A time-honored classic design, good quality parts, low price, and even the opportunity to participate in its creation. What more can you ask?

It’s not exactly a secret that Passion amplifiers come from the same factory as the Antique Sound Lab products. The company supplies products to order, promising no exclusivity (we were actually offered models with theUHF logo on them). However it isn’t necessary to stick to what is in the Chinese wholesale catalog. Both North American distributors are marketing products that are different from the others, because they asked for -- and got -- improvements and custom features.
     Passion Audio Kit is a division of a Québec City high end audio store, Rotac. The company’s original idea was to sell tube electronics in kit form, to make a sweet deal even sweeter. It may have been surprised to discover that so many buyers turned down the challenge, preferring to order the gear built and tested. Either way, as we shall see, we are talking bargain. However note the reduced warranty if you buy a Passion as a kit.
     We should add that the kit version is not for beginners, and requires actual circuit construction, not just simple mechanical assembly as in some kits. This means a kit builder should not be picking up a soldering iron for the first time in his life. Fortunately you can actually download the assembly manual from the Web site (www.rotac.com) and see what you’re in for. The price differential is such that your hourly saving may come in well below the minimum wage, but cost isn’t everything. There’s something special about listening to an amplifier you’ve made with your own hands.
     The circuit is classic. That should not be taken to mean old fashioned, but it is certainly time-tested. Each channel includes two 6550 tubes in push-pull. That now ubiquitous tube is similar to the KT88 and other offshoots of the original 6L6 beam power pentode. It is currently fashionable to tie the plate and the screen grid together in order to make it operate as a triode. The A11, like some other Chinese amplifiers (and like some of our other favorite tube amps), uses a mode halfway between triode and pentode operation. This mode, known since time immemorial as Ultra-Linear, requires a special output transformer with extra taps for the screens. Ultra-Linear may be a compromise, but it allows near-pentode power output (42 watts per channel in this case) with a transconductance curve that is closer to that of a triode.
     (If this strikes you as gibberish, we’ll summarize it this way: it’s a way of having your cake and having it too, but it isn’t some newfangled scheme that experience will show up as a major mistake.)
     The rest of the circuit is likely to be familiar to anyone familiar with tube design. There are four ECC82/12AU7 tubes, acting as buffer, phase inverter and drivers for the output tubes. Though we photographed the amplifier without a cage, the assembled version does come with one (see the picture on the next page), to keep fingers out of places where they risk getting singed. With the kit it’s an extra cost option: C$99 or US$64
     The tubes are not self-biasing, but bias alignment can be done without opening the chassis (where potentially lethal voltages lurk) with nothing more than a voltmeter.
     The front panel of the A11 is simple, as you would expect from a power amplifier: just an on-off switch and a small power indicator. The rear panel has the usual good quality inputs jacks, output binding posts, and IEC connector for the supplied power cord, or (we suggest) a better one. The line fuse is easily accessible, as it should be.
     As with the other Chinese amplifier tested in this issue, the A11 has a 16 ohm output as well as 8 and 4 ohms. This surely isn’t because Rotac thinks you may be running 16 ohm speakers (though very old B&W’s and some other vintage British speakers did have that impedance). But it is now common among some audiophiles who will settle for less than maximum output power to use the highest impedance output, because the transformer winding has less wire in it.
     Though the binding posts are well machined, we did run into a minor problem. We usually tighten hexagonal posts with our Dynaclear Postman wrench, designed to allow proper tightness without permitting enough torque to shear off the post. The Chinese posts are oversized, however, and so the Postman won’t fit. We used a ratchet wrench set with some trepidation, being very careful not to turn too hard. We stopped when, to our horror, we actually saw the post rotate in its hole. We would have liked a tighter connection, but we would then have risked internal damage to the amplifier. Our suggestion for the designers: a keyed hole that doesn’t let the post turn.
     Our A11 was brand new, and we ran up some 72 hours, operating at a third of rated power into a dummy load. We then placed it into our Omega system. In case you’re wondering, we used the 4 ohm output. Why not the 16 ohm output? Though our Reference 3a speakers are efficient (91 dB), we run them loud enough that we want to harvest every watt of which an amplifier is capable.
     We began the formal listening session with Aaron Copland’s Fanfare for the Common Man (Reference Recordings RR-93CD), with its tympany, its large bass drum, its gong, and of course its brass ensemble. What we heard was impressive, though Reine thought it sounded very different from our reference amplifier’s rendition: with dryer impact on the attacks. Gerard heard it quite differently, finding those impacts a trifle soft.
     Still, there was no denying the amplifier’s virtues, nor its virtuosity. The trombones were excellent, and each of the brass instruments was easily distinguishable even within the ensemble. The A11 showed little sign of lacking energy, even on the bass drum. The depth was very good, if slightly reduced.
     We continued with William Walton’s Façade, a deliciously satirical piece for small orchestra (Reference Recordings RR-2102), with its many instrumental solos. Albert found the piece less fascinating than usual, perhaps recalling the LP version we have often used. Still, the many moods of the piece came through well, as did its humor. “It’s still softer than our reference,” commented Gerard, “but I’ll take soft over shrill anytime.”
     We were unanimous in praising the fine detail that the A11 was able to dig out of this recording. The brass shone convincingly. The bassoon was hilarious, as it is meant to be. And we all noticed the coherent “rightness” of the cymbals, including their decay into silence at the end of one section. The percussionist barely touches his cymbals at one point during the bassoon solo, and the shimmering sound that results is soft but clear, with a sound that hangs on nicely.
     We very much enjoyed Buddy Bolden’s Blues (from Come Love, Opus 3 CD19703). The clarity allowed the timbres of the individual instruments -- saxophone, clarinet, sousaphone -- to emerge with gratifying clarity. The latter instrument had slightly less weight than with our far more powerful reference amplifier, but only by comparison was this evident. Tonal balance was excellent. “The sax is bright,” said Gerard, “but I mean that in the good sense.”
     We all noticed the image too. This recording has an unusually tactile stereo image, and with the A11 we could have walked into the hall to be with the musicians.
     We’ve heard amplifiers (and other components, from CD players to cables) really mess up with Papa John from Doug McLeod’s You Can’t Take My Blues (Audioquest AQHD1041), but not this one. The rendition was flawless, with detail, rhythm and power. This may be the liveliest piece on the album, thanks in part to the bewitched (and bewitching!) violin solo, and the A11 let it all through. “McLeod was singing for me personally,” said Reine with enthusiasm.
     We closed the session with Bïa’s Ballade pour un matin and Golden Slumber (Audiogram ADCD10132). It was outstanding. The harmonica sounded natural, and so did Bïa’s guitar. We could even pick out the small bit of reverberation after the guitar chords. “You even notice what isn’t right about the recording,” commented Albert. “For instance, the guitar and the harmonica wouldn’t be the same loudness if the musicians were really here.”
     Bïa’s voice was also very fine, with not just the words but also a certain ironic smile coming through. This is the song of someone who has just awakened but isn’t in a rush to get out of bed...and the sense came through wonderfully well.
     We took the A11 to the test bench and confirmed that, at most frequencies, it more than meets its 42 watt per channel power rating. Only at 20 Hz did it fail to do so, exhibiting considerable distortion beyond a level of 16.5 watts, with both channels driven. This is a common failing in tube amplifiers: the output transformer becomes magnetically saturated at low frequencies. The solution would be to use a larger transformer with more iron, adding to the weight and the size of the amplifier, and of course to its cost. It is only fair to add that this happens at the very bottom of the audible range...assuming you consider 20 Hz to be even audible.
     We went looking for misbehavior at very low level. That is rarer with tube gear than with solid state circuits, and we didn’t find any.
     Noise was commendably low, and it was broadband, with neither hum nor hiss dominating. We did notice some high frequency pulses riding along with the noise, possibly thermal noise from the tubes. There was no ringing, however, and at no time were the pulses audible.
     The A11 is a well-made amplifier with more than merely adequate performance. It draws on the virtues of the classic Ultra-Linear circuit, all the while delivering the advantages you would expect from a modern amplifier, tube or solid state.
     We couldn’t find anything that the A11 does poorly, and it does most things outstandingly well. That summary should be enough to put it on a lot of short lists.

