Workingprinciple
Usethecurrentcontrolfunctionofthetriodeorthevoltagecontrolfunctionofthefieldeffecttubetoconvertthepowerofthepowersupplyintoacurrentthatchangesaccordingtotheinputsignal.Becausesoundiswavesofdifferentamplitudesandfrequencies,thatis,ACsignalcurrent,thecollectorcurrentofthetransistorisalwaysβtimesthebasecurrentintheamplificationarea,andβisthecurrentamplificationfactorofthetransistor.Applyingthispoint,ifthesmallsignalisInjectintothebase,thecurrentflowingthroughthecollectorwillbeequaltoβtimesthebasecurrent,andthenisolatethissignalwithaDCblockingcapacitortoobtainalargesignalwithacurrent(orvoltage)thatisβtimestheoriginal.Becometheamplifyingeffectofthetriode.Aftercontinuouscurrentamplification,poweramplificationiscompleted.
Maincategories
Traditionaldigitalvoiceplaybacksystemsincludetwomainprocesses:
1.Theconversionofdigitalvoicedatatoanalogvoicesignals(usinghigh-precisionDigital-to-analogconverterDAC)toachieve;
2.Useanalogpoweramplifiersforanalogsignalamplification,suchasClassA,ClassBandClassABamplifiers.Sincetheearly1980s,manyresearchershavedevotedthemselvestothedevelopmentofdifferenttypesofdigitalamplifiersthatdirectlyamplifypowerfromdigitalvoicedatawithoutanalogconversion.SuchamplifiersareusuallycalleddigitalpoweramplifiersorclassDamplifiers.
ClassAamplifier:
ThemainfeatureoftheClassAamplifieris:theoperatingpointQoftheamplifierissetnearthemidpointoftheloadline,andthetransistorisintheTheinputsignalisonduringtheentirecycle.Theamplifiercanworkinasingletubeorpush-pull.Sincetheamplifierworksinthelinearrangeofthecharacteristiccurve,transientdistortionandalternatingdistortionaresmall.Thecircuitissimpleandthedebuggingisconvenient.Buttheefficiencyislow,thetransistorpowerconsumptionislarge,thetheoreticalmaximumefficiencyisonly25%,andthereisalargenonlineardistortion.Therefore,theefficiencyisrelativelylow.
ClassBamplifier:
ThemainfeatureofClassBamplifieris:thestaticpointoftheamplifierisat(VCC,0),whenthereisnosignalinput,Theoutputendconsumesalmostnopower.InthepositivehalfcycleofVi,Q1isturnedonandQ2isturnedoff,andtheoutputisapositivehalf-cyclesinewave;inthesameway,whenViisanegativehalf-wavesinewave,twotubesmustbeusedforpush-pullwork.Itischaracterizedbyhighefficiency(78%),butbecausetheamplifierhasasectionofworkinthenon-linearregion,itsdisadvantageisthatthe"crossoverdistortion"isrelativelylarge.Thatis,whenthesignalisbetween-0.6V~0.6V,bothQ1andQ2cannotbeturnedon.Sothistypeofamplifierisgraduallyabandonedbydesigners.
ClassABamplifier:
ThemainfeatureofClassABamplifieris:thetransistor'son-timeisslightlylongerthanhalfacycle,andtwotubesmustbeusedforpush-pulloperation..Canavoidcrossoverdistortion.Thealternatingdistortionislarge,whichcanoffsetevenharmonicdistortion.Ithasthecharacteristicsofhigherefficiencyandlowertransistorpowerconsumption.
ClassCamplifier:
ThemainfeatureofClassCamplifieristhatthetransistoronlyworkswithinashortperiodofeachcycleoftheinputsignal.Whenthecircuitisworking,anegativebiasisusuallyprovidedtotheamplifiertubetoensurethatthetransistordoesnotworkinaClassBstate.ItscollectorloadisnotaresistorbutanLCparallelresonantcircuit,sotheclassCamplifierisalsocalledaresonantamplifiercircuit.Thefrequencyselectionfunctionisachievedbyadjustingthecapacitancevalueofthecapacitorortheinductancevalueoftheinductor.TheconversionefficiencyofclassCamplifiersisextremelyhigh,reaching98%.However,becausetheloadisaresonantcircuit,thecircuitoftenworksathighfrequency,sothedistortionislarge.Therefore,theclassCamplifierisnotsuitableasanaudiopoweramplifier.Onthecontrary,itiswidelyusedintheradioworldbecauseofitsoptionalfrequencycharacteristics,soitisusuallyusedasaradiofrequency.Amplifiers,tuningamplifiersandfrequencymultipliers.
ClassDamplifier:
ClassD(digitalaudiopower)amplifierisakindofinputanalogaudiosignalorPCMdigitalinformationintoPWM(pulseWidthmodulation)orPDM(PulseDensityModulation)pulsesignal,andthenusePWMorPDMpulsesignaltocontrolthehigh-powerswitchingdeviceon/offaudiopoweramplifier,alsoknownasswitchingamplifier.Hastheoutstandingadvantageofhighefficiency.Thedigitalaudiopoweramplifieralsolookslikeaone-bitpowerdigital-to-analogconverter.Theamplifierconsistsofaninputsignalprocessingcircuit,aswitchingsignalformingcircuit,ahigh-powerswitchingcircuit(half-bridgeandfull-bridge)andalow-passfilter(LC)andotherfourparts.ClassDamplifierordigitalamplifier.Thesystemusesaveryhighfrequencyswitchcircuittoamplifytheaudiosignal.
Advantages:
1)Ithasaveryhighefficiency,whichcanusuallyreachmorethan85%;
2)ItissmallinsizeandcanbesavedcomparedtoanalogamplifiercircuitsLargespace;
3)Nocrackingnoiseisconnected;
4)Lowdistortion,goodfrequencyresponsecurve.Fewperipheralcomponents,easytodesignanddebug.
ClassA,ClassBandClassABamplifiersareanalogamplifiers,andClassDamplifiersaredigitalamplifiers.ClassBandClassABpush-pullamplifiershavehigherefficiencyandlessdistortionthanClassAamplifiers.Thepoweramplifiertransistorsconsumelesspowerandhavebetterheatdissipation.However,ClassBamplifierswillhavepoorswitchingcharacteristicsduringthetransitionbetweentransistoronandoffstates.Oralternatedistortionduetoimproperselectionofcircuitparameters.TheClassDamplifierhashighefficiencyandlowdistortion,andagoodfrequencyresponsecurve.Advantagesoffewerperipheralcomponents.ClassABamplifiersandClassDamplifiersarethebasiccircuitformsofaudiopoweramplifiers.
Tclassamplifier:
ThepoweroutputcircuitoftheTclasspoweramplifieristhesameasthepulsewidthmodulationclassDpoweramplifier,andthepowertransistoralsoworksintheon-offstate.,TheefficiencyisequivalenttothatofaclassDpoweramplifier.ButitisdifferentfromordinaryclassDpoweramplifiers:
Firstofall,itdoesnotusepulsewidthmodulation.Tripathcompanyinventedadigitalpoweramplifierprocessorcalled"DigitalPowerProcessing(DPP)""Digitalpowertechnology,itisthecoreoftheT-classpoweramplifier.Itusestheadaptivealgorithmandpredictionalgorithmforsmallsignalprocessingincommunicationtechnologyhere.AftertheinputaudiosignalandthecurrententeringthespeakeraredigitallyprocessedbyDPP,theyareusedtocontroltheturn-onandturn-offofthepowertransistor.Sothatthesoundqualitycanachievehigh-fidelitylinearamplification.
Secondly,theswitchingfrequencyofitspowertransistorisnotfixed,andthepowerspectrumoftheuselesscomponentsisnotconcentratedinthenarrowfrequencybandsonbothsidesofthecarrierfrequency,butspreadoverawidefrequencyband.Sothatthedetailsofthesoundcanbe"heard"intheentirefrequencyband.
Inaddition,ClassTpoweramplifiershaveawiderdynamicrangeandflatfrequencyresponse.TheemergenceofDDPhaspushedthepoweramplifierofthedigitalagetoanewlevel.Intermsofhighfidelity,thelinearityisevenbetterthantraditionalABpoweramplifiers.
Basiccomposition
Thepoweramplifierisusuallycomposedofthreeparts:preamplifier,driveramplifier,andfinalpoweramplifier.
