VTL Siegfried Power Amplifier & 7.5 Series II Preamplifier

Power, Power, and More Power

If amplification happens to be the topic, then mentioning anything other than tubes in Luke Manley’s presence is apt to ensure that a look of mild distress starts to cross his face. Luke, who prizes the ability of tubes to act as voltage-controlled devices, can talk about their virtues for hours. Tubes, you could even say, run in his bloodlines. His father, David, was designing tube gear back in the 1960s and 1970s, when solid-state looked like the ticket for the future. Then, over a decade ago, Luke bought the Vacuum Tube Logic (VTL) company outright from his old man and set off on his own path. That path has remained resolutely grounded in the venerable tradition of two-channel high-end audio.

While other companies have moved on to newfangled things such as switching power supplies or shifted to an emphasis on the home-theater market, VTL, like Audio Research, has stuck to making what it knows best. That, as the company name indicates, is old-fashioned tubed equipment. Drawing on the basic circuit used by his father—two 6350 tubes and one 12AT7 in the input section—Luke first made a splash in the late 1990s by producing the 1250-watt Wotan amplifier, which is still probably the most powerful and refulgent tubed amplifier ever constructed, as well as a baby-brother 750-watt version featuring half the number of output tubes as its big brother—a mere twelve 6550Cs in each chassis. Both models received high praise in TAS. (I have been using the Wotan and 750 in an actively biamped configuration with the Magnepan 20.1.)

Now, in a bold attempt to reinvigorate the VTL line, Luke has made another foray into the Wagnerian sphere. The result is the massive and spectacular sounding 800-watt Siegfried monoblock amplifier.

The first thing that should be said about the Siegfried is that it marks quite a break with past VTL amplifiers. It represents an audacious attempt to marry old with new technology. The Siegfried seeks to accomplish the age-old dream of uniting the slam and transparency of solid-state designs with the blissfulness of tubes. It can be run in either tetrode mode, which I preferred, or triode, which halves the power output. The technology behind the amplifier forms the basis for VTL’s claim to have produced a fundamentally new high-powered tube amplifier rather than simply a modified design.

For starters, the models of yesteryear relied on brute force, regulating the input stage but not the output stage. The Siegfried, by contrast, regulates both. It boasts a precision power supply. The regulator, which is built around five MOSFETs, is placed between two massive banks of capacitors to ensure that the B+ voltage to the output tubes does not sag. In addition, the Siegfried has an automatic-biasing system—no more messing around with individual trim-pots and a voltage meter to bias the tubes manually. VTL says that the auto-bias system disengages whenever music is playing. When the amplifier is on, a microprocessor is supposed to ensure that the tubes are optimally biased. And that isn’t all. The microprocessor also can sense when a tube has a low-current fault, or is about to blow. If the tube has a lowcurrent fault, the microprocessor shuts down just that tube. If the tube is about to blow, the microprocessor shuts down the entire amplifier. In either case, the tube that caused the problem is indicated so that it can be replaced. No more guesswork about which tube quietly failed or went up like a Roman candle. (Having seen more than one tube go nuclear in other amplifiers as I raced over to shut the amplifier off, I can attest that this is entirely a good thing. The sound of a B+ fuse blowing after a tube fails is not for the faint of heart—more than once I’ve been convinced that my tweeter simply had to have blown, though so far it hasn’t.)

Should the amplifier itself fail, you can hook up your computer to it via a bi-directional RS232 control port and send the diagnosis to VTL. In essence, the amplifier is like an Erector Set; any part can be dismantled and returned to the factory for repair without sending back the entire unit. The auto-bias and control hardware can be removed with basic tools—which, incidentally, come supplied by VTL in a separate case inside one of the amplifier crates—leaving the amplifier core and power supply intact as the components least likely to fail. (The amplifier requires 20-amp power cords, and the stock supplied cords should be replaced with something heftier—I used Shunyata Helix Alpha.) Unlike the older units, the Siegfried could not be more user-friendly. Nevertheless, the Siegfried, as befits its name, is hardly a cuddly amplifier. Instead, it looks intimidating Weighing in at over 200 pounds, it’s no lightweight—and it doesn’t sound like one, either.

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