# CAMS-1 PCB design notes (match dual-mid / LM3886 quality bar)

## Boards to fabricate

| PCB | Size (start) | Layers | Copper | Contents |
|-----|--------------|--------|--------|----------|
| **CAMS-XO-R1** | 100 × 80 mm | 2 | 1 oz | INA134, master pot footprint/header, OPA2134 ×2, all XO R/C @ 2.5 kHz |
| **CAMS-AMP-R1** | 120 × 100 mm | 2 | **2 oz** preferred | Dual LM3886TF, mute, Zobel, Thiele, local 100n+1000u per rail/channel |
| PSU | Chassis | — | — | Toroid, bridge, 10000 µF bulk, 7815/7915 on plate (not forced onto small PCB) |

Open root schematic: [`../kicad/cams1_root.kicad_sch`](../kicad/cams1_root.kicad_sch)

## KiCad workflow (same as earlier mid amp)

1. Open `cams1_root.kicad_sch` in **KiCad 8+**.  
2. Annotate → assign footprints from [`COMPONENTS_COMPLETE.csv`](COMPONENTS_COMPLETE.csv).  
3. ERC clean.  
4. PCB Editor: import netlist; place LM3886 at board edge for heatsink.  
5. DRC: 0.25 mm clearance min; 1 mm power traces; fill GND pour on both layers.  
6. Export Gerbers + drill + BOM → JLCPCB / local fab.

## Layout rules (critical)

1. **100 nF** within **5 mm** of every LM3886 and OPA2134 supply pin.  
2. Star **0V** at bulk capacitor common — no daisy-chain speaker returns.  
3. Keep **film XO caps** away from toroid and ±25 V traces.  
4. Separate **MID** and **HF** output traces; twisted pair to drivers.  
5. Mute RC near each LM3886 mute pin.  
6. Heatsinks **outside** the sealed box through the rear Al plate.  
7. IEC earth → chassis once; do not create ground loops to XLR pin 1 incorrectly (follow INA134 datasheet).

## Exact XO parts (@ 2.5 kHz) — “double” stages like before

| Path | Stage | Parts |
|------|-------|-------|
| MID LP | 1 and 2 (identical) | R1=R2=**3.0 kΩ**, C1=**15 nF**, C2=**30 nF** (2×15 nF) |
| HF HP | 1 and 2 (identical) | C1=C2=**6.8 nF**, R1=**6.8 kΩ**, R2=**13.6 kΩ** (2×6.8 kΩ) |

```bash
python3 ../../active-crossover/calculator/calculator.py 2500 --series E24
```

## Amp channel parts (each of MID and HF)

Same as [`../../lm3886-poweramp/docs/BOM.csv`](../../lm3886-poweramp/docs/BOM.csv):  
Cin 1µF, Rin 1k, Rbias 1M, Rf 20k, Ri 1k, Cf 20pF, Ci 220µF, Zobel 10R+0.1µF, Lout 0.68µH\|\|10R, mute 100k+10µF, rails 100n+1000µF.

HF only: **Rpad1=Rpad2=5.6 kΩ** (~−6 dB) before Cin_H.

## VERIFY before ordering PCBs

- LM3886TF vs T pin/tab isolation  
- INA134 / THAT1200 pin numbers  
- 7915 pinout  
- Transformer primary voltage for your country  
- Net volume / driver cutouts (mechanical — not PCB)