Effectrode SR-71 User manual

Specifications
• Input impedance:Greaterthan1MOhm
• Outputimpedance: Less than 1KOhm+10dBu
• Controls: DedicatedBass, Mid, Treble,Volume
controls foreachchannel(Gainondrivechannel)
• Features: Separatecleanandoverdrivechannels
• All tube: Hot-roddedoverdrivechannelbasedon4
class Atube stages. ‘Blackfaced’clean channel
• Direct out: 600Wbalanced transformerisolated
+16dBuoutput via¼”TRS(stereo)jack socket
• True bypass: With‘anti-pop’foot-switching circuitry
• Powerrequirements: 12VDC@1Acentrepositive
• Dimensions: width7.5"; depth4.8";height 1.3”
• Weight: 2lb(on Earth);2 ´109lb(aneutron star)
• Construction:Soliddie-cast aluminum alloycase
• Finish: Toughgraphiteblack powdercoat
Serial#
Copyright ©2012 Effectrode
â
AudiophilePedals
Owner’sManual
12 BroughtonCrescent,Barlaston,
Staffs,UK.ST12 9DB
www.effectrode.com
SR-71

Introduction
The SR-71 Blackbird vacuumtubepreamptakesit’s
namefromthe fastestand coolestplaneeverbuilt
– the SR-71whichcouldfly atMach3+,fastenough
tooutrun missiles!Likeit’s counterpartthe Blackbird
preampputsyou wayaheadandinfull controlof
yourcoredrivesound.Thedrivechannelis 100%
analogue,class Aandis basedon exactly the same
4-stage circuitry found intop oftherange boutique
tube amps.Theseampsareinaclass oftheir own
whenitcomestotone,being exceptionally
expressiveand touchsensitivegiving artistsaccess
toahugetonalpalettefrommildbluesy breakupto
complex,harmonically rich,saturated drivesounds
– an incredibly responsiveandmusicaltone.
Additionally,the fundamentaltoneofthe Blackbird
can betailored byadjusting tubebiaspointsand
swappingouttubes.Aswithall ourpedals,
audiophilegrade componentsareused throughout
the circuitwithlow-noise,precision resistors and
polyestercoupling capacitors mounted on acircuit
boardwith22-carat gold-platedtracks.
Thankyouforsupporting Effectrode pedals!Iwish
you manyyears ofmusicalenjoymentfromthis very
specialhand-built, all-tube pedal.
Phil Taylor– Designer
Tubes
The 12AX7tubesinthe Blackbird can be swapped
withequivalentminiature9-pindoubletriodetubes
fromothermanufacturers -Mil-SpecNOS tubesare
recommended!Thetube inthe top righthand corner
is the firstgainstageandreplacingthis withtypes
12AV7,12AT7or12AY7will yieldlowergainand
shift the biaspointtocreatedifferentbreakup
characteristic,tonaldifferencesand widenthesweet
spot formildbluesy toneson the overdrivechannel.
Pots
This pedalis fitted withcustommanufactured Omeg
sealed forlifepotentiometers.Thesesealedpots
preventdustand dirtfromgetting inside themand
theydonot requireperiodic cleaningorlubricating.

