Stromtank S-4000 ProPower MK-II XT

COMPUTER-CONTROLLED BATTERY POWER SOURCE

- JASON VICTOR SERINUS

In my enthusiastic 2022 review of the Stromtank S-1000 ($16,900), I described the Stromtank as a computer-controlled lithium iron phosphate (LiFePO) battery array that, coupled with its AC inverters and all the trimmings, supplies clean, constant, stable off-grid AC power to hi-fi components. By softly depressing a single button on the front panel, Stromtank owners can easily switch from wall-connected mode (when the Stromtank's dimmable front-panel meter is blue) to a disconnected, battery-only state (when the meter is green). At the end of a listening session, users can return to blue mode to recharge the battery array.

When a Stromtank is fully charged, the needle on the meter rests at zero,² and a horizontal array of small green LEDs below the meter is fully illuminated. As battery charge dissipates, the number of illuminated LEDs decreases; the power meter's needle continues to rest at zero until the voltage starts to sag. If the Stromtank discharges fully during playback, the Stromtank automatically shifts from green to blue and begins to recharge. As it recharges, you can still play music, but the AC is no longer completely isolated from the vagaries of wall power.

After I spent many months with the Stromtank S-1000, Stromtank company founder/CEO/chief technical engineer Wolfgang Meletzky³ sent me an S-2500 Quantum MK-II ($29,000), which has enough capacity to enable longer green mode sessions. The S-2500 MK-II remained in my system through the spring of 2024, when it began to buzz while in green mode. Simultaneously, the power supply of my reference D'Agostino Momentum HD preamplifier also started to buzz, but at a maddeningly different frequency. Not even Arnold Schönberg would have been happy.