The Hattor Audio Tube Active Stage is specifically intended for use with the Hattor Audio Ultimate Passive Pre (The Big).  The price for the unit, $1,900, is in addition to the price for the passive preamp.  However, you can use this unit as a standalone buffer/gain stage with other passive preamps, or as the buffer for a component with very weaker output.  

The Tube Active Stage uses the finest parts available from MIFLEX, SIZEI toroidal power transformer, AMRG resistors and quality jacks (either RCA or XLR). 

Tubes - ECC82 (12AU7/5963) from JAN PHILIPS

The stage has sufficiently low output impedance to drive two power amplifiers.