Tube Power Amp Reviews

"How natural the sound," wrote Jonathan Scull in March 1994, in his Follow-Up on the original Jadis JA 200 monoblock amplifier, which then cost $18,990/pair. "How easy it was to follow the musical line and fall into the music. How deep, controlled, tight, and satisfying the bass. How magnifique the midrange—the traditional strength of the Jadis presentation. How full and satisfying the lower midrange. How open, airy, how right the highs—not at all hard, but very extended and natural. How involving their presentation. How full, how harmonically correct, how wonderfully compelling. How magical."

Dick Olsher's original review of the JA 200, published in November 1993, hadn't been as sunny. Dick had found the lower midrange "somewhat meager," the sweetness, sheen, and vitality of violin overtones and soprano voices "blunted" and "subdued." Nonetheless, he called the JA 200 "one of the most musically appealing amplifiers money can buy. It's certainly the most impressive high-power tube amp I've heard."

With such praise still in mind, in 2002 I bought a used, considerably less expensive Jadis Defy7 Mk.II stereo amplifier (approximately $6500 when new) made in about 1993, and repeatedly risked electrocution in numerous expletive-laced sessions of tube biasing that also necessitated backbreaking heavy lifting. A glutton for punishment, I eventually upgraded to the Defy7's successor, the DA-7 Luxe (approximately $11,000 when new, discontinued). After changing some of its tubes and internal wiring at the suggestion of Jadis' former North American distributor, I finally caught a glimpse of the Jadis "magic."

In April 2017, at the AXPONA audio show in Chicago, in the room of Kyomi Audio, a Chicago-based dealership run by pianist George Vatchnadze, I heard brand-new Jadis JA200 Mk.II monoblocks ($33,900/pair). Despite their insufficient break-in, I was moved to write: "I was so taken by the sound that all I wanted to do was sit and listen, and then listen some more. And it wasn't just the fabled Jadis midrange that had me in its grip; the bass was also quite good, and the highs divine."

I learned that the JA200 Mk.II is an auto-bias design; remembering how close I had come, years before, to permanent injury, that feature seemed a gift from the gods. In addition, the amp's adjustable output transformer strapping, designed to work with speakers rated from 1 to 16 ohms, suggested that it would mate well with my Wilson Audio Specialties Alexia loudspeakers, whose impedance drops to 2 ohms in the bass region. In his Measurements sidebar to Dick Olsher's review of the original JA 200, Thomas J. Norton had observed that "The Jadis's output impedance was admirably low for a tube amplifier." This, too, indicated that JA200 Mk.IIs might work well with the Alexias, given that amps of lower output impedance have an easier job driving speakers with complex impedance curves.

The power behind the gold (brass, actually)
Like the founders of so many other high-end audio companies, French music lover and amateur radio operator André Calmettes began by designing and building an amplifier for his own use. Several friends heard it, and asked him to build copies for them. Demand grew. In 1983, Calmettes and a friend cofounded Jadis.

The new company's first production model, the JA80 push-pull power amp, is still in production, albeit in what Calmettes's son, Jean-Christophe "JC" Calmettes, calls an "evolutionary" form: the JA80 Mk.II. Like all of Jadis's long-standing models, the JA80's basic circuitry and Jadis-made output transformers remain unchanged. The circuits of nearly all Jadis amps share the same basic push-pull design, have the same number of stages, and use only a small amount of negative feedback. The goal is to maintain the Jadis sonic signature throughout the line.

"We wind and pot our transformers ourselves," JC explained when he and Richard Colburn, of Jadis's US distributor, Bluebird Music, visited me in Port Townsend, Washington, to install the JA200 Mk.IIs. "The output transformer is the heart of the amp. Its quality is of significant importance when it comes to speaker matching.

"All stages in our amps are fed by our very strong power supply. We use big transformers and a lot of capacitors to produce the cleanest possible signal. Our super-low output impedance causes our amplifiers to exhibit the same low output impedance of many high-end solid-state amplifiers." Jadis is so confident in their transformers that they come with lifetime warranties.

Because Jadis's website and the JA200's manual are short on technical details, and JC's command of English is limited, I asked Colburn to confirm which parts of Dick Olsher's 1993 technical description of the JA 200 also describe, a quarter-century later, the JA200 Mk.II. Those parts are:

"The heart of any power amp is its power supply—the reservoir of current for the output stage. . . . Jadis did not skimp here in terms of parts quality or reservoir rating. Solid-state bridge rectification is used exclusively, followed by an RC filter network. Filament voltages are regulated, but, as is almost always the case, plate-supply voltages are unregulated.

"Using the two halves of a 12AU7A dual-triode tube, the input/phase-splitter stage comprises a Schmitt cathode-coupled circuit. This clever push-pull stage has rarely been used in audio amps, primarily because it requires two tubes and offers only moderate amplification. It was originally intended for scientific instruments (eg, oscilloscopes) for which extended low-frequency response is desirable. Coupling caps are not required, and hence frequency extension to DC with good balance is easy to achieve with this circuit. The phase splitter is DC-coupled to a driver stage that uses a 12AX7A dual-triode. Thus, the entire front-end of the JA 200 is DC-coupled."

In the JA200 Mk.II, launched in 2016, the power transformer and cathode circuit have been modified to accept Russian-made Tung-Sol KT150 power tubes. The chassis are made of 304L polished stainless steel, and the characteristic Jadis golden plating is brass.

Setup
Listening to music in stereo with the JA200 Mk.IIs requires not two but four chassis: each monoblock has its own outboard power supply, attached to the amp proper via a supplied umbilical cord. At the center of the front panel of each of the four boxes comprising a pair of JA200 Mk.IIs is a single power-on light. When the Power switch on the left side of a power supply's front panel is flipped up, the tubes are warmed up to operate at 30% of capacity, and the lights on the amp and its supply glow red. After 10–15 minutes, it's okay to turn the switch on the right side of the supply's front panel from Standby to Operate, to run the tubes at full capacity. Doing so turns both indicator lights green. JC told me that it was unnecessary to wait longer to hear all the JA200 Mk.IIs had to offer, but I invariably did. Jadis cautions users to always turn on their preamplifiers before turning on the amps, and to reverse that procedure to turn the amps off. I did as instructed, using the dCS Vivaldi DAC's volume control instead of a preamp.

After we'd unpacked the amps—they'd already been broken in—JC Calmettes removed their tube cages and installed the total of 24 tubes. The review samples each sported 10 KT150 power tubes—the most powerful JC could supply. "When I talk about value with tubes," he said, "a tolerance of 7 to 10% is normal." This helped explain why he told me that the JA200 Mk.II can output 170W, though its manual and the Jadis website specify 160W. Written on each tube's box was a number corresponding to its proper socket in the amp, as indicated in the manual.