Tube Power Amp Reviews

Let us pretend . . . you have a pair of loudspeakers that have proven themselves to sound articulate and musically responsive in your room, without excess boom, bloom, or frail leanness. They mate with your décor and impress your friends. But maybe you're bored, and feel certain that your speakers would sound better with a better amplifier than the one you have now. Maybe you feel an urge to spend money? Perhaps a new amp will make your records sound the way you imagine they should sound?

I have had these thoughts many times.

The good news: It is much easier to find the right amp for your speakers than it is to find the right speakers for your amp.

The bad news: Finding the perfect amp for a beloved pair of speakers can still be difficult, because every amp you try will make your speakers sound different—better, or worse. Your perfect power amp is surely hidden in plain sight, somewhere on the Internet or at your local audio salon—but you don't know where to begin looking.

You might start by visiting your local dealer, and telling him about those speakers you love, and about your psychoacoustic eccentricities, and about your budget. Then listen—to him, to the advice of his salespeople, to his demonstrations—with relaxed ears and an open, trusting mind. I know this to be a good plan.

But before you begin that process, I recommend that you try what I do all the time: Ask a lot of questions that represent your concerns, and study a wide range of anecdotal accounts of amplifiers and speakers by interrogating your friends, audio-salon gurus, and random Facebook ideologues. Study your favorite reviewers, blogs, and audio forums. This is usually fun, and can be a mind-expanding way to make new friends. These conversations won't solve your problem, but they should make you less lonely, and may narrow the field to a manageable list of choices. If your loudspeaker model has been around a while and is reasonably popular, there will be scores of other owners willing to share their experiences with various amps—and for me, shared experiences are always the best place to start.

Then, armed with shared wisdoms, visit your dealer, tell him what you've learned anecdotally, and begin listening to music with greater confidence.

Recently, while reviewing Falcon Acoustics' LS3/5a speakers (footnote 1), I asked this question of an online forum devoted to the BBC's LS3/5a Type II minimonitor: "What are the best amps to drive these new Falcons?" I received dozens of suggestions, but there was little consensus. Most people mentioned old stuff: the Musical Fidelity A1, the Naim Nait, the Sugden A21, the Harman/Kardon Citation V, the Bedini 25/25, etc., etc. But one amplifier brand was mentioned more often than any other, and it was not a maker of classic, discontinued models now available only used and in need of expensive rebuilds: "Try a PrimaLuna!," many forum respondents said. Some suggested that I try the DiaLogue Premium HP integrated amplifier ($4399), reviewed two years ago by Stereophile's most charming audio sage, Robert Deutsch.

I knew little about PrimaLuna, so I called their US distributor, Kevin Deal of Upscale Audio, and told him that my peeps insisted I try a PrimaLuna amp with the Falcon LS3/5a's. He told me that PrimaLuna amplifiers are designed in the Netherlands, made in China, built like tanks, and work very well with the Falcons. He recommended their lowest-priced, basic stereo power amplifier, the ProLogue Premium ($2199).

Description
Long ago, I repaired vintage tube amps for a living. It was zero fun. I hated that lonely, underpaid drudgery. Worse, I didn't like the sounds of most of those amps—with two extremely memorable exceptions: the Western Electric 91A (single-ended, 300B tube) and the Marantz 8B (push-pull, EL34 tubes). The 91A looked industrial-hip and delivered the best midrange ever—but even long ago, it was rare as unobtainium. I serviced a lot of elegant-sounding Marantz 8Bs, and felt honored to be even touching this venerable Sid Smith design. For me, the 8B is the best-looking amp ever. It played my Rogers LS3/5a's with such satisfying musical charm that I wish I had one now—if only to put on a shelf for display.

Why wouldn't I put an 8B in my system? Because, while the ProLogue Premium can't match the museum-quality beauty of the 8B's classic case, the PrimaLuna has a 21st-century tube spirit that can reproduce recordings with levels of high-frequency purity, low-frequency force, and pulsing musicality that exceed the venerable Marantz in every way.

The ProLogue Premium acknowledges its 8B influence with its steel-box–covered transformers, elegant tube deck, and hand-rubbed lacquer finish. Like the 8B, the ProLogue Premium uses solid-state rectifiers and push-pull EL34/6CA7 pentode tubes operating in class-AB to achieve 35Wpc. Inside, the PrimaLuna boasts hand-wired components of a high quality similar to that of the classic Marantz.

When I was done admiring the point-to-point wiring, choke-filtered B+ supply, and Nichicon capacitors, I noticed all the little green boards containing PrimaLuna's Adaptive AutoBias circuitry. This is neither an auto-bias with a cathode resistor nor an "intelligent" fixed-bias circuit, but a unique logic circuit that monitors the operating environment and condition of each output tube, and keeps each one locked to the flattest part of its plate characteristic. PrimaLuna claims that, with the Adaptive AutoBias and their soft-start circuits, "you never have to worry about biasing your amp ever again, and the need for matched tubes is eliminated." Kevin Deal says that these circuits also greatly extend tube life, and that "All PrimaLuna amps give you about 18W from each EL34, 20W from a KT88, 21W from a KT120, and 24W from a KT150." All this with no global negative feedback.

The ProLogue Premium has a ³/₈"-thick brushed-aluminum front panel with a green LED power-on indicator recessed in its center. The on/off switch is at the front of the left side panel, and the switch for selecting between EL34 and KT88 tubes is in the matching position on the right. Voltage gain, phase splitting, and the driver stage are handled by two ECC82 or 12AU7 twin-triode tubes per channel.

Comparing the rear panels of the Marantz and PrimaLuna, it's obvious that fuse holders, AC power cords, speaker binding posts, and RCA sockets have improved a lot since the Golden Age of Marantz. So have output-transformer winding strategies and core materials: PrimaLuna winds their output transformers in-house, to their own wideband specifications. I suspect that most of the audible characteristics I'm about to describe are the results of the quality of PrimaLuna's output transformers and the design intelligence of PrimaLuna's founder, Herman van den Dungen.

Messe de la Septuagésima through Falcon Acoustics' LS3/5a speakers In the Christian calendar, Lent prepares believers for Holy Week, which concludes with Good Friday and Easter. Approximately 70 days before Easter, and just before the beginning of Lent, is Septuagesima (Latin for seventieth): a preparation for Lent and a stern foreshadowing that invades parishioner's consciousness as the liturgy suddenly darkens and grows serious. At this point, Christmas is officially over.

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Footnote 1: The Falcons cost $2195/pair.