

Looper main
4-track Eurorack Looper
- Size
- 20 × 110.1 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 25
- Nets
- 21
- Pads
- 119
- Tracks, vias
- 180, 1
- Pours
- 4
- Routed
- Yes
- KiCad
- KiCad 8.0 (file 20240108)
- Created
- 21 Nov 2023
- Updated
- 13 Feb 2025
Overview
Looper main is an open-source printed circuit board by GugeNet, from the GugeNet/Loop repository on GitHub, published under the MIT licence. It is a 2-layer board of 20 × 110.1 mm with 25 parts on 21 nets, routed with 180 tracks and 1 via.
It is built around the MMBT3904. Its parts include 8 resistors, 7 connectors, 6 switches and 1 transistor. It belongs with the audio and music boards of this library.
Main components
1README
README.mdLoop
4-track Eurorack Looper
A 4 hp wide 3U Eurorack module designed to be as simple as possible, but not simpler.
The user interface is limited but based on an idea of creating a linguistic model.
Not all of the ideas are implemented yet.
The commands consists of verbs: record, clear and loop. There are buttons for record and clear, a trigger input for loop. In most situations there is also an implicit verb, such as mute. The time aspect in the commands are either immidiate or suspended until loop. A short press means now, a long press means after the next loop command. The objects are the four tracks. The module will ask the user to select track by blinking the four track-buttons, or simetimes only the applicable tracks if appropriate.
Examples:
While playing click a green button and the track is muted and the button goues off. Press the button for half a second instead of cust clicking and the button will blink green and start playing after the next loop.
Hold down record and notice all tracks blinking red as the module wants to know where to record. You can press one or more tracks and they will record after loop.
Another foundational idea is that every button has a function in any situation. There is no illegal action and the module is never unresponsive. The user is boss and presumably always has some intention.
So if the button for a blank track is pressed, it is presumed that record is the correct operation, while play is implicit for a track with sound.
The connections are stereo inputs and stereo outputs and a trigger input for loop.
There are six buttons. One bi-color illuminated pushbutton for each of the four tracks, one for clearing and one for record.
The basic operation of the module is to record to or play from four sound buffers and then on trigger loop to the beginning.
The module will always pass incoming sound through. Recording is additive, that is to say it doesn't remove existing sound from the track before recording. Recording takes just the incoming sound.
Playing also adds sound to the incoming sound and when several tracks are playing they are all added equally to the incoming sound.
On reception of the loop trig the following scenarios are performed:
Playing -> Playing Recording -> Playing Muted -> Muted
The user can cue playing, recording or muting to happen on loop.
Record -> Track (long) Track (long) Clear -> Track (long)
Parts
25| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | 130 | Resistor_SMD:R_0603_1608Metric | R1, R2, R3, R4 |
| 4 | ~ | 1_Geirs_Library:D6RLRDGNF1LFS | SW1, SW2, SW3, SW4 |
| 2 | 100K | Resistor_SMD:R_0603_1608Metric | R11, R29 |
| 2 | MountingHole_2.7mm_M2.5 | MountingHole:MountingHole_2.7mm_M2.5 | MOUNT1, MOUNT1 |
| 1 | 10K | Resistor_SMD:R_0603_1608Metric | R26 |
| 1 | 1K | Resistor_SMD:R_0603_1608Metric | R27 |
| 1 | Clear | 1_Geirs_Library:SW_TS02-66-140-BK-160-LCR-D | S1 |
| 1 | Conn_01x05 | Connector_PinHeader_2.54mm:PinHeader_1x05_P2.54mm_Vertical | J12 |
| 1 | Conn_01x06_Pin | Connector_PinHeader_2.54mm:PinHeader_1x06_P2.54mm_Vertical | J9 |
| 1 | Device_Audio_Electrosmith_Daisy_Seed_Rev4 | Device_Audio_Electrosmith_Daisy_Seed:Device_Audio_Electrosmith_Daisy_Seed | A1 |
| 1 | In left | AudioJacks:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical | J2 |
| 1 | In right | AudioJacks:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical | J5 |
| 1 | MMBT3904 | Package_TO_SOT_SMD:SOT-23 | Q1 |
| 1 | Out left | AudioJacks:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical | J4 |
| 1 | Out right | AudioJacks:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical | J1 |
| 1 | Record | 1_Geirs_Library:SW_TS02-66-140-BK-160-LCR-D | S2 |
| 1 | Trig Loop | AudioJacks:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical | J3 |
Questions
How big is the Looper main PCB?
It measures 20 × 110.1 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Looper main use?
25 parts, built around the MMBT3904. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Looper main KiCad files?
From the GugeNet/Loop repository on GitHub, at the commit this page was made from: the board is Hardware/PCB/Looper_main.kicad_pcb and its schematic Hardware/PCB/Looper.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Looper main design in my own project?
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).
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