QuadPreRecorder unrouted

Quad Preamp and Recorder

Compact four-channel ambisonic electret preamp, 192 kHz/24-bit recorder, real-time binaural monitor, and touchscreen controller.

The hardware is derived from jdg511/Quadelectretpre and is redesigned as a mixed-signal two-layer PCB in a Hammond 1590XX enclosure.

Project layout

• hardware/ — KiCad project, fabrication package, design notes, and reviews.
• tools/ — reproducible schematic, PCB, and fabrication-generation scripts.
• firmware/ — recorder/DSP interface, pin map, file-naming rules, and implementation requirements. Production firmware is not included in Rev A.

Revision status

The current design is Rev C (2026-09-08), routed for the compact Hammond 1590XX (138 x 114 mm board, 145 x 121 x 39 mm enclosure). Rev C takes the Rev B board and:

• adds a USB-C receptacle (J9) on the rear wall — 5 V power from any charger, power bank or computer port (TPS61175 boost + ADP7142 low-noise LDO make the 9 V analog rail), SD-card file transfer (MTP) and firmware updates; the 9 V barrel (J1) stays as an alternative input and moved to the rear-left wall;
• mutes the 1/4-inch line out with a signal relay (K1) while a computer is attached (ground-loop protection, on-screen warning with override);
• replaces the headphone pot with a TPA6130A2 I2C-volume headphone amp (encoder / touchscreen control) and the pad toggle with a GPIO-driven level shifter (pad is a touchscreen control);
• changes the display to the LCDWiki MSP3526 3.5-inch IPS module with FT6336U capacitive touch (the MSP3520 named in Rev B is resistive).
• adds an internal LiPo battery (5000 mAh, 6-7 h) with a BQ24074 USB charger and a two-button soft-power gesture (hold RECORD + encoder push).

Walls: rear = SD slot + 9 V + USB-C, left = mic RJ45 (Amphenol RJHSE-5380), right = headphones, front = line out; lid = display, record button, gain encoder. Rev C3 (2026-09-12) removed the J6/J7 test headers (probe at component pads or the TP3-TP14 pads), moved to a 4-layer SIG/GND/GND/SIG stack, and made the mic input switchable from the screen: electret bias off / 5 V / 9 V (one setting for all four channels) and, with the bias off, the four RJ45 pairs become true balanced inputs for dynamic microphones (two-op-amp instrumentation stage, +20.1 dB, SPICE-checked CMRR 58-67 dB worst case across the audio band). The 9 V analog LDO is an ADP7142 (the TPS7A4701 it replaces had no distributor depth) and every BOM line was re-checked for stock and price the same day. See hardware/reviews/audio-rules-check-revC3-fixes.md, hardware/mechanical.md, hardware/connector-pinout.md and firmware/docs/REV-C-CONTROL-MODEL.md.

ERC is clean and DRC (--all-track-errors --schematic-parity --severity-error) reports 0 violations, 0 unconnected pads, 0 parity issues on the routed board. The Gerbers, drills, BOM, placement CSVs, STEP and PDFs in hardware/manufacturing/ are regenerated from it (QuadPreRecorder-RevC-PCBWay-handoff.zip). Rev B outputs are archived in hardware/manufacturing/revb-archive/.

Still a human check before ordering: the physical Hammond 1590XX fit (wall cutouts, button/shaft reach, the purchased MSP3526 module) — see hardware/enclosure-1590XX-desk-study.md and hardware/reviews/rev-c-preorder-review.md.

This is still new mixed-signal hardware, not a bench-proven production revision. Read the prototype confirmations in hardware/requirements.md and the order/bring-up notes in hardware/manufacturing/README.md before ordering.

Rebuild

• tools/route_pcb.ps1 regenerates the schematic/footprints/placement, runs Freerouting 1.9.0 (tools/cache/freerouting19.jar, single-threaded — the 2.2.4 jar drops nets from its session export on this board), imports the route, adds the GND pours, and checks DRC. Allow ~35-60 minutes.
• python tools/build_manufacturing.py regenerates the complete PCBWay handoff with KiCad 10's command-line tools.

The checked-in routed board is the release artifact; rerouting is not required to order it.