Dusky D2O User manual

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D₂OAmplifier
UserManual
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DuskyElectronics,LLC
Durham,NCUSA
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Introduction
CongratulationsonyourpurchaseoftheD₂OAmplifierfromDuskyElectronics.
Youramplifierisdesignedtoprovideyoualifetimeofdependableserviceand
superiorsound,whileallowingyoutoachieveyourartisticgoalswithaminimum
offuss.
WeencourageyoutoregisteryouramplifierattheDuskyElectronicswebsite.You
candosoathttps://duskyamp.com/pieces/register
Youdonothavetobetheoriginalownertoregister.Registrationisrequiredfor
anywarrantyworkfortheoriginalownerandmayalsohelptoestablisharecord
ofownershipintheeventitmayberequiredforinsurancepurposesortracking
downtheprovenanceofastolenamp.
Overview
TheDuskyElectronicsD₂OAmplifierisa32wattvacuumtubeinstrument
amplifierheaddesignedforusewithanyelectronicinstrument,especiallyelectric
guitarorbass.TheD₂OAmplifiersupportsspeakerloadsof4Ω,8Ω,or16Ω.The
32wattoutputmaybereducedto8wattsbymeansofarearmountedtoggle
switch,allowingagreateramountofbreakupdistortiontobeachievedatlower
soundpressurelevels.TheD₂OAmplifier'scomplementoftonecontrolsisunique
inthemarketandallowsawiderangeofcontrolwhileremainingeasytouse,
makingtheD₂Ouniquelyadaptabletojustaboutanyinstrument,speaker
cabinet,ormusicalsituation.
TheD₂OAmplifierisanew,originaldesignamplifierthatemploysaclassic
architecture—aminimal,cleantwostagepreamplifierdrivingacathodebiased
poweramplifiersection.Assignallevelincreasesthepoweramplifiersectionis
drivenintodistortionjustalittlebeforethepreamplifiersection,muchlikemany
classicguitarsamplifiersfromthe1950sand1960s.
TheFrontandRearPanels
PicturedhereisthefrontcontrolpaneloftheD₂OAmplifier:

Fromlefttorightwehave:

INThisistheinputjackoftheamplifier.Itacceptsastandard¼”phonepluglike
thatfoundonanystandardinstrumentcable.Theoutputofyourinstrument,or
ofthelasteffectinyoureffectschainifyouareusingeffects,shouldbe
connectedhereusingastandardinstrumentcable.
VOLThisknobcontrolstheoutputleveloftheamplifier.Thisknobnotonly
affectsthesoundpressurelevelultimatelyproducedbyyourspeakercabinet,but
theamountofdistortionproducedinternallyinsideoftheamplifier.Bothsound
pressurelevelanddistortionincreaseasthecontrolisrotatedclockwise.
BASSMIDTREBLECUTThesefourknobs,collectively,areusedtocontrolthe
frequencyresponseoftheamplifier,allowingittoadapttodifferentinstruments,
speakercabinets,andtheuser'smusicalintention.Seethesectionontone
controlsformoreinformation.
STDBYThisswitch,whendown,mutestheoutputofthepoweramplifierstage.
Iftheunitispoweredon,useofthisswitchcankeeptheoutputoftheamplifier
mutedwhileallowingthetubestoremainwarmandreadytoamplify,thus
keepingtheamplifierinahotstandbymode.Withtheswitchintheupposition,
thepoweramplifierstageisunmutedandtheunitoperatesnormally.
POWERThisswitchturnsontheamplifier.Thereisasmalltimelag(15to20
seconds)betweenwhentheunitisturnedonandwhenthetubeshavewarmed
upenoughtobeginamplifying.Oncethetubeshavewarmeduptheamplifieris
readyforuseandwilloperatenormally.