1.Thepreamplifierplaysamatchingrole,itsinputimpedanceishigh(notlessthan10kΩ),itcanabsorbmostoftheprevioussignal,andtheoutputimpedanceislow(belowtensofΩ),whichcanincreasethesignalPartiallysentout.Atthesametime,itisitselfacurrentamplifier,whichconvertstheinputvoltagesignalintoacurrentsignal,andgivesitappropriateamplification.
2.Thedriveamplifieractsasabridge.Itfurtheramplifiesthecurrentsignalsentbythepreamplifierandamplifiesitintoamediumpowersignaltodrivethefinalpoweramplifiertoworknormally.Ifthereisnodriveramplifier,thefinalpoweramplifiercannotsendouthigh-powersoundsignals.
3.Thefinalpoweramplifierplaysakeyrole.Itformsahigh-powersignalfromthecurrentsignalsentbythedriveamplifiertodrivethespeakertosound.Itstechnicalindicatorsdeterminethetechnicalindicatorsoftheentirepoweramplifier.
Thecompositionofactivedevicesusedinpoweramplifiers
Theactivedevicesusedinpoweramplifiersaremainlytransistors(bipolarorfield-effecttransistors),whichoperateathighfrequenciesorrequirehighoutputpower.Inlargeandotheroccasions,electrontubes(includinghigh-powertransmittingelectrontubes)arealsoused;travelingwavetubesareusedinthemicrowaverange.PoweramplifierscanbedividedintoClassA(A),ClassAandB(AB),ClassB(B),ClassC(C)andClassD(D)accordingtotheoperatingpointsoftheiractivedevices.Thetableliststhehighestefficiencythatpoweramplifiersofdifferentworkingtypescanachieveagainstsinewaves.
Poweramplifiersareoftenusedintheoutputstageofbroadcastandcommunicationtransmitters,theoutputstageofaudiosystems,andtheamplifiersofthecontrolsystemtodrivetheactuators.Differentapplicationoccasions,differentperformancerequirements,circuitcompositionandworkingtypesarealsodifferent.Commonlyusedarelinearpoweramplifiers,resonancepoweramplifiers,broadbandpoweramplifiercircuitsandsoon.Inordertoincreasetheoutputpower,powersynthesistechnologycanbeused.
Linearpoweramplifierisusedforoccasionsrequiringlownonlineardistortion.Commonlyusedcircuitformsincludesingletubeamplifiercircuitandpush-pullamplifiercircuit.Thecircuitformofthesingle-tubeamplifiercircuitissimilartothatofthevoltageamplifier.ItmustworkinClassA,withthelowestefficiency,andismostlyusedforsmallpoweramplifiers.Thepush-pullamplifiercircuitiscomposedoftwoactivedevices,whicharerespectivelyexcitedbyinputsignalswithaphasedifferenceof180°,andthentheiroutputsignalsareinverselysuperposedandsuppliedtotheload.Figure1showstheprinciplecircuitofapush-pullamplifierthatusesatransformertoachieveinversesuperposition.Intheory,thetwodevicescanworkinclassB,andtheoutputisundistorted.However,theactualactivedevicecharacteristicsarenotcompletelyideal,andtheyneedtoworkinClassAandB.Thepush-pullamplifiercircuitcanalsobecomposedofcomplementarypairsofCPNP-typeandNPN-typebipolartransistorsorapairofN-channelandP-channelfieldeffecttransistorswithoppositepolarities.Thecircuitconstructedbyusingtheircomplementarycharacteristicsdoesnotneedtwoinputsignalswithaphasedifferenceof180°,andtheoutputsignaldoesnotneedtobereversedandsuperimposed.Thiskindofcircuitcanbecomposedentirelyoftransistorsandresistors,whichiseasytointegrateandismostlyusedinintegratedamplifiers.
ResonantpoweramplifierAresonantcircuitastheloadofactivedevices,anamplifierthatspecializesinamplifyingnarrow-bandsignals.Thiskindofamplifierallowslargedistortionofthecurrentwaveform,andthenusestheresonantcircuittofilterouttheharmonics;itcanmaketheactivedeviceworkinClassCtoobtainhighefficiency;itismostlyusedinthefinalstageofhigh-powertransmitters.Iftheresonancecircuitistunedtotheharmonicsoftheinputsignalandanappropriateoperatingpointisselected,afrequencymultipliercanbeformed.
Thebroadbandpoweramplifierusesthetransmissionlinetransformerastheloadoftheactivedevice.Theupperlimitfrequencyofthiskindofpoweramplifiercanreachseveralhundredmegahertz,andthebandcoverageiswide.Thetransmissionlinetransformerisconstructedaccordingtotheworkingprincipleofthetransmissionlineandthetransformer.
PowersynthesistechnologyMultipleamplifiersamplifythesameinputsignal,andthenusethesynthesismethodtoaddtheoutputpowerofeachamplifier.Figure2istheprinciplecircuitofpowersynthesis,whichiscomposedofamplifiers,powersynthesisanddistributionnetworks.Thesynthesisanddistributionnetworkisusuallycomposedoftransmissionlinetransformers.Thecharacteristicofthissynthesistechniqueisthattheworkingstateofoneoftheamplifierschanges,andtheworkoftheotheramplifiersisnotaffected.
Inordertofurtherimprovetheefficiencyofthepoweramplifier,theinputsignalisfirstconvertedintoapulsesequence,andthenconvertedintoananalogsignalafteramplification.Thiskindofpoweramplifierworksinpulseamplification,thetheoreticalefficiencycanreach100%,anditiscalledD(D)classamplifier.
Duetotheunsatisfactoryswitchingcharacteristicsofactivedevices,increasingtheoperatingfrequencyofthistypeofamplifierislimited.
Inthepoweramplifier,duetothelargeheatloss,themainheat-generatingpartoftheactivedeviceneedstobeaddedwithaheatsink,andsometimesair-cooled,water-cooledorevaporativecoolingisusedtoreducethetemperatureriseofthedevice.
Purchaseskills
Whenchoosingapoweramplifier,youmustfirstpayattentiontosomeofitstechnicalindicators:
1.Inputimpedance:usuallyindicatestheresistanceofthepoweramplifierTheinterferenceabilityisgenerally5000-15000Ω.Thelargerthevalue,thestrongertheanti-interferenceability;
2,thedistortiondegree:referstothedistortiondegreeoftheoutputsignalcomparedwiththeinputsignal,thesmallerthevalue,thequalityThebetter,generallybelow0.05%;
3.Signal-to-noiseratio:referstotheratiobetweenthemusicsignalandthenoisesignalintheoutputsignal.Thelargerthevalue,thecleanerthesound.
Inaddition,whenpurchasingapoweramplifier,itisnecessarytomakeclearthepurchaseintention.Ifyouwanttoinstallasubwoofer,itisbesttobuya5-channelpoweramplifier.Usually2-channeland4-channelspeakerscanonlybeusedtopromoteThefrontandrearspeakers,andthesubwoofercanonlybeequippedwithadditionalpoweramplifiers.A5-channelpoweramplifiercansolvethisproblem.Theoutputpowerofthepoweramplifiershouldalsobegreaterthantheratedpowerofthespeakers.
Commontypes
Radiofrequencypoweramplifier:
Radiofrequencypoweramplifier(RFPA)isanimportantcomponentofvariouswirelesstransmitterspart.Inthepre-stagecircuitofthetransmitter,thepoweroftheradiofrequencysignalgeneratedbythemodulationoscillatorcircuitisverysmall,anditneedstogothroughaseriesofamplification,abufferstage,anintermediateamplifierstage,andafinalpoweramplifierstagetoobtainsufficientRFpowerbeforeitcanbefed.Radiatetotheantenna.InordertoobtainsufficientRFoutputpower,aRFpoweramplifiermustbeused.
RFpoweramplifierisanimportantpartoftransmittingequipment.ThemaintechnicalindicatorsofRFpoweramplifiersareoutputpowerandefficiency.Inaddition,theharmoniccomponentsintheoutputshouldbeassmallaspossibletoavoidinterferencetootherchannels.
High-frequencypoweramplifier:
Thehigh-frequencypoweramplifierisusedinthefinalstageofthetransmittingstage,anditsfunctionistoamplifythehigh-frequencymodulatedwavesignal.,Inordertomeettherequirementsofthetransmissionpower,andthenradiateittothespacethroughtheantenna,toensurethatthereceivingstageinacertainareacanreceiveasatisfactorysignallevel,anddoesnotinterferewiththecommunicationofadjacentchannels.
