Aion Electronics CERULEAN User manual

CERULEAN AMP OVERDRIVE 1
PROJECT NAME
CERULEAN
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Marshall®Bluesbreaker®
A classic overdrive effect that was designed to mimic the Marshall Bluesbreaker amplifier from the
1960s. Also the source circuit for a number of high-dollar “boutique” guitar pedals.
Amp-like overdrive 2.0.0 (2022-11-25)
Actual size is 2.3” x 1.86” (main board) and 2.3” x 0.86” (bypass board).
BUILD DIFFICULTY
Easy

CERULEAN AMP OVERDRIVE 2
TABLE OF CONTENTS
1Project Overview 7Drill Template
2Introduction & Usage 8Enclosure Layout
3-4 Parts List 9Wiring Diagram
5Build Notes 10 Licensing
6Schematic 10 Document Revisions
INTRODUCTION
The Cerulean Amp Overdrive is an updated version of the Marshall Bluesbreaker pedal, originally
released in 1991. In 1995, Marshall moved production from England to Korea, and around this time they
made some tweaks to the circuit, increasing the gain and reducing the bass. It was discontinued in 1999
to make way for the Bluesbreaker II, a redesign that is universally seen as inferior to the originals.
The Bluesbreaker is the source circuit for a number of expensive boutique pedals including the
Analogman King of Tone, which is two Bluesbreakers in the same box with a few modifications. The
Cerulean project borrows the expanded clipping options from the King of Tone, allowing you to select
either soft clipping (stock), hard clipping, or no clipping (boost mode).
We have also added an internal DIP switch to select between three different gain range settings.
Normally to increase the gain range of an overdrive, you’d just raise the value of the drive pot. However,
the Bluesbreaker has a unique dual-stage gain control setup such that increasing the potentiometer
value will also lower the minimum gain along with raising the maximum gain, so this method is not very
useful. But by adding resistance to just the first stage, we can shift the overall gain range higher and get
a lot more tones than the original pedal was capable of.
The third addition is a toggle switch to go between the pre-95 (V1) and post-95 (V2) versions. It’s not a
drastic difference, but there’s enough lore surrounding the two versions that we thought it’d be worth
including this as a setting.
The Cerulean V2 is a complete overhaul of the original Cerulean, which combined features from the
JHS Morning Glory as well as the Presence trimmer from the King of Tone. The first version is no longer
available, but the legacy 1590B version of the project is largely the same and will remain stocked. The
King of Tone is available as the Theseus and the Prince of Tone is available as the Achilles.
USAGE
The Bluesbreaker has the same control layout as most overdrive or distortion effects:
• Tone controls the treble response of the effect.
• Drive controls the amount of gain in the op-amp feedback diode clipping stage.
• Volume controls the overall output.
• Clipping (toggle switch) lets you choose between soft clipping (stock), hard clipping, or no clipping.
• Mode (toggle switch) changes between the V1 and V2 Bluesbreaker circuits.

CERULEAN AMP OVERDRIVE 3
PARTS LIST
This parts list is also available in a spreadsheet format which can be imported directly into Mouser for
easy parts ordering. Mouser doesn’t carry all the parts—notably potentiometers—so the second tab lists
all the non-Mouser parts as well as sources for each.
View parts list spreadsheet →
PART VALUE TYPE NOTES
R1 1M Metal film resistor, 1/4W
R2 470k Metal film resistor, 1/4W
R3 120k Metal film resistor, 1/4W
R4 27k Metal film resistor, 1/4W
R5 5k6 Metal film resistor, 1/4W Switched in parallel with R4 for the V2 value of 4.7k.
R6 33k Metal film resistor, 1/4W
R7 3k6 Metal film resistor, 1/4W Switched in parallel with R6 for the V2 value of 3.3k.
R8 10k Metal film resistor, 1/4W
R9 220k Metal film resistor, 1/4W
R10 6k8 Metal film resistor, 1/4W
R11 1k Metal film resistor, 1/4W
R12 6k8 Metal film resistor, 1/4W
R13 10k Metal film resistor, 1/4W
R14 10k Metal film resistor, 1/4W
R15 100R Metal film resistor, 1/4W
RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor. Can be as low as 1M.
LEDR 10k Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 10n Film capacitor, 7.2 x 2.5mm
C2 47pF MLCC capacitor, NP0/C0G
C3 10n Film capacitor, 7.2 x 2.5mm
C4 10n Film capacitor, 7.2 x 2.5mm
C5 100n Film capacitor, 7.2 x 2.5mm
C6 47pF MLCC capacitor, NP0/C0G
C7 10n Film capacitor, 7.2 x 2.5mm
C8 10n Film capacitor, 7.2 x 2.5mm
C9 1uF Film capacitor, 7.2 x 3.5mm
C10 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C11 47uF Electrolytic capacitor, 5mm Voltage reference filter capacitor.
C12 100n MLCC capacitor, X7R Power supply filter capacitor.

