aion NOMAD User manual

NOMAD OTA COMPRESSOR 1
PROJECT NAME
NOMAD
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Valve Wizard Engineer’s Thumb
A full-featured yet surprisingly simple OTA-based compressor design that operates on a feed-forward
principle for better performance and lower noise.
Compressor 1.0.0 (2023-03-24)
BUILD DIFFICULTY
Easy
Actual size is 2.3” x 1.86” (main board) and 1.78” x 0.87” (bypass board).

NOMAD OTA COMPRESSOR 2
TABLE OF CONTENTS
1Project Overview 7Enclosure Layout
2Introduction & Usage 8Wiring Diagram
3-4 Parts List 9Licensing
5Schematic 9Document Revisions
6Drill Template
INTRODUCTION
The Nomad OTA Compressor is based on the Valve Wizard Engineer’s Thumb, a DIY classic that was
first invented in 2012.
Unlike most OTA-based compressors such as the Ross or Dyna Comp, the Engineer’s Thumb uses the
LM13700 as a current-controlled feedback resistor in an op-amp gain stage. This reduces noise and
significantly increases headroom compared to other designs. The audio path of the circuit actually has a
lot more in common with optical compressors such as the Flatline Compressor.
The Engineer’s Thumb has four official revisions, with the most recent being in 2019. While most DIY
projects are based on V1 or V2, the Nomad is based on this latest revision, with all of the suggested
modifications for a true 5-knob compressor. It’s a simple and cheap build with a deluxe control set.
USAGE
The Nomad has the full control set of a deluxe compressor:
• Attack controls the speed at which the compressor reacts and clamps down on the signal.
• Release sets the length of time the compressor “holds on” to the signal before resetting and
awaiting the next trigger.
• Ratio blends the uncompressed signal back with the compressed response.
• Threshold controls the signal level being sent to the sidechain. By reducing it, the compression
portion is less sensitive to the input signal.
• Level controls the overall output.
• Treble (toggle switch) boosts the treble slightly to compensate for some of the perceived loss of
brightness that is inherent to most compressors.

NOMAD OTA 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—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 1k Metal film resistor, 1/4W
R2 4k7 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 220R Metal film resistor, 1/4W
R7 4k7 Metal film resistor, 1/4W
R8 100k Metal film resistor, 1/4W
R9 1k Metal film resistor, 1/4W
R10 220k Metal film resistor, 1/4W
R11 100R Metal film resistor, 1/4W
R12 100k Metal film resistor, 1/4W
R13 1k Metal film resistor, 1/4W
R14 1k Metal film resistor, 1/4W
R15 1M Metal film resistor, 1/4W
R16 220R Metal film resistor, 1/4W
R17 220R Metal film resistor, 1/4W
R18 100k Metal film resistor, 1/4W
R19 100k Metal film resistor, 1/4W
R20 33R Metal film resistor, 1/4W Power supply filter resistor.
RPD 2M2 Metal film resistor, 1/4W Input pull-down 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 10n Film capacitor, 7.2 x 2.5mm
C2 100pF MLCC capacitor, NP0/C0G
C3 4n7 Film capacitor, 7.2 x 2.5mm
C4 1uF Film capacitor, 7.2 x 3.5mm
C5 1uF Electrolytic capacitor, 4mm
C6 1uF Electrolytic capacitor, 4mm
C7 10uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C8 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C9 100n MLCC capacitor, X7R Power supply filter capacitor.

NOMAD OTA COMPRESSOR 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
D1 1N5817 Schottky diode, DO-41
D2 3mm red LED, 3mm, red diffused
D3 3mm red LED, 3mm, red diffused
D4 1N914 Fast-switching diode, DO-35
D5 1N914 Fast-switching diode, DO-35
IC1 TL072 Operational amplifier, DIP8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 TL072 Operational amplifier, DIP8
IC2-S DIP-8 socket IC socket, DIP-8
IC3 LM13700 Operational amplifier, DIP8 Can also use NE5517.
IC3-S DIP-16 socket IC socket, DIP-16
RATIO 1MA 16mm right-angle PCB mount pot
ATTACK 10kA 16mm right-angle PCB mount pot Can also be 100kA (Rev2 and most DIY projects).
RELEASE 500kB 16mm right-angle PCB mount pot
THRESHOLD 1MB 16mm right-angle PCB mount pot
LEVEL 10kA 16mm right-angle PCB mount pot
TREBLE SPDT on-on Toggle switch, SPDT on-on
LED 5mm LED, 5mm, red diffused
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.
FSW 3PDT Stomp switch, 3PDT
BATT. 9V 9V battery snap Soft vinyl type. The hard-shell type will not fit.
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

NOMAD OTA COMPRESSOR 5
SCHEMATIC
GND
2M2
1N5817
100uF
1MA
GND
10kA
10kA
+9V
100n
VA
33R
10uF
100k
100k
GND GND
TL072P
TL072P
TL072P
TL072P
VB
VA
VA
GND
GND
1k
10n
GND 100pF
LM13700N
LM13700N
LM13700N
LM13700N
10k
VB
VB
10k
4n7
VB
10k
220R
1uF
100k
1N914
1N914 100R
100k
1uF
1k
GND
1uF
GND
2N3906
1k
VB
1M
1MB
VB
500kB
220k
GND
VA
220R
220R
VB
4k7
VB
4k7
GND
1k
GND
VB
IN
OUT
RPD
D1
C8
1
2
3
RATIO
LEVEL
1
2
3
ATTACK
1
2
3
C9
R20
C7
R18
R19
IC1B
6
5
7
IC1A
2
3
1
IC2B
6
5
7
IC2A
2
3
1
84
84
R1
D2 D3
C1
C2
IC3A
3
4
5
1
2
IC3_BUF1
V+
7
8
IC3B
14
13
12
16
15
IC3_BUF2
V+
10
9
R3 R4
C3
2
3 1
TREBLE
R5 R6
C4
R8
D4
D5 R11
R12
C5
R13
C6
Q1
R14
R15
THRESHOLD
1
2
3
RELEASE
1
2
3
R10
116
R16
R17
R2
R7
R9
GND

NOMAD OTA COMPRESSOR 6
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.
x: -0.775, y: +1.71 x: +0.775, y: +1.71
ø9/32” ø9/32”
x: -0.775, y: +0.41
ø9/32”
x: 0, y: +1.71
ø9/32”
x: 0, y: +0.41
ø1/4”
x: +0.775, y: +0.41
ø9/32”
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
CENTER (0,0)
125B
THRESHOLDATTACKRELEASE
RATIOTREBLELEVEL
FOOTSWITCHLED
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN
0 1 2
CM
0 1
INCH

NOMAD OTA COMPRESSOR 7
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

NOMAD OTA COMPRESSOR 8
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.

NOMAD OTA COMPRESSOR 9
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 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 (2023-03-24)
Initial release.