• Created:2026/05/07
• Updated:2026/05/07
• Author:
  Takeshi Takatsudo

Eurorack Power Distribution Best Practices

Lessons learned from commercial Eurorack power systems, particularly the Toppobrillo Eurobus.

Introduction

When designing a Eurorack power supply, the distribution system is just as important as the power regulation itself. This document explores best practices from commercial designs and their applicability to DIY/JLCPCB-compatible builds.

Case Study: Toppobrillo Eurobus

The Toppobrillo Eurobus is a high-end Eurorack power distribution system that represents best-in-class design practices.

Specifications:

• Power: +12V @ 3.5A, -12V @ 2A, +5V @ 1.5A
• 20 keyed power connectors
• 4-layer PCB with stitched ground plane
• Zone-filtered distribution
• Soft-start and comprehensive protection

Key Design Philosophy:

"By utilizing the full width of the busboard for thicker traces and uninterrupted ground planes, routing and return paths are optimized - reducing impedances, improving power delivery, and lowering noise across the board."

Critical Design Features

1. Keyed Connectors (Critical Safety Feature)

What: Polarized/keyed 16-pin IDC connectors that physically prevent reverse insertion.

Why important:

• Eurorack modules can be destroyed instantly by reverse polarity
• +12V to GND short creates catastrophic failure
• Users work in cramped cases with poor visibility
• Ribbon cables are easy to connect backwards

Standard vs Keyed:

Standard 2x8 Header (No Keying):
  Can be inserted either way
  ❌ No protection against reverse connection
  ❌ User must check red stripe alignment
  ⚠️  Risk of module destruction

Keyed 2x8 Header:
  Physical key prevents backward insertion
  ✅ Impossible to connect backwards
  ✅ Foolproof connection
  ✅ Critical for beginners and low-light conditions

Implementation Options:

Approach	PCB Side	Cable Side	JLCPCB Compatible	Safety Level
Standard (our current)	Standard pin header	Standard IDC	✅ Yes	⚠️ Low (user dependent)
Hybrid (recommended)	Standard pin header	Keyed IDC connector	✅ Yes	✅ High (cable-side keying)
Full keyed	Keyed pin header	Keyed IDC connector	❌ No	✅✅ Highest

Recommendation for DIY builds:

• Use standard pin header on PCB (JLCPCB compatible)
• Strongly recommend keyed IDC connectors on ribbon cables (user-sourced)
• Document the pinout clearly with pin 1 marked

Where to source keyed connectors:

• Tayda Electronics: 16-pin box headers
• Mouser/Digikey: Keyed IDC connectors
• Modular synth suppliers: Pre-made keyed cables

2. Zone Filtering Architecture

What: Multiple decoupled power distribution zones instead of a single point.

Eurobus approach:

Power Input
    │
    ├─→ Zone 1 (Connectors 1-10)
    │   ├─→ Bulk capacitor (470µF)
    │   ├─→ Ceramic decoupling (100nF × N)
    │   └─→ 10× Output connectors
    │
    └─→ Zone 2 (Connectors 11-20)
        ├─→ Bulk capacitor (470µF)
        ├─→ Ceramic decoupling (100nF × N)
        └─→ 10× Output connectors

Benefits:

• Isolates noise between module groups
• Reduces voltage sag from distant modules
• Lowers ground bounce and crosstalk
• Better current distribution

Our current design:

Power Input
    │
    └─→ Single output point
        ├─→ Bulk capacitor (470µF)
        ├─→ Ceramic decoupling (100nF)
        └─→ 1× Output connector

When to implement zones:

• Systems with >10 modules
• Multiple cases/busboards
• High-power digital modules (sampling, DSP)

For single-output designs (like ours):

• Zone filtering not necessary
• Good decoupling at regulator output is sufficient
• Keep output connector close to final filter caps

3. PCB Design for Low Impedance Distribution

Eurobus best practices:

4-Layer PCB Stackup

Layer 1 (Top):     Signal traces, component pads
Layer 2 (Inner):   Ground plane (continuous)
Layer 3 (Inner):   Power planes (+12V, -12V, +5V)
Layer 4 (Bottom):  Ground plane, return paths