Thehigh-frequencypoweramplifierisanimportantcomponentofthetransmittingdeviceinthecommunicationsystem.Accordingtothewidthofitsworkingfrequencyband,itisdividedintotwotypes:narrow-bandhigh-frequencypoweramplifiersandbroadbandhigh-frequencypoweramplifiers.Narrow-bandhigh-frequencypoweramplifiersusuallyuseafrequencyselectivecircuitwithfrequencyselectivefilteringasanoutputloop,soitisalsocalledatunedpoweramplifierorResonantpoweramplifier;theoutputcircuitofthebroadbandhigh-frequencypoweramplifierisatransmissionlinetransformerorotherbroadbandmatchingcircuit,soitisalsocalledanuntunedpoweramplifier.Thehigh-frequencypoweramplifierisanenergyconversiondevicethatconvertstheDCenergysuppliedbythepowersupplyintoahigh-frequencyACoutput.Itisknowninthe"lowfrequencyelectroniccircuit"coursethatamplifierscanbedividedintothreetypesofworkingstates:A,B,andCaccordingtothecurrentconductionangle.ThecurrentflowangleoftheClassAamplifieris360o,whichissuitableforsmallsignallow-poweramplification.ThecurrentflowangleoftheclassBamplifierisapproximatelyequalto180o;thecurrentflowangleoftheclassCamplifierislessthan180o.BothClassBandClassCaresuitableforhigh-powerwork.TheoutputpowerandefficiencyoftheClassCworkingstatearethehighestamongthethreeworkingstates.Mosthigh-frequencypoweramplifiersworkinClassC.However,thecurrentwaveformdistortionoftheClassCamplifieristoolarge,soitcannotbeusedforlow-frequencypoweramplification,andcanonlybeusedforresonantpoweramplificationwithatuningloopasaload.Duetothefilteringcapabilityofthetuningloop,theloopcurrentandvoltagearestillveryclosetothesinusoidalwaveform,andthedistortionissmall.Inadditiontotheabove-mentionedworkingstatesclassifiedbythecurrentflowangle,therearealsoClassDamplificationandClassEamplificationthatmaketheelectronicdeviceworkintheswitchstate.TheefficiencyoftheClassDamplifierishigherthanthatoftheClassCamplifier,theoreticallyupto100%,butitsmaximumoperatingfrequencyislimitedbythepowerconsumptionofthedevice(collectordissipationpoweroranodedissipationpower)generatedatthemomentofswitching..
Ifthecircuitisimprovedtominimizethepowerconsumptionoftheelectronicdeviceatthemomentofon-offtransition,theoperatingfrequencycanbeincreased.ThisistheClassEamplifier.Inordertoobtainsufficientlow-frequencyoutputpowerinthelow-frequencyamplifiercircuit,alow-frequencypoweramplifiermustbeused,andthelow-frequencypoweramplifierisalsoanenergyconverterthatconvertstheenergyprovidedbytheDCpowersupplyintoanACoutput.Thecommoncharacteristicsofhigh-frequencypoweramplifierandlow-frequencypoweramplifierarelargeoutputpowerandhighefficiency,buttheworkingfrequencyandrelativebandwidthofthetwoarequitedifferent,whichdeterminestheessentialdifferencebetweenthem.Theworkingfrequencyoflowfrequencypoweramplifierislow,buttherelativefrequencybandwidthisverywide.Forexample,from20to20000Hz,theratioofhightolowfrequencyreaches1000times.Therefore,theyalluseuntunedloadssuchasresistorsandtransformers.Theworkingfrequencyofhighfrequencypoweramplifierishigh(fromseveralhundredkHztoseveralhundred,severalthousandoreventensofthousandsMHz),buttherelativefrequencybandisverynarrow.Forexample,thebandwidthofanAMbroadcastingstation(bandrangeof535-1605kHz)is10kHz.Ifthecenterfrequencyissetto1000kHz,therelativebandwidthisonlyequivalenttoonehundredthofthecenterfrequency.Thehigherthecenterfrequency,thesmallertherelativebandwidth.Therefore,high-frequencypoweramplifiersgenerallyuseafrequency-selectivenetworkastheloadloop.Becauseofthislatterfeature,theworkingconditionsofthetwoamplifiersaredifferent:low-frequencypoweramplifierscanworkinClassA,ClassA,B,orClassB(limitedtopush-pullcircuits);high-frequencypoweramplifiersgenerallyworkinCClass(SomespecialcircumstancescanworkinClassB).
Eachintermediatestageofthebroadbandtransmitteralsowidelyusesanewtypeofbroadbandhigh-frequencypoweramplifier,whichdoesnotuseafrequency-selectivenetworkasaloadloop,butusesatransmissionlinewithawidefrequencyresponseasaload.Inthisway,itcanchangetheoperatingfrequencyinawiderangewithoutre-tuning.Insummary,itcanbeseenthatthecommonpointofhigh-frequencypoweramplifierandlow-frequencypoweramplifieristhattheyrequirelargeoutputpowerandhighefficiency;theirdifferenceisthattheirworkingfrequencyandrelativebandwidtharedifferent,sotheloadnetworkandworkingThestatusisalsodifferent.
Themaintechnicalindicatorsofhigh-frequencypoweramplifiersare:outputpower,efficiency,powergain,bandwidth,andharmonicsuppression(orsignaldistortion).Theseindexrequirementsarecontradictory.Whendesigninganamplifier,someindexesshouldbehighlightedaccordingtospecificrequirements,andsomeotherindexesshouldbetakenintoconsideration.Forexample,insomecircuitsinpractice,preventinginterferenceisthemaincontradiction,andrequireshigherharmonicsuppression,whilethebandwidthrequirementscanbeappropriatelyreduced.Theefficiencyofthepoweramplifierisaprominentproblem,anditsefficiencyisdirectlyrelatedtotheworkingstateoftheamplifier.TheworkingstateoftheamplifiercanbedividedintoClassA,ClassBandClassC.Inordertoimprovetheworkingefficiencyoftheamplifier,itusuallyworksinClassBandClassC,thatis,thetransistoroperationextendstothenon-linearregion.However,thereareseriousnonlineardistortionsbetweentheoutputcurrentandtheoutputvoltageoftheamplifierundertheseworkingconditions.Low-frequencypoweramplifierscannotuseresonantcircuitsasloadsduetothelargefrequencycoverageoftheirsignals,sotheygenerallyworkinClassAstate;theycanworkinClassBwhenusingpush-pullcircuits.High-frequencypoweramplifierscanuseresonantcircuitsasloadsduetotheirlowsignalfrequencycoverage.Therefore,theyusuallyworkinClassC.Throughthefrequencyselectionfunctionoftheresonantcircuits,theharmoniccomponentsinthecollectorcurrentoftheamplifiercanbefilteredout.Thefundamentalcomponentthusbasicallyeliminatesnonlineardistortion.
Therefore,high-frequencypoweramplifiershavehigherefficiencythanlow-frequencypoweramplifiers.Becausehigh-frequencypoweramplifiersworkinthenon-linearstateoflargesignals,linearequivalentcircuitanalysiscannotbeused.Inengineering,analyticalapproximateanalysismethods-brokenlinemethodsaregenerallyusedtoanalyzetheirworkingprinciplesandworkingconditions.Thephysicalconceptofthisanalysismethodisclear,andtheanalysisworkstatusisconvenient,butthecalculationaccuracyislow.Amongthevarioustypesofhigh-frequencypoweramplifiersdiscussedabove,narrow-bandhigh-frequencypoweramplifiersareusedtoprovidesufficientlystrongnarrow-bandsignalpowercenteredonthecarrierfrequency,ortoamplifynarrow-bandmodulatedsignalsortoachievefrequencydoubling.ItusuallyworksinBClass,ClassCstatus.Broadbandhigh-frequencypoweramplifier:usedfortheintermediateamplifierstagesofsomecarriersignalswithalargefrequencyrangeofshortwaveandultrashortwaveradiostations,soastoavoidcumbersometuningofdifferentfc.UsuallyworkinaClassAstate.
Mainindicators
Technicalindicators
1.Ratedpower(ratepower):referstothecontinuoussinewavepower,at500HzsinewaveinputandcertainUnderload,theharmonicdistortionislessthan1%oftheoutputpower,expressedasW/CH(wattsperchannel).Generallyspeaking,thehighertheratedpower,thehigherthecost.