PicturedhereistherearcontrolpaneloftheD₂OAmplifier:

Fromlefttorightwehave:
POWERThepowerinletacceptsastandardIECpowercablemuchlikeyoumay
beaccustomedtousingwithcomputersorotherelectronicequipment.Obviously,
acablemustbeattachedhereandpluggedintoapowersourceinorderforthe
amplifiertofunction.AmplifierssoldinNorthAmericawillcomewithapower
cableincluded.AmplifierssoldoutsideofNorthAmericawillbesoldwithouta
powercable.Theuserwillneedtoprovideapowercablethatfitslocalelectrical

outlets.Thepowerinletwillbelabeledwiththevoltageyouramplifieriswiredto
accept,whichwillvarydependingonthecountrywhereitisintendedtobeused.
SerialNumberYourunit'sserialnumberwillbelocatedjustbeneaththepower
inlet.
FUSEThisisthefuseholderforthemainssafetyfuse.Ifthefuseblowsreplace
onlywithafuseofthelabeledtype,whichwillvarydependingonthecountryof
intendedusage.Iftheamplifierblowsmorethanonefuseinashortperiodof
time,thisindicatesaproblemwiththeamplifier.Pleasereferyouramplifierto
DuskyElectronicsortoaqualifiedtechnicianforrepair.
HIGH/LOWWhenthisswitchisintheupposition,theamplifieroperatesatfull
powerandcandeliverupto32wattsofpowertoanattachedspeakerload.When
theswitchisinthedownposition,availableoutputpowerisroughly¼or8watts.
IMPEDANCEThisswitchcanbeturnedwithaflatheadscrewdriver,coin,or
heavyguitarpick.Itshouldbesettomatchtheimpedanceofthespeakerload
attachedtotheamplifier.Seethesectiononspeakerloadbelow.
SPEAKERSOneortwospeakercabinetsmaybepluggedintothesespeaker
outputs,whichacceptstandard¼”plugs.Ifonlyonespeakercabinetisused,it
shouldbepluggedintotheoutputlabeledMAIN.
ToneControls
BassandTreble
ThefirstpreampstageincludestheBassandTreblecontrolsbasedonthe
classic"James"tonestack.Thisconfigurationallowsindependentcontrolofbass
ortreble,allowingeitherrangetobecutorboostedwithoutaffectingtheother
frequencyrange.
FlatEQisachievedwithbothcontrolssetatapproximately11o'clock.
Middle
TheMiddlecontrolislocatedinthenextpreampstage,completelyisolatedfrom
theBassandTreblecontrols.TheMiddlecontrolisapassivemidrangefilter
tunedforthelowermiddlefrequenciesthatareoftendescribedassounding
“muddy.”
WiththeMiddleknobsetfullyclockwise,verylittlemidrangeisbeingcut.Asthe
controlisrotatedcounterclockwise,progressivelymorelowermidrangeis
scoopedout,allowingyoutogofromverywarmsoundingtoveryscooped.

FlatEQisachievedwiththiscontrolsetfullyclockwise.
Cut
TheCutcontrolisapassivetreblecutlocatedinthepowerampsection.This
controlcantametheupperregistersbeyondthefrequencyrangeemphasizedby
theTreblecontrol.Thisisespeciallyusefulifyou'reoverdrivingthe
amplifier—allowingyoutotametheharmonicsaddedbydistortionintroducedin
earlierstagesandinthepoweramplifieritself.
Foracrankedtone,turnuptheTreblecontrol—whichwillpushthetubesalittle
harder—andalsoturnuptheCutcontrol,inturn,totametheresultinghighend.
FlatEQisachievedwiththiscontrolsetfullycounterclockwise.
AdditionalInformationonFlatEQ
Although,technically,flatEQisachievedwiththeTrebleandBasscontrolsat
around11o'clock,theMiddlecontrolfullyclockwise,andtheCutcontrolfully
counterclockwise,mostguitarplayersareusedtoplayingamplifierswitha
midscoopedsound,sotheD₂Omayactuallysoundsubjectivelyneutralwithall
controlssetat12o'clock.
Itisdifficulttomakethisamplifiersoundbad!Experimentationwithextremeand
bizarreEQsettingsishighlyencouraged.Don'tbeafraidtotrysettingknobsall
thewayuporallthewaydown.Tryalotofdifferentsettingsandseewhatworks
foryou.
MatchingSpeakerLoad
Acommonpointofconfusionishowtosettheoutputimpedanceoftheamplifier
inordertomatchtheattachedspeakerload.Ifonlyusingasinglespeaker
cabinet,thisiseasy.Settheimpedanceselectorswitchtomatchtheimpedance
ofyourspeakercabinetandplugyourspeakercabinetintotheMAINspeaker
output.
ThetwospeakeroutputsontheD₂Oarewiredinparallel.Whenconnectingtwo
speakercabinets,usingboththeMAINandAUXoutputs,theruleisthatboth
speakercabinetsmustbethesameimpedanceandthetotalimpedanceseenby
theamplifierwillbehalf  theimpedanceofonespeakercabinetbyitself.For
example,ifyouconnecttwo8Ωspeakers,onetoeachoutputjackoftheD₂O,
youshouldsettheimpedanceselectorswitchto4Ω.