Shifting the biaspointwill reducethegainand
increasethe sensitivityofa12AX7tube sothatit
performsmorelikealowergain12AY7giving a
widersweet-spot forbreakup andbluessounds.
BiasingPreampTubes
The RCAReceiving TubeManual (the samebook
Leo Fenderusedwhen he designed his amplifiers in
the early 1950s) containschartswithvaluesforbias
resistors used inresistancecoupledamplifiertest
circuits–the sametype ofcircuitry asused intube
preamps.Thesecircuitsutiliseatest100KWanode
resistorand thecathodebiasresistoris chosen to
setthe anode currentfordifferenttypesoftubes
according tothe tablebelow.
TubeType mmResistor(W)
12AX7 100 1K8
5751 70 1K6
12AT7 60 3K
12AY7 45 1K6
12AU7 20 4K7
6189 20 2K7
Ametercan be used toconfirmthe resistanceofthe
biasresistororthe biasvoltageifnecessary.When
measuring resistanceofthe cathode resistormake
surethe pedalis disconnectedfromthe power
outlet. Placetestprobesbetweengroundand the
wiperof the trimpot.
Controls
Classic/Creamy toggleswitchselectsbetween
classicrock/bluesdrivetones(switch‘up’) and more
moderncreamydistortion (switch‘down’) on the hot-
roddeddrivechannel.In‘Classic’ mode the
Blackbird clipsthe signalasymmetrically producing
strong evenorderharmonics.This createsarobust
and musicalsoundingoverdrivethatseriously
thickensand enrichesthetone oflowoutputsingle
coil pickupsand is amazing withHumbuckers for
creating authentic 70srock distortion.Inthis mode it
is easy totransition frommellowbreakup intoa
singing drivebysimply digging inoreasingoff with
the pick.‘Creamy’ mode producesmoresymmetrical
clipping distortion, whichis richinbotheven andodd
orderharmonics forasaturated,sustaining
distortion.Inthis modethe Blackbird can effortlessly
climbthe gaincurvetoproduceahugespectrumof
powerfulheavy metalsounds.Theresponsealways
remainsfocusedand tightforexcellentstring-to-
string definition and ensureseachpickup retainsits
owncharacter,nomatterhowmuchgainyou pile
on.
Gain knob adjustssignallevelandtheamountof
clipping across fourtubestagesonthedrive
channel.It hasawidesweepforfinecontrolover
lowergainsettings.Withthecontrolturned down
below12 o’clock you’lldiscoversomebeautiful
warmand musicalbluestones.Turningtheknob
clockwisecausesclipping inmorestagessothatthe

overdriveincreasesuntil atthe Blackbird is
producingabalancedand robustdistortion.Asthe
Gainis furtherwound-upthepedalwill beginto
produceprogressively moresaturated singing lead
tonesand effortless pinchharmonics.
ClassicToneStack Eachchannelhasit’s own
dedicatedBass,MiddleandTrebletonecontrols.
Thesetone controls arebased on the passivetone
stacks found on the ‘Blackface’ FenderTwinReverb
Amp.Thesetonecontrols areinteractiveandallow
foragreat dealof toneshaping flexibility.
BypassFootswitch enablesselection between
effectified and non-effectified (dry) signal.Silenttrue
bypass switching ensuresthat‘pops’ or‘thumps’ are
kepttoaminimumwhen engaging the effectand
thereis absolutely no loss oftonefromyourguitarto
yourampwhen the effect is disengaged.
ChannelSelectFootswitch enablesselection of
the cleanoroverdrivechannel.
BalancedDirectOut ¼”TRS(stereo)jack socket
allowsconnectionofthe Blackbird tomixing desk,
computersoundcardorexternalaudiocapture
device.This outputis balanced and transformer
isolated,eliminatingearthloopsandreducing hum
toanabsoluteminimum. The Triad Magnetics audio
transformeralsoimpartsit’s owncharacter,further
enhancing andsweeteningthetone.This outputis
driven byadiscreteclass AB amplifiercircuit-
essentially aminiaturised powerampoutputstage.
There’s no substituteforthe soundofarealtube
ampmoving someair,howeverthe directoutputis
usefulforrecordinginvenueswithpoorroom
acoustics orexcessivebackground noise.Reverb,
eq orcabinetimpulseresponsescan be added post
recording toobtainavery realistic approximation of
amiked guitarampinanidealacoustic space.
ExternalSelect ¼”TRS(stereo)jack socket. This
enablesan externalfootswitch(suchasthe Fender
TwinReverbAmp tremolo/reverbfootswitch)tobe
utilised forremoteswitching ofclean/overdrive
channeland‘Classic’/’Creamy’ modes.
Bias toggleswitchselectsbetween3differentbias
operatingpointsforthefirsttube stage on the drive
channel.This tubeis located onthetop-rightofthe
pedalandcan be swapped forotherminiatureB9A
typestomodifythesensitivity,feeland responseof
the drivechannel.The middleposition selects
biasing fora12AU7whichis alowmm(amplification
tube)tube.The up position selectsbiasing forahigh
mm12AX7and inthedownposition selectsbiasing
foramediummm12AY7tube.Thebiasing forthis
position is adjustableviaan internaltrimpot-
unscrewing the six screwson the basepanelofthe
pedalaccessesthis.Rotatingthetrimpotclockwise
increasesthe biasvoltage,‘hot’biasing the firsttube
stage and rotatinganti-clockwise‘cold’biasesthe
tube.This affectsthepre-ampgain,sensitivityand
the tonalresponse.