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AMB χ1: Complete

Yesterday evening I finished up retrofitting my AMB Mini³ headphone amplifier with the AMB χ1. This is a battery management board which replaces the original charging circuitry and 9VDC NiMH battery resulting in a considerably faster charge and longer runtime. By using a Lithium-ion polymer (LiPo) battery the runtime has been extended to ~25 hours (for my high performance version) while the charging time has been reduced to ~1.5 hours. ( claims that this is a 10x improvement in charge time and a 3x improvement in run time.)

The photo above shows the rear end of the Mini³ without the end panel, showing the two LiPo packs (the silver / strapping tape pieces) the edge of the χ1 PCB (top), and the bi-color charge/fault indicator LED. Assembling this involved removing a small handful of diodes, regulators, and resistors from the Mini³’s PCB, adding a header in place of the LM7812 voltage regulator, and plugging the χ1 into that. As documented on AMB’s site building the χ1 was pretty straightforward and involved only a handful of medium-size (and easy to solder) surface mount parts. I almost wish the design was all surface mount so I wouldn’t have to deal with as much through hole, but I understand his desire to not go all-SMT in order to keep things easy to assemble.

I use this headphone almost every day at work while listening to music from my iPod, and thus far it’s sounded great. However, due to my weird patterns of not being in the office I haven’t been leaving it plugged in for long enough lately, so whenever I’ve been wanting to use it I must plug it in to use it. Hopefully this new version with a shorter charge time and longer run time will sort out that problem.

Now I want to build something else, but I’m not really sure what. I’m somewhat considering a beefy Class A amp and new monitor speakers for my desk at home, all nicely integrated with a USB DAC and tucked under my desk. I could even build the monitors themselves, but this would end up being a pretty big project and I’m not sure it’d get me enough benefit…

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