Aion Electronics AURORA User manual

AURORA COMPRESSOR/SUSTAINER 1
PROJECT NAME
AURORA
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Ross Compressor & MXR Dyna Comp
The original guitar compressor, still a favorite of guitarists after over 40 years. The Aurora makes several
improvements to the original circuit as well as adding a few new features.
Compressor / Sustainer 1.0.0 (2018-07-04)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 1.86” (main board) and 2.3” x 0.86” (bypass board).

AURORA COMPRESSOR/SUSTAINER 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 Aurora Compressor/Sustainer is an updated version of the MXR Dyna Comp and the Ross
Compressor. One of the rst compressor circuits designed for guitar, the MXR Dyna Comp has been a
consistent favorite among guitarists, and the circuit is legendary in the DIY community.
The Ross Compressor was an updated clone of the Dyna Comp that got a lot of attention when it was
“rediscovered” in the 1990s by Trey Anastasio of Phish. It has better power supply ltering and thus
lower noise, but is otherwise very similar to the Dyna Comp.
The Aurora takes things a step further by adding a couple of modications. First, the obsolete CA3080
has been replaced by the LM13700, which is essentially just a dual CA3080 but with the advantage of
still being in production and easy to nd.
The output section has also been modied to take the signal from a different part of the envelope
detector. This results in drastically reduced ripple (which is perceived as distortion on the otherwise
clean signal). Some people like this distortion, so the Aurora was designed so you can still build the
“stock” version and use the classic output stage. See the build notes for more details.
USAGE
The Aurora has the following controls:
• Sustain controls the amount of compression. As you turn it up, it increases the sustain but also the
noise level. If you keep it down lower than 12:00, the effect acts more like a limiter.
• Release allows you to set the amount of time after the input signal falls below the threshold before
the compressor “resets” and is ready to compress again. It’s also called an “Attack” control in the
Boss CS-2 and Keeley Compressor.
• Level is the overall output volume of the effect.
• Treble controls the amount of treble attenuation immediately after the signal is compressed.
• Input is an internal trimmer that attenuates the signal going into the compressor, allowing you to
use it with high-output instruments such as keyboards or active pickups.

AURORA COMPRESSOR/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 →
PART VALUE TYPE NOTES
R1 10k Metal lm resistor, 1/4W
R2 470k Metal lm resistor, 1/4W
R3 470k Metal lm resistor, 1/4W
R4 10k Metal lm resistor, 1/4W
R5 10k Metal lm resistor, 1/4W
R6 1M Metal lm resistor, 1/4W
R7 1k Metal lm resistor, 1/4W
R8 1k Metal lm resistor, 1/4W
R9 220k Metal lm resistor, 1/4W
R10 220k Metal lm resistor, 1/4W
R11 1M Metal lm resistor, 1/4W
R12 15k Metal lm resistor, 1/4W
R13 150k Metal lm resistor, 1/4W
R14 27k Metal lm resistor, 1/4W
R15 10k Metal lm resistor, 1/4W
R16 10k Metal lm resistor, 1/4W
R17 1M Metal lm resistor, 1/4W
R18 100R Metal lm resistor, 1/4W Use 10k here if using a real 150kC pot for the Release control.
R19 220k Metal lm resistor, 1/4W Parallel resistors to change the 500kB release pot into 150kC. Jumper
R19 and omit R20 if using a real 150kC pot. See build notes for more.
R20 10k Metal lm resistor, 1/4W
R21 1M Metal lm resistor, 1/4W
R22 1k Metal lm resistor, 1/4W Part of Q6 mod. See build notes.
R23 10k Metal lm resistor, 1/4W Part of Q6 mod. See build notes.
R24 10k Metal lm resistor, 1/4W Part of Q6 mod. See build notes.
R25 10k Metal lm resistor, 1/4W
R26 56k Metal lm resistor, 1/4W
R27 27k Metal lm resistor, 1/4W
RPD 2M2 Metal lm resistor, 1/4W Input pulldown resistor. Can be as low as 1M.
LEDR 4k7 Metal lm resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.

AURORA COMPRESSOR/SUSTAINER 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C1 220pF MLCC capacitor, NP0/C0G Omit for Dyna Comp. Keeley Compressor uses 150pF.
C2 10n Film capacitor, 7.2 x 2.5mm
C3 1uF Electrolytic capacitor, 4mm
C4 1uF Electrolytic capacitor, 4mm
C5 1uF Film capacitor, 7.2 x 3.5mm
C6 2n2 Film capacitor, 7.2 x 2.5mm
C7 1uF Electrolytic capacitor, 4mm
C8 10n Film capacitor, 7.2 x 2.5mm
C9 1uF Electrolytic capacitor, 4mm
C10 180pF MLCC capacitor, NP0/C0G
C11 330pF MLCC capacitor, NP0/C0G
C12 820pF MLCC capacitor, NP0/C0G
C13 10n Film capacitor, 7.2 x 2.5mm
C14 10uF Electrolytic capacitor, 5mm
C15 10n Film capacitor, 7.2 x 2.5mm
C16 100n Film capacitor, 7.2 x 2.5mm Part of Q6 mod. See build notes.
C17 1n Film capacitor, 7.2 x 2.5mm Optional. Allows a slight treble boost above 3kHz at the output.
C18 47uF Electrolytic capacitor, 5mm Power supply lter capacitor.
C19 10uF Electrolytic capacitor, 5mm Voltage reference lter capacitor.
C20 100n MLCC capacitor, X7R Power supply lter capacitor.
CX1 OMIT Film capacitor, 7.2 x 2.5mm See build notes for when to use this.
D1 1N5817 Schottky diode, DO-41
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
IC1 LM13700N Transconductance amplier, DIP16
Q1 2N5088 BJT transistor, NPN, TO-92
Q2 2N5088 BJT transistor, NPN, TO-92
Q3 2N5088 BJT transistor, NPN, TO-92
Q4 2N5088 BJT transistor, NPN, TO-92
Q5 2N5088 BJT transistor, NPN, TO-92
Q6 2N5088 BJT transistor, NPN, TO-92 Part of Q6 mod. See build notes.
INPUT 100k trimmer Trimmer, 10%, 1/4" Allows the input signal to be attenuated for use with high input levels.

