Compressor front

Compressor front board

A 35 × 110 mm board that sits flat behind the faceplate and carries everything on the panel: the five pots, the four toggles, and both LED meters with their two LM3914 drivers. It joins the main board with a 30-way ribbon from J1 here to J2 on the main board, pin for pin, with the same net names in both schematics.

The parts are the ones drawn in the main schematic. They stay drawn there (excluded from that board and its BOM) so the circuit still reads as one piece.

How it sits

• The front of the board faces the panel. Pots, toggles, LEDs, the driver ICs and their small parts all go on the front.
• J1 (a plain 2×15 pin header) and C38 (47 µF, too tall for the front) go on the back.
• The toggles are Salecom mini toggles from Altronics: S1350 (DPDT) for BYPASS, S1315 (SPDT) for KEY, HPF and LINK. Their body stands 10.4 mm off the board and the Altronics 9 mm pots stand 10.6 mm, so the board sits about 10.6 mm behind the panel, with the pot bodies against the back of the panel and the toggles 0.2 mm short of it.
• Alps RK09K pots, if you use them instead, are shorter: make up the difference with a nut behind the panel, which may need the longer bushing version.
• The LEDs need spacers to reach the panel: about 7.8 mm for the 2 mm flat-tops drawn here (10.6 mm gap less the 2.8 mm LED).
• Each meter is a column of ten LEDs on a 3.0 mm pitch, so the LED bodies are 0.2 mm apart. The LED footprints' courtyards and silkscreen are trimmed to suit (DRC lists them as differing from the library). 3 mm LEDs no longer fit.
• The pots' 5 mm bushing leaves under 2 mm of thread through a 3.18 mm panel: see panel/README.md on panel thickness. The toggles' 8.9 mm bushing is plenty.
• The pins of all four toggles come through the back by about 0.8 mm.
• The main board's front edge is set back 24 mm from the panel to clear this board, the header and the ribbon plug. The board's back face is now about 12.2 mm behind the panel, so check the plug on J1 still clears it, especially with single-way sockets (taller than an IDC plug).

Joining the boards

The boards are joined only by the ribbon; each one is fixed to the faceplate on its own.

• Ribbon: 30-way, 2.54 mm pitch, with an IDC socket crimped on each end. Main board J2 is a shrouded box header; J1 here is a plain pin header, so it isn't keyed. Put the red stripe on pin 1 at both ends (pin 1 is marked on the back silkscreen). Altronics has no 30-way IDC parts, so bom/altronics.csv lists a plain 2×15 header for J2 as well and a 150 mm socket-to-socket strip of single-way leads (P1023) for the ribbon. It works, but nothing keys it: keep lead 1 on pin 1 at both ends. For a proper IDC ribbon, buy the box header, two sockets and cable from element14.
• Length: about 150 mm, folded once between the boards. J2 sits roughly 30 mm behind the panel and about 35 mm higher than J1, and the sideways distance depends on where the main board sits in your rack, so lay the boards out and check before crimping.
• Front board to panel: the nuts on the five pot and four toggle bushings.
• Main board to panel: an L-bracket from the back of the panel to H1 and H2, the two M3 holes by the main board's front edge (85 mm apart). The front edge is 24 mm behind the panel, so the bracket leg along the board needs to reach that far: 25 × 25 mm aluminium angle, or a short angle with standoffs. H2 is plated and tied to CHASSIS (J1 pin 1), so the bracket also grounds the panel as the faceplate guide asks. Mask the anodise where the bracket touches the panel. The 3D-printed faceplate in panel/print/ has this bracket built in: two ears that H1 and H2 screw to with M3 × 6 screws into captive nuts, and a wall that runs back along the main board to cover its solder side.

Coordinates

The panel outline and every hole are drawn on User.Drawings, with the grid origin on the panel's top-left corner. The board editor's coordinates read the same as the panel drawing, and panel/make_panel.py takes its hole positions from this board.

3D models

Every part has a 3D model, so the 3D viewer and a STEP export (for the Fusion 360 assembly) show both boards complete.

• Most come from KiCad's own library.
• The pots use Alps' official RK09K1130 model. It's the maker's file, so it isn't kept in git: run sh tools/get_3d_models.sh once to fetch it into 3dmodels/. The pots use a project copy of the stock RK09K footprint that points at it.
• The toggles use simple models built to the Altronics drawings by tools/make_toggle_models.py (case, bushing, lever and pins).
• The main board's edge fingers are copper, not a part, so J1 there has no model.

Check before ordering

• The toggle footprints follow the drawings on Altronics' S1315 and S1350 pages: pins on 4.70 mm, 1.3 mm holes, the DPDT's two rows 4.83 mm apart. The S1332 (centre off) has the same drawing as the S1315, so it drops into any SPDT position. Check one switch against the footprint before ordering boards.
• The toggles sit at x = 7.15 and 30.95 mm (panel coordinates), 0.25 mm in from the old sub-miniature positions, so the S1350's 11.4 mm body stays on the board. The pot footprint's courtyard was trimmed to its pads so it doesn't overlap the S1350's.
• The Altronics 9 mm pots (R19xx) have the RK09K's pin and lug pattern (lugs 8.6 mm apart, pins 7.0 mm behind them), so they use the same footprint. Their drawing doesn't place the shaft relative to the lugs; the RK09K's is 0.5 mm beyond them. Check before cutting the panel.
• SW3 (HPF) and SW4 (LINK) are single-pole in the schematic and use the SPDT footprint's top and centre pins; the bottom pin is unused.
• There are no mounting holes: the nine bushing nuts hold the board. Add standoffs if it flexes.