Tube Preamp Reviews

Sidebar 1: Robert Harley's System

The LS5 Mk.II has been part of my reference system for the past few months. I also had on hand an original LS5 for side-by-side comparisons at matched levels, to refresh my memory, as well as a Sonic Frontiers SFL-2. The associated components I used to evaluate the LS5 Mk.II included Audio Research's VT150 tubed monoblocks—the best power amplifiers I've heard in my system. While I had some criticisms of the original LS5, I had absolutely no reservations about the VT150's wonderful musicality. Loudpeakers were Thiel CS3.6es—a moderately difficult load, and a loudspeaker that tends to be amplifier-sensitive—and Genesis II.5 loudspeakers, helped in the bass by the II.5's bass servo amplifier. Loudspeaker cable was primarily AudioQuest Sterling. Interconnects were 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 LS5 was done with a Sonic Frontiers SFD-2 driven by Theta Data Basic or Mark Levinson Reference No.31 CD transports via AES/EBU interface (the excellent Wonder Link). The Mark Levinson No.31 also drove a Mark Levinson No.30.5 Reference digital processor via the Audio Alchemy DTI Pro. Interconnects between the SFD-2 and 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