2.Totalharmonicdistortion(THD):referstothepercentageofhigh-orderharmonicstothefundamentalwave.Thesmallerthetotalharmonicdistortion,thebetter.Thetotalharmonicdistortionofagoodpoweramplifiercanreach0.02%
3.Slewrate:thevoltageamplituderisingperunittime,involts/microsecond,itreflectsthepoweramplifier'sabilitytotracktransientsoundsignals,whichisatransientstateCharacteristicindicators.
4.Dampingfactor:Itisdefinedastheloadimpedanceofthepoweramplifier(theinternalresistanceofthehigh-powertubeplusthewiringresistanceofthespeaker),suchas8Ω:0.04Ω=200:1,generallyTheratioisrequiredtoberelativelylarge,butnottoolarge.Iftheratioistoolarge,thespeakerwillfeelthin,andifitistoosmall,thesoundlevelwillbepoorandthesoundimagedistributionwillbepoor.
5.Outputimpedance(orratedloadimpedance):usually8Ω,4Ω,2Ω,etc.Thesmallerthevalue,thestrongertheloadcapacityofthepoweramplifier.Intermsofasinglechannel,apoweramplifierwitharatedloadof2Ωcandrive4speakerswithanimpedanceof8Ωtoproducesoundwithverylittledistortion.
Performanceindicators
RegardlessofAVamplifierandHi-Fipoweramplifier,therequirementsforpoweramplifierareverystrict,intermsofoutputpower,frequencyresponse,distortion,signal-to-noiseratio,outputimpedanceanddampingcoefficientThereareclearrequirementsinotheraspects.
Outputpower:
Outputpowerreferstothepowerdeliveredbythepoweramplifiercircuittotheload.Peopleareveryinconsistentwiththeoutputpowermeasurementmethodandevaluationmethod,sobecarefulwhenusingit.
1.Ratedpower(RMS):Itreferstothemaximumpowerthatthepoweramplifiercanoutputforalongtimewithinacertainharmonicrange(strictlyspeaking,itisasinewavesignal).Theaveragepowerwhentheharmonicdistortionis1%isoftenreferredtoasratedoutputpowerormaximumusefulpower,continuouspower,undistortedpower,etc.Obviously,whentheprescribeddistortionprerequisitesaredifferent,theratedpowervaluewillbedifferent.
2.Maximumoutputpower:Whenthedistortionisnotconsidered,theoutputpowerofthepoweramplifiercircuitcanbemuchhigherthantheratedpower,anditcanalsooutputalargervalueofpower.ThemaximumpoweritcanoutputiscalledthemaximumOutputpower,theaforementionedratedpowerandmaximumoutputpowerareoutputpowerswithtwodifferentprerequisites.
3.Musicoutputpower(MPO):MusicoutputpowerMPOistheabbreviationofMusicPowerOutpurinEnglish.Itreferstotheoutputpowerwhenthepoweramplifiercircuitworksonmusicsignals,thatis,theoutputdistortiondoesnotexceedtheregulationsUndertheconditionofthevalue,theinstantaneousmaximumoutputpowerofthepoweramplifiertothemusicsignal.
Themusicoutputpowercanbeusedtoevaluatethedynamiclisteningeffectofthepoweramplifier.Forexample,afterasteadymusicprocess,astrongimpactofpercussionsoundssuddenlyappears.SomepoweramplifiercircuitscanprovidegreatTheoutputpowergivesasenseofstrength,whichisendless;somepoweramplifiersseemtobepowerlessandlackofconfidence.Inordertoreflecttheabilityofsuddenoutputpoweratthismoment,musicoutputpowercanbeusedtomeasure.
4.Peakmusicoutputpower(PMPO):Itisthemaximummusicoutputpower,whichisanotherdynamicindicatorofthepoweramplifiercircuit.Ifthedistortiondegreeisnotconsidered,themaximummusicpowerthatthepoweramplifiercircuitcanoutputisthepeakmusicoutputpower.
Usuallythepeakmusicoutputpowerisgreaterthanthemusicoutputpower,themusicoutputpowerisgreaterthanthemaximumoutputpower,andthemaximumoutputpowerisgreaterthantheratedoutputpower.Accordingtopracticalstatistics,thepeakmusicoutputpoweris5-8timestheratedoutputpower.
Frequencyresponse:
Thefrequencyresponsereflectstheabilityofthepoweramplifiertoamplifyeachfrequencycomponentoftheaudiosignal,andthefrequencyresponserangeofthepoweramplifiershouldnotbelowerthanthatofhumans.Theauditoryfrequencyrangeoftheear,sounderidealcircumstances,theworkingfrequencyrangeofthemainchannelaudiopoweramplifieris20-20000Hz.Internationallystipulatedthatthefrequencyrangeofgeneralaudiopoweramplifieris40-16000Hz±1.5dB.
Distortion:
Distortionisaphenomenoninwhichthewaveformofthereproducedaudiosignalchanges.Therearemanycausesandtypesofwaveformdistortion,mainlyincludingharmonicdistortion,intermodulationdistortion,andtransientdistortion.
Dynamicrange:
Theratiooftheminimumsignaltothemaximumsignalleveloftheamplifierwithoutdistortionisthedynamicrangeoftheamplifier.Inactualapplication,theratiousesdBtoindicatetheleveldifferencebetweenthetwosignals,andthedynamicrangeofthehigh-fidelityamplifiershouldbegreaterthan90dB.
Variousnoisesinnatureformthesurroundingbackgroundnoise,andthesurroundingbackgroundnoiseisverydifferentfromthesoundintensityoftheperformance.Undernormalcircumstances,thisdifferenceinintensityiscalleddynamicrange,agoodsoundsystemWhenastrongsignalisinput,itshouldnotproduceoverloaddistortion,andwhenaweaksignalisinput,itshouldnotbeoverwhelmedbythenoisegeneratedbyitself.Forthisreason,agoodaudiosystemshouldhavealargedynamicrange,andthenoisecanonlybeminimized,butItisimpossiblenottogeneratenoise.
Signal-to-noiseratio:
Signal-to-noiseratioreferstotheproportionalrelationshipbetweenthesizeofthesoundsignalandthesizeofthenoisesignal.Thenumberofdecibelscomparedtothevariousoutputnoiselevelsiscalledthesignal-to-noiseratio.
Outputimpedanceanddampingcoefficient:
1.Outputimpedance:Theequivalentinternalimpedanceshownbytheoutputendofthepoweramplifierandtheload(speaker)iscalledTheoutputimpedanceofthepoweramplifier;
2.Dampingcoefficient:Thedampingcoefficientreferstotheabilityofthepoweramplifiercircuittoprovideresistancetotheload.
Relatedterms
Workingrange
Workingrangereferstotheworkingbandwidthofthepoweramplifierunderthespecifieddistortionandratedoutputpower,thatis,thepoweramplifierTherangefromthelowestoperatingfrequencytothehighestoperatingfrequency,inHz(hertz).Theactualoperatingfrequencyrangeoftheamplifiermaybegreaterthanthedefinedoperatingfrequencyrange.
Workingmodes
Theworkingmodesofthepoweramplifieraremainlyasfollows:
Timedivisionduplex(TDD)mode:
InamobilecommunicationsysteminTDDmode,receivingandtransmittingareindifferenttimeslotsofthesamefrequencychannel(ie,carrier),andtheguaranteedtimeisusedtoseparatethereceivingandtransmittingchannels.
TheTDDsystemhasthefollowingcharacteristics:
1.Itdoesnotrequirepairedfrequenciesandcanusevariousfrequencyresources.Itissuitableforasymmetricuplinkanddownlinkdatatransmissionrates,andisespeciallysuitableforIP-typedataservices;
2.Theuplinkanddownlinkworkatthesamefrequency,andthesymmetricalcharacteristicsofradiowavepropagationmakeiteasytousenewtechnologiessuchassmartantennastoachievethepurposeofimprovingperformanceandreducingcosts.
TimeDivisionMultipleAccess(TDMA)mode:
TDMAistheEnglishabbreviationforTimeDivisionMultipleAccess.Thecarrierofthesamefrequencyisdividedintoseveralequalsmalltimeperiodswithinacertainperiodoftime,sothatuserswithdifferentnumberscanusedifferentsmalltimeperiodstorealizetheconnectedcommunicationmode.Inshort,itisadigitalwirelesstechnologythatdividesanarrowwirelesschannelintoframedtimesegments(especially3and8),andallocateseachtimesegmenttoeachuser.