AURORA COMPRESSOR/SUSTAINER 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
SUS 500kC 16mm right-angle PCB mount pot Stock Ross/Dyna uses 500kB, but C (reverse audio) works much better.
REL 500kB 16mm right-angle PCB mount pot Parallel resistors are used to get a nal value of 150kC (reverse audio).
LEVEL 50kB 16mm right-angle PCB mount pot
TREB SPDT Toggle switch, SPDT center off
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.

AURORA COMPRESSOR/SUSTAINER 6
BUILD NOTES
The Q6 Mod
One little-known modication to the Ross/Dyna circuit is to change the output section so it takes its
signal from a different place in the envelope detector. By doing this, you eliminate the ripple on the
compressed signal which is heard as a slight distortion. It’s a vast improvement on the original circuit
without changing the characteristic of the tone.
The default conguration of the Aurora is to use this Q6 mod. However, if you do want to build a fully-
stock Ross or Dyna Comp, you can use a 47n lm capacitor for CX1 and omit R22-24 and Q6.
The C17 Mod
One way of getting a little more “snappiness” to the circuit is to use a 1n capacitor for C17 to bypass the
R25 resistor. This will give a slight increase in treble content above 3kHz at the output of the effect. You
can increase this value to lower the frequency. For example, 1.5n will increase the treble above 2.2kHz.
Release Control
The default conguration of the Aurora includes a “Release” control which is adapted from the Boss CS-
2. (Boss called it “Attack”, which is not entirely wrong, but it’s more accurate to say that it controls the
release at the decay of the signal rather than the attack at the beginning.) When the pot is turned all the
way down, it’s the stock Ross/Dyna circuit.
The optimal pot value for this is 150k reverse audio (antilog) taper, but this value has to be custom-
ordered and none of the DIY parts suppliers have it in the right-angle type. Instead, this project uses a
more common 500kB (linear) pot with parallel resistors to drop the value down to 150k and change the
taper to mimic reverse audio.
The one side effect of this is that the pot can’t get all the way to zero like a normal pot. As a result, the
R18 resistor (normally 10k) has been decreased to 100R.
If you are using a true 150kC pot, you’ll need to jumper R19 and change R18 to 10k. Omit R20 entirely.
Treble Switch
The Treble switch is adapted from the Janglebox. The Janglebox actually omits C10 entirely so there’s
no treble attenuation after the OTA, but after testing out a number of different combinations, it felt
best to have at least a very small capacitor connected at all times. These three capacitor values (180pF,
330pF and 820pF) are the ones that were chosen after testing. With the switch in the “up” position,
the result is the stock value of 1n. The “down” position is 510pF (a bit of treble boost) and the center
position is 180pF (a bit more treble boost).

AURORA COMPRESSOR/SUSTAINER 7
SCHEMATIC
GND
2M2
4k7
5MM
+9V
10k 470k
10k
1M
220k 220k
10k
56k
27k
1M
15k
150k
10k10k
1M
1M
470k
27k
150pF
10n
1uF
2n2
10n
820p 360p180p
10n
10n
100n
2N5088
2N5088
2N5088 2N5088
2N5088
GND
1uF 1uF1uF
1uF
100K
GND GND
1N914
1N914
500KC
50KB
1k 1k
GND
GND
GND GND
GND GND GND GND GND GND GND GND GND GND GND GNDGND GND
150kC
10k
VA VB
1N5817
LM13700N
LM13700N
LM13700N
LM13700N
GND
VA
VBVB VA VA VA VA
1k 2N5088
10k
100n
10k
GND
VA
10k
1n
10uF
10uF47uF
100n
300k 15k
RPD
LEDR
LED
A2
A3 A1
FSA
B2
B3
B1
FSB
C2
C3 C1
FSC
1B-1
IN
OUT
3B-2 3B-3 1A-1
1A-2
1A-3
3A-1
3A-2 3A-3
2A-1
2A-2
2A-3
2A-4
R1 R2
R5
R6
R9 R10
R4
R26
R27
R11
R12
R13
R15R16
R17
R21
R3
R14
C1 C2
C5
C6
C8
C12 C11C10
C13
C15
CX1
Q1
Q2
Q3 Q4
Q5
C3 C7C4
C9
INPUT
1
2
3
D2
D3
SUSTAIN
1
2
3
LEVEL
1
2
3
R7 R8
ATTACK
1
2
3
R18
D1
IC1A
3 4
5
1
2
IC1_BUF1
V+
7
8
IC1B
14 13
12
16
15 IC1_BUF2
V+
10
9
V+ V-
116
R22 Q6
R23
C16
R24
R25
C17
C14
C19C18
2
3
1
TREBLE
C20
R19 R20
JUMPER
FOOTSWITCH BOARD
GND

AURORA COMPRESSOR/SUSTAINER 8
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
LEVEL
TREBLE RELEASE
SUSTAIN
FOOTSWITCHLED
0 1 2
CM
0 1
INCH

AURORA COMPRESSOR/SUSTAINER 9
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

AURORA COMPRESSOR/SUSTAINER 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.

AURORA COMPRESSOR/SUSTAINER 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 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.