CERULEAN AMP OVERDRIVE 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
D1 1N5817 Schottky diode, DO-41
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
D4 1N914 Fast-switching diode, DO-35
D5 1N914 Fast-switching diode, DO-35
D6 1N914 Fast-switching diode, DO-35
D7 1N914 Fast-switching diode, DO-35
D8 1N914 Fast-switching diode, DO-35
D9 1N914 Fast-switching diode, DO-35
IC1 TL072 Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
CLIP DPDT center off Toggle switch, DPDT, on-off-on See build notes for more options.
MODE DPDT on-on Toggle switch, DPDT, on-on
DRIVE 100kB 16mm right-angle PCB mount pot Linear taper.
TONE 25kB 16mm right-angle PCB mount pot Linear taper.
VOL 100kA 16mm right-angle PCB mount pot Audio (log) taper.
IN 1/4" stereo 1/4" phone jack, closed frame Switchcraft 112BX or equivalent.
OUT 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X or equivalent.
DC 2.1mm DC jack, 2.1mm panel mount Mouser 163-4302-E or equivalent.
BATT Battery snap 9V battery snap Optional. Use the soft plastic type—the hard-shell type will not fit.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

CERULEAN AMP OVERDRIVE 5
BUILD NOTES
Clipping switch
The clipping switch allows you to select between soft clipping (stock Bluesbreaker), hard clipping (King
of Tone) and no clipping (boost mode).
You can change the function of this control by using a different type of switch.
• Use a DPDT on-on-on if you want the middle setting to be “both” instead of “neither”. However, be
aware that the hard-clipping mode has a lower threshold than soft-clipping mode, so soft + hard
mode will not sound much different than hard mode by itself.
• Use a DPDT on-on if you only want to have hard and soft clipping modes available.
Mode switch
The Mode switch selects between V1 (pre-95) and V2 (post-95) versions of the circuit. The only
differences are the values of two resistors, R4 and R6, coming off the first op-amp stage feedback loop.
In the first version, these resistors were 27k and 33k respectively. In the second version, these were
dropped to 4.7k and 3.3k, which raises the gain and reduces the bass somewhat.
The Mode switch changes these two resistors from V1 to V2 values. Rather than switching between two
different resistors, it adds resistors in parallel with the existing ones for the same effective value (or at
least within 2%, which is well inside of the 5% tolerance of the carbon film resistors used in the original).
By doing it this way, we can avoid momentarily disconnecting the feedback loop’s path to ground, which
could cause an audible pop when the switch is used.
Gain range switch
The DIP switch sets the gain range of the Drive control. In normal mode, it’s equivalent to the stock
Bluesbreaker circuit. Medium- and high-gain modes shift the range higher, allowing for an extended
range of tones not found in the original pedal.
The DIP switch settings are as follows:
ON
1 2
DIP
ON
1 2
DIP
ON
1 2
DIP
Normal Medium High
Note: Position 1 overrides position 2, so if both switches are in the up position, it will be in normal mode.