125B · 3 knobs
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
Report a wrong parse| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 23 | ||||
| R1 | 22k | 22k | Metal film resistor, 1/4W | |
| R2 | 150k | 150k | Metal film resistor, 1/4W | |
| R3 | 1k5 | 1.5k | Metal film resistor, 1/4W | |
| R4 | 47k | 47k | Metal film resistor, 1/4W | |
| R5 | 560k | 560k | Metal film resistor, 1/4W | |
| R6 | 120k | 120k | Metal film resistor, 1/4W | |
| R7 | 10k | 10k | Metal film resistor, 1/4W | |
| R8 | 10k | 10k | Metal film resistor, 1/4W | |
| R9 | 680k | 680k | Metal film resistor, 1/4W | |
| R10 | 36k | 36k | Metal film resistor, 1/4W | |
| R11 | 47k | 47k | Metal film resistor, 1/4W | |
| R12 | 1k | 1k | Metal film resistor, 1/4W | |
| R13 | 47k | 47k | Metal film resistor, 1/4W | |
| R14 | 100k | 100k | Metal film resistor, 1/4W | |
| R15 | 100k | 100k | Metal film resistor, 1/4W | |
| R16 | 4k7 | 4.7k | Metal film resistor, 1/4W | |
| R17 | 4k7 | 4.7k | Metal film resistor, 1/4W | |
| R18 | 100k | 100k | Metal film resistor, 1/4W | |
| R19 | 100k | 100k | Metal film resistor, 1/4W | |
| R20 | 100k | 100k | Metal film resistor, 1/4W | |
| R21 | 100R | 100 | Metal film resistor, 1/4W | Power supply filter resistor. |
| RPD | 2M2 | 2.2M | Metal film resistor, 1/4W | Input pulldown resistor. Can be as low as 1M. |
| LEDR | 10k | 10k | Metal film resistor, 1/4W | LED current-limiting resistor. Adjust value to change LED brightness. |
| Capacitors 11 | ||||
| C1 | 1uF | 1u | Film capacitor, 7.2 x 3.5mm | |
| C2 | 100n | 100n | Film capacitor, 7.2 x 2.5mm | |
| C3 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C4 | 100n | 100n | Film capacitor, 7.2 x 2.5mm | |
| C5 | 100n | 100n | Film capacitor, 7.2 x 2.5mm | |
| C6 | 1n | 1n | Film capacitor, 7.2 x 2.5mm | |
| C7 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C8 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C9 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C10 | 100uF | 100u | Electrolytic capacitor, 6.3mm | Power supply filter capacitor. |
| C11 | 100n | 100n | MLCC capacitor, X7R | Power supply filter capacitor. |
| Diodes 3 | ||||
| D1 | 1N5817 | 1N5817 | Schottky diode, DO-41 | |
| D2 | 1N4001 | 1N4001 | Rectifier diode, DO-41 | |
| D3 | 1N4001 | 1N4001 | Rectifier diode, DO-41 | |
| Transistors 4 | ||||
| Q1 | 2N3904 | 2N3904 | BJT transistor, NPN, TO-92 | |
| Q2 | 2N3904 | 2N3904 | BJT transistor, NPN, TO-92 | |
| Q3 | 2N3904 | 2N3904 | BJT transistor, NPN, TO-92 | |
| Q4 | 2N3904 | 2N3904 | BJT transistor, NPN, TO-92 | |
| Potentiometers 3 | ||||
| BLEND | 250kB | B250k | 16mm right-angle PCB mount pot | |
| OCTAVE | 1MB | B1M | 16mm right-angle PCB mount pot | |
| VOLUME | 100kB | B100k | 16mm right-angle PCB mount pot | |
| Switches 2 | ||||
| OCT. SW. | SPDT cntr off | SPDT CNTR OFF | Toggle switch, SPDT on-off-on | |
| FSW | 3PDT | 3PDT | Stomp switch, 3PDT | |
| LEDs 1 | ||||
| LED | 5mm | 5MM | LED, 5mm, red diffused | |
| Jacks & sockets 3 | ||||
| IN | 1/4" stereo | 1/4" STEREO | 1/4" phone jack, closed frame | Switchcraft 112BX or equivalent. |
| OUT | 1/4" mono | 1/4" MONO | 1/4" phone jack, closed frame | Switchcraft 111X or equivalent. |
| DC | 2.1mm | 2.1MM | DC jack, 2.1mm panel mount | Mouser 163-4302-E or equivalent. |
| Hardware 2 | ||||
| BATT | Battery snap | BATTERY SNAP | 9V battery snap | Optional. Use the soft plastic type—the hard-shell type will not fit. |
| ENC | 125B | 125B | Enclosure, die-cast aluminum | Can also use a Hammond 1590N1. |