Transmissiongain
referstotheratioofamplifieroutputpowertoinputpower,andtheunitisusuallyexpressedin"dB"(decibel).Theoutputgainofthepoweramplifierincreasesorattenuatesasthefrequencyoftheinputsignalchanges.Thisindicatoristhemostimportantbasisforassessingthequalityofpoweramplifiers.Thesmallerthedecibelvalue,theflatterthefrequencyresponsecurveofthepoweramplifier,thesmallerthedistortion,andthestrongerthesignalrestorationandreproducibility.
Outputpower
Strictlyspeaking,thepowerindexofthepoweramplifierisdividedintothenominaloutputpowerandthemaximuminstantaneousoutputpower.Theformeristheratedoutputpower,whichcanbeinterpretedasthemaximumvalueoftheoutputpowerwhentheharmonicdistortionchangeswithinthestandardrangeandcanworksafelyforalongtime;thelatterreferstothe"peak"outputpowerofthepoweramplifier,whichisinterpretedasthepoweramplifieracceptsWhenanelectricalsignalisinput,themaximumoutputpowerthatcanbewithstoodinstantaneouslyunderthepremiseofensuringthatthesignalisnotdamaged.
Receivinggain
Gainisoneofthemainindicatorsoftheantenna.Itistheproductofthedirectivitycoefficientandtheefficiency,andistheperformanceoftheantennaradiationorthesizeofthereceivedradiowaves.Thechoiceofgaindependsontherequirementsofthesystemdesignfortheradiowavecoveragearea.Simplyput,underthesameconditions,thehigherthegain,thefarthertheradiowavetravels.Thelargerthereceivinggainvalueofthepoweramplifier,thestrongerthereceivingperformance.
Lightningprotection
Commondirectlightningprotectionmeasures:
Lightningrods:Lightningrodsareusedtoprotectindustrialandcivilhigh-risebuildings,powerplants,andtransformersubstations.Powerdistributiondevices,individualsectionsoftransmissionlines,andwhenthelightningpilotcircuitextendstotheground,willgraduallyturntoandhitthelightningrodduetotheinfluenceofthelightningroddistortioncircuit,therebypreventingthelightningfromleadingtotheprotectedequipmentanddestroyingtheprotectedequipmentAndconstructionpossibilities.Itcanbeseenthatthelightningrodisactuallyalightningrod,whichleadsthelightningtoitself,therebyprotectingotherequipmentfromlightningstrikes.
Lightningwire:Lightningwireisalsocalledoverheadgroundwire.Itiserectedalongthelineatthetopofthetowerandhasawell-groundedmetalwire.Lightningwireisthemainlightningprotectionmeasurefortransmissionlines.
Lightningprotectionbeltsandlightningprotectionnets:metalgridslaidalongthecorners,ridges,eavescornersandeavesofbuildingsthatarevulnerabletolightningstrikes.Theyaremainlyusedtoprotecttallcivilbuildings.
Surgeprotection
Surgeisalsocalledsurge,asitsnameimplies,itisaninstantaneousovervoltagethatexceedsthenormaloperatingvoltage.Essentially,asurgeisaviolentpulsethatoccursinjustafewmillionthsofasecond.Thepossiblecausesofsurgesare:heavyequipment,shortcircuits,powerswitching,orlargeengines.Theproductscontainingsurgeblockingdevicescaneffectivelyabsorbsuddenhugeenergytoprotecttheconnectedequipmentfromdamage.
Surgeprotector,alsocalledsignallightningprotector,isanelectronicdevicethatprovidessafetyprotectionforvariouselectronicequipment,instruments,andcommunicationlines.Whenaspikecurrentorvoltageissuddenlygeneratedintheelectricalcircuitorcommunicationcircuitduetoexternalinterference,thesurgeprotectorcanconductandshuntinaveryshorttime,soastopreventthesurgefromdamagingotherequipmentinthecircuit.
Mattersneedingattention
Theamplifiercircuitwhosemainfunctionistoprovidepowertotheloadisusuallycalledapoweramplifiercircuit.Itsmainfeaturesareasfollows:
1.OutputpowerItreferstotheproductofalternatingvoltageandalternatingcurrent,thatis,ACpower;
2,ACpowerisdefinedwhentheinputisasinewaveandtheoutputwaveformisbasicallyundistorted;
3.Theoutputpowerislarge,sotheenergyconsumedinthecircuitandtheenergyprovidedbythepowersupplyarealsolarge;
4.Thetransistoroftenworksintheextremeapplicationstate,soitisnecessarytoconsiderthenecessaryheatdissipationmeasuresandovercurrent,Overvoltageprotectionmeasures.
Impedancematching
Inallelectronicaudiovisualequipment,thereisaproblemofthebestsolutionforpoweroutput,thatis,inordertoobtainthemaximumpoweroutputwithoutincreasingtheinvestmentcostofthecircuit,Thisisthebestcombinationofpoweramplifierandspeakersystem.
Thepurposeofthepoweramplifiercombinationistoachievetheminimumequipmentinvestmentandobtainthemaximumpoweroutput.
Inordertoachievethemaximumoutputpower,thesizeoftheloadshouldmaximizetheproductofthecurrentoutputandthevoltageoutputofthepowertube.Thestateatthistimeiscalledthepowermatchingstate.Inthespeakersystemoftheaudioequipment,theoutputimpedanceoftheaudioshouldbethetotalimpedanceofthespeakercombinationstate,sothattheoutputpoweroftheaudioisthemarkedratedstandardpower,otherwisetheoutputpoweroftheaudiowillnotmeettherequirements.
Forexample:theaudiostandardconnectorismarkedas4Ω,100W,thentheimpedanceontheconnectoristheparallelconnectionoftwo8Qspeakers,eachspeakercanget50W,sotheintegratedspeakersystemis4Ω,100W,Otherwise,thepoweroutputof100wcannotbeachieved.
Protectivemeasures
Thepowertubeisthemostvulnerabledeviceinthepoweramplifiercircuit.Mostofthereasonsforthedamagearethattheactualpowerdissipationofthetubeexceedstheratedvalue.Inaddition,ifthepoweramplifierandthespeakeraremismatchedorthespeakerisoverloadedforalongtime,itisalsoveryeasytodamagethespeaker(orspeaker).Therefore,inaudioequipment,thepurposeofprotectionistoprotectexpensivepoweramplifiersandspeakers.Theoverloadandshort-circuitprotectionofthespeakeriscompletelynecessary.
1.Powersupplyprotection:Whenusingaswitchingpowersupply,thereisaspecialprotectioncontrolterminal,aslongastheinputofover-currentorover-voltagesignalscanachievethepurposeofprotection.
2.Poweramplifiertransistorprotection:Inadditiontopayingattentiontotheambienttemperatureandselectingasuitableheatsinkinuse,thepoweramplifiertransistormainlyconsiderstheproblemsofovercurrentandovervoltageprotection.TheappliedintegratedcircuitsareallequippedCurrentlimitprotectionandthermalcut-offprotectionfunction,soyoumustpayattentiontoovervoltageprotectionwhenmakingyourownpoweramplifier.
3.Speakerspeakersystemprotection:Theprotectionoftheaudiosystemhastwomeanings:oneistheoverloadoftheaudiospeaker;theotherisnottheexcessiveaudiopower,butthedeviationoftheDCpotential,resultinginOCLorBTLcircuitspeakerswithoutcapacitorisolationareburntout.
Mainfeatures
Poweramplifiersareabbreviatedaspoweramplifiers.Intermsoftheirmainpurposes,poweramplifierscanbedividedintotwomaincategories,namelydedicatedpoweramplifiersandcivilianpoweramplifiers.Thepoweramplifiersusedinstadiums,movietheaters,dancehalls,conferencehalls,publicplaces,soundreinforcement,andrecordingmonitoring,etc.,generallyhavesomeuniquerequirementsintheirtechnicalparameters.ThistypeofpoweramplifierisusuallycalleddedicatedPoweramplifierorprofessionalpoweramplifier.
ThepoweramplifiersusedforhomeHi-Fimusicappreciation,AVsystemplayback,andkaraokeentertainmentareusuallycalledcivilianpoweramplifiersorhomepoweramplifiers.
Althoughspecialpoweramplifiersandcivilianpoweramplifiersaredifferentinsomecharacteristicparameters,itisdifficulttosaythatthereisaclearboundary.Forexample,thepoweramplifierusedformusicrecordingmonitoringislikelytobeahomeHi-FiisevenaHi-endamplifier.
