External Features

2.1 Front Panel

Thefrontpanelhasthefollowingfeatures(seeFig.2.1)

• Powerswitchandbattery-levelmeter.

Ifthepowersupplyiscorrect,thebattery-levelmeterwillpointtothegreenzone.Ifitpoints

totheredzone,eitherthebatteriesarelowandshouldbechanged(seesection3.1)orthe

externalDCsupplyvoltageistoolow.

• SysCheckpush-button.

Pressandholdtoactivatethe1000HzSysCheckgenerator.Thesignalfromthegenerator

willbeavailableonpin1(seeFig.2.2)ofeachPreamplierInputsocket.

• SysCheckadjustmentpotentiometers(Ch.A/Ch.B).

UseasmallscrewdrivertoadjusttheleveloftheSysChecksignalavailableonpin1(see

Fig.2.2)ofthePreamplierInputsocket.Adjustmentisindividualforeachchanneland

rangesfrom0to5.6VRMS.

• PreamplierInputChannels(In. A/In. B).

7-pinLEMOinputconnectorformicrophonepreamplier.WiringdiagramshowninFig.2.2

• GainswitchesandOverloadLEDs(In. A/In. B).

Adjustthegainofeachchannel(attenuator/amplier)individuallytosuitrequirementsand

withoutoverloadingtheinputcircuits(OverloadLEDlightsup).Gainsettingsarefrom

–20dBto+40dBin20dBsteps.DisabledifDirectmodeisselected(seesection3.2).

Whensetto+40dB,theOverloadLEDlightsupwithopeninput.Thisisnormal.

Fig. 2.1 Front panel of the Power Module Type 12AA

Battery-levelindicator

SysCheckpushbutton

PreamplierinputCh.A

PreamplierinputCh.B

Power,On/Offtoggleswitch

OverloadLEDCh.A

SysCheckadjustmentCh.A SysCheckadjustmentCh.B

OverloadLEDCh.B

GainCh.A,rotaryswitch

(-20,0,+20and+40dB)

GainCh.B,rotaryswitch

(-20,0,+20and+40dB)

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 8

2.2 Rear Panel

Therearpanelhasthefollowingfeatures(seeFig.2.3)

• Twist/releaseholderfor315mA,250Vlow-impedance(<1.5Ω)fuse.

• Inputsocketforanexternalpowersupplyof12 - 18 V DC;centrepin+terminal.Theuseof

anexternalpowersupplyautomaticallydisablespowerfromthebatteries.

• Remote SysCheck Start.

MiniJackinputforremoteSysCheckstart.Applya+DCvoltageof4-9V(e.g.fromthe

RS232outputofacomputer)toactivatetheSysCheckgenerator;centrepin+terminal.

• Ouputchannels(Out A/Out B).

BNCsocketfortheoutputsignaleitherviasignalconditioningordirectlyfromthemicro-

phonepreamplier.

• Lockingscrew

Unscrewtoremovebaseplateandgainaccesstointernalsettingswitches.

Fig. 2.3 Rear panel of the Power Module Type 12AA

Fig. 2.2 7-pin LEMO female socket 1B (external view)

Fuse315mA(<1.5Ω),250V

Inputforexternalpowersupply

12-18VDC

RemoteSysCheckstart

OutputCh.A

OutputCh.B

Lockingscrewfor

baseplate

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 9

3. Internal Features

Note:switchtheType12AAoffanddisconnectitfromanyexternalpowersupplybeforeremov-

ingthebaseplateforanyreason.Afterwardsreplacethebaseplate.

Thebatterypackanduser-servicableswitchesarecontainedwithinthecabinetoftheType

12AA.Togainaccesstothese,rstremovetheknurledlockingscrew(seeFig.2.3)andslide

thebaseplateoff.

Fig. 3.1 Showing the battery pack of the Power Module Type 12AA

3.1 Battery Pack

Takeoutthebatterytray(Fig.3.1)andreplaceallthebatteries(10xLR6(AA)standardalkaline

cells),makingsurethatthepolarityisasindicatedonthebatterytray.

3.2 User-servicable Switches

The(internal)user-servicableslideswitchesareshowninFig.3.2.

• Filter selection(applicabletobothchannels,disabledifDirectmodeisselected):3-posi-

tionsignal-conditioningswitch;

- Lin.

routesthesignalthroughtheamplieralone

- H.P.

routesthesignalthroughtheamplierandthe20Hzhigh-passlter(e.g.tosupress

infra-sound)

- A-w

routesthesignalthroughtheamplierandtheA-weightingnetwork

• Direct mode select:2-positionswitch(oneforeachchannel):

- Dir.

selectstheDirectmodeandby-passestheFilter selectionswitchforthischannel

andtheampliercircuit(seeabove)

- Ampl.

enablestheFilter sectionswitchforthischannelandtheampliercircuit(seeabove)

• Preampliersupplyselectpairofswitches:

- Polarization voltage2-positionswitch(applicabletobothchannels)selects:

0 V  forprepolarized(electret)microphones

or 200 V forexternally-polarizedmicrophones

- Supply voltage2-positionswitch(applicabletobothchannels)selects:

120 V formaximumdynamicrange

or 28 V forminimumpowerconsumption

G.R.A.S. Sound & Vibration

Power Module Type 12AA - Page 10

Fig. 3.2 Showing the internal switches of the Power Module Type 12AA

Filterselection

• Linear

• HighPass

• A-weighting

Ch.B

• Directmode

• Ampliermode

Ch.A

• Directmode

• Ampliermode

Polarization voltage

• 0 V

• 200 V

Supplyvoltage

• 120 V

• 28 V

Note:

SwitchoffthePower

Modulebeforechang-

inganypreamplier

power settings

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