Aion Electronics Convex User manual

CONVEX PARALLEL COMPRESSOR 1
PROJECT NAME
CONVEX
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Dinosaural OTC-201 Opticompressor
An exceptionally rare and unique optical compressor designed by Dan Coggins of Lovetone fame.
Parallel Optical Compressor 1.0.3 (2019-08-21)
BUILD DIFFICULTY
Intermediate
Actual size is 2.3” x 2.43” (main board) and 2.3” x 0.86” (bypass board).

CONVEX PARALLEL COMPRESSOR 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 Convex Parallel Compressor is a clone of the Dinosaural®OTC-201 Opticompressor, an all-original
optical compressor designed by Dan Coggins, the chief engineer & circuit designer for Lovetone.
The OTC-201 was made in very small numbers between 2013 and 2016 and remain exceedingly rare
today. Despite this, they are universally acclaimed by the few who have had a chance to try one, and an
OTC-201 can even be found on the pedalboard for Ed O’Brien of Radiohead.
Today, an updated version of the Opticompressor called the “Fat General” is available from ThorpyFX,
also designed in collaboration with Dan Coggins. This version adds a treble control to allow a more
jangly tone to be dialed in, but is otherwise the same circuit as the original.
The Convex is a direct clone of the original OTC-201, with two modifications. First, the internal Mode
switch has been moved to the outside, so the blend/direct modes can be more conveniently switched
between. Second, while the original OTC-201 was buffered bypass, the Convex adds an internal slide
switch that allows you to select between true bypass or buffered bypass.
USAGE
The Convex has the following controls:
• Sustain sets the compression threshold and amount of sustain, from subtle limiting to squish.
• Balance is either a blend control or a volume control depending on the position of the Mode switch.
• Mode (toggle switch, 2 positions) selects between Signal Blend (SB) and Direct (Z) modes. In Signal
Blend mode, the Balance control becomes a blend between the dry and compressed signal, with the
center position being 50/50. In Direct mode, the Balance control is a standard output volume knob
and the signal is 100% compressed.
• Level (toggle switch, 3 positions) sets the amount of pre-gain: -3dB cut, no gain, or a +3dB boost.
Called “Axematch” in the original, the goal was to be able to compensate for low-output or hot
guitars, but it can also be used as a tool to change the character of the compression.

CONVEX PARALLEL COMPRESSOR 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 10k Metal film resistor, 1/4W
R2 1M Metal film resistor, 1/4W
R3 10k Metal film resistor, 1/4W
R4 10k Metal film resistor, 1/4W
R5 10k Metal film resistor, 1/4W
R6 13k Metal film resistor, 1/4W
R7 10k Metal film resistor, 1/4W
R8 10k Metal film resistor, 1/4W
R9 39k Metal film resistor, 1/4W
R10 330k Metal film resistor, 1/4W
R11 10k Metal film resistor, 1/4W
R12 8k2 Metal film resistor, 1/4W
R13 4k7 Metal film resistor, 1/4W
R14 100k Metal film resistor, 1/4W
R15 2k2 Metal film resistor, 1/4W
R16 180R Metal film resistor, 1/4W
R17 4k7 Metal film resistor, 1/4W
R18 100k Metal film resistor, 1/4W
R19 180R Metal film resistor, 1/4W
R20 2k2 Metal film resistor, 1/4W
R21 180R Metal film resistor, 1/4W
R22 39k Metal film resistor, 1/4W
R23 180R Metal film resistor, 1/4W
R24 39k Metal film resistor, 1/4W
R25 100R Metal film resistor, 1/4W
R26 10k Metal film resistor, 1/4W
R27 1k8 Metal film resistor, 1/4W
R28 8k2 Metal film resistor, 1/4W
RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor. Can be as low as 1M.
LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.

CONVEX PARALLEL COMPRESSOR 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C1 33n Film capacitor, 7.2 x 2.5mm
C2 470n Film capacitor, 7.2 x 3mm
C3 330pF MLCC capacitor, NP0/C0G
C4 220n Film capacitor, 7.2 x 2.5mm
C5 10n Film capacitor, 7.2 x 2.5mm
C6 330pF MLCC capacitor, NP0/C0G
C7 33n Film capacitor, 7.2 x 2.5mm
C8 10uF Electrolytic capacitor, 5mm
C9 33n Film capacitor, 7.2 x 2.5mm
C10 10uF Electrolytic capacitor, 5mm
C11 1uF Film capacitor, 7.2 x 3.5mm
C12 1uF Film capacitor, 7.2 x 3.5mm
C13 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C14 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C15 10n MLCC capacitor, X7R Power supply filter capacitor.
C16 10uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C17 10uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C18 100n MLCC capacitor, X7R Power supply filter capacitor.
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
VACT_1 VTL5C4 Vactrol, VTL5C4 or equivalent Recommended to use Xvive reissues.
VACT_2 VTL5C4 Vactrol, VTL5C4 or equivalent Recommended to use Xvive reissues.
IC1 TL072 Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
Q1 2N5457 JFET, N-channel, TO-92 Substitute. Original uses J113.
Q2 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses BC549C.
Q3 2N5087 BJT transistor, PNP, TO-92 Substitute. Original uses BC307B.
Q4 2N5087 BJT transistor, PNP, TO-92 Substitute. Original uses BC307B.
Q5 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses BC549C.