PowerTubeRolling
TheoutputtubesocketsoftheD₂OAmplifierarewiredinsuchawaythatthey
arecompatiblewithboth6L6GCandEL34powertubes,aswellasmanysimilar
tubetypeswithcompatiblepinouts.Thankstocathodebiasing,thereisnoneed
torebiasthepowerampwhenswappingtubes.
Differenttubetypesdosounddifferentfromoneanother,andalittle
experimentationcanopenupsomenewanddifferentpossibilities.Theextentto
whichthismightbeworthittoyoudependssomewhatuponhowyouusethe
amp.Ifyoutendtoplayclean,differencesbetweendifferenttubetypeswilltend
tobesubtle.Theharderyoupushtheoutputtubesthemorethedifferences
amongtubetypesbecomesapparent—withdifferenttubetypeshavingdistinctly
differentbreakupcharacteristics.
Sometubesthatareknowntoworkinclude:6L6GC,EL34,E34L,KT66,KT88,
KT120,6550,and7581.
Avoid6L6GBor6L6GA,asthesearenotratedforthepowerorvoltage
seenintheD₂Ocircuitandmayfailcatastrophicallyintheworstcaseand
justnotlastaslonginthebestcase.Therearenocurrentproductiontubes
ofthistype,soyouwouldonlyencountertheseamongvintagetubes.Ouradvice
istosaveyourvintageandnewoldstocktubesforcircuitsthatarespecifiedto
usethosetubes.
7591sarenotpincompatible,norwouldtheyworkinthiscircuitunmodifiedeven
iftheywere.6V6scannothandletheconditionsfoundintheD₂Oand
shouldneverbeused.
RoutineMaintenance
TheD₂OAmplifierdoesn'treallyrequiremuchinthewayofroutinemaintenance
andshouldbeabletobeusedforyearsatatimewithoutdoinganything.
Thefollowingarethingsyouarelikelytoencounter:
ReplacingTubes
Themostcommonmaintenancetaskisreplacementofthevacuumtubes,as
thesedowearoutorintermittentlyfail.Toreplacethetubes,poweroffthe
amplifierandlettheamplifiersitlongenoughforthetubestocooloffenoughto
behandled.Powertubesgetquitehotinthecourseofnormaloperation
andcancauseseriousburnsifhandledwhilehot.Oncethetubeshave
cooled,removetheamp'slidbyremovingthefourscrewsthatholdthelidonto

thebottomchassis—twooneachend—andremovethelid.Removetheoldtubes
fromtheirsocketsandinsertnewtubes.Replacethelidandthefourscrewsthat
holditinplacewhenfinished.
Thepreamptubesshouldbereplacedonlywithtubesofthesametype:6SL7.At
thetimeofthiswriting,theonlycurrentproductiontubeofthistypeavailableis
theTungSolbrand.Thesearegood,reliabletubes,andlessproneto
microphonicsthanvintagetubes.
YoumayalsofindSovtek6SL7savailableforpurchase.Theseareactuallynew
oldstockSovieteratubes,andourexperiencewiththemisthattheysoundgood
untiltheystartgettingmicrophonicornoisy—whichtendstobeearlyandoften.
Forthisreason,Sovteksarenotrecommended.Preamptubes,ingeneral,don't
wearoutinthesamewayaspowertubes,sounlessatubeisnoticeably
problematic,there'sprobablynotmuchreasontoreplaceit.
Asfarasreplacingthepowertubes,seetheabovesectiononPowerTube
Rolling.
Thereareabewilderingvarietyofmanufacturersandtubetypesthatwillworkas
thepowertubesinthiscircuit.Thegoodnewsisthattheyalmostallsoundpretty
good,sodon'tsweatittoomuch.WeuseTungSol6L6GC“STR”tubesand
recommendthesewithoutreservation.Theperformanceofpowertubescan
degradeovertime,sosometimesreplacingthepowertubescancreatean
impressionofbreathingnewlifeintoanamplifier.Howlongthistakestohappen
variesand,ofcourse,dependsuponhowoftenandhowhardtheampisplayed.
In“typical”usage,powertubesshouldlastseveralyearsbeforereplacement
yieldsanoticeableimprovement.
Whenreplacingpowertubesyoushouldpurchaseandinstallmatchedpairs,
replacingbothpowertubesatthesametime.Thereisnosuchmatching
requirementforthepreamptubes.
ReplacingtheFuse
Youmightalsohaveafusefail,inwhichcaseitshouldbereplacedwithafuseof
thesametypeandrating.Makesureanyreplacementfuseisaslowblowtype.
2Afusesareusedincountrieswith120Vand100Vpower.1Afusesareusedin
countrieswith230V.Thefuseholderislocatedontherearoftheamplifier.Ifthe
fusefailsmorethanonceinashortperiodoftimethisindicatesthatthereisa
problemwiththeamplifier,inwhichcaseitshouldbereferredtoDusky
Electronicsoraqualifiedtechnicianforrepair.

