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January 2014
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Triode Lab 2A3-S Vacuum Tube Power Amplifier
Triode Lab is the little company that can.
Review By Rick Becker


Triode Lab 2A3-S Vacuum Tube Power Amplifier  In our last episode of High Efficiency Adventure, the review of the Zu Audio Union loudspeaker, I spoke with delight about the 2A3 Classic Mk2 power amp mated with the very high efficiency Zu speaker. To review, I wrote:

After reading my review of the EL84TT, Carl Ng offered to send me their 2A3 Classic Mk2 stereo power amp ($2888 CDN). It had arrived that same day and while Tom listened to classical music I cut open the box and inserted the tubes. It uses a pair of Sino 2A3C (a new variant of the 2A3) from Guiguang, rumored to be a sister company of the more widely known Shuguang, and it is favored by Carl for its sound, fit, looks and price. It looks like a 2/3 scale version of a 300B larger than you might expect for its 3.5 watt output. The rectifier tube is a NOS Mullard GZ32 favored by many, but easily replaced thanks to Triode Lab's unique "Uni-fy rectifier stage" to tune the amp to your preference. And the 6SN7 tubes are OTK Military Grade which is the cheapest 6SN7 you can buy but accurate, neutral and laid back. The amp is Class A with an auto-bias circuit and unusually, it is AC heated by preference. Triode Lab also makes a hot rodded 2A3-S special edition for $3888 CDN with premium transformers and a chassis that will likely satisfy your desire for audio jewelry. The S version is for the connoisseur who not only likes to roll tubes, but roll amplifiers as well.

We put the CD into forward, listened for a brief moment, looked at each other and simultaneously broke out into laughter. This is a seriously good amplifier in spite of its humble appearance. The top end is rolled off. The presentation is dark, being centered on the lower midrange with a full, sumptuous bass. Attack is good, decay is long, midrange focus is very good and the holographic music grabs your gut and pulls you right into the collective soul of the performers. Forget about a subwoofer. With the highs rolled off and the ripe mid-bass you don't miss the lowest octave because you're so emotionally engrossed in the music. In fact, if I wasn't so indoctrinated in the philosophy of the so-called high-end audio, I could call this an end game and move on to another hobby called high fidelity all the while enjoying the music. Should I put this paragraph to rap music? No wonder Carl tells me a lot of his customers with Zu speakers own this amp. These could be the 3.5 most important watts on the planet. And if not these watts, I'd be tempted to ante up for the 2A3-S. (Can you hear me now, Carl?) Combined with the transparency, dynamics and focus of the Zu Union, you get all the pace, rhythm, timing and timbre that's on the recording. You ask about the Chinese Drum cut? It barely required more than the first watt yet the Triode Lab delivered as much slam and more delicious timbre than I've ever heard from this piece. Tom went home about 11 pm and I fell into bed at 2 am after "just one more song".  

Well, Carl Ng heard me, all right. But had I painted myself into a corner with the rave remarks about the Classic Mk2? The adventure continued as it had before with Carl hand delivering the 2A3-S to my home. I was excited because I expected it to be a lot better than the Classic Mk2 and the suspense over which color he would deliver was over-stimulating me. It comes in either Mercedes Benz Design Tri-Coat White or Porsche Bordeaux/Rubin Red. Both appear luscious in the photos on their website, though the white is clearly the more understated choice. I would have loved either. As I pulled the amp from the red silk-like bag with Triode Lab logo and "Made in Canada/Fait au Canada" silk-screened on it, my eyebrows twitched upward and a subtle smile came to my face. It was Porsche red with mat black paint and gold emblems on the James transformers and a gold Triode Lab emblem on the front face. The Cardas RCA connectors and the speaker binding posts out back were also gold plated. Simply beautiful!

I had suggested to Carl that he add wood side panels like I had seen on other amps on their website, but what he came up with was rather ordinary looking thick blocks for the review sample. The revised Plan A would be to call Chris Harban at Woodsong Audio out in Idaho. Chris specializes in Linn LP12 turntable plinths that are visually stunning. He indicated to me that side plates for amplifiers would be easy for him to make. They won't be inexpensive ($175 to $250), but the 2A3-S and the higher end Triode Labs amps will be taken to the pinnacle of design by adding them.

Triode Lab 2A3-S Vacuum Tube Power AmplifierThe 2A3-S uses a pair of Tung Sol 6SN7 GTB tubes from Russia rather than a more generic 6SN7 tube that is also sourced from Russia that came on the Classic Mk2. I used the very same CV 593 rectifier tube and 2A3C tubes with gold pins in both the Classic Mk2 and the S versions although they suggest you can use a variety of rectifier tubes to fine-tune the amplifier. Other sonic differences come with the use of the very finely crafted James Audio Transformers and the Mundorf Silver/Gold/Oil capacitors in the 2A3-S. I've already indicated in the Zu review (quoted above) that the 2A3 Classic Mk2 is considerably different sounding than the previously reviewed EL84TT integrated amplifier but let's delineate some of the basics of these amps so you don't become hopelessly entangled in the technobabble.

EL84TT: Uses Hammond output transformers, Hammond choke filter, Hammond power transformer, Mundorf ZN Tin Foil capacitors and EL84 tubes. It is an integrated amplifier with a passive input stage, putting out 6 watts per channel.

2A3 Classic Mk2: Uses Tomiko Kyushu Output transformers, Hammond choke filter, Hammond power transformer, Mundorf ZN Tin Foil capacitors and 2A3 power tubes. It is a power amp that puts out 3.5 watts per channel.

