Aion Electronics HALO User manual

HALO DISTORTION/SUSTAINER 1
PROJECT NAME
HALO
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Electro-Harmonix Big Muff Pi
One of the most classic guitar effects of all time, its sound falls somewhere between a distortion effect
and a fuzz with an incredibly long sustain.
Distortion / Sustainer, Fuzz 1.0.0 (2018-07-04)
BUILD DIFFICULTY
Easy
Actual size is 2.3” x 1.86” (main board) and 2.3” x 0.86” (bypass board).

HALO DISTORTION/SUSTAINER 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 Halo Distortion/Sustainer is a recreation of the Electro-Harmonix Big Muff Pi, rst released in
1969. Originally marketed as a “harmonic distortion sustain”, it has been lumped together with fuzz
effects, although it’s a very different animal than classic fuzz effects like a Fuzz Face or a Tone Bender.
The Big Muff is something of a “rite of passage” for pedalbuilders. It’s a pretty easy build and there
aren’t a lot of things that can be messed up. There’s no biasing or gain sorting, and no rare or specialized
parts are needed. It’s endlessly tweakable, with dozens of different variants (some of which sound very
different) that are just a matter of substituting a few parts.
The Big Muff circuit was adapted by a number of other pedal manufacturers in the 1970s. Notably, the
4th version of the Colorsound Tone Bender, called the Supa Tone Bender and released in 1973, was
based on the Big Muff circuit. The next version of the Tone Bender, called the Jumbo Tone Bender and
released in 1976, changed the standard Big Muff circuit by removing the 4th transistor, a make-up gain
stage after the tone control. This 3-transistor variant was copied by other manufacturers as well.
The Halo PCB allows you to easily build either the 4-transistor or the 3-transistor variant.
USAGE
The Halo has the following controls:
• Sustain controls the amount of drive or distortion, which also affects the amount of sustain.
• Tone is a control that pans between a low-pass lter (high cut) and a high-pass lter (low cut). At the
12:00 position, the bass and treble are at, and the midrange tone response is based on the setting
of the Mids switch.
• Volume is the overall output.
• Mids allows you to switch between Mid Scoop (the stock setting), Mid Hump, or Flat Mids.

HALO DISTORTION/SUSTAINER 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 →
Note: Values shown are for the Violet Ram’s Head (2nd edition).
PART VALUE TYPE NOTES
R2 39k Metal lm resistor, 1/4W
R3 100k Metal lm resistor, 1/4W
R4 470k Metal lm resistor, 1/4W
R5 100R Metal lm resistor, 1/4W
R6 15k Metal lm resistor, 1/4W
R7 1k Metal lm resistor, 1/4W
R8 8k2 Metal lm resistor, 1/4W
R9 100k Metal lm resistor, 1/4W
R10 470k Metal lm resistor, 1/4W
R11 100R Metal lm resistor, 1/4W
R12 15k Metal lm resistor, 1/4W
R13 8k2 Metal lm resistor, 1/4W
R14 100k Metal lm resistor, 1/4W
R15 470k Metal lm resistor, 1/4W
R16 100R Metal lm resistor, 1/4W
R17 15k Metal lm resistor, 1/4W
R18 33k Metal lm resistor, 1/4W
R19 33k Metal lm resistor, 1/4W
R20 390k Metal lm resistor, 1/4W
R21 100k Metal lm resistor, 1/4W
R22 10k Metal lm resistor, 1/4W
R23 2k2 Metal lm resistor, 1/4W
R24 47R Metal lm resistor, 1/4W
RPD 2M2 Metal lm resistor, 1/4W
LEDR 4k7 Metal lm resistor, 1/4W
C1 100n Film capacitor, 7.2 x 2.5mm
C2 470pF MLCC capacitor, NP0/C0G
C3 100n Film capacitor, 7.2 x 2.5mm

