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1、StandalonePhonoPre-ampAHIGH-PRECISIONPHONOPREAMPLIFIERbyFredNachbaur,Dogstar1997,1:INTRODUCTIONTherehasbeenmuchpresslatelyaboutthemerits(anddrawbacks)ofthevenerablevacuumtube.Howmuchofthisretromovementisbasedindemonstrableprinciples,andhowmuchisrooted
2、innostalgiaorsubjectivityisadebatethatcouldfillvolumes.Whatisclearisthatthereisconsiderablerenewedinterestinvacuumtubes,atechnologythateventwodecadesagowasconsideredasobsoleteasspatsandtophats.Nowthetrendisreversing,andanumberofmanufacturersareagainsu
3、pplyingtubegearforaudiophiles,musiciansandhobbyists.Inmanycases,thesearesimplyvintagecircuitsinnewpackaging.Otherproductsoffernewapproachestovacuumtubetechnology,addingwhatwe'velearnedinthemeantimetocomeupwithsometrulynoteworthydesigns.Theprojectdescr
4、ibedherefitsintothelattercategory.Whyusetubesanyway?Thecentralargumentforthepro-tubemovementisthatspecscanbealmostmeaningless,andthatwhatcountsishowitsoundstotheindividuallistener.Highlysubjectivedescriptionsarethereforeused,insteadofthetechno-babblew
5、e'vemore-or-lessgottenusedtoinrecenttimes.Theoppositecampclaimsthatnumbersdon'tlie,andthatyoucan'timprovesomethingbyaddingdistortionofanykind.Bothcampshavevalidpoints.Mostofushaveheardexpensivegearwithspectacularspecifications,butwereleftcoldbythe"too
6、goodtobetrue,"almostclinicalsoundofsuchequipment.Similarly,mostpeoplewillagreethatjustbecausesomethinghastubesinitdoesn'tmakeitworthlisteningto.Turnononeofthoseold"All-AmericanFive"table-topAMradiosifyouwantastrikingdemonstrationofjusthowbadvacuumtube
7、equipmentcansound.Perhapsawayofreconcilingthetwoviewpointsistoconsiderthedistinctionbetweenmusicalequipment,andreproductionequipment.Formusicalgear,theindividualfrequency,waveformandphasedistortionsarepartofwhatdefinesthesoundof,say,aFendertubeamp.Jus
8、tasno-onewouldtrytodefineafineStradivariusviolinwithspecsanddistortionfigures,soalsoitwouldbespecioustoarguethatacertaintubeguitaramphasover12%THD(totalharmonicdistortion)at35watts.Reproductionequipment,ontheotherhand,hasalwaysbeenexpectedtogi
