Akashic Guitar effects PCB lookup
OCTAVEBLENDVOLUME

125B · 3 knobs

Aion FX

ObscuraOctave Blend

Based on the Prescription Electronics COB

Category
Fuzz· Octave fuzz
Controls
Octave · Blend · Volume
Difficulty
Easy
Price
$12.50in stock

From the vendor

Based on the octave section of the fOXX Tone Machine, this circuit adds a clean blend and a knob to change the character of the octave effect.

The Obscura Octave Blend is an adaptation of the Prescription Electronics COB (Clean Octave Blend), an octave fuzz with blendable clean signal.

Prescription Electronics (PEI) was one of the original boutique pedal companies, founded in 1993 by Jack Brossart in Portland, OR. The COB was introduced within a couple of years and was produced up until the company closed its doors in 2014. PEI made a brief comeback in 2019 and reissued most of their lineup, but after Jack’s passing that same summer, they seem to have disappeared for good.

The COB is a very unique effect. The octave section is clearly based on the fOXX Tone Machine with a few value tweaks, but it’s missing both a tone and a gain control. Instead, the Octave knob loads down the octave stage in a way that does not actually add or remove the octave, but changes its character. At some settings it’s much more suitable for blending, and at others it sounds good on its own with no clean signal. There are a few great YouTube demos of the COB if you want to get an idea of how it works and what it’s capable of, but suffice it to say, it’s far from a typical octave fuzz.

The Obscura is a direct clone of the COB except for one addition: a switch that disables the octave, adapted from our Vulcan (fOXX Tone Machine) project. Its behavior is very different in this circuit. Typically you’ll want to leave it in the down (stock) position because the octave is the whole point of the effect. But there are some interesting and unique sounds in the other two modes, especially in combination with the blend control, so we felt like it was a worthwhile addition.

Schematic

The schematic is in the vendor's build document, page 6. Open the build document. No KiCad fragment has been drawn for this circuit yet.

Parts list 52 rows

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RefValueNormalizedTypeNotes
Resistors 23
R122k22kMetal film resistor, 1/4W
R2150k150kMetal film resistor, 1/4W
R31k51.5kMetal film resistor, 1/4W
R447k47kMetal film resistor, 1/4W
R5560k560kMetal film resistor, 1/4W
R6120k120kMetal film resistor, 1/4W
R710k10kMetal film resistor, 1/4W
R810k10kMetal film resistor, 1/4W
R9680k680kMetal film resistor, 1/4W
R1036k36kMetal film resistor, 1/4W
R1147k47kMetal film resistor, 1/4W
R121k1kMetal film resistor, 1/4W
R1347k47kMetal film resistor, 1/4W
R14100k100kMetal film resistor, 1/4W
R15100k100kMetal film resistor, 1/4W
R164k74.7kMetal film resistor, 1/4W
R174k74.7kMetal film resistor, 1/4W
R18100k100kMetal film resistor, 1/4W
R19100k100kMetal film resistor, 1/4W
R20100k100kMetal film resistor, 1/4W
R21100R100Metal film resistor, 1/4WPower supply filter resistor.
RPD2M22.2MMetal film resistor, 1/4WInput pulldown resistor. Can be as low as 1M.
LEDR10k10kMetal film resistor, 1/4WLED current-limiting resistor. Adjust value to change LED brightness.
Capacitors 11
C11uF1uFilm capacitor, 7.2 x 3.5mm
C2100n100nFilm capacitor, 7.2 x 2.5mm
C310uF10uElectrolytic capacitor, 5mm
C4100n100nFilm capacitor, 7.2 x 2.5mm
C5100n100nFilm capacitor, 7.2 x 2.5mm
C61n1nFilm capacitor, 7.2 x 2.5mm
C710uF10uElectrolytic capacitor, 5mm
C810uF10uElectrolytic capacitor, 5mm
C910uF10uElectrolytic capacitor, 5mm
C10100uF100uElectrolytic capacitor, 6.3mmPower supply filter capacitor.
C11100n100nMLCC capacitor, X7RPower supply filter capacitor.
Diodes 3
D11N58171N5817Schottky diode, DO-41
D21N40011N4001Rectifier diode, DO-41
D31N40011N4001Rectifier diode, DO-41
Transistors 4
Q12N39042N3904BJT transistor, NPN, TO-92
Q22N39042N3904BJT transistor, NPN, TO-92
Q32N39042N3904BJT transistor, NPN, TO-92
Q42N39042N3904BJT transistor, NPN, TO-92
Potentiometers 3
BLEND250kBB250k16mm right-angle PCB mount pot
OCTAVE1MBB1M16mm right-angle PCB mount pot
VOLUME100kBB100k16mm right-angle PCB mount pot
Switches 2
OCT. SW.SPDT cntr offSPDT CNTR OFFToggle switch, SPDT on-off-on
FSW3PDT3PDTStomp switch, 3PDT
LEDs 1
LED5mm5MMLED, 5mm, red diffused
Jacks & sockets 3
IN1/4" stereo1/4" STEREO1/4" phone jack, closed frameSwitchcraft 112BX or equivalent.
OUT1/4" mono1/4" MONO1/4" phone jack, closed frameSwitchcraft 111X or equivalent.
DC2.1mm2.1MMDC jack, 2.1mm panel mountMouser 163-4302-E or equivalent.
Hardware 2
BATTBattery snapBATTERY SNAP9V battery snapOptional. Use the soft plastic type—the hard-shell type will not fit.
ENC125B125BEnclosure, die-cast aluminumCan also use a Hammond 1590N1.