Hi-FipoweramplifierandAVpoweramplifier:
Hi-FipoweramplifierandAVpoweramplifierarethetwomaincategoriesofhouseholdpoweramplifiers.Thesetwotypesofpoweramplifiersareusedfordifferentpurposes,andtheirdesignfocusesaredifferent.Hi-Fipoweramplifiersareusedtoenjoymusic,andwhatuserspursueistobeas"authentic"aspossible.TheusersofAVpoweramplifierspursuethe"live"effectthatmatchesthescreen,oreventheexaggerated"live".Effect.Thesetwotypesofpoweramplifiersarenotverygoodanddirectlycomparewhichoneisbetter.Forexample,Hi-FipoweramplifiersandAVpoweramplifiersthatarepricedatthesamepriceofmorethanthreethousandyuan,thecostofHi-Fipoweramplifiersisonlyontwochannels,whileAVpoweramplifiersThecostinvestmentmusttakeintoaccount5-6channels,butalsohaveacertaineffectprocessingfunction.Ifyouonlylookattheinputofitstwomainchannels,itisdefinitelylowerthantheinputofthetwochannelsoftheHi-Fiamplifier.Thedifferenceintheplaybackeffectisobvious.ButwhetheritisHi-FipoweramplifierorAVpoweramplifier,therearehigh-endboutiquetypeandvalue-addedpopulartype.
Generallyspeaking,itisdifficulttohaveanAVamplifierthatisfullycompatiblewithHi-FiandAV.ItisaconditionforAVamplifierstotakeintoaccountHi-Fimusicappreciation.ThisconditionisthatusersenjoymusicTimerequirementsandstandards.Iftheuserisonlyusedtoenjoysomecasualmusic,oronlyrequirestobeabletohearthemelodyofthemusic,theAVamplifierisrelativelyeasytomeet,butiftherearehigherrequirementsformusicappreciation,itisgenerallyAVpoweramplifiersaredifficulttosatisfy.
Transistoramplifiersandtubeamplifiers:
TheamplifiersusedforHi-Fiappreciationcanbedividedintotwocategories:transistoramplifiersandtubeamplifiers.Theywerestillusefulinthepast.Hi-Fipoweramplifiersforintegratedcircuitsormodularcircuitsarerarenow.Thereisnodifferencebetweentheadvantagesanddisadvantagesoftransistorpoweramplifiersandtubepoweramplifiers.Theonlydifferenceisthatthedevicesusedaredifferent(oneisatransistorandtheotherisatube).Becausethetwotypesofdevicesaredifferent,theirphysicalprinciplesandcircuitcharacteristicsarealsodifferent..
Theelectriccurrentoftheelectrontubeisformedbythemovementofelectronsattractedbytheelectricfieldforceinthevacuum.Thecurrentofthetransistorisformedbythetransferofthepositionoftheouterelectronofthesemiconductorelementundertheactionoftheelectricfieldforce.Thisdifferenceinphysicalfundamentalsresultsindifferentcircuitcharacteristicsinpracticalapplications.Relativelyspeaking,theworkingvoltageofthetubepoweramplifierisrelativelyhigh,buttheworkingcurrentisrelativelysmall,whiletheworkingvoltageofthetransistorpoweramplifierisrelativelylowandtheworkingcurrentisrelativelylarge.Thetimbreofthetubeamplifierandthetransistoramplifierisindeeddifferent,andtheresponseofthetwototransientsignalsisalsodifferent.Thisdifferencehasbeenadaptedtodifferenttypesofmusicanddifferentmusiclisteners,soHi-Fipoweramplifiershaveformedthecoexistenceoftransistorpoweramplifiersandtubepoweramplifiers.However,intermsofbrand,model,andquantity,theshareoftransistorpoweramplifiersisstilldefinitelygreaterthanthatoftubepoweramplifiers.
ClassApoweramplifierandClassBpoweramplifier:
TheworkingstateoftransistorpoweramplifieroutputstagetransistorcanbedividedintoClassAandClassB.Theso-calledtypeAsimplymeansthattheoutputstagetransistorsworkinthelinearregionduringthepositiveandnegativehalfcyclesofthesinusoidalACsignal,whilethetypeBonlymakestheoutputstagetransistorsworkinthepositivehalfcycle(ornegativehalfcycleofthesinusoidalACsignal).)Workinthelinearregion.Duetothedifferentworkingstatesoftheoutputstagetransistors,thepowerutilizationefficiencyoftheoutputstage(thatis,theratiooftheoutputpoweramplifiertothepowerconsumption)isalsodifferent.Inapracticaloutputcircuit,theefficiencyofTypeBis2-3timeshigherthanthatofTypeA.
ThereisnocrossoverdistortionintheClassApoweramplifier,andregardlessoftheactualoutputpower,theinternalresistanceoftheoutputstagecrystalisconstant.AndClassBpoweramplifiersalwayshaveacertainamountofcrossoverdistortion(althoughthisdistortionmaybeextremelysmall).Inaddition,theinternalresistanceoftheoutputstagetransistorisrelativelysmallwhentheoutputislarge,buttheinternalresistanceoftheoutputstagetransistorisrelativelylargewhentheoutputissmall..Thesedifferencesresultinadifferentsenseofhearing.ThesoundoftheClassApoweramplifierissofterthanthatoftheClassBpoweramplifier.Inaddition,thelowfrequencycontrolpowerofthespeakersisstrongerthanthatoftheClassBpoweramplifier,especiallythebasstextureisbetteratlowvolume.ThesecharacteristicsofClassApoweramplifiersmakeClassApoweramplifiersdonotneedalargeoutputpowermargininpracticalapplications.A20W-30WClassApoweramplifiercanalreadypromotemostspeakersverywell.
Asmentionedearlier,thepowerefficiencyofClassApoweramplifiersislow,whichcausesalotofheattobedissipatedwhenClassApoweramplifierswork.Inordertokeeptheworkingtemperatureofthetransistorwithinacertainlimit,aradiatorwithalargervolumeandareaisrequired,whichmakesthevolumeandweightoftheClassApoweramplifierrelativelylarge.
Purepoweramplifierandmonopoweramplifier:
Commonpoweramplifiersarepreamplifiers(preamplifiers)andpoweramplifiersthatamplifysmallsignals.Theamplifier(post-stage)isbuiltinacabinet.Thistypeofpoweramplifierisoftencalleda"combinedpoweramplifier".Thecombinedpoweramplifieriseasytouseandhasarelativelygoodprice-performanceratio.Butthiskindofcombinedpoweramplifierhassomeinherentshortcomings.Amongthem,themostdifficultthingtoovercomeistheproblemofmutualinterferencebetweenthefrontstageandtherearstage.Inordertosolvethisproblem,thefrontstageandtherearstageareseparatelymadeintwocabinets,sothatthereisapurerearstagepoweramplifier.Mostpurepoweramplifiershaveadual-channelstructure,butthisstructuremakesitdifficulttosolvetheproblemofmutualinterferencebetweenthetwochannels.Inordertosolvethemutualinterferencebetweenthetwochannels,therearetwoSinglechannelpurepoweramplifierwithseparatechannels.
Themainsignificanceofdividingthepoweramplifierintopieceslikethisistoimprovethequalityofthepoweramplifier,nottopursuethisform.Ifthemutualseparationisachievedonlyinform,althoughthemutualinterferenceproblemcanbesolved,otherparametershavenotbeensignificantlyimproved,sothisseparationisstilllimitedtotheimprovementoftheoverallqualityofthepoweramplifier.
Poweramplifiersaredividedintotransistorsandelectrontubes,andthefrontstagealsohastransistorsandelectrontubes.Foraudioenthusiastsandmusiclovers,thereareavarietyofcombinationsintheselectionoffrontandrearstages,anddifferentcombinationshavedifferentsoundcharacteristics,whichgivesusersmoreroomforchoice.
Thepre-amplifierconnectedtothepurepost-amplifierhasagreaterimpactontheprosandconsoftheentireaudiosystem.Firstofall,itmusthaveacertainquality,otherwise,theadvantagesofapureback-endormonowillnotbeabletoplayout,anditmayevenhighlightthe"problems"ofapoor-qualityfront-end,andtheoverallsoundeffectwillbeworse.Inaddition,differentfrontandrearstageshavedifferenttimbrecharacteristics,anduserscanchoosedifferentcombinationsaccordingtopersonalpreference.