2A3-S: Uses James output transformers, James choke filter, Hammond power transformer, Mundorf EVO Silver/Gold/Oil capacitors and 2A3 power tubes. It is a power amp that puts out 4 watts per channel.


The Zu Union speaker was used to review all of these amps, sometimes in conjunction with a pair of prototype Tekton Design powered subwoofers that were connected via speaker cables from the amplifier (not with a line level input from the preamp). This coaxial Zu speaker with a 10" nearly full range driver and a concentric tweeter that crosses over at 12 kHz was short lived. Product improvements using nano coating of the 10" cone and improvements in the minimal crossover to the (super) tweeter improved the majority of speakers in the Zu line. This brought the updated Soul model ($2000) very close in sound quality to the Union. The difference in price did not justify the difference in sound, so they kept the less expensive updated Soul and dropped the Union. This is important, because my comments should be taken in the context of the older Zu speakers, not the current production that reportedly has a smoother upper treble. I haven't heard any of the new Zu speakers, but it is a typical case of the good just getting better and better something that happens with regularity in this hobby. Using even more costly amplification than we're looking at here, I achieved outstanding results with the Zu Unions and gave it a Blue Note Award for 2013.


The Plug-In
Triode Lab 2A3-S Vacuum Tube Power AmplifierFor all my expectations of sonic splendor, given the beauty of the little beast, the plug-in was a let-down. Word is that the oil capacitors need a long break-in period of 200 hours. I pulled my vintage Musical Design SP-1out of mothballs and let it drive the amp for a couple of weeks while I worked on my TAVES show report. When I returned to listening in earnest, the soundstage had really filled out, becoming as wide as anything I've used, and deeper than anything else I've had in the system. "Wider" is more typically a function of room dimension and speaker placement. I have the speakers on the long wall about 5.5' in front of the front wall with the side walls more than 10' beyond the speakers. I almost always achieve excellent soundscape width. Depth is another matter, seemingly more dependent on an amplifier's ability to delineate subtle differences in volume that places instruments closer or farther away. Not only was the soundstage deeper with the 2A3-S, but the focus at the far end was very good. The music had also developed a full bloom that is so highly valued with single ended triode (SET) amplifiers, but nothing that you could call syrupy. The soundstage was holographic and the music was full of rich tonal color. The 2A3-S also sounded smoother than the Mk2, which is to say it was exceptionally smooth since the Mk2 was already pretty much grain-free. Overall, listening to the 2A3-S driven by my Coincident Statement Line Stage was a very pleasurable and relaxing experience, regardless of the genre. But eventually a shortcoming became noticeable. Some of you might think of it as a divine intervention. The mid-treble begins to roll off and the high treble is missing at least for my aging ears. If you are young-to-middle age and have excellent hearing you might perceive more music in this upper range that escapes me, but cymbals are definitely attenuated when struck and forget about hearing delicate brush-work on them. Upper harmonics simply disappear in what is a perfect example of an error of omission. For those who love the Zu but find fault with the crossover and tweeter, the 2A3-S should resolve your issues. Drummers, on the other hand, may feel like they got short-changed in the mix.

Moreover, the missing upper treble becomes more apparent when using a subwoofer, causing the center of the spectrum of the music to shift toward the lower midrange. As I said in my review of the Zu, the speaker blends very nicely with subwoofers because it drops off cleanly and quickly when the speakers are placed out into the room away from the walls and corners. The downside of adding a subwoofer here is that the missing upper-treble becomes more noticeable with the additional mid and lower bass information. So it's a bit of a trade-off. The quality of the mid and low bass coming from the subwoofer when fed directly from the power amp with speaker cables was taught and dynamic much better than I expected coming from a 4 watt SET tube. As for the volume of the mid and lower bass, that is controllable with the twist of a knob on the back of the subwoofers. Suit yourself. But if you should have a larger speaker that digs down into the 20-30Hz range your only recourse for controlling bass output will be in positioning the speakers in the room. If you have such a full-range speaker, you may want to consider selecting the ZN capacitors that will give you a more prominent top end to balance off the deep bass.

Triode Lab 2A3-S Vacuum Tube Power AmplifierThe other minor shortcoming I found with the 2A3-S is the somewhat diminished dynamics when compared to the 2A3 Classic Mk2 and the EL84TT. The attack of the notes and the hard rim shots literally leap into the room with these other amps, contributing to their greater sense of transparency and dynamics. Such dynamic drive also commands more attention to the music and it can wear you out more quickly. The 2A3-S was always pleasurable never irritating or tiring. Carl readily admits that this is why so many of his customers prefer the 2A3-S with their Zu speakers. He also suggested the difference lay in the transformers. He wrote:

The input sensitivity [of the Classic Mk2 and the 2A3-S] is the same, just the output transformer is differently designed in its approach and presentation. The Tomiko [in the Classic Mk2] might sound louder at first, but could be breaking up faster in max volume. Whereas the James comes in nice and smooth, then gradually increases its loudness. On measurement, the James is supposed to be better, whereas the Tomiko is less ideal (more edgy on the curve seen on the scope). However, like many people say, measurement is always not the first priority. (This argument is often used by lower grade/cheaper parts sellers, as they claim their sound is #1). But for me, and most other engineers I know, measurement and specifications is still the #1 priority. And to have both [good] sound and specs, the transformer will usually cost significantly more. But I have to say, the Classic MK2 is already a very best voice to beat.

The power amp resides in the middle of the chain so it sees what is handed down to it and feeds whatever speaker you might have. At one point, thinking I had not burned in the amplifier sufficiently, I re-installed my Musical Design preamp and did some critical listening with the 2A3-S. Totally catching me off-guard, the transparency seemed to pick up a notch, the dynamics kicