参考学习资料 手工制作 Linsley Hood Class1969.pdf

WirelessWorld,April1969

SimpleClassAAmplifier

A10-WdesigngivingsubjectivelybetterresultsthanclassB

transistoramplifiers

byJ.L.LinsleyHood,M.I.E.E.

Duringthepastfewyearsanumberofexcellentdesignshavebeenpublishedfordomesticaudio

amplifiers.However,someofthesedesignsarenowrenderedobsolescentbychangesintheavailability

ofcomponents,andothersareintendedtoprovidelevelsofpoweroutputwhichareinexcessofthe

requirementsofanormallivingroom.Also,mostdesignshavetendedtoberathercomplex.

Inthecircumstancesitseemedworthwhiletoconsiderjusthowsimpleadesigncouldbemadewhich

wouldgiveadequateoutputpowertogetherwithastandardofperformancewhichwasbeyondreproach,

andthisstudyhasresultedinthepresentdesign.

Outputpoweranddistortion

InviewoftheenormouspopularityoftheMullard5-10valveamplifier,itappearedthata10-wattoutput

wouldbeadequatefornormaluse;indeedwhentwosuchamplifiersareusedasastereopair,thetotal

soundoutputatfullpowercanbequiteastonishingusingreasonablysensitivespeakers.

TheoriginalharmonicdistortionstandardsforaudioamplifierswerelaiddownbyD.T.N.Williamsonina

seriesofarticlespublishedinWirelessWorldin1947and1949;andthestandard,proposedbyhim,for

lessthan0.1%totalharmonicdistortionatfullratedpoweroutput,hasbeengenerallyacceptedasthe

targetfigureforhigh-qualityaudiopoweramplifiers.Sincethemainprobleminthedesignofvalveaudio

amplifiersliesinthedifficultyinobtainingadequateperformancefromtheoutputtransformer,andsince

moderntransistorcircuittechniquesallowthedesignofpoweramplifierswithoutoutputtransformers,it

seemedfeasibletoaimat