aion Onyx User manual

ONYX VOLUME SWELL 1
PROJECT NAME
ONYX
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
BOSS® SG-1 Slow Gear
One of the rarest BOSS effects, it acts as a sort of slow noise gate by gradually fading in the signal when
it detects pick attack.
Automatic volume swell 1.0.0 (2023-09-08)
BUILD DIFFICULTY
Easy
Actual size is 2.3” x 1.86” (main board) and 1.78” x 0.86” (bypass board).

ONYX VOLUME SWELL 2
TABLE OF CONTENTS
1Project Overview 8Drill Template
2Introduction & Usage 9Enclosure Layout
3-5 Parts List 10 Wiring Diagram
6Build Notes 11 Licensing
7Schematic 11 Document Revisions
INTRODUCTION
The Onyx Volume Swell is an adaptation of the BOSS SG-1 Slow Gear, first released in 1979. It’s one
of the very first BOSS effects pedals and still among the rarest. It has notably been used by Adam
Granduciel (The War on Drugs) and Billy Corgan among others.
The Slow Gear can be described as an attack delay, automatic volume swell, or reverse compressor. It
mutes the signal normally, and once the signal level crosses a certain threshold it fades it in at a set rate.
The resulting effect is similar to using a volume pedal, providing a violin-like “attackless” onset of the
notes. Internally, it’s more or less a tweaked noise gate—and in fact, the BOSS NS-1 Noise Suppressor is
a nearly identical circuit, just tuned for more sensitivity and faster attack.
It’s a simple circuit, far from perfect in execution, but once you adapt your playing to its quirks, it’s a very
unique effect that can add a new type of sound to your toolbox.
The Onyx is a direct adaptation of the SG-1 with one modification: we’ve added a Release switch that
selects between two additional time constants that determine how quickly the trigger resets after it
falls below the signal threshold. This offers a little extra flexibility to help accommodate different playing
styles and speeds. It seems to impact the swell speed as well, which extends the usefulness. More on this
in the build notes if you’re curious.
USAGE
The Onyx has the following controls:
• Attack sets the speed of the volume swells. It’s highly interactive with the Release toggle.
• Sensitivity sets the signal level going into the envelope detector.
• Release (toggle switch) sets the time constant of the “hold” on the signal, which also impacts the
onset speed of the swell. The stock position is in the middle, which is the fastest setting, while the
other two positions increase the swell time.

ONYX VOLUME SWELL 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 (most 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 470k Metal film resistor, 1/4W
R2 10k Metal film resistor, 1/4W
R3 22k Metal film resistor, 1/4W
R4 470k Metal film resistor, 1/4W
R5 1M Metal film resistor, 1/4W
R6 10k Metal film resistor, 1/4W
R7 1M Metal film resistor, 1/4W
R8 1M Metal film resistor, 1/4W
R9 47k Metal film resistor, 1/4W
R10 470R Metal film resistor, 1/4W
R11 220k Metal film resistor, 1/4W
R12 1M Metal film resistor, 1/4W
R13 390R Metal film resistor, 1/4W
R14 390k Metal film resistor, 1/4W
R15 4k7 Metal film resistor, 1/4W
R16 4k7 Metal film resistor, 1/4W
R17 100k Metal film resistor, 1/4W
R18 100k Metal film resistor, 1/4W
R19 10k Metal film resistor, 1/4W
R20 22k Metal film resistor, 1/4W
R21 22k Metal film resistor, 1/4W
R22 1k Metal film resistor, 1/4W
R23 3k3 Metal film resistor, 1/4W
R24 1k Metal film resistor, 1/4W
R25 1k Metal film resistor, 1/4W
R26 100k Metal film resistor, 1/4W
R27 47R Metal film resistor, 1/4W Power supply filter resistor.
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 47n Film capacitor, 7.2 x 2.5mm
C2 1uF Film capacitor, 7.2 x 3.5mm
C3 1uF Film capacitor, 7.2 x 3.5mm

