Featuring microphone-level, line-level, and hi-Z instrument inputs, the 2BA-221 continuously variable impedance microphone preamp utilizes separate and individually controlled solid-state input controls to mix the microphone input with the hi-Z or line input into the variable vacuum tube output. Mix them together through the 12AX7A/ECC83 vacuum tube output or seperately through individual solid-state outputs. The 2BA-221 also features a stackable input design; multiple 2BA-221's can be linked together to form a modular mixing device with individual outputs, inserts per channel, and a final vacuum tube gain stage. Its swept highpass filter, multiple simultaneous tube and solid-state outputs, insert jack, and internal power supply make the 2BA-221 a powerful tracking and mixing tool.