HALO DISTORTION/SUSTAINER 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C4 100n Film capacitor, 7.2 x 2.5mm
C5 470pF MLCC capacitor, NP0/C0G
C6 100n Film capacitor, 7.2 x 2.5mm
C7 100n Film capacitor, 7.2 x 2.5mm
C8 470pF MLCC capacitor, NP0/C0G
C9 100n Film capacitor, 7.2 x 2.5mm
C10 3n9 Film capacitor, 7.2 x 2.5mm
C11 10n Film capacitor, 7.2 x 2.5mm
C12 100n Film capacitor, 7.2 x 2.5mm
C13 100n Film capacitor, 7.2 x 2.5mm
C14 100uF Electrolytic capacitor, 6.3mm Power supply lter capacitor.
C15 100n MLCC capacitor, X7R Power supply lter capacitor.
CX1 10n Film capacitor, 7.2 x 2.5mm
CX2 3n9 Film capacitor, 7.2 x 2.5mm
CX3 JUMPER Clipped wire lead Jumper for a standard 4-transistor Big Muff. Use a 100n lm capacitor
here if building a 3-transistor variant such as the Jumbo Tone Bender.
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
Q1 2N3904 BJT transistor, NPN, TO-92
Q2 2N3904 BJT transistor, NPN, TO-92
Q3 2N3904 BJT transistor, NPN, TO-92
Q4 2N3904 BJT transistor, NPN, TO-92
TONE 100kB 16mm right-angle PCB mount pot LED current-limiting resistor. Adjust value to change LED brightness.
SUS 100kB 16mm right-angle PCB mount pot
VOL 100kA 16mm right-angle PCB mount pot
MIDS DPDT Toggle switch, DPDT on-on-on A more common on-on switch can be used if that’s all you can nd, but
the at mids mode will be unavailable.
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 t.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

HALO DISTORTION/SUSTAINER 5
BUILD NOTES
Bypassing Q4
Some Muff variants such as the Jumbo Tone Bender will eliminate the last transistor gain stage. The
Halo PCB makes this easy to do: just jumper the “Q4 Bypass” pads in the upper-right and omit R20-23,
Q4, and C13. Also, use a 100n lm capacitor for CX3 (normally jumpered). Better instructions for these
variants will be added in a future version of the documentation.
Important: If you are building a normal 4-transistor Muff, you need to jumper CX3. You can use a jumper
wire between the pads if you want, but even more conveniently, there are two SMD pads to the left of
CX3 that can be easily connected with a bead of solder to save the hassle of using a jumper wire.
Mids Switch
The midrange switch is a DPDT on-on-on. There are two different types of on-on-on congurations for
the center position depending on the manufacturer:
Fortunately, the way the switch is set up in this circuit, it doesn’t matter which type of switch you have.
The EQ response will still be at in the middle. Just don’t use an on-off-on switch - that’s very different.
If you aren’t able to nd a DPDT on-on-on switch, you can also just use a standard DPDT on-on switch.
You will still have the mid hump and mid scoop modes, but you will not have the at mode.
Mids Switch vs. Presence Control
Previous versions of the Halo came with an optional modication, adding a fourth knob to control the
midrange contour, called “Body” or “Presence”. (This mod was created by Jack Orman of AMZ. More
information can be found in his AMZ Presence Control article.)
The trouble with this modication is that while it adds a good deal of tonal exibility, there is no position
on the body knob that removes it from the circuit and makes it 100% identical to a regular 3-knob Muff.
If you look at an EQ graph of the tone control with the presence modication, it just doesn’t have quite
the same curve in any of the positions as the original circuit.
As a result, the new version of the Halo has been changed so that it has a 3-way switch that goes
between the stock setting (scooped mids), a mid hump, or a fully at frequency response. (The tone
control still pans between a bass cut and a treble cut, only the midrange is affected.)
Some people absolutely loved the presence knob modication, and for them, they should use the
previous version of the Halo which will continue to be available. But one of the requirements for the
new line of Aion FX 125B projects was that if they had modications, they still had to have a way of
getting stock tones, e.g. a switch setting or a knob position—and the Presence control did not do that.
CONFIGURATION 1 CONFIGURATION 2

