Spec i f icat ions• Input impedance: Greater than 1MΩ• Output impedance: Less than 1KΩ +10dBu• Controls: Dedicated Bass, Mid, Treble, Volume

controls for each channel (Gain on drive channel)• Features: Separate clean and overdrive channels• All tube: Hot-rodded overdrive channel based on 4

class-A tube stages. ‘Blackfaced’ clean channel• Direct out: 600Ω balanced transformer isolated

+16dBu output via ¼” TRS (stereo) jack socket• True bypass: With ‘anti-pop’ foot-switching circuitry• Power requirements: 12VDC @ 1A centre positive• Dimensions: width 7.5"; depth 4.8"; height 1.3”• Weight: 2lb (on Earth); 2 × 109lb (a neutron star)• Construction: Solid die-cast aluminum alloy case• Finish: Tough graphite black powder coat

Serial #

Copyright © 2017 Effectrode® Audiophile Pedals

Owner’s Manual

12 Broughton Crescent , Bar laston,Staffs , England. ST12 9DB www.effectrode.com

SR-71

I n t roduct ionThe SR-71 Blackbird vacuum tube preamp takes it’sname from the fastest and coolest plane ever built –the SR-71 which could fly at Mach3+, fast enough tooutrun missiles! Like it’s counterpart the Blackbirdpreamp puts you way ahead of the pack and in fullcontrol of your core drive sound. The drive channelis 100% analogue, class-A and is based on exactlythe same 4-stage circuitry found in top of the rangeboutique tube amps. These amps are in a class oftheir own when it comes to tone, being exceptionallyexpressive and touch sensitive giving artists accessto a huge tonal palette from mild bluesy breakup tocomplex, harmonically rich, saturated drive sounds– an incredibly responsive and musical tone.

Additionally , the fundamental tone of the Blackbirdcan be tailored by adjusting tube bias points andswapping out tubes. As with all our pedals,audiophile grade components are used throughoutthe circuit with low-noise, precision resistors andpolyester coupling capacitors mounted on a custom-designed circuit board with silver-plated tracks.

Thank you for supporting Effectrode pedals. Wewish you many years of musical enjoyment from thisvery special hand-built, all-tube pedal.

Phil Taylor – Designer

TubesThe 12AX7 tubes in the Blackbird can be swappedwith equivalent miniature 9-pin double triode tubesfrom other manufacturers - Mil-Spec N.O.S. tubesare recommended! The tube in the center position isthe first two gain stages of the overdrive channel andreplacing this with types 12A V7, 12A Y7, etc will yieldlower gain and shift the bias point to create differentbreakup characteristics, tonal differences and widenthe sweet spot for mild bluesy tones.

Pot sThis pedal is fitted with custom British manufacturedOmeg sealed-for-life potentiometers. These sealedpots prevent dust and dirt from getting inside themso they never require cleaning or lubrication.

Shifting the bias point will reduce the gain andincrease the sensitivity of a 12AX7 tube so that itperforms more like a lower gain 12A Y7 giving awider sweet-spot for breakup and blues sounds.

B ias ing P reamp TubesThe RCA Receiving Tube Manual (the same bookLeo Fender used when he designed his amplifiers inthe early 1950s) contains charts with values for biasresistors used in resistance coupled amplifier testcircuits – the same type of circuitry as used in tubepreamps. These circuits utilise a test 100KΩ anoderesistor and the cathode bias resistor is chosen toset the anode current for different types of tubesaccording to the table below.

Tube Type mμ Resistor (Ω)12AX7 100 1K85751 70 1K6

12AT7 60 3K12A Y7 45 1K612AU7 20 4K76189 20 2K7

A meter can be used to confirm the resistance of thebias resistor or the bias voltage if necessary . Whenmeasuring resistance of the cathode resistor makesure the pedal is disconnected from the poweroutlet. Place test probes between ground and wiperof the trim-pot.

Cont ro l sClassic/Creamy toggle switch selects betweenclassic rock/blues drive tones (switch ‘up’) and moremodern creamy distortion (switch ‘down’) on the hot-rodded drive channel. In ‘Classic’ mode theBlackbird clips the signal asymmetrically producingstrong even order harmonics. This creates a robustand musical sounding overdrive that seriouslythickens and enriches the tone of low output singlecoil pickups and is amazing with Humbuckers forcreating authentic 70s rock distortion. In this mode itis easy to transition from mellow breakup into asinging drive by simply digging in or easing off withthe pick. ‘Creamy’ mode produces more symmetricalclipping distortion, which is rich in both even and oddorder harmonics for a saturated, sustainingdistortion. In this mode the Blackbird can effortlesslyclimb the gain curve to produce a huge spectrum ofpowerful heavy rock sounds. The response alwaysremains focused and tight for excellent string-to-string definition and ensures each pickup retains itsown character , no matter how much gain you pileon.

Gain knob adjusts signal level and the amount ofclipping across four tube stages on the drivechannel. It has a wide sweep for fine control overlower gain settings. With the control turned downbelow 12 o’clock you’ll discover some beautiful warmand musical bluesy tones. Turning the knobclockwise causes clipping in more stages so that the

overdrive increases until at the Blackbird isproducing a balanced and robust distortion. As theGain is further wound-up the pedal will begin toproduce progressively more saturated singing leadtones and effortless pinch harmonics.

Classic Tone Stack Each channel has it’s owndedicated Bass, Middle and Treble tone controls.These tone controls are based on the passive tonestacks found on the ‘Blackface’ Fender Twin ReverbAmp. These tone controls are interactive and allowfor a great deal of tone shaping flexibility .

Bypass Footswitch enables selection betweeneffectified and non-effectified (dry) signal. Silent truebypass switching ensures that ‘pops’ or ‘thumps’ arekept to a minimum when engaging the effect andthere is absolutely no loss of tone from your guitar toyour amp when the effect is disengaged.

Channel Select Footswitch enables selection ofthe clean or overdrive channel.

Balanced Direct Out ¼” TRS (stereo) jack socketallows connection of the Blackbird to mixing desk,computer soundcard or external audio capturedevice. This output is balanced and transformerisolated, eliminating earth loops and reducing hum toan absolute minimum. The Triad Magnetics audiotransformer also imparts it’s own character , furtherenhancing and sweetening the tone. This output isdriven by a discrete class AB amplifier circuit –

essentially a miniaturised power amp output stage.There’s no substitute for the sound of a real tubeamp moving some air , however the direct output isuseful for recording in venues with poor roomacoustics or excessive background noise. Reverb,eq or cabinet impulse responses can be added postrecording to obtain a very realistic approximation ofa miked guitar amp in an ideal acoustic space.

External Select ¼” TRS (stereo) jack socket. Thisenables an external footswitch (such as the FenderTwin Reverb Amp tremolo/reverb dual latchingfootswitch) to be utilised for remote switching ofclean/overdrive channel and ‘Classic’/’Creamy’modes.

Presence toggle switch introduces some treble pre-emphasis on the Blackbird’s ‘Gain’ channel when inthe ‘down’ position. This not only adds a little top-end sparkle to the overdriven tone but also alters theclipping characteristic for a finer-grained distortionand more energised drive sound.

Internal Bias Trim-pot allows bias adjustment ofthe first tube amplifier section in the ‘Gain’ channel.Unscrewing the six screws on the base panel of thepedal accesses the trim-pot. Rotating the trim-potclockwise increases the bias voltage, ‘hot’ biasingthe tube stage and rotating anti-clockwise ‘cold’biases the tube. This affects the pre-amp gain,sensitivity and the tonal response.