ALM HPO ()
That moment when your modular rig finally sounds open and alive through headphones. It's a utility, and it's the quiet hero of your skiff.
Overview
The ALM HPO is also known as the ALM019 HPO or ALM HPO Stereo Headphone Output Module. It isn't flashy. It's a no-frills, super slim headphone output for Eurorack modular synthesizers, designed by ALM/Busy Circuits for people who need a compact, reliable way to monitor their patches without eating up panel space. It's just 2hp wide, so it fits into the tightest skiff builds where every millimeter counts. Owners report using it for headphones and also as a line-level output to feed external gear like the Synthstrom Deluge or audio interfaces.
There are no expansion points, no balanced outputs and no extra routing options. You get a single 1/8" (3.5mm) stereo headphone jack, a volume knob, and the ability to double a mono signal into stereo. 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.” It may not have the headroom or dual high-impedance drive of something like the WMD Pro Output, but many find its sound perfectly transparent. 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.”
It has 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. Some users have successfully used TRS cables with proper settings, but the outputs themselves are unbalanced. The Joranalogue Transmit 2, by comparison, offers balanced XLR outs. The volume knob is also 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 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.”
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. Used units have been observed selling for $75 in “like new” condition, while new units list around $80.12, which suggests stable pricing in the current market. One forum user noted it was £70 ($82) less expensive than the Joranalogue Transmit 2. There's no data on original MSRP, production years, or common failures, and no widespread reports of circuit issues. There isn't much in it to go wrong. It's widely regarded as sounding “perfectly fine” or “great” depending on who you ask.
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