The variable-impedence Summit Audio 2BA-221 Tube Mic and Line Module is a microphone preamp that has individual controls to mix mic with Hi-Z or line inputs for variable vacuum tube output. You can mix them together through 12AX7A/ECC83 tube output or separately through individual solid state outputs. A stackable input design allows multiple 2BA-221s to be linked for a modular mixing device with individual outs, inserts per channel, and a final vacuum tube gain stage. Its swept high-pass filter, multiple simultaneous tube and solid state outputs, insert jack, and internal power supply makes the 2BA-221 a powerful tracking and mixing tool.