125B · 5 knobs
NomadOTA Compressor
Based on the Engineer's Thumb· 1 other board clones it
- Category
- Compressor
- Controls
- Attack · Release · Ratio · Threshold · Level
- Difficulty
- Easy
- Price
- $12.50in stock
From the vendor
A full-featured yet surprisingly simple OTA-based compressor design that operates on a feed-forward principle for better performance and lower noise.
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 from 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.
Schematic
The schematic is in the vendor's build document, page 5. Open the build document. No KiCad fragment has been drawn for this circuit yet.
Parts list 56 rows
Report a wrong parse| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 22 | ||||
| R1 | 1k | 1k | Metal film resistor, 1/4W | |
| R2 | 4k7 | 4.7k | Metal film resistor, 1/4W | |
| R3 | 10k | 10k | Metal film resistor, 1/4W | |
| R4 | 10k | 10k | Metal film resistor, 1/4W | |
| R5 | 10k | 10k | Metal film resistor, 1/4W | |
| R6 | 220R | 220 | Metal film resistor, 1/4W | |
| R7 | 4k7 | 4.7k | Metal film resistor, 1/4W | |
| R8 | 100k | 100k | Metal film resistor, 1/4W | |
| R9 | 1k | 1k | Metal film resistor, 1/4W | |
| R10 | 220k | 220k | Metal film resistor, 1/4W | |
| R11 | 100R | 100 | Metal film resistor, 1/4W | |
| R12 | 100k | 100k | Metal film resistor, 1/4W | |
| R13 | 1k | 1k | Metal film resistor, 1/4W | |
| R14 | 1k | 1k | Metal film resistor, 1/4W | |
| R15 | 1M | 1M | Metal film resistor, 1/4W | |
| R16 | 220R | 220 | Metal film resistor, 1/4W | |
| R17 | 220R | 220 | Metal film resistor, 1/4W | |
| R18 | 100k | 100k | Metal film resistor, 1/4W | |
| R19 | 100k | 100k | Metal film resistor, 1/4W | |
| R20 | 33R | 33 | Metal film resistor, 1/4W | Power supply filter resistor. |
| RPD | 2M2 | 2.2M | Metal film resistor, 1/4W | Input pull-down resistor. Can be as low as 1M. |
| LEDR | 10k | 10k | Metal film resistor, 1/4W | LED current-limiting resistor. Adjust value to change LED brightness. |
| Capacitors 9 | ||||
| C1 | 10n | 10n | Film capacitor, 7.2 x 2.5mm | |
| C2 | 100pF | 100p | MLCC capacitor, NP0/C0G | |
| C3 | 4n7 | 4.7n | Film capacitor, 7.2 x 2.5mm | |
| C4 | 1uF | 1u | Film capacitor, 7.2 x 3.5mm | |
| C5 | 1uF | 1u | Electrolytic capacitor, 4mm | |
| C6 | 1uF | 1u | Electrolytic capacitor, 4mm | |
| C7 | 10uF | 10u | Electrolytic capacitor, 5mm | Reference voltage filter capacitor. |
| C8 | 100uF | 100u | Electrolytic capacitor, 6.3mm | Power supply filter capacitor. |
| C9 | 100n | 100n | MLCC capacitor, X7R | Power supply filter capacitor. |
| Diodes 5 | ||||
| D1 | 1N5817 | 1N5817 | Schottky diode, DO-41 | |
| D2 | 3mm red | 3MM RED | LED, 3mm, red diffused | |
| D3 | 3mm red | 3MM RED | LED, 3mm, red diffused | |
| D4 | 1N914 | 1N914 | Fast-switching diode, DO-35 | |
| D5 | 1N914 | 1N914 | Fast-switching diode, DO-35 | |
| Transistors 1 | ||||
| Q1 | 2N3906 | 2N3906 | BJT transistor, PNP, TO-92 | |
| ICs 3 | ||||
| IC1 | TL072 | TL072 | Operational amplifier, DIP8 | |
| IC2 | TL072 | TL072 | Operational amplifier, DIP8 | |
| IC3 | LM13700 | LM13700 | Operational amplifier, DIP8 | Can also use NE5517. |
| Potentiometers 5 | ||||
| RATIO | 1MA | A1M | 16mm right-angle PCB mount pot | |
| ATTACK | 10kA | A10k | 16mm right-angle PCB mount pot | Can also be 100kA (Rev2 and most DIY projects). |
| RELEASE | 500kB | B500k | 16mm right-angle PCB mount pot | |
| THRESHOLD | 1MB | B1M | 16mm right-angle PCB mount pot | |
| LEVEL | 10kA | A10k | 16mm right-angle PCB mount pot | |
| Switches 2 | ||||
| TREBLE | SPDT on-on | SPDT ON-ON | Toggle switch, SPDT on-on | |
| FSW | 3PDT | 3PDT | Stomp switch, 3PDT | |
| LEDs 1 | ||||
| LED | 5mm | 5MM | LED, 5mm, red diffused | |
| Jacks & sockets 6 | ||||
| IC1-S | DIP-8 socket | DIP-8 SOCKET | IC socket, DIP-8 | |
| IC2-S | DIP-8 socket | DIP-8 SOCKET | IC socket, DIP-8 | |
| IC3-S | DIP-16 socket | DIP-16 SOCKET | IC socket, DIP-16 | |
| IN | 1/4" stereo | 1/4" STEREO | 1/4" phone jack, closed frame | Switchcraft 112BX or equivalent. |
| OUT | 1/4" mono | 1/4" MONO | 1/4" phone jack, closed frame | Switchcraft 111X or equivalent. |
| DC | 2.1mm | 2.1MM | DC jack, 2.1mm panel mount | Mouser 163-4302-E or equivalent. |
| Hardware 2 | ||||
| BATT. | 9V | 9V | 9V battery snap | Soft vinyl type. The hard-shell type will not fit. |
| ENC | 125B | 125B | Enclosure, die-cast aluminum | Can also use a Hammond 1590N1. |
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