From LR Baggs:

The M1 Active’s plug-and-play design features a preamp with audiophile circuitry for that pure acoustic sound we are known for. The built-in electronics boosts the pickup’s output for a full and direct signal to any acoustic amplifier or P.A. system, eliminating the need for any external preamps. The M1 Active includes a volume control and adjustable pole pieces for perfect balance and tone between the strings.