Vacuum Tube Logic TL-7.5 Reference line preamplifier Series II Follow-Up, June 2007
Just as I was submitting my May 2007 Follow-Up on the VTL TL-7.5 Series II Reference line-stage preamplifier ($16,500), a flurry of e-mails from VTL's Luke Manley passed through Stereophile HQ. I had driven the TL-7.5 with power supplied by AC conditioners from Shunyata Research and Audience. VTL had discovered that the TL-7.5 II is sensitive to power conditioners in some installations, so John Atkinson and I agreed that I would explore and comment on any interactions between the preamp and my conditioners.
Resetting the clock: In my Follow-Up, I'd said that the TL-7.5 Series II surpassed the original in terms of resolution and neutrality, produced a larger, more open soundstage, and was significantly more dynamic, particularly at the frequency extremes. I also noted, however, that it didn't "vanish" into my system the way the original had. The new model's wide-open dynamics and slightly forward perspective always called attention to its presence.
In revisiting the TL-7.5 Series II, I listened to the system in three configurations: the entire system fed AC through a power conditioner, the preamp alone plugged into the wall, and the entire system plugged into the wall. I used the Shunyata Hydra and Audience AdeptResponse power conditioners and their matching AC cords, and when the VTL was plugged into the wall, I also tried Synergistic Research's AC Master Coupler cord—as well as the VTL's supplied cord and the Shunyata and Audience AC cords.
After a month of listening, comparing, taking careful notes, and agonizing over sonic subtleties, I concluded that the TL-7.5 Series II was affected by the use and choice of power conditioner and/or cord—but only slightly. In fact, it was less affected by these than most components I audition, including the Sutherland Direct Line Stage I reviewed in the September 2006 issue, and the Placette Active Line Stage (review in progress), neither of which is particularly finicky about its input power.
The usual caveats apply: This was in my room, using my system, my software, and my ears. Your results may vary. However, my AC supply is quite good. I live in a rural area, and a separate, dedicated subpanel feeds my audio system, with close attention paid to minimizing and equalizing all AC wiring runs, and ensuring a solid, consistent ground.
The TL-7.5 Series II, as well as my other components, sounded cleanest, fastest, and most detailed with the Audience conditioner and cords. Feeding it directly from the wall softened the focus and transient precision just the slightest bit, and slightly widened the soundstage. The TL-7.5's performance with the Shunyata setup was somewhere in between. A phrase often used to describe a close race, "you could throw a blanket over all of them," is far too gross to use here. You could have covered the range of differences I heard with a hankie, and a very small one at that. There were no differences even remotely comparable to the performance gap between the original TL-7.5 and its contemporaries, or between the TL-7.5 and its own Series II.
The last word: As noted in my original Follow-Up, the Series II significantly improved on the original's performance in some areas, particularly resolution, speed, openness, and dynamics at the frequency extremes. These improvements were significant, immediately obvious, and consistent, regardless of how I fed AC to the unit. Despite these gains—or perhaps because of them—the Series II didn't "vanish" into my system as the original had. It consistently imposed a sonic thumbprint on the sound that the original had not, regardless of whether or not I used a power conditioner and/or an aftermarket AC cord.
VTL's TL-7.5 Series II Stereo Reference line stage is one of the very best high-end components available at any price. Anyone assembling an ultimate system should have it on his or her "must audition" list, and owners of the original TL-7.5 should arrange to hear a Series II at home and consider upgrading their units. The Series II upgrade costs $4500 and significantly improves on the original's performance in several key areas (see my Follow-Up in the May issue), and while those improvements weren't perfectly synergistic with the balance of my system, they were dramatic, and confirmed that VTL's design team is at the vanguard of redefining what is possible.—Brian Damkroger