HPM: wired IEMs done right

Wireless IEMs are expensive, and most wired IEM solutions are half-baked at best. Either they’re mono, or stereo over two cables, or stereo over one cable with shoddy adapters that short pin 3 to ground, or they require batteries, or any other of a long list of annoyances.

So, I figured I’d just do it myself.

I set out with three goals:

  1. The product must pass a stereo mix
  2. There can be only one cable hanging from the performer’s belt
  3. There can be no extra power requirements

I am pleased to report that I solved all three of these problems with a relatively inexpensive wired IEM solution.

Here is a brief overview of the features of the HPM:

  • Performers can get a stereo mix over a single, readily-available XLR microphone cable
  • Only the “last mile” of cable is unbalanced — long cable runs from the mixer to the HPM units or between HPM units are 100% balanced
  • The HPM system performs “true” unbalancing using transformers, not by shorting one of the signal lines to ground
  • Compared to a passive mono wired IEM solution without proper unbalancing, the HPM provides at least 6 dB more signal in each ear
  • Louder signal means battery-powered headphone amps may not be necessary

The system works in two parts: the HPM Bravo base unit and the HPM Romeo extender.

The HPM Bravo

Barely bigger than a DI box, two combo jacks on the Bravo allow you to connect a stereo pair of XLR or TRS outputs from your mixer. The Bravo gives us two options for this stereo signal:

  1. Unbalance the inputs and combine them into a stereo signal over a single mic cable.
  2. Combine the balanced signals and output them over a 5-pin XLR connection to a Romeo unit.

The first option is great for when the performer happens to be standing near an output from the mixer. Perhaps they are close to a stage box, or standing at the side of the stage next to the monitor position. In this case, all we need to do is feed a stereo pair of signals to the Bravo, then plug a standard XLR cable into the 3-pin XLR output on the Bravo and run that cable to a performer. With an appropriate beltpack (such as the Behringer PM1 or P2, the ART HP-1, Fischer Amps In-Ear Stick, etc), this provides a stereo in-ear mix with only a single lightweight, readily-available microphone cable. Overall, we have the following configuration:

Mixer » 2x XLR3 » Bravo » 1x XLR3 » Beltpack

If the performer is far enough from an output that running two cables would clutter the stage, the second option allows us to leave the Bravo near the mixer or stage box and run a balanced stereo connection over a longer 5-pin XLR cable to the performer’s position instead. The actual “unbalancing” step happens at the Romeo, and the Bravo simply acts as a dual 3-pin to single 5-pin combiner. Here, the configuration would be as follows:

Mixer » 2x XLR3 » Bravo » 1x XLR5 » Romeo » 1x XLR3 » Beltpack

The HPM Romeo

At half the size of the Bravo, the Romeo is right at home under a mic stand or next to a pedalboard. Its function is simple: take a 5-pin XLR connection from the Bravo, carrying a pair of balanced stereo signals, and unbalance them to be sent over a single 3-pin XLR cable. This allows the Romeo to be placed anywhere on stage, providing a stereo mix from the Bravo with only one cable.

The Romeo technically can be used on its own without a Bravo if you build an appropriate 2x XLR3 to XLR5 adapter. The pinout must be as follows:

XLR5 P1: GND
XLR5 P2: LEFT +
XLR5 P3: LEFT –
XLR5 P4: RIGHT +
XLR5 P5: RIGHT –

This will give you a simple stereo XLR3 pair to single XLR5 adapter. From there you can run an XLR5 cable from the adapter to the Romeo, without a Bravo.

I do recommend using the Bravo however as it is an all-in-one solution that allows you to use Romeos or use it standalone when near a stage box. Ultimately it’s up to you.

Parts lists

I provide the parts lists here in good faith and under the assumption that my work will not be used to generate profit without my consent. You are welcome to build your own HPM system, but you may not sell my designs nor any finished or unfinished products created with the aid of my designs.

If you wish to have me build them for you, I am happy to do so for a nominal fee.

Parts list (for one HPM Bravo):

Parts list (for one HPM Romeo):

Instructions

The assembly process is simple:

  1. Install the connectors. Orientation does actually matter for the Bravo!
    • One side gets two NCJ6FAH combo connectors.
    • One side gets one NC3MAH on the left and one NC5MAH on the right when looking at the connectors with the box in an upright position. Look at the pictures posted here for help.
    • For the love of God use the A-SCREW-1-8 with a Pozidriv bit. Regular Phillips bits will destroy the screws.
  2. Solder the transformers onto the PCBs. The instructions are printed on the PCB. Look at the pictures if you’re confused.
  3. Drop the PCB onto the chassis connector pins so that the transformers go inside the box. Instructions are printed on the PCB.
  4. Solder the PCB onto the chassis connectors.
  5. Assemble the steel box with the included screws and feet.

If you have any questions or comments, feel free to send me an e-mail at info@highpass.ca.

Gallery

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