Octave Audio RE 290 power amplifier
I've chosen roughly 85% of the components I've reviewed for Stereophile, those choices made on the bases of what I find interesting, and what I think readers would like to know about. It's as simple as that.
I'd never heard of Octave Audio until JA e-mailed to ask if I'd like to review one of their amps. The RE 290 intrigued me because it was built around the new KT120 tube (which is also my new favorite output tube), it costs about the same as the Audio Research Reference 150 amplifier ($12,995) I wrote about in July, and I was interested in Octave's Black Boxes: add-on devices that can boost the capacitance of an Octave amp as much as tenfold. I contacted Michael Manousselis of Dynaudio North America, Octave's US distributor, and asked for a silver RE 290 (it also comes in black) and a Super Black Box.
Perfect Octave
Octave Audio is the brainchild of its founder, executive director, and chief designer, Andreas Hoffman. The company prides itself on engineering most of its electronic components in-house, and every Octave product is handbuilt at the company headquarters in Karlsbad, Germany.
The RE 290 stereo power amplifier is the successor to the RE 280, introduced in 1990. A push-pull pentode design, the RE 290 delivers 100Wpc RMS output power into 4 ohms and is based on the new KT120 power tube. The RE 290 offers only one transformer tap per speaker, presumably optimized for 4 ohm loads. However, stability into low-impedance speakers is achieved through Octave's output transformers, which are designed and wound in-house. A switch on the rear panel allows the user to choose between High Power mode (for use with the KT120) and a Low Power mode of 70Wpc (if using KT88, KT90, 6550, or KT100 tubes). The RE 290 can use EL34s, but only with speakers with impedances above 4 ohms. Loads below 2 ohms are not recommended for use with the RE 290 with any of the tubes it can use.
Pushing the left-hand knob on the amp's faceplate turns the amplifier on. The bias of each output tube is checked using the right-hand knob. With the tubes warmed up but without music playing, you turn the knob to select each of the four output tubes in turn, each time illuminating one of the five small LEDs on the top of the amplifier behind the tubes. You dial in the bias for each tube with its precision multi-turn pot until the middle, green LED, not the flanking yellow or red LEDs, lights. It was so easy to check tube bias with the RE 290 that I did it way more than I needed to. After setting the initial bias, only once during my listening did I have to adjust a tube, and then only slightly. I believe that perfectly biased tubes are crucial to getting good sound from a tube amp, and tube bias can drift for any number of reasons. I'm getting tired of poking around tube amps with my voltmeter, burning my hands on the tubes and wondering if my bias is correct. Octave's approach to tube biasing should be the standard for all tube amps—it's easy, effective, and elegant.
The RE 290 also features what Octave calls ECOmode, a power-saving feature. Activated by a switch on the amplifier's rear panel, ECOmode reduces heat and unnecessary power consumption when the RE 290 is switched on but not in use. This system reduces power consumption when the amplifier hasn't received a signal for 10 minutes. In this sleep mode, the RE 290 draws only 20W idle power, compared with 180W in normal operation. The RE 290 produces virtually no heat while in ECOmode, and the heater voltage and the high voltage for the power-amp section are switched off. When the RE 290 detects a signal, the ECOmode circuit turns it back on, with a warm-up/start-up delay of about 30 seconds.
I loved this feature. Not only did I never have to remember to turn off the amplifier, but I found that the warm-up time for the tubes, and subsequently the time it took the amp to sound its best, was much shorter than for any other tube amp I've used when turned on from a cold start.
The RE 290 is equipped with a multistage Soft-Start/Turn-On protection circuit claimed to considerably extend the lives of components and tubes by protecting them against the stresses caused by the typically high currents present during turn-on. The RE 290's input and output tube heaters, as well as its high-voltage rails, are controlled to ensure that the conduction of the output tubes and the input-stage voltages are constantly monitored by what Octave calls its Power Management System, designed to protect the tubes, rectifiers, electrolytic caps, switches, etc., against excessive turn-on current.
The RE 290 offers true balanced operation via its XLR inputs, but will also take a single-ended signal via its RCA jacks. A switch on the amplifier's rear lets you toggle between the two. The two speaker terminals are robust and well spaced, which made it easy for me to get a good connection with my Kimber Kable BiFocal speaker cables, even when I couldn't easily reach the Octave's rear panel.
The RE 290's design, fit, and finish are topnotch. Pictures don't do it justice, but the RE 290 is the most understated and elegantly designed amplifier I've ever used. The quality of its exterior parts and assembly was a joy to behold; it's the sort of amplifier you want to proudly display in your living room, rather than tuck away in the darker recesses of your Man Cave. It's also quite small, and one of the denser amps I've lifted. Every time I was about to lift it, I thought, "Oh, aren't you a cute little amplifier? Yes, you are! I'm just going to pick you right up!" Wrong. Lifting this 54-lb amp had me occasionally acting out a scene from The Sword in the Stone; let's just say I hadn't been cast as the young Arthur. Luckily, two well-placed handles on the top panel, along the sides, make moving it pretty easy—as long as you remember that this is one heavy amp.
Everybody, Everybody Strike It Up
The RE 290, like all Octave amplifiers, is available with two intriguing add-ons. The Black Box ($1200) and Super Black Box ($3500) hook up to the amplifier via an umbilical cord and, respectively, increase the capacitance four- or tenfold. Octave claims that the added capacitance allows the RE 290 to more ably drive speakers with impedances as low as 2 ohms. I spent much of my time with the RE 290 hooked up to the Super Black Box (SBB), and gave both amp and Box some 200 hours of break-in before I began taking any listening notes. In my experience, capacitors need lots of break-in to sound their best.
I ran the RE 290 directly from my Bel Canto Design e.One DAC 3.5 VB Mk.II digital/analog converter via a Sain Line Systems Reference balanced cable. The DAC 3.5 was fed digital data from a Bel Canto e.One CD2 CD transport or a Sony Vaio laptop via Bel Canto's Light Link USB bridge, and analog from a Clearaudio Ovation turntable.
RE 290 with Super Black Box
During my time with the RE 290 and the Super Black Box, I edited and coproduced an album of mostly unaccompanied choral music performed by the Portland State University Chamber Choir, conducted by my friend Ethan Sperry. Most of the sessions were produced by Grammy-winning producer Steve Barnett, while I batted cleanup and helmed the final two sessions. I then went through the session files, picked the best takes, and edited, mixed, and mastered the album. The disc is a collection of works ranging from 20th-century Russian Orthodox music to new works by my favorite young composer, Eriks Esenvalds, and from a tour-de-force arrangement of Leonard Cohen's "Hallelujah" to Haitian voodoo music.
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Source : stereophile[dot]com
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