Why 4 layers:

• Continuous ground reference reduces impedance
• Power planes minimize voltage drop
• Better EMI/noise performance
• More routing flexibility

2-layer alternative (cost-optimized):

Layer 1 (Top):     Signal + power traces (thick copper)
Layer 2 (Bottom):  Ground plane + power traces

Trade-offs:

• 4-layer: Better performance, higher cost (~2-3× PCB cost)
• 2-layer: Adequate for small systems, lower cost

Copper Thickness

Standard: 1oz copper (35µm) Eurobus: Extra-thick copper (2oz or more)

Benefits of thick copper:

• Lower resistance → less voltage drop
• Better current capacity
• Improved thermal dissipation

Voltage drop calculation:

Example: 10cm trace, 1.2A current

1oz copper (35µm), 1mm width:
  Resistance: ~17mΩ
  Voltage drop: 1.2A × 17mΩ = 20mV ⚠️

2oz copper (70µm), 2mm width:
  Resistance: ~4.3mΩ
  Voltage drop: 1.2A × 4.3mΩ = 5mV ✅

Recommendation:

• Power traces: 2oz copper, 2mm+ width
• Ground pour: Maximum copper area
• Signal traces: 1oz acceptable

Ground Plane Stitching

What: Multiple vias connecting top and bottom ground planes.

Bad (High Impedance):
  Top GND ═══════════════ Few vias
                          ↕ (long path)
  Bot GND ═══════════════

Good (Low Impedance):
  Top GND ═╪═╪═╪═╪═╪═╪═╪═ Many vias
           ↕ ↕ ↕ ↕ ↕ ↕ ↕  (short paths)
  Bot GND ═╪═╪═╪═╪═╪═╪═╪═

Guidelines:

• Via spacing: Every 5-10mm on ground areas
• Around high-current components: 2-3mm spacing
• Creates "stitched" ground plane with low impedance

4. Distributed Decoupling Strategy

Eurobus approach:

• Bulk electrolytic capacitors at each zone
• Multiple ceramic capacitors distributed along bus
• Low-ESR polycapacitors for high-frequency filtering

Capacitor placement hierarchy:

1. Regulator output (immediate):
   └─→ Large electrolytic (470µF) + ceramic (100nF)

2. Zone/distribution point (medium distance):
   └─→ Electrolytic (100-470µF) + ceramic (100nF)

3. Each connector (local):
   └─→ Small ceramic (10-100nF) very close to pin

Why distributed:

• Large electrolytics: Bulk energy storage, slow response
• Small ceramics: Fast transient response, low ESR
• Multiple locations: Reduces inductance from wire length

Practical implementation:

Poor (single-point decoupling):
  Regulator → [470µF] → 50cm trace → Connector
                                     ↑ Inductance kills fast response

Good (distributed decoupling):
  Regulator → [470µF][100nF] → 25cm → [100µF][10nF] → Connector
              ↑ Bulk              ↑ Local            ↑ Very close

5. Thermal Management

Eurobus achievement: 90% efficiency, runs "relatively cool"

Heat sources in power supplies:

1. DC-DC converters (switching losses)
2. Linear regulators (dropout voltage × current)
3. PTCs when tripped (self-heating)

Thermal design checklist:

✅ Component spacing:

• Keep heat-generating components apart
• LM7812 away from PTC fuses
• DC-DC converters in open area

✅ PCB heat dissipation:

• Large copper pours act as heatsinks
• Thermal vias under hot components (TO-263 packages)
• Multiple vias from thermal pad to ground plane

✅ Airflow:

• Don't block component top side
• Consider case ventilation
• Modular cases are usually well-ventilated

Thermal via pattern example:

TO-263 Package (top view):
  ┌─────────────┐
  │  [Thermal]  │ ← Large thermal pad
  │  [[[[]]]]]  │ ← 5-9 vias to bottom ground
  │  Pin Pin    │
  └─────────────┘

Bottom layer:
  Large copper pour connected via thermal vias
  Acts as heatsink (dissipates to case/air)

