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
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COMMENTS
... 40dB below the fundamental, one has to wonder whether you're listening to the music or to the distortion?
Is it those relatively high levels of both harmonic and inter-modulation distortion that contribute to the allegedly "magic" sound quality?
Did RH ever compare the VT-150 with the Threshold S/550e?
These ARC VT-150 mesurements are somewhat similar to recently reviewed ARC Ref.160M and ARC Ref.160S (reviewed in Feb. 2020 issue) :-) ........
BTW .... A rose by any other name still sounds (smells) the same :-) .........
Sound to die for (S2D4) :-) ........
Not sure how that VT-150 SE differs from the VT-150, but it's interesting regardless.
More commonly the output transformer of an "ultralinear" configured amplifier (eg Dynaco MkIV) simply includes taps on the primary to connect to the screen grids, so those taps share the same B+ power supply voltage with the anodes, which requires suboptimal voltage on the anodes to prevent too much at the screen grids, and that compromise often results in lower than optimal voltage at the anode and higher than optimal voltage at the screen grids with shortened life and degraded performance. This amplifier (at least the SE edition of this amplifier) takes the better approach of providing a separate center tapped winding for the screen grids, allowing those to be operated at reduced power supply voltage than the anodes, which significantly reduces nonlinear distortion and lengthens usable life of the output tubes. Also there are four separate cathode feedback tapes, one for each output tube. For an unchanged level of global feedback, utilizing cathode feedback tapes further reduces nonlinear distortion and reduces output impedance by including the transformer in a local degenerative feedback loop with the output tubes' cathodes.
I had this amp, worked well on my watt puppies, wounder how it would sound today and if it will hold against current ARC.
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