Capturing Cockpit Audio: Designing a Custom GA Cockpit Audio Adapter PCB

Whether debriefing a cross-country navigation flight, reviewing local pattern communications, or capturing flight footage, having crisp cockpit audio is just as critical as having clear video. Modern action cameras like GoPros or external voice recorders do a phenomenal job with visual details, but without a dedicated audio interface to the aircraft’s avionics, you end up recording little more than deafening engine roar, prop wash, and wind buffeting.

When I looked into off-the-shelf patch cables designed to tap into GA headset jacks, buying a commercial adapter easily ran around $100 USD once you factor in international shipping and import fees to Israel. Paying triple digits for what amounts to a couple of connectors and basic passive components made zero sense.

The entire motivation behind this project boiled down to three simple goals:

Learn KiCad.
Save $100.
Get clean cockpit audio recordings.

Special thanks to forum user bullojm1 for sharing the original idea and schematic—without that write-up, this adapter would not exist. Thank you! The original concept was hand-wired, so my goal was to take that circuit, lay it out on a proper PCB in KiCad, and design a durable 3D-printed enclosure so it wouldn’t rely on messy point-to-point wiring or floating components.

The Problem with Tapping General Aviation Audio

General aviation audio systems don’t behave like standard consumer line-out jacks. Plugging an off-the-shelf recorder or smartphone directly into an aircraft headset circuit introduces several technical challenges:

Hot Signal Levels & Clipping: Aircraft headphone lines (the standard 0.250-inch PJ-055 / M642/4-1 jack) deliver high voltage swings to drive 300Ω or 600Ω aviation headset speakers. Plugging that straight into a consumer mic-level input results in harsh, unlistenable clipping every time ATC speaks or an alert tone chimes.
Ground Loops & Avionics Noise: Aircraft electrical systems are electrically noisy environments. Alternator whine, strobe flash capacitor charging, and magneto pulses can easily couple into recording equipment through ground loops if reference planes and grounds are poorly managed.
Intercom Impedance Loading: An audio adapter must be transparent. If the input impedance of the recording tap is too low, it can load down the intercom bus, dropping sidetone volume or degrading audio clarity for the pilots.

System Architecture

The adapter sits as a passive bridge inline between the aircraft’s headphone output and the recording device:

[ Aircraft Audio Jack (PJ-055) ]
              │
              ├──► [ Standard Pilot Headset (Thru-Port) ]
              │
              ▼
   [ Impedance Matching & Attenuation Divider ]
              │
              ├──► [ TRS Output  (Cameras, GoPros, Field Recorders) ]
              └──► [ TRRS Output (Smartphones & Tablets) ]

Hardware Design & Engineering Choices

1. Inline Attenuation & Impedance Matching

To bring aircraft headphone signals down to clean mic/line levels:

A precision resistor divider scales down the signal without distorting frequency response across the speech band (300 Hz – 3.5 kHz).
High-value input resistance ensures the circuit presents a high impedance load to the aircraft intercom, preventing any detectable drop in headset listening volume.

2. Dual Output Routing: Why We Need Both TRS and TRRS

Consumer recording gear is split across two standard 3.5mm connector formats with entirely different pinouts:

TRS (Tip-Ring-Sleeve) for Dedicated Cameras & Recorders: Cameras (GoPro with mic adapter, DJI Action, DSLRs) and dedicated audio field recorders expect a standard 3-pole TRS jack.
- Pinout: Tip is Left Input, Ring is Right Input, and Sleeve is Ground.
- Wiring: The attenuated mono cockpit audio is bridged to both the Tip and the Ring so the camera records dual-channel audio without needing post-production channel duplication.
TRRS (Tip-Ring-Ring-Sleeve) for Smartphones & Tablets: Smartphones (CTIA standard) and tablets treat a 3.5mm port as a combined headphone output and external microphone input.
- Pinout: Tip is Left Headphone Out, Ring 1 is Right Headphone Out, Ring 2 is Ground, and Sleeve is Microphone In.
- Wiring: If you plug a standard TRS cable into a phone, the microphone pin shorts to ground and the phone ignores the input, recording through its internal ambient mic instead. The dedicated TRRS output routes the attenuated cockpit signal specifically to the Sleeve (Mic In), allowing phones to detect the connection as an external microphone and record directly in voice memo or video apps.

3. Dedicated PCB Layout & Custom Enclosure

Rather than hand-wiring resistors inside a connector barrel or using perfboard:

Designed a custom 2-layer PCB in KiCad that anchors all jacks and attenuation resistors securely.
Plated through-hole pads provide solid mechanical durability against cable tugs and cockpit vibrations.
Clear visual trace segregation keeps input stages cleanly separated from output stages.
Packaged the assembled board into a snug, 3D-printed enclosure with integrated strain reliefs so it holds up inside a flight bag.

Flight-Testing & Debriefing

Field testing the board across cross-country flights and traffic pattern training showed an immediate difference:

Zero Intercom Degradation: Headset volume and ATC reception remain completely unchanged when plugging or unplugging the recorder.
Crystal-Clear ATC & Sidetone: Tower transmissions, pilot readbacks, and cockpit intercom speech come through sharp and intelligible, without clipping during louder transmissions or background buzz while idling.
Plug-and-Play Device Support: Swapping between an action camera (TRS) and a phone logging notes (TRRS) works seamlessly without fiddling with loose dongles or adapters.
Reliable Form Factor: Encased in the custom enclosure, the adapter fits neatly into a flight bag or clips out of the way on the cockpit side panel.

Open-Source Hardware Repository

The complete KiCad schematic, board layout, and bill of materials (BOM) are fully open-source:

🔗 GitHub: meirtolpin11/GA-Cockpit-Recorder-PCB

If you fly and want a reliable, clean way to record ATC radio and intercom audio without spending $100 on import markups, the design files and schematics are ready to inspect and build.