Comparison: Eurobus vs Our Design

Feature	Eurobus	Our USB-PD Design	Gap
Power Output	+12V@3.5A, -12V@2A, +5V@1.5A	+12V@1.5A, -12V@1A, +5V@1.5A	Smaller capacity (suitable for ~10 modules)
Connectors	20× keyed	1× standard	⚠️ No keying, single output
Zone Filtering	2 zones	Single point	Not needed for 1 output
PCB Layers	4-layer	TBD (recommend 4)	Should specify
Copper Thickness	Extra-thick	TBD (recommend 2oz)	Should specify
Protection	OCP, OVP, thermal, soft-start	4-layer (USB-PD, DC-DC, LM78xx, PTC)	✅ Comparable
Decoupling	Polycaps, distributed	Electrolytic + ceramic	✅ Good
Auto-reset	Yes (electronic)	Yes (PTC)	✅ Excellent
JLCPCB Compatible	No (custom parts)	Yes (100% JLCPCB parts)	✅ Major advantage

Our design strengths:

• ✅ Full JLCPCB compatibility (low cost, high availability)
• ✅ 4-layer protection (exceeds most commercial designs)
• ✅ PTC auto-reset (better than manual fuses)
• ✅ Low-noise architecture (DC-DC + linear)

Areas for improvement:

• ⚠️ Add keyed connector recommendation to documentation
• ⚠️ Specify 4-layer PCB in design files
• ⚠️ Specify 2oz copper for power traces
• ⚠️ Add thermal via guidelines

Recommendations for Our Design

Immediate (Documentation Updates)

1. Update BOM connector section:

**Strongly recommended for cable assembly:**
Use keyed IDC connectors instead of standard ribbon cable connectors.
This prevents reverse insertion and protects modules from damage.

Sources:

- Tayda Electronics: 16-pin box header connectors
- Mouser/Digikey: Keyed IDC cable assemblies

2. Add PCB design guidelines:

• Recommend 4-layer PCB (or explain 2-layer trade-offs)
• Specify 2oz copper on power layers
• Thermal via pattern for TO-263 regulators
• Ground stitching recommendations

3. Add assembly notes:

• Mark Pin 1 clearly on silkscreen
• Add polarity warning labels
• Include Eurorack pinout diagram on PCB

Future Enhancements (v2.0)

If expanding to multiple outputs:

1. Implement zone filtering (2 zones, 10 connectors each)
2. Add distributed decoupling at each zone
3. Consider larger current capacity (2A per rail)

If moving to custom PCB manufacturer:

1. Source keyed pin headers (not on JLCPCB)
2. Specify 2oz+ copper thickness
3. Add mounting holes for robust mechanical connection

Key Takeaways

1. Keying is Critical for Safety

Reverse polarity destroys modules instantly. While not available on JLCPCB, strongly recommend keyed IDC connectors on cable side.

2. PCB Design Matters

4-layer PCB with thick copper significantly reduces noise and voltage drop. Worth the extra cost for >10 module systems.

3. Distributed Decoupling Works

Multiple capacitor types at multiple locations provides better transient response than single-point decoupling.

4. Our Design is Competitive

4-layer protection + PTC auto-reset exceeds many commercial designs. JLCPCB compatibility is a major advantage for DIY builders.

5. Thermal Management is Essential

Component spacing, thermal vias, and copper pours keep the supply cool and reliable. Don't neglect thermal design.

References

Commercial Systems Studied

• Toppobrillo Eurobus: High-end zone-filtered distribution
  • Product Page
  • MOD WIGGLER Discussion
  • Perfect Circuit

Related Documentation

• Protection Strategy: /doc/docs/learning/protection-fuse-strategy.md
• Bill of Materials: /doc/docs/overview/bom.md
• Circuit Diagrams: /doc/docs/overview/circuit-diagrams.mdx

Further Reading

• Buyer's guide: Eurorack cases and power - Signal Sounds
• Eurorack power best practices (modular synth community wikis)
• PCB thermal design guidelines (various manufacturers)