BufferedMult

Eurorack Buffered Multiple (SKiDL + KiCad 10)

A precision Triple 1-to-3 (Normalized to 1-to-6 / 1-to-9) Eurorack Buffered Multiple designed in Python using SKiDL and targeting KiCad 10.

This project is a SKiDL re-implementation and 3-channel expansion of domesticmouse/Buffered-Mult, omitting the LED feedback circuitry.

Interactive Course & Tutorial: https://domesticmouse.github.io/BufferedMult-SKiDL/ (published via GitHub Pages from tutorial/)

Features & Architecture

• Triple 1-to-3 / Cascaded 1-to-6 / 1-to-9 Routing:
  • Channel 1: 1 input (IN_1) driving 3 individually buffered outputs (OUT_1A, OUT_1B, OUT_1C). When IN_1 is unpatched, its normalled switch contact (TN) grounds the input to 0V.
  • Channel 2: 1 input (IN_2) driving 3 individually buffered outputs (OUT_2A, OUT_2B, OUT_2C). When IN_2 is unpatched, its normalled switch contact (TN) receives the buffered signal from Channel 1 (CH1_BUF), cascading Channels 1 and 2 into a 1-to-6 buffered multiple with zero loading droop between channels. Patching a cable into IN_2 breaks the normal connection for independent channel operation.
  • Channel 3: 1 input (IN_3) driving 3 individually buffered outputs (OUT_3A, OUT_3B, OUT_3C). When IN_3 is unpatched, its normalled switch contact (TN) receives the buffered signal from Channel 2 (CH2_BUF), cascading all three channels into a 1-to-9 buffered multiple (or a 1-to-3 + 1-to-6 split if IN_2 is patched while IN_3 is unpatched). Patching a cable into IN_3 breaks the normal connection for independent triple 1-to-3 operation.
• Dedicated Input & Output Buffering:
  • Each channel uses one quad TL074H (TL074HIDR) op-amp (SOIC-14):
    • Stage A: Unity-gain input follower protected by a PESD12VL1BA (SOD-323) bidirectional 12V TVS/ESD diode, a 100K input pull-down resistor (0603), and a 1K series input current-limiting resistor (0603).
    • Stages B, C, D: Three independent unity-gain output followers, each isolated with a 470R series output protection resistor (0603).
• Eurorack Power Supply Protection:
  • Standard 10-pin (2x5) through-hole shrouded IDC power header (±12V, GND).
  • Reverse-polarity protection via 1N5819WS Schottky diodes (SOD-323, or B5819W in SOD-123 as a larger alternative).
  • 10uF radial through-hole electrolytic bulk bypass capacitors per rail plus 100nF (0603) local ceramic decoupling capacitors at each op-amp's V+ and V- pins.

Signal Flow

flowchart LR
    subgraph CH1["Channel 1 (U1: TL074H)"]
        J_IN1["IN_1 Jack<br/>(TN -> GND)"] --> TVS1["PESD12VL1BA TVS<br/>+ 100K to GND"]
        TVS1 --> R_IN1["1K Series"] --> U1A["U1A Input Buffer"]
        U1A --> U1B["U1B Buffer + 470R"] --> OUT_1A["OUT_1A Jack"]
        U1A --> U1C["U1C Buffer + 470R"] --> OUT_1B["OUT_1B Jack"]
        U1A --> U1D["U1D Buffer + 470R"] --> OUT_1C["OUT_1C Jack"]
    end

    subgraph CH2["Channel 2 (U2: TL074H)"]
        J_IN2["IN_2 Jack<br/>(TN <- CH1_BUF)"] --> TVS2["PESD12VL1BA TVS<br/>+ 100K to GND"]
        TVS2 --> R_IN2["1K Series"] --> U2A["U2A Input Buffer"]
        U2A --> U2B["U2B Buffer + 470R"] --> OUT_2A["OUT_2A Jack"]
        U2A --> U2C["U2C Buffer + 470R"] --> OUT_2B["OUT_2B Jack"]
        U2A --> U2D["U2D Buffer + 470R"] --> OUT_2C["OUT_2C Jack"]
    end

    subgraph CH3["Channel 3 (U3: TL074H)"]
        J_IN3["IN_3 Jack<br/>(TN <- CH2_BUF)"] --> TVS3["PESD12VL1BA TVS<br/>+ 100K to GND"]
        TVS3 --> R_IN3["1K Series"] --> U3A["U3A Input Buffer"]
        U3A --> U3B["U3B Buffer + 470R"] --> OUT_3A["OUT_3A Jack"]
        U3A --> U3C["U3C Buffer + 470R"] --> OUT_3B["OUT_3B Jack"]
        U3A --> U3D["U3D Buffer + 470R"] --> OUT_3C["OUT_3C Jack"]
    end

Bill of Materials (BOM)

The design separates SMT components (factory-assembled on B.Cu by JLCPCB) from Through-Hole (THT) components (hand-soldered after receiving the boards):

Getting Started

Prerequisites

• KiCad 10 installed (default macOS symbol/footprint path /Applications/KiCad/KiCad.app/Contents/SharedSupport/ is detected automatically by buffered_multiple.py).
• Python 3.12–3.14 and uv.

