Aion NOMAD Manuel utilisateur

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

+9V

100n

33R

10uF

100k

GND GND

TL072P

GND

10n

GND 100pF

LM13700N

10k

4n7

10k

220R

1uF

100k

1N914

1N914 100R

100k

1uF

GND

1uF

GND

2N3906

1MB

500kB

220k

GND

220R

4k7

GND

OUT

RPD

RATIO

LEVEL

ATTACK

R20

R18

R19

IC1B

IC1A

IC2B

IC2A

D2 D3

IC3A

IC3_BUF1

V+

IC3B

IC3_BUF2

V+

TREBLE

D5 R11

R12

R13

R14

R15

THRESHOLD

RELEASE

R10

116

R16

R17

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

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

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.

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