Forexample,manyaudioandmusicloversliketousethecombinationof"beforethegallbladder,behindthestone"(i.e.thefrontstageofthetubeandtherearstageofthetransistor).Theyfeelthatthiscombinationnotonlyexertsthepoweroutputofthetransistorrearstage.Thecharacteristicsoflarge,goodtransientresponse,andatasteofthesweetandmellowtimbreofthetubefrontstage,butthiscombinationisnota“goldenrule”,becausethespecificfrontstageandtherearstagehavetheirowncharacteristics.Thepreferencefortimbrevariesfrompersontoperson,anduserscanfindtheirfavoritecombinationaccordingtothespecificsituation.
HowmuchoutputpowershouldtheHi-Fiamplifierhave:
TheoutputpoweroftheHi-Fiamplifierisaffectedbymanyfactors.Firstofall,thisoutputThepowerhasagreaterrelationshipwiththespeakersthatareconnected,andsecondly,itisrelatedtothequalityofthepoweramplifier,andthenitisrelatedtotheenvironmentused,thatis,thespacevolumeoftheroom.
Thespeakerhasaparametercalledsensitivity,anditsunitisdB/m?W,whichmeansthesoundpressure(dB)producedat1mawayfromthespeakerwhenthespeakerreceives1Wofelectricpower.Ifthesensitivityofacertainspeakeris90dB,then1Wofpowerisneededtodrivethesoundpressureof90dBat1m.Togetasoundpressureof100dB,10Wofpowerisneededtodriveit.Butifthesensitivityofthespeakeris80dB(suchasATC'sSCM-10),ifyouwanttoachieveasoundpressureof100dB,youneed100Wofpowertodriveit.Thesensitivityofmostspeakersisabout85dB-90dB.Forthesespeakers,10W-30Wofundistortedpowercanalreadyhaveenoughsoundpressure.
Thequalityofthepoweramplifieritselfiscloselyrelatedtotheoutputpowerthatthepoweramplifiershouldhave.Oneoftheparametersofthepoweramplifieriscalledthedampingcoefficient,whichisaparameterthatindicatestheabilitytocontrolthespeaker,butthisparameterhasamoderaterangeandisdirectlyrelatedtothespecificspeaker.Generallyspeaking,ifthequalityofapoweramplifierisverygood,itcanstillmaintainitsperformanceparametersatacertainlevelwhentheoutputis30W.Thenthereisnoneedtorequireagreaterpoweroutputfromthepoweramplifier.However,ifthequalityofthepoweramplifierisnotideal,anditsperformanceparameterswilldeterioratewhentheoutputpowerincreases,thentheoutputpowerofthepoweramplifiershouldhaveacertainmargintoensurethattherearestillcertaingoodparametersunderthepracticaloutputpower..Undernormalcircumstances,whenthepoweramplifierisaClassAoutputoratubepoweramplifier,thereisnoneedtohavetoomuchoutputpowermargin,andtheoutputpowerof20W-30Wisenough.ButifitisaClassBpoweramplifierorapoorqualitypoweramplifier,thentheoutputpowerofthepoweramplifiershouldhavealargermargin.Inaddition,iftheconnectedspeakerisalarge-scaleinverter,thepoweramplifiershouldalsohavealargeroutputpowermargin.Whenconsideringtheoutputpowerofthepoweramplifierfromthequalityofthepoweramplifieritself,selectingalargerpowermargincanindeedimprovethefitbetweenthepoweramplifierandthespeaker.
Themainsignificanceofchoosingapoweramplifierwithalargeroutputpowerisnotbecauseoftheneedforsuchalargesoundpressure,buttoimprovethefitofthepoweramplifiertothespeakers.Ifapoweramplifierwithamoderateoutputpowercancontrolthespeakershandily,thenthereisnoneedtoputforwardhigheroutputpowerrequirementsforthispoweramplifier.
Theuseenvironment,thatis,thespacevolumeoftheroomisalsorelatedtothepoweroutputofthepoweramplifier.Theoutputpowermentionedaboveisbasedonthespacevolumeoftheroombelow40.IftheroomThevolumeofthespaceislarger,sotheoutputpowerofthepoweramplifiershouldbeincreased.
Characteristicsoftheoutputstageofthetubeamplifier:
Thepoweroutputstageofthetubeamplifierhasthreecircuittypes,oneisthepush-pulloutputcircuitwithoutputtransformer.Thistypeofoutputcircuitoccupiesthevastmajorityoftubepoweramplifiers.Intheoutputtransformerofthepush-pullcircuit,theDCcomponentisverysmall,andthesecondharmonicdistortionisalsoverysmall.Theoutputpowerofthistypeofcircuitcanbemaderelativelylarge,sothescopeofapplicationisrelativelylarge.Generallyspeaking,foraudioenthusiastswhoareinterestedinthesoundofthetubeamplifier,thistypeofoutputstagetubeamplifierisverysuitable.However,forthistypeofpoweramplifier,thedesignandprocessoftheoutputtransformerisveryimportant.Ifthedesignandprocessoftheoutputtransformerhaveshortcomings,thefrequencyresponseandtransientresponseofthistypeofpoweramplifierareoftennotideal.Inaddition,duetothelimitationoftheoutputtransformer,theadaptablerangeofmatchingspeakersisrelativelysmall.
Thecircuittypeofanothertypeofpoweroutputstageisasingle-endedClassAcircuit.Thistypeofcircuitalsohasatransformer,buttheoutputtransformerofthistypeofcircuithasalargeDCcomponent,andtherequirementsfortheoutputtransformerarehigherthanthoseforoutputtransformationinthepush-pulloutputcircuit.Inaddition,therequirementsforpowersupplyarerelativelyhigh.Thecharacteristicofthistypeofoutputcircuitisthattherearemoresecondharmoniccomponents.Althoughthisisakindofharmonicdistortion,formusicsignals,thesecondharmonicisahighlyconsonantsound,soitsoundsveryear-like.Thisfeaturemakesthepowerofthisoutputcircuitveryuniqueinthetimbreofthesound,especiallywhenthepoweramplifierstageusesatriode,thehumanvoicesoundssweet,andthestringsinchambermusicsoundverydelicate,orinotherwords,Thesoundofthistypeofpoweramplifierisveryflavorful.However,theoutputpowerofthistypeofpoweramplifierisnoteasytobelarge,soifthesensitivityofthespeakerislow,itwillbemorereluctanttobroadcastlarge-scaleorchestralmusic.Thistypeoftubeamplifierisverypopularwithaudioplayers.Inadditiontoahigh-powertransistoramplifier,thereisalsoonesuchamplifier.Iwanttocomplementeachotherintone.However,thisalsoshowsthatthistypeofamplifierThetimbrecharacteristicsofitareindeedtouching.
ThereisalsoanOTLcircuitfortheoutputstageofatubepoweramplifier.Theso-calledOTLcircuitisacircuitwithoutanoutputtransformer.TheoutputstagesofmoderntransistorpoweramplifiersarealmostallOTLcircuitsorimprovedversionsofOTLcircuits.Thecharacteristicparametersoftubesandtransistorsaredifferentfromtheirworkingconditions.Transistoramplifiersareeasilysuitableforspeakerswithimpedancesof4-8,whiletubeamplifiersrequiresometroubleiftheydonotneedanoutputtransformertoadapttospeakerswith4-8.SincetheoutputtransformerisremovedfromthetubeOTLpoweramplifier,itstechnicalparametersaregreatlyimprovedcomparedwiththetwotypesofcircuitsmentionedabove.Thesoundofthistypeofoutputcircuitpoweramplifierisverydistinctive.Comparedwiththeprevioustwotypesofoutputcircuits,itIthasamagnificentmomentumandawidesoundfield.Comparedwithatransistorpoweramplifier,itssoundiswarmanddelicate.Sincethistypeofpoweramplifierdoesnothaveanoutputtransformer,itcanadapttoawiderangeofspeakerimpedance.However,thepoweramplifierofthistypeofoutputstagehaslowpowersupplyefficiency,andthedesign,technology,anddebuggingarerelativelycomplicated.Thepoweramplifierofthistypeofoutputcircuitisonlyfoundinsomehigh-endmodels,anditisdifficulttoseelow-pricedpopularmodels.
Currentcharacteristics:
Theunderstandingorevaluationofthepoweramplifiercircuitismainlyconsideredfromthethreeaspectsofoutputpower,efficiencyanddistortion.