ONYX VOLUME SWELL 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C4 1uF Film capacitor, 7.2 x 3.5mm
C5 33n Film capacitor, 7.2 x 2.5mm
C6 680n Film capacitor, 7.2 x 4.5mm
C7 2.2uF Electrolytic capacitor, 5mm Part of the Release switch mod. Increase for more range.
C8 10uF Electrolytic capacitor, 4mm Part of the Release switch mod. Increase for more range.
C9 22n Film capacitor, 7.2 x 2.5mm
C10 22n Film capacitor, 7.2 x 2.5mm
C11 1uF Electrolytic capacitor, 4mm
C12 1n Film capacitor, 7.2 x 2.5mm
C13 1uF Electrolytic capacitor, 4mm
C14 1uF Electrolytic capacitor, 4mm
C15 47n Film capacitor, 7.2 x 2.5mm
C16 10uF Electrolytic capacitor, 5mm
C17 47uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C18 47uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C19 47uF Electrolytic capacitor, 5mm Power supply filter capacitor.
C20 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C21 100n MLCC capacitor, X7R Power supply filter capacitor.
Z1 1N5232B Zener diode, 5.6V, DO-35
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
IC1 LM741 Operational amplifier, single, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
Q1 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC732TM-GR.
Q2 2SK208-GR JFET, N-channel, SOT-23 Available from Aion FX. Original uses 2SK30A-GR.
Q3 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC732TM-GR.
Q4 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC945.
Q5 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC945.
Q6 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC945.
TRIM 10k trimmer Trimmer, 10%, 1/4” Bourns 3362P or similar.

ONYX VOLUME SWELL 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
ATTACK 20kB Film capacitor, 7.2 x 3.5mm
SENS. 100kA Film capacitor, 7.2 x 2.5mm
RELEASE SPDT on-off-on Film capacitor, 7.2 x 4.5mm
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.

ONYX VOLUME SWELL 6
BUILD NOTES
Setting the trimmer
The trimmer sets the output volume of the effect when the gate is open (i.e. no signal attentuation). This
can easily be set by ear, but here is the factory calibration procedure.
Use a signal generator to input a -20dBm 1kHz sine wave. Set Sensitivity to 12:00 and Attack to full.
Adjust the trimmer for -25dBm +/-0.1dBm at the output. This will change based on the supply voltage,
so ideally the unit should be calibrated at the normal operating voltage.
Release switch
We added a switch to select between three different capacitor values in the position that sets the speed
of release. However, in testing this, we found that this capacitor also has a significant impact on the
attack time, with larger capacitors giving a slower swell effect. This is fortunate, because at the stock
setting, even at maximum Attack it’s almost unusably fast! But it also means that the “release” label is
not quite accurate. We will probably rename this to something like “Range” in a future version of the
PCB, so you may want to follow suit on your own build.
We chose 2.2uF and 10uF for the default values, but if you want even longer, you might try 10uF and
47uF. Keep in mind you can always dial it back with the Attack knob.

ONYX VOLUME SWELL 7
SCHEMATIC
1N5817
100uF
100kA
GND
20kB
+9V
100n
VA
47n
22k47R
22k
47uF
GND GND
VB
470k
VB
VA
1k
47uF
VC
GND
2N5088
2N5088
2SK208-GR
10k
VA
GND
22k
1uF 1uF
1M
VA
1uF
10k
GND
3k3
VA
5.6V
GND
47uF
GND
VD
VD
1M
33n
1M
47k
680n
10uF2.2uF
GND
GND
22n
470R
GND
22n
220k
VB
LM741N
VC
GND
1M
390R
1uF
GND
390k
1n
2N5088
4k7
VA
4k7
GND
1uF1uF
1N9141N914
100k100k
2N5088
2N5088
1N914
47n
10uF
GND
10k
GND
10k
VD
GND
IN
D1
C20
1
2
3
SENSITIVITY
1
2
3
ATTACK
C21
C1
R20R27
R21
C17
R1
R22
C18
Q1
Q3
Q2
R2
R3 C2
R4 470k
C3
R5
C4
R6
R23
Z1
C19
R7
C5
R8
R9
C6
C8C7
2
3
1RELEASE
C9
R10
C10
R11
5
1
2
3
6
8
74
IC1
R12
R13
C11
R14
C12
Q4
R15R16
C13C14
D2D3
R17R18
Q5
Q6
D4
C15
C16
1
2
3
TRIM
R19
GND
GND
1k
100k
OUT
R25
R26
2M2
1k
RPD
R24
GND

ONYX VOLUME SWELL 8
DRILL TEMPLATE
Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended
to first 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.
0 1 2
CM
0 1
INCH
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” 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
ATTACK
RELEASE
SENSITIVITY
FOOTSWITCHLED
x: 0, y: +0.41
ø1/4”

ONYX VOLUME SWELL 9
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

ONYX VOLUME SWELL 10
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.

ONYX VOLUME SWELL 11
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 cannot be 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 configurations. However, not all the
modifications 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 specifically 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 (2023-09-08)
Initial release.