Tube Power Amp Reviews

Sidebar 1: System

The VT-150s drove Thiel CS3.6es—a moderately difficult load, and a loudspeaker that tends to be amplifier-sensitive. Loudspeaker cable was primarily AudioQuest Sterling. Interconnect was Expressive Technologies IC-1 or AudioQuest Lapis.

Source components included a variety of digital processors and transports, but most of the critical evaluation of the VT-150s was done with a Sonic Frontiers SFD-2 driven by Theta Data Basic or Mark Levinson No.31 transports via AES/EBU interface (the excellent Wonder Link). Interconnects between the SFD-2 and Audio Research LS5 were AudioQuest Diamond. Because the SFD-2 is balanced in the digital domain, the LS5 is fully balanced internally, and the VT-150 has balanced topology, the signal is processed from before the DACs all the way to the loudspeaker as a fully differential signal. From the SFD-2's output stage, the signal path was also pure tube.

The analog front end was a Well-Tempered Turntable fitted with Lary Pederson's new reworked Well-Tempered Arm and an AudioQuest AQ7000nsx moving-coil cartridge. The phono stage was the Vendetta Research SCP2B, whose single-ended output was converted to balanced by the BL2 before driving the LS5. Alternately, I used ARC's PH2 phono stage. The analog front end sat on a Merrill Stable Table.—Robert Harley