Aion Electronics Soma Vintage Overdrive User manual

SOMA VINTAGE OVERDRIVE 1
PROJECT NAME
SOMA
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Cornish SS-3 Soft Sustain
An evolution of the MXR Distortion+ that adds two passive tone-cut controls as well as the classic
Cornish input buffer.
Overdrive 1.0.0 (2019-11-15)
Actual size is 2.3” x 2.43” (main board) and 2.3” x 0.87” (bypass board).
BUILD DIFFICULTY
Intermediate

SOMA VINTAGE OVERDRIVE 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 Soma Vintage Overdrive is adapted from the Pete Cornish SS-3, traced by Aion FX in 2019.
Cornish pedals are best known for being extremely expensive. There are two reasons for this. First, the
build quality and reliability is unmatched. Second, the mysterious nature of them, partially due to the
fact that the circuit is obscured and partially because of the A-list of clients such as Brian May and Pete
Townshend.
The SS-3 in particular is owned by Jeff Beck, David Gilmour, Keith Urban and Carlos Santana among
many others. It’s an update to the earlier SS-2 that adds a low-cut control, since the original was fairly
bass-heavy. With the low cut control set fully clockwise, the circuit is identical to the SS-2.
Under the hood, the SS-3 appears to have originated from the MXR Distortion+ circuit and then had
passive low & hi-cut tone controls added, along with the classic Cornish buffer at the input.
The Soma is a faithful reproduction of the SS-3 circuit, but with one major addition: an internal slide
switch allowing the pedal to be used in true-bypass mode instead of buffered bypass. As with the Klon
KTR, the buffered mode is “almost always better”, but with this feature, you can determine for yourself.
USAGE
The Soma has the following controls:
• Sustain controls the amount of drive or distortion, which also affects the amount of sustain.
• Low Cut is a two-stage filter that cuts bass at 60 Hz when counter-clockwise. When this control is
fully clockwise, the low-end response is identical to the SS-2.
• Hi Cut is a basic passive treble control, starting with a steep 6KHz cut at minimum, and a slight
boost when fully clockwise.
• Volume is the overall output.

SOMA VINTAGE 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 (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 10M Metal film resistor, 1/4W
R2 1k Metal film resistor, 1/4W
R3 120k Metal film resistor, 1/4W
R4 120k Metal film resistor, 1/4W
R5 200k Metal film resistor, 1/4W
R6 7k5 Metal film resistor, 1/4W
R7 10k Metal film resistor, 1/4W
R8 51R Metal film resistor, 1/4W
R9 1M Metal film resistor, 1/4W
R10 10k Metal film resistor, 1/4W
R11 1M Metal film resistor, 1/4W
R12 100k Metal film resistor, 1/4W
R13 510R Metal film resistor, 1/4W
R14 15k Metal film resistor, 1/4W
R15 1k6 Metal film resistor, 1/4W
R16 1k6 Metal film resistor, 1/4W
R17 1M Metal film resistor, 1/4W
R18 1M Metal film resistor, 1/4W
R19 1M Metal film resistor, 1/4W
R20 2k4 Metal film resistor, 1/4W
R21 10k Metal film resistor, 1/4W
R22 6k8 Metal film resistor, 1/4W
R23 10k Metal film resistor, 1/4W
R24 91R Metal film resistor, 1/4W
R25 100R Metal film resistor, 1/4W
R26 150k Metal film resistor, 1/4W
R27 180k Metal film resistor, 1/4W
R28 100R Metal film resistor, 1/4W
R29 91R Metal film resistor, 1/4W
R30 51k Metal film resistor, 1/4W

SOMA VINTAGE OVERDRIVE 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 100n Film capacitor, 7.2 x 2.5mm
C2 4.7uF Electrolytic capacitor, 4mm
C3 1n Film capacitor, 7.2 x 2.5mm
C4 22uF Electrolytic capacitor, 5mm
C5 10n Film capacitor, 7.2 x 2.5mm
C6 220pF MLCC capacitor, NP0/C0G
C7 470n Film capacitor, 7.2 x 3mm
C8 3n3 Film capacitor, 7.2 x 2.5mm
C9 10uF Electrolytic capacitor, 5mm
C10 10n Film capacitor, 7.2 x 2.5mm
C11 220n Film capacitor, 7.2 x 2.5mm
C12 10n Film capacitor, 7.2 x 2.5mm
C13 220n Film capacitor, 7.2 x 2.5mm
C14 220pF MLCC capacitor, NP0/C0G
C15 10uF Electrolytic capacitor, 5mm
C16 22uF Electrolytic capacitor, 5mm
C17 100n MLCC capacitor, X7R Power supply filter capacitor.
C18 220uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C19 10uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C20 220uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
D1 1N5817 Schottky diode, DO-41
D2 1N34A Germanium diode, NOS Exact part number is unimportant, any NOS germanium diode should
work about the same here. Can also substitute BAT46 Schottky diode.
D3 1N34A Germanium diode, NOS
Q1 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses BC549C.
IC1 TL071 Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 TL071 Operational amplifier, DIP8
IC2-S DIP-8 socket IC socket, DIP-8
SUST. 50kC 16mm right-angle PCB mount pot
LO CUT 10kB dual 16mm right-angle PCB mount pot Available from Tayda Electronics (see parts list spreadsheet).
HI CUT 25kB 16mm right-angle PCB mount pot
VOL. 10kA 16mm right-angle PCB mount pot
TB-BUF 4PDT slide Slide switch, 4PDT E-Switch EG4208 (4mm lever) or EG4208A (6mm lever)