1.Inordertoobtaintherequiredoutputpower,thecircuitmustselectatransistorwithalargeenoughcollectorpowerconsumption,andtheworkingcurrentandcollectorvoltageofthepoweramplifiertubearealsohigh.Incircuitdesignanduse,wemustfirstconsiderhowtogivefullplaytothefunctionofthetriodewithoutdamagingthetriode.Sincetheworkingstateofthepoweramplifiertubeinthecircuitisoftenclosetothelimitvalue,becarefulwhenadjustingandusingthepoweramplifiercurrent,andshouldnotexceedthelimit.
2.Fromtheperspectiveofenergyconsumption,theoutputpowerofthepoweramplifierisultimatelyprovidedbythepowersupply.Forexample,thepowerconsumptionofthepoweramplifierintheradioaccountsfor2/3ofthewholemachine,sowemustpaygreatattentiontoimprovingthecircuitefficiency,namelyTheratioofoutputpowertopowerconsumption.
3.Theinputsignalofthepoweramplifiercircuithasbeenamplifiedinseveralstageswithsufficientstrength,whichwillmaketheworkingpointofthepoweramplifiertubemovesignificantly,sothepoweramplifiercircuitisrequiredtohavealargerdynamicrange.Iftheworkingpointofthepoweramplifiertubeisnotproperlyselected,theoutputwillbeseverelydistorted.
Tips
Thepoweramplifierdominatesthewholesystemtoacertainextentwhetheritcanprovidegoodsoundqualityoutput.
Formanypeople,theydon’tknowmuchaboutamplifiers,andtheydon’tknowwhichaccessoriesareneededtoconfigurethepoweramplifierspeakersinordertoplaytheeffectofthepoweramplifiertoanoptimalstate.
Thefirsttypeistoinstallaresistorunderthespeakerforcurrentsampling.Infact,thefeedbackisstillthevoltagesignal,whichistheanalogcurrentfeedback.Themostpeopledoit,butthecircuitisflawed.Therearetworeasons:
1.Hisoutputgainwillchangewiththechangeofimpedance.Asaresult,thevoltageappliedtothehorn2isnotconstant,asifthepowerappliedtothehorncanbemadeconstant.
Becausethesoundpressurecharacteristiccurveoftheloudspeakeristestedunderconstantpressureoutput,thiskindofcircuitisnotgoodsound,thehearingisnotgood,anditisfun.However,thereareimprovedcircuits.Voltagenegativefeedbackisthemainone.Addinganappropriateamountofthistypeofcurrentnegativefeedbackcanmakeagoodsound,butatthistime,theroleofcurrentnegativefeedbackistochangethedampingcoefficientofthepoweramplifier,whichhaslittleeffectontheamplitude-frequencycharacteristics.
2.Thesamplingpointisbelowthehorn.Thehornisaninductor.Thephaseofthecurrentflowingthroughtheinductorwillchange.Thelowfrequencyisgood,butthehighfrequencycanbeshiftedby90degrees,andthephasecharacteristicsareextremelypoor.
Thesecondtype:Negativeimpedanceamplifier,exceptinsomespecialoccasions,thefirsttobeusedinaudioandsucceededisYAMAHA,itsmainfunctionistoimprovetheextensionoflowfrequency.Itiseffective,butitwilldegradethesoundqualityforfrequenciesabove200Hz,soitisgenerallyusedinultra-lowfrequencyactivespeakers.
Actually,thiskindofcircuitisusedinconjunctionwiththespeaker,andthereisnopracticaluseofitalone.Itsworkingprincipleis:ifthespeakerisarigidbody,thenaddingatubecanbecomeanidealHolmozresonancebox,thennomatterthesizeoftheboxandthethicknessofthetube,aslongasitmeetstheHolmozresonanceCalculationformula.Eventheresonancepointof20Hzcanbeachieved.Thesizeoftheboxisjusttheefficiency.Duetothepresenceofthespeaker,thespeakerismovingwhenitsounds.Thespeakerisnotarigidbody,sotheboxwillnotproduceHolmozresonated.
Therefore,ifthediaphragmofthehornisstationarywhenitissounding.Then,theboxisclosetoarigidbody,whichcanmeettheconditionsofHolmozresonance,andtheresonancepointofthisboxcanbearbitrarilydesigned.Thejobofkeepingthehornstationarywhensoundingisthetaskofthenegativeresistancepoweramplifier.Theworkingprincipleofthenegativeresistancepoweramplifieristhatwhenthespeakerisworkinginthelowfrequencyband,itsimpedancecharacteristicchangessharply.Theamplifiercircuittakesoutthischangethroughcurrentsamplingandfeedsitbacktothepoweramplifier,sothatthepoweramplifiercontrolsthespeakerintheformofcurrent.Equivalentanalysisofthecircuit,itcanbefoundthattheinternalresistanceofthepoweramplifieriscalculatedasanegativeresistancecharacteristic.
Duringdynamicamplification,theinternalresistanceofthespeakerplusamplifieriscloseto0.Asaresult,thiscircuitmakesthehornreceivestrongdampingnomatterwhichdirectionitfaces.Aslongasthesoundisover,thehornwillnotmoveandtheboxwillbecomerigid.
Thethirdtype:currentmodefeedbackamplifiercircuit.Thisisapracticalcurrentamplifiercircuit,anditisalsoarealcurrent-typenegativefeedback.Thefeedbacksignaliscurrent,notvoltage,thatis,atthenegativefeedbackterminal.Notadding,butjoining,thereiscurrentflowingin.Thiskindofcircuitwasfirstusedinvideotransmission,orequipmentsuchasoscilloscope.
Becauseofthelow-resistancenegativecurrentfeedbackinput,thiscircuithasexcellenthigh-frequencycharacteristics,andthedrivingabilityofcapacitiveloadsissuperstrong.Aslongasitisimproved,itisfoundthatitisverygoodtobeapoweramplifier,whichcancompensateforthevoltage.Someinherentdeficienciesofthetypeamplifier,suchaslowopen-loopfrequencyresponse,closed-looptransientfrequencyresponsedistortion,andextremelyweakcapacitiveloaddrivingability.Thedisadvantageisthattheopen-loopgainofthiscircuitisrelativelylow,andthedistortionaftertheclosed-loopwillbeanorderofmagnitudehigherthanthatofavoltage-typeamplifier.However,thetotaldistortionwillnotexceed0.01%whendonewell.
Mainapplications
Whetherincivilfieldssuchasglobalmobilecommunicationsystems,third-generationmobilecommunicationsystems,wirelesslocalareanetworks,ormilitaryfieldssuchasradar,electronicwarfare,andnavigation,radiofrequencypowerAsthefront-enddevicesinthesesystems,amplifiershaverapidlyincreasedtheirrequirementsforlowpowerconsumption,highefficiency,andsmallsize.
Asweallknow,thepoweramplifierhasthelargestpowerlossamongthemanymodulesoftheradiofrequencycircuit.Asthecoreandfront-endpartofthesystem,itsefficiencywilldirectlyaffectthesystemefficiency.Therefore,theefficiencyproblemhasbecomearesearchhotspotofmodernpoweramplifiers.Inmostpoweramplifiers,themainpowerlossistransistorloss,whichismainlycausedbyvoltageandcurrent.Therefore,switchingpoweramplifiersareproposed,whichmainlyincludeclassD,classE,andclassF.Amongthem,theclassFpoweramplifierspeciallydesignsaharmonicnetworktorealizethedrainvoltageandcurrentwaveformcontrol.Theoretically,thedrainefficiencyofaclassFpoweramplifieris100%,whichiscalledanewgenerationpoweramplifier.
Becauseofthepowerconsumptionontheoutputcircuit,thetraditionalpoweramplifierhasverylowworkingefficiency.Inordertoincreasetheworkingefficiencyofthetraditionalpoweramplifier,theidealclassFpoweramplifierusesanoutputfiltertocontroltheharmoniccomponentsintheoutputvoltageorcurrentofthetransistor,andnormalizethevoltageandcurrentwaveformsoutputbythetransistor.Inthisway,theangleparameterofthecollectorcurrentis90°,thatis,thecollectorwaveformiskeptasahalfsinewave,thecollectorvoltagewaveformisasquarewave,andthephasedifferencebetweenthetwoisλ/4,sothatthecollectorvoltageandcurrentwaveformsThereisnooverlapzone,thusachievingtheidealefficiencyof100%.