CONVEX PARALLEL COMPRESSOR 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
SUST. 100kB 16mm right-angle PCB mount pot
BAL. 10kA 16mm right-angle PCB mount pot
MODE SPDT Toggle switch, SPDT on-on
LEVEL SPDT cntr off Toggle switch, SPDT on-off-on
TB-BUF 4PDT slide Slide switch, 4PDT E-Switch EG4208 (standard lever) or EG4208A (longer lever)
LED 5mm LED, 5mm, red diffused
IN 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X 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.

CONVEX PARALLEL COMPRESSOR 6
BUILD NOTES
Bypassing the true bypass / buffer switch
The E-Switch EG4208 slide switch used for the true bypass/buffer selector is available from Mouser
Electronics worldwide. However, it may not be accessible to everyone, and there are no real substitutes.
If you are unable to obtain it, you can hard-wire the switch to either true bypass mode or buffered mode
by soldering jumpers to the switch pads as shown.
Vactrol selection
The original uses two Excelitas VTL5C4 vactrols. The original part is no longer made and difficult to find,
but fortunately the Xvive reissues (same part number) work just as well in this circuit. They’re pricey, but
it’s easier & more reliable than trying to make your own with an LED and LDR.
The VTL5C4 is presently only available from Cabintech in the USA. Small Bear Electronics carries a
Macron work-alike called the MI1210CLC-R. The Macron part hasn’t been tested in this circuit, but the
Convex isn’t too picky so it should perform well.
Transistor selection
Being from the UK, the original OTC-201 uses BC549C NPN and BC307B PNP transistors in the vactrol
section.
The Convex board is designed for USA equivalents: 2N5088 or 2N3904 for NPN and 2N5087 or
2N3906 for PNP. They will perform identically in this circuit and are more commonly available
worldwide. As such, the PCB uses the E-B-C pinout convention, with the pads marked on the silkscreen.
If you want to use the original BC parts, you will probably need to rotate them 180° from the component
outline. When using substitutes, though, always confirm pinout with the datasheet!
BUFFER BYPASS
TRUE BYPASS

SCHEMATIC
CONVEX PARALLEL COMPRESSOR 7
TO FX GND
TO PCB IN
TO INPUT JACK
TO OUTPUT JACK
FROM BUFFER OUT
FROM EFFECT OUT
1N5817
100uF
100kB
10kA
+9V
100n
GND
10k
1M
10k
33n
470n
2N5457
GND
VA
VA
100R
10n
GND
VD
10k 1k8
8k2
100uF
GND
VB
GND
10uF
GND
10uF
GND
VC
VD
VC
GND
10k
10k
13k
10k
TL072P
TL072P
10k
330pF
VB
GND
VA
39k
180R
220n
330k
GND
GND
VD
2M2
GND
10k
8k2
10n
VB
330pF
33n
4k7100k
GND
2k2
10uF
VA
GND
180R
GND
33n
4k7
100k
VA
180R
VA
2k2
GND
10uF
GND
VA
GND
180R
1uF
39k
GND
1uF
39k
GND
GND
BYP_GND
BYP_GND
D1
C14
SUSTAIN
1
2
3
BALANCE
1
2
3
A2
A3
A1 FSA
C2
C3
C1 FSC
IN EFFECT OUT
BUFFER OUT
C18
R1
R2
R3
C1
C2
Q1
D2D3
R25
C15
R26 R27
R28
C13
C16 C17
R4
R5
R6
R7LEVEL
2
3 1
IC1A
2
3
1IC1B
6
5
7
R8
C3
D4D5
R9
R23
C4
R10
84
RPD
R11
R12
C5
C6
VACT_1A
VACT_1B
VACT_2A
VACT_2B
C7
R13R14
Q2
Q3
R15
C8
R16
C9
R17 R18 R19
Q4
Q5
R20
C10
D6D7
R21
C11
R22
MODE
2
3
1
C12
R24
SW1A
2
3
1
SW1B
5
6
4
SW1C
8
9
7
SW1D
11
12
10

CONVEX PARALLEL COMPRESSOR 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 requires the use of closed-frame jacks like the Switchcraft 111X. Open-frame jacks will
not fit in layouts with 5 or more knobs due to the placement of the DC jack.
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: -0.65, y: +0.41
ø1/4”
x: 0, y: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
CENTER (0,0)
125B
SUSTAINBALANCE
MODE
x: +0.65, y: +0.41
ø1/4”
LEVEL
FOOTSWITCHLED
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN

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

CONVEX PARALLEL COMPRESSOR 10
WIRING DIAGRAM
125B
IN +VF.GND GND BUF FX
PCB
IN
FX
GND
+V +V JACK GND JACK
OUTIN
GND BUF
OUT
FX
OUT

CONVEX PARALLEL COMPRESSOR 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
1.0.3 (2019-08-21)
Corrected taper of Balance pot.
1.0.2 (2019-08-11)
Corrected D2 & D3 in parts list.
1.0.1 (2019-08-07)
Added Q1-5 to parts list.
1.0.0 (2019-08-04)
Initial release.