SOMA VINTAGE OVERDRIVE 5
PARTS LIST, CONT.
PART VALUE TYPE NOTES
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.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

SOMA VINTAGE OVERDRIVE 6
BUILD NOTES
Transistor selection
The original SS-3 uses a BC549C transistor. The pinout on the Soma PCB is for the USA “E-B-C”
convention, e.g. 2N3904 and 2N5088. The 2N5088 will operate identically to the BC549C, but if you do
want to use the original transistors, just note that the pinout is different. Typically they would need to be
rotated 180 degrees, but check the datasheet for your brand as they do vary.
Bypassing the true bypass / buffer switch
The E-Switch EG4208 slide switch used for the true bypass/buffer selector is available from Mouser
Electronics but may not be accessible to everyone. 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.
Low Cut potentiometer
The 10kB dual potentiometer used by the Low Cut control is an uncommon value and not carried by any
of the major distributors. However, Tayda Electronics has it available here with very cheap worldwide
shipping.
BUFFER BYPASS
TRUE BYPASS

SCHEMATIC
SOMA VINTAGE OVERDRIVE 7
TO PCB IN
BUFFER OUT
TO INPUT JACK
TO OUTPUT JACK
FROM BUFFER OUT
FROM EFFECT OUT
SWITCH POSITIONS SHOWN
Slide switch: TBP mode
Footswitch: Bypass mode
1N5817
220uF
GND
+9V
100n
VA
100R
100R
220uF
GND
VB VC
91R
51k
10M
100n
1k
120k
120k200k
1n
4u7
2N5088
7k5
22uF
10k
51R
GND GND GND
GND
1M
GND
GND
GND 150k
180k
10uF
GND GND
22uF
10k
91R
GND
VC
VC
10k
10n
1M
VB
TL071P
VA
GND
220pF
100k
470n
510R
3n3
50kC
GND
GND
10kB DUAL
10kB DUAL
25kB
10uF
15k
1k6
1N34A
GND GND
10n
GND
220n
1k6
GND
10n
GND
1M
GND
220n
1M
TL071P
VA
1M2k4
10k
GND
VA
GND
220pF
6k8
10uF
10kA
GND
D1
C20
A2
A3
A1 FSA
C2
C3
C1 FSC
IN
OUT
C17
R28 R25
C18
SW1A
2
3
1
SW1B
5
6
4
SW1C
8
9
7
SW1D
11
12
10
R29
R30
R1
C1
R2
R3
R4R5
C3
C2
Q1
R6
C4
R7
R8
R9
R26
R27
C19
C16
R23
R24
R10
C5
R11
5
1
2
3
6
8
74
IC1
C6
R12
C7
R13
C8
SUSTAIN
1
2
3
1
2
3
LO_CUT A
LO_CUT B
1
2
3
HI_CUT
1
2
3
C9
R14
R15
D2
D3
C10
C11
R16
C12
R17
C13
R18
5
1
2
3
6
8
74
IC2
R19R20
R21
C14
R22
C15
VOLUME
1
2
3

SOMA VINTAGE OVERDRIVE 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
ø3/8” ø1/2”
0.385”
0.625” 0.625”
x: -0.65, y: +1.71 x: +0.65, y: +1.71
ø9/32” ø9/32”
x: -0.65, y: +0.41
ø9/32”
x: +0.65, y: +0.41
ø9/32”
x: 0, y: -1.775
ø15/32”
x: -0.775, y: -1.775
ø5/16”
CENTER (0,0)
ø3/8”
125B
OUT
HIGH CUT LOW CUT
VOLUME SUSTAIN
FOOTSWITCHLED
DC IN

SOMA VINTAGE OVERDRIVE 9
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

SOMA VINTAGE OVERDRIVE 10
WIRING DIAGRAM
125B
IN +VGND N.C. BUF FX
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND BUF
OUT
FX
OUT

SOMA VINTAGE OVERDRIVE 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 (2019-11-15)
Initial release.