[goto2003]

I have been using my SM for more than 200 hours and it's fully burned in. Though it sounds fantastic with batteries alone, I would say it performs better with AC power than with batteries. With the AC adaptor plugged in, the SM deliver more consistent and better separated sound image while playing complex music. And SM seems to sound the best when plugged in the AC adaptor with rechargeable batteries in, but I am not quite sure as the sound difference with/without batteries in is subtle. Is it just because both AC power and batteries provide current for SM when playing complex music?

 

[Earwax]

On the fixup site he explains the power-saving battery only mode vs. the AC/DC full power mode.
Quote:

The DC-in jack is meanwhile a switch for battery-save mode. It controls two electronic switches that control the current of BUF634s. If nothing plugged into this jack, SuperMacro works at battery-save mode. The BUF634s work at relatively lower current and bandwidth to save battery. When you are home and plug in the AC adapter, SuperMacro will automatically turn off the battery-save mode. The BUF634s then work at relatively higher current and bandwidth for better sound. If you don't care much about battery life, you can defeat the battery-save mode by using a dummy DC plug or simply a plastic tube. See benchmarks for the performance difference, which is not that big; so I suggest you leave the battery-save mode enabled when you are using batteries.