ElectrolyticCapacitors
Theonlyothermaintenancetaskthatislikelytocomeupmightbechangingthe
electrolyticcapacitors.Electrolyticcapacitorscontainadielectricgelthatcandry
outovertimeandcompromisetheperformanceofthecapacitor.Ingeneral,this
takesaverylongtime  tohappen,ifithappensatall.Withmodern,highquality
parts,likethoseusedintheD₂OAmplifier,we'reprobablytalkingsomethingon
theorderof20yearsorso.Thistaskmustbeperformedbyaqualifiedrepair
technician.
Troubleshooting
We'vetriedtothinkofsomescenariosyoumightencounterandhowyoumight
goabouttroubleshootingthem.
Theampdoesnotpoweron.
Hopefullyyou'vecheckedtomakesureitispluggedin.Ifitispluggedintoa
surgeprotectoryou'vemadesurethatthatsurgeprotectorispluggedinandis
turnedon.Checkthefuse.Makesuretheamplifieristurnedoffbefore
checkingthefuse.Removethefusefromthefuseholderandexaminethefuse
visually.Usually,ifthefusehasburntoutyouwillseesomeblackcharinsidethe
glassenvelope,andyou'llseethatthefilamentisnolongercontinuousfromone
endofthefusetotheother.Ifyouhaveamultimeteryoucancheckforelectrical
continuityacrossthefuse.Replacethefusewiththepropertypeoffuse.Seethe
abovesectiononreplacingthefuse.Iftheampstilldoesnotpoweronorifanew
fuseburnsout,yourampwillneedtobeseenbyaqualifiedrepairtechnician.
Theamppowersonbutnosoundcomesfromthespeaker.
Whenyouturnthevolumeupalltheway,doyouhearanyhisscomingfromthe
speaker?Ifyes,thenthepoweramplifierisworkingandyouhaveasolid
connectiontothespeakercabinet.(Turntheamptoyournormalusablelevel.)
Checktomakesureyou'reactuallygettingasignalattheinput.Ifyouhaveany
effectsbetweenyourinstrumentandtheamplifier,tryremovingthemfromthe
signalchainandpluggingyourinstrumentdirectlyintotheinputoftheamplifier.
Ifthereisstillnosound,makesurethevolumecontrolisuponyourinstrument.
Tryswappingouttheinstrumentcabletoseeifthatmakesadifference.Ifyou
haveanotheramplifier,trypluggingyourinstrumentintothattoseeifthereisa
problemwiththeinstrument.
Ifthereisnohisscomingfromthespeakercabinetwiththevolumealltheway
up,thenthereisaproblemwithamplifier,theamplifier'sconnectiontothe

