This adapter lets you use in-ear headphones or headset with electret mic and a 3.5mm TRRS phono connector, with a theatrical/broadcast comms panel or beltpack with 4-pin male XLR headset connector.

It is confirmed to work with Riedel Bolero and Artist panels/beltpacks, provided that they are in auto or electret mic mode. It should work just fine with any other comms pack that supports providing 5V mic bias.

Important Notes

If the comms device only supports dynamic mic headsets, this adapter will not work for microphone! It will however still work for the (mono) headphone side.

This adapter only supports in-ear or particularly high-sensitivity on-ear headsets, as it relies on transformer isolation of the headphones. Unfortunately this means it is not recommended for use with any over-ear headphones! The sound will be quiet and distorted.

Design

I designed H2X as I was sick of sharing uncomfortable and unhygienic comms headsets at work in a theatre, but Bluetooth is not always supported for comms headset connection.

I discovered that due to the difference in circuit design of broadcast headset (separate mic and mono speaker) and phone headset (shared ground between mic and stereo speakers), directly wiring up an adapter did not work, but caused horrific feedback on the mic input.

This adapter includes a tiny high-quality 1:1 isolation transformer on the speaker side, to maintain the isolation between speaker and mic circuits and appear like a regular electret-mic comms headset. This means it is completely passive and does not require any additional power.

After prototyping as a dongle, the design was miniaturised to fit entirely within the high-quality Neutrik XLR-FXX connector shell.

I've used it on several productions, and users have found it reliable and a huge relief when comms headsets are uncomfortable. Microphone quality of course depends entirely on the headphones used, but was never an issue.

Any buttons on the 3.5mm headset have no function, as no comms devices support controls on 4-pin headset connector.