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IDescriptionLM1875isapoweramplifierintegratedblockchip.Itssuperiorperformanceandattractivetonehavebeenacceptedbymanyenthusiasts,anditwasalltherageinthe1990s.LM1875adoptsTO-220packagestructure,whichisshapedlikeamid-powertube,smallinsize,simpleinperipheralcircuits,andlargeinoutputpower.Theintegratedcircuitintroducedinthisblogisequippedwithoverload,overheatingandinductiveloadreversepotentialsafetyprotection,whichisoneoftheidealchoicesforhigh-endaudio.Figure1.LM1875CatalogIDescriptionIILM1875ParametersIIILM1875CircuitPrincipleIVLM1875CircuitAssemblyandDebuggingVIntheEndOrdering&QuantityIILM1875ParametersVoltageRange16~60VQuiescentCurrent50MmAOutputPower25WHarmonicDistortion0.02%,whenf=1kHz,RL=8,P0=20WRatedGain26dB,whenf=1kHzWorkingVoltage25VConversionRate18V/SIIILM1875CircuitPrincipleThiscircuitiscomposedofanattenuatedtonecontrolcircuitcontrolledseparatelyforhighandlowsounds,LM1875amplifiercircuitandpowersupplycircuit.Amongthem,thesoundqualitycontrolpartusesanattenuatedtonecircuitcontrolledseparatelyforhighandlowsounds.Thespecificcomponentsareasfollows:R02,R03,C02,C01,W02formabasscontrolcircuit;C03,C04,W03formatreblecontrolcircuit;R04istheisolationresistance;W01isthevolumecontroller,whichadjuststhevolumeoftheamplifier;C05isanisolationcapacitortopreventthedownstreamLM1875DCpotentialelementfromaffectingtheprevioustonecircuit.TheamplifyingcircuitmainlyadoptsLM1875,whichiscomposedof1875,R08,R09,C066,etc.ThemagnificationofthecircuitisdeterminedbytheratioofR08toR09;C06isusedtostabilizethedriftoftheLM1875s4thpinDCzeropotential,butithasacertainimpactonthesoundquality;C07andR10functiontopreventtheamplifierfromgeneratinglow-frequencyself-excitation.InAddtion,theloadimpedanceofthisamplifieris416.Figure2.LM1875CircuitWhataboutthepowersupplycircuitofthepoweramplifier?Pleasetakealookatthepicturebelow.Inordertoensurethesoundqualityofthepoweramplifierboard,weneedtopayattentiontothefollowingwhendesigningthecircuit:Theoutputpowerofthepowertransformershallnotbelessthan80W;Theoutputvoltageis2*25V;Thefiltercapacitorusestwo4700UF/25Velectrolyticcapacitorsinparallel;Positiveandnegativepowersuppliesshare44700UF/25Vcapacitors;Thetwo104basecapacitorsarehigh-frequencyfiltercapacitors;Onlyiftheaboverequirementsaremet,theamplifiercanmaintainbettersoundquality.Figure3.LM1875CircuitIVLM1875CircuitAssemblyandDebuggingThisblogwillintroducethenecessarytoolsforcircuitassembly,howtoprepareforsoldering,andfinallyhowtodebugthecircuit.Ofcourse,ifyoustillfeellikeyouarestillcannotgetenough,intheendyoucanevenfollowourtipstotryanextrainterestingexperimentwiththiscircuit.ToolsThatYouNeedA20Welectricsolderingiron,preferablywithadjustabletemperature;Amultimeter;Apairofneedlenosepliers;Ascrewdriver;Somesolderwireandpineperfume.HowtoPrepareforWeldingWeldingsequence:①Weldingjumpers;②Weldingresistance;③Weldingcapacitor;④Weldedrectifiertube;⑤Weldingpotentiometer;⑥WeldLM1875.NotesFixtheLM1875withscrewsontheheatsinkbeforeweldingLM1875,otherwisethescrewswillbedifficulttodriveinwhentheheatsinkisinstalledattheend;ThepartofLM1875incontactwiththeheatsinkmustbecoatedwithasmallamountofheatdissipationgreasetofacilitateheatdissipation;Payattentiontotheweldingqualitywhenwelding.Forbeginners,youcanpracticeafewmoretimesontheoldcircuitboard,andthenformallysolder.HowtoDebugCorrectlyThedebuggingofthispoweramplifierboardisverysimple.Afterthecircuitboardissolderedwithelectroniccomponents,wemustcarefullycheckthecircuitboardforsolderingerrors.Specialattentionshouldbepaidtoelectronicpartswithpolarity,suchaselectrolyticcapacitorsandbridgerectifiers.Oncetheweldingisreversed,thereisariskofburningthecomponents.Whenthetransformerisconnected,theoutputterminaloftheamplifierisnotconnectedtothespeaker,butconnectedtoamultimeter(preferablydigitaldisplay,andthemultimeterissettoDC*2V).Inaddition,payattentiontothereadingofthemultimeterwhenpoweringonthepoweramplifierboard.Undernormalcircumstances,thereadingshouldbewithin30mV,otherwiseweshouldimmediatelycutoffthepowertocheckthecircuitboard.Ifthereadingoftheelectricmeteriswithinthenormalrange,itindicatesthatthefunctionofthepoweramplifierboardisbasicallynormal.Atthistime,weconnectedthespeaker,theninputthemusicsignal,andthenpoweronthetestmachine.Underthecorrectproceduresandspecifications,turnthevolumepotentiometer,thevolumeshouldchange,andturnthehighandlowknobs,thetoneofthespeakerwillchange.Figure4.LM1875ExperimentWorthTryingFirst,wewillshort-circuitC6andmeasuretheDCpotentialattheoutputofLM1875withamultimetertoseeifitiswithin30MV.Then,connectthespeakerandtestfortwohours.UseamultimetertomeasuretheDCpotentialattheoutputoftheLM1875toseeiftheDCpotentialiswithin30MV.IftheDCpotentialiswithin30MV,thecapacitorC6canbeomitted.Inthiscase,theamplifierboardbecomesapureDCpoweramplifier.VIntheEndSofar,thepoweramplifierboardhasbeensuccessfullyinstalledandadjusted.Lookingatthispieceofworkthatyoucanbeproudofandenjoyingthewonderfulmusic,areyousatisfied?

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