speakercabinet,orthespeakercabinetitself.IstheSTDBYswitchintheup
position?IsthereaspeakercabinetpluggedintotheMAINspeakeroutput?Have
youtriedadifferentspeakercable?Mostspeakercabinetsmaketheelectrical
connectiontothespeakersviaquickconnecttabsthatcansometimesfalloff.
Checktomakesureeachspeakerinthecabinethastwosecurewired
connectionstoitandtherearenodangling,disconnectedwiresinsidethespeaker
cabinet.Ifyouhaveanotheramplifier,useittotestthespeakercabinet.
Ifyoudeterminetheproblemiswiththeamplifierandnotwiththeinstrument,
instrumentcable,speakercabinet,orspeakercable,yourampwillneedtobe
seenbyaqualifiedrepairtechnician.
Thereisunwantednoisecomingfromthespeakerortheampsuddenly
soundsbad.
Inthevastmajorityofcases,thiswillbecausedbyafailingvacuumtube.  See
thesectionaboveonreplacingtubes.Iftheproblempersistsdespitereplacing
tubes,yourampwillneedtobeseenbyaqualifiedrepairtechnician.
FrequentlyAskedQuestions
DoIneedtobiasmyampwhenchangingpowertubes?
BecausetheDuskyElectronicsD₂OAmplifier'spowersectioniscathodebiased,
whichisselfadjusting,noadjustmentsneedtobemadewhenchangingpower
tubes—evenfortubesofdifferenttypes.Seethesectionaboveonpowertube
rolling.
Isthereaspecialpoweron  procedureIshouldfollow?
Theshortansweris“no.”Ifthatsatisfiesyou,youcanmoveon.
Mostusersoftubeguitarandbassamplifierswillbefamiliarwithloreregarding
poweronandpoweroffproceduresalongthelinesof“turnonthepowerfirst,
wait30seconds,thenturnonthestandby.”
Theconventionalwisdombehindthisprocedureisthatapplyingfullpowertothe
tubesbeforetheirheatershavehadachancetowarmupcanleadtocathode
stripping,wherematerialisliterallypulledoffofthetube'scathodeandpulledto
thetube'splate,damagingthetube.Whilethisisarealphenomenonthataffects
largeradiotransmissiontubesthatoperateatkilovoltandmegavoltpotentials,
thereisnoevidencethatthisphenomenonoccursatthesmallerscaleof
receivingtubesusedbyaudioamplifiers.

It'ssafetosaythatmostofthelorearoundtheproperwaytoturnatube
amplifieronoroffisapocryphawithlittlebasisinpracticalapplication.Which
makessenseifyouthinkaboutit.Iftubeamplifierswerereallysuchfragile
objectsthattheyrequireaspecialproceduretoturnthemonoroff,careless
musicianswouldbedamagingtheirgearallthetime.Inpractice,musicians
regularlyusevintagetubeamplifiersthathaven'tseenanykindofservicein
decadesthatcontinuetofunctionreliably.
Theuniversalabsenceofastandbyfeatureontubehifigearshouldbeanother
cluethatsuchafeatureisnotstrictlynecessaryforpreventingdamagetothe
amplifier.
Aroundhere,wetendtoleavetheSTDBYswitchintheuppositionandonlyflipit
tothedownpositionwhentheampisalreadyonandwewanttotemporarily
muteitsoutput.Thisis,infact,theintendedfunctionoftheSTDBYswitch.
CanIchangethepowerswitchsettingwhiletheampison?
Yes.Thisfeatureishotswitchable.Youmighthearalittlebitofapop.  Thereisno
needtopowerofftheamplifierorengagestandby.
CanIunplugorpluginspeakerswhiletheampison?
Whenplugginginorunpluggingspeakers,theampshouldbepoweredofforthe
standbyshouldbeengaged.
CanIchangetheoutputimpedancesettingwhiletheampison?
Whenadjustingtheimpedanceselectorswitch,theampshouldbepoweredoffor
thestandbyshouldbeengaged.
WhatifIplugaspeakercabinetintotheAUXoutputwithnothing
attachedtoMAIN?
TheMAINoutputusesashortingjackthatshortstheamplifier'soutputwhenno
speakerisconnectedinordertopreventdamagetotheamplifierintheevent
thatausermistakenlypowerstheamplifieronwithoutaspeakerconnectedto
theoutput.Therefore,ifyouplugasinglespeakercabinetintotheAUXoutput
withnospeakerattachedattheMAINoutput,theamplifier'soutputwillremain
shortedandlittleornosignalwillreachtheconnectedspeaker.
WhatifIruntheampwithnospeakerattached?
Generallyspeaking,it'snotagoodideatorunatubeampwithoutanattached
speakerload.Thiscancausedamagetothepoweramplifiertubesortheoutput
transformer.Theoutputtransformerisafairlyexpensivepartthatyoudon'twant