Brand/model: Passion PAK-A11
Price: C$1849/US$1200 (assembled), C$1399/US$895 (kit)
Dimensions: 42 x 32 x 22 cm
Warranty: 5 years non transferable, except 2 years on kit, and 180 days on tubes
Most liked: Solid musical performance
Least liked: Limited power at very low frequency
Verdict: Easy to afford, easy to love

CROSSTALK

     This amplifier has a personality utterly different from that our reference, though you should not take that to mean it is without interest. Quite the contrary, it reveals a number of important qualities.
     I shall speak first of its impeccable image and its broad spatiality. They result in a remarkable clarity and focus that give us access to a whole panoply of effects: inflections, modulations, and the sounds of the subtlest percussion. Instrumental textures are gorgeous, the human voice natural and warm, words clear.
     I do have a small reservation concerning the way it treats the piccolo, whose tessitura is an assault on the ear, but then again you don’t find piccolos on every recording, especially not playing at the top of their range.
     The Passion A11 renders everything so faithfully that it lets you divine what the musicians are feeling, not merely playing: the mocking smile of a singer for instance. Naturally, every medal has two faces. Faithfulness also means clear rendition of flaws, such as an excess of sibilance. That said, I rate it nearly perfect.
--Reine Lessard

     Talk about a nice surprise! A few minutes into the listening session I felt it could easily handle any kind of music. And it did. Actually the real surprise turned out to be no surprise. Reliability was my main impression, this comforting adaptability which let me relax without apprehension before each musical piece...knowing that what I’ll hear, I’ll most probably like.
     It is rare to be able to hear such subtle details as a cymbal’s soft decay floating in space, and yet still experience the low end, high-impact, smack-in-the-gut power of a giant bass drum. I did expect good detail but not such great bass too. The sound was open, the stage was clearly set, and the instruments were on it. Right there.
     And in each piece, without fail, was that satisfying richness in the midrange which never let me down. No surprises, I tell you.
--Albert Simon

     The key to this amplifier is balance. It isn’t shrill or aggressive, like even some other tube amplifiers, nor is it mushy and indistinct. The rhythm is strong, but there’s no heaviness to drag the music down. It’s warm, but it doesn’t color everything in sepia tones.
     It has good energy, too. Its power is probably more than adequate for most modern loudspeakers. Put it alongside our reference amplifier and it will seem a little less focused, with less of that bottomless bass. But swap it for most amps, including ones that cost a lot more than th

(This is a full article from issue No. 63 of UHF Magazine. To read the entire isue, just order it on line at our secure server.)

Complete articles from this issue:
Soundproofing, Big Screen TV's to Stay Away From, Passion A11, State of the Art

Excerpted articles from this issue:
Comparing the Incomparable: Listening in the Store, Antique Sound Lab Leyla, Vecteur Espace, Two Interconnects, Five Speaker Cables, Four Power Cords