XIN SuperMini-IV

If you want something smaller and thinner, then SuperMini-IV is the favorite. You still get all the features of SuperMacro-IV, including 4 switches (internal though), internal charging (not fast though) and OPAMP rolling (dual only though). With the latest 5.5V boost technology, its 2 AAA cells can power almost any headphones. Its DC jack allows you to use 3-7.5V external power. Battery life is 120 hours for the default tube-alike chipset or 50 hrs if DC-DC boost is enabled.

2.4"x1.9"x0.6", 2.0 oz (w/batt.), 2 AAA, internal charging, 5.5V boost, jumpers for 4 features, dual opamp sockets.