ALM HPO ()
That moment when your modular rig finally sounds open and alive through headphones — more than just a utility, it’s the quiet hero of your skiff.
Overview
The ALM HPO — also known as the ALM019 HPO or ALM HPO Stereo Headphone Output Module — isn’t flashy, and it’s definitely not trying to be. It’s a no-frills, super slim headphone output built for Eurorack modular synthesizers, designed by ALM/Busy Circuits for people who need a compact, reliable way to monitor their patches without eating up precious panel space. At just 2hp wide, it’s skiff-friendly by design, fitting snugly into even the tightest builds where every millimeter counts. Owners report using it not only for headphones but as a line-level output to feed external gear like the Synthstrom Deluge or audio interfaces, making it a dual-purpose workhorse despite its minimal footprint.
It’s not trying to impress with bells and whistles. There are no expansion points ready to go, no balanced outputs, no extra routing options — just a single 1/8" (3.5mm) stereo headphone jack, a volume knob, and the ability to double a mono signal into stereo. That simplicity is part of its charm. One user summed it up: “I use the HPO in a small on-the-side case, and it does what it’s supposed to do.” Another put it more emphatically: “HPO is great. I'd go as far to say it's almost the standard for a headphone out in euro.” And while it may not have the headroom or dual high-impedance drive of something like the WMD Pro Output, many find its sound perfectly transparent — even transformative. One owner noted a dramatic difference when switching from their MOTU interface’s headphone output: “when I don’t go out of the rack and use the ALM HPO headphones module it sounds great. The sound really opens up.”
Still, it’s not without quirks. The 3.5mm output means you’ll likely need 1/8"-to-1/4" male-to-male TR phono cables to connect to full-size headphones, and while some users have successfully used TRS cables with proper settings, the outputs themselves are unbalanced — a limitation when compared to modules like the Joranalogue Transmit 2, which offers balanced XLR outs. There’s also a practical concern: the volume knob is small and can be slow to reach in an emergency. One user warned, “if I ever get an unexpected audio burst, it will take me ages before I get to the volume knob.” Another ran into issues with hot signal levels when connecting to an iPad, reporting the input came in “VERY hot” with “almost no room for adjustments of that little knob.” So while it’s trusted and widely used, it demands a bit of caution and cable prep.
Specifications
| Manufacturer | ALM/Busy Circuits |
| Product type | Headphone output module for Eurorack modular synthesizers |
| Width | 2hp |
| Outputs | 1/8" (3.5mm) stereo headphone output |
| Output type | Unbalanced |
| Features | Volume control, ability to double up a mono signal into stereo |
| Design | Affordable super slim and skiff friendly no frills |
| Expansion points | None ready to go |
Collectibility & Value
The ALM HPO isn’t a collector’s grail, but it’s a staple — the kind of module you don’t notice until it’s missing. Used units have been observed selling for $75 in “like new” condition, while new units list around $80.12, suggesting stable pricing in the current market. One forum user noted it was £70 ($82) less expensive than the Joranalogue Transmit 2, highlighting its value as a budget-conscious choice. There’s no data on original MSRP, production years, or common failures, and no widespread reports of circuit issues — likely because there’s not much to go wrong. It’s simple, solid, and widely regarded as sounding “perfectly fine” or “great” depending on who you ask. If you're building or touring with a compact modular setup, the HPO isn’t a luxury — it’s a quietly essential link in the chain.
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