I have a G.T. Electronics (Groove Tubes) STP-B Studio Series Tube Preamp For Bass. These units were built for Groove Tubes by SWR, and it is the same preamp found in SWR's Studio 220 and SM-400 heads. 12AX7 tube Limiter Aural Enhancer Bass and treble shelving controls Four band semi-parametric EQ (31Hz-1.5Hz)(footswitchable) Variable crossover Balanced output Headphone jack Effects loop It is in excellent shape. I'll post some pictures soon. I am not using all the bells and whistles, so I am looking to convert to an Alembic F-1X or a Demeter. $275 shipped to the lower 48, or trade +/- cash for an Alembic, Demeter, or something tube driven.