Setup & Run

1. Create the virtual environment and install dependencies:

   uv venv --clear --python 3.14 .venv
   uv pip install skidl markdown-it-py pyyaml

2. Generate the circuit outputs and run Electrical Rules Checking (ERC):

   .venv/bin/python buffered_multiple.py

3. Generate or update the 4HP Eurorack front panel PCB and Gerbers:

   /Applications/KiCad/KiCad.app/Contents/Frameworks/Python.framework/Versions/Current/bin/python3 \
       .agents/skills/eurorack-panel/scripts/generate_eurorack_panel.py \
       --main-pcb BufferedMult.kicad_pcb \
       --output BufferedMult_Panel.kicad_pcb \
       --title "BUF MULT" \
       --subtitle "1:3 / 1:6 / 1:9" \
       --gerber-dir production/panel \
       --zip production/BufferedMult_Panel.zip \
       --drc

4. Build and validate the interactive tutorial HTML from Markdown (optional, for local previewing; GitHub Actions automatically builds and publishes to GitHub Pages via .github/workflows/pages.yml):

   .venv/bin/python tutorial/build.py --check

5. Lint and format with ruff:

   ruff check --fix buffered_multiple.py buffered_multiple_sklib.py tutorial/build.py && ruff format buffered_multiple.py buffered_multiple_sklib.py tutorial/build.py

Generated Files

Running buffered_multiple.py produces:

• buffered_multiple.net — KiCad 10 netlist with deterministic hierarchical tstamps and Power / Signal net classes.
• buffered_multiple_bom.xml — KiCad XML Bill of Materials.
• buffered_multiple_jlcpcb_bom.csv — Grouped JLCPCB SMT PCBA Bill of Materials (Comment,Designator,Footprint,LCSC Part #), excluding hand-soldered THT parts by default.
• buffered_multiple.erc / buffered_multiple.log — SKiDL ERC report and execution log (0 errors, 0 warnings).
• buffered_multiple_sklib.py — Auto-generated SKiDL backup symbol library.

KiCad 10 PCBs & Fabrication Outputs

Both the main circuit board and a mated 3U × 4HP Eurorack front panel are included in the repository:

• Main Circuit PCB (BufferedMult.kicad_pro / BufferedMult.kicad_pcb):
  • Dimensions: 20.0 × 109.0 mm (4HP, Rev V2.0), 2-layer PCB with stitched F.Cu and B.Cu GND planes and 0.5 mm ±12V power spines.
  • Assembly: Full 3-channel (44-component) layout with single-sided SMT placement on B.Cu (29 SMD parts) and hand-soldered THT jacks/bulk caps on F.Cu (J2–J13, C1, C2) plus the 10-pin power header on B.Cu (J1), complete with a -12V orientation knockout, V2.0 revision marking, and repository URL on B.SilkS.
• 4HP Eurorack Front Panel (BufferedMult_Panel.kicad_pro / BufferedMult_Panel.kicad_pcb):
  • Dimensions: 20.0 × 128.5 mm (Doepfer A-100 3U × 4HP standard).
  • Features: 12× 6.2 mm PTH grounded jack cutouts aligned to the +6.48 mm WQP-PJ398SM (Thonkiconn) bushing centers (14.40 mm uniform vertical row pitch), 2× 3.2 × 5.5 mm NPTH M3 mounting slots, exposed F.Mask copper/finish graphics (BUF MULT title, input callout badges for IN 1 / IN 2 / IN 3, and normalling cascade indicators), F.SilkS jack labels and TL074 callout, and solid F.Cu / B.Cu copper shield planes with exposed rear ground rings.
• Fabrication Archives (production/):
  • production/BufferedMult.zip — Main PCB Gerbers and Excellon drill files.
  • production/BufferedMult_Panel.zip — 4HP Front Panel Gerbers and Excellon drill files (also unpacked in production/panel/).
  • production/positions.csv, production/bom.csv, production/designators.csv, production/netlist.ipc — Fabrication Toolkit pick-and-place, BOM, and IPC-D-356 netlist files (use buffered_multiple_jlcpcb_bom.csv for SMT-only JLCPCB assembly).

Interactive Course & Tutorial (tutorial/)

The repository includes an 8-lesson interactive Hardware-as-Code course published at https://domesticmouse.github.io/BufferedMult-SKiDL/ (authored in Markdown under tutorial/ and compiled via tutorial/build.py). Starting from an empty Python file, the lessons progressively grow buffered_multiple.py and its post-netlist PCB, front-panel, and pre-fab verification scripts:

Printable Reference Sheets (tutorial/reference/)

• skidl-cheatsheet.md — SKiDL API, pre-import KiCad 10 configuration, dest=TEMPLATE, part.fields, u.p[n] vs u["V+"], @subcircuit, NetClass, and ERC() syntax cheat sheet.
• kicad-jlcpcb-lookup.md — Four-step programmatic component discovery workflow (search, show, search_footprints, jlcpcb_search.py) and verified BOM pinout/LCSC table.
• eurorack-power-and-normalling.md — Doepfer A-100 10-pin power header pinout, Schottky & bulk capacitor polarity, WQP-PJ398SM switched jack mechanics, and the 1:3 / 1:6 / 1:9 normalling truth table.
• GLOSSARY.md — Standardized SKiDL, KiCad 10, JLCPCB PCBA, and Eurorack hardware terminology.

Documentation & Guides

• Interactive Tutorial on GitHub Pages (domesticmouse.github.io/BufferedMult-SKiDL) — Hosted HTML edition of the 8-lesson (0001–0008) course and 4 reference sheets, built automatically by .github/workflows/pages.yml.
• PCB_LAYOUT_GUIDE.md — Step-by-step KiCad 10 PCB layout, component placement, routing, and JLCPCB export guide.
• FRONT_PANEL_GUIDE.md — 4HP Eurorack front panel mechanical dimensions, bushing offset coordinate table, and automated generation workflow.
• DESIGN_REVIEW.md — Full schematic, PCB, DRC, Gerber, and EMC pre-compliance design review report.

License

Licensed under the Apache License, Version 2.0. See LICENSE.txt for details.

This is not an official Google product.