I have owned my FAP-V1 for over five years and have been absolutely delighted by it's sound quality! A smooth, holographic, full-bodied sound that is simply a joy to listen to, be it in it's Pro Logic II processor mode or simply as a straight two channel preamp. It uses nine 6N1P tubes and a 5AR4 rectifer. There is no schematic available due to the unit's proprietary design, so I'm not sure how the 6N1Ps are used in the circuit. The outstanding build quality on this unit is in a class by itself, and reflects it's cost no object design—I'm just glad I got mine second hand. I'm very much into surround sound, and the all-analog Pro Logic II processing blows away any and all digital Pro Logic II processors, no matter how well made they are. It's simply the circuit that is being used. I've retired my Sansui QSD-1 quad synthesizer since getting the FAP-V1, that's how good it is. Jim Fosgate really outdid himself creating this unit. This is a keeper for life!