HALO DISTORTION/SUSTAINER 6
SCHEMATIC
GND
2M2
+9V
GND GND GND GND GND
GND
GND
GND
GND GNDGND GNDGND GND
39k
100k
470k
100R 15k
1k
8k2
100k
470k
100R 15k
8k2
100k
470k
100R 15k
33k
33k
390k100k
10k2k2
47R
100n
470pF
100n
100n
470pF
100n
100n
470pF
100n
3n9
10n
100n
100n
100uF 100n
2N3904 2N3904 2N3904
2N3904
100kB
100kB
100kA
1N5817
VA
VA
VA VA
VA
VA
1N914
1N914
1N914
1N914
10n
3n9
GND
100n
RPD
IN
OUT
R2
R3
R4
R5 R6
R7
R8
R9
R10
R11 R12
R13
R14
R15
R16 R17
R18
R19
R20R21
R22R23
R24
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14 C15
Q1 Q2 Q3
Q4
SUSTAIN
1
2
3
TONE
1
2
3
VOLUME
1
2
3
D1
D2 D3
D4 D5 MIDSA
A2
A3 A1
MIDSB
B2
B3
B1
CX1
CX2
CX3
CX3_BYP
Mid switch:Shown with Violet Ram’s Head (2nd edition) values 1 (A1-2, B1-2): Stock (Mid Scoop) 2 (A2-3, B1-2): Flat Mids 3 (A2-3, B2-3): Mid Hump

HALO DISTORTION/SUSTAINER 7
DRILL TEMPLATE
Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended
to rst use a center punch for each of the holes to help guide the drill bit.
Ensure that this template is printed at 100% or “Actual Size”. You can double-check this by measuring
the scale on the printed page.
Top jack layout assumes the use of closed-frame jacks like the Switchcraft 111X. If you’d rather use
open-frame jacks, please refer to the Open-Frame Jack Drill Template for the top side.
LED hole drill size assumes the use of a 5mm LED bezel, available from several parts suppliers. Adjust
size accordingly if using something different, such as a 3mm bezel, a plastic bezel, or just a plain LED.
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” ø9/32”
x: -0.85, y: +0.66
ø1/4”
x: 0, y: +0.66
ø9/32”
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
CENTER (0,0)
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN
125B
VOLUME
MIDS TONE
SUSTAIN
FOOTSWITCHLED
0 1 2
CM
0 1
INCH

HALO DISTORTION/SUSTAINER 8
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

HALO DISTORTION/SUSTAINER 9
WIRING DIAGRAM
125B
IN +VGND N.C. N.C. OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT
Shown with optional 9V battery. If battery is omitted, both jacks can be mono rather than one being stereo.
Leave the far-right lug of the DC jack unconnected.

HALO DISTORTION/SUSTAINER 10
LICENSE & USAGE
No direct support is offered for these projects beyond the provided documentation. It’s assumed
that you have at least some experience building pedals before starting one of these. Replacements and
refunds cannotbe offered unless it can be shown that the circuit or documentation are in error.
All of these circuits have been tested in good faith in their base congurations. However, not all the
modications or variations have necessarily been tested. These are offered only as suggestions based on
the experience and opinions of others.
Projects may be used for commercial endeavors in any quantity unless specically noted. No
attribution is necessary, though a link back is always greatly appreciated. The only usage restrictions
are that (1) you cannot resell the PCB as part of a kit without prior arrangement, and (2) you cannot
“goop” the circuit, scratch off the screenprint, or otherwise obfuscate the circuit to disguise its source.
(In other words: you don’t have to go out of your way to advertise the fact that you use these PCBs, but
please don’t go out of your way to hide it. The guitar effects industry needs more transparency, not less!)
DOCUMENT REVISIONS
1.0.0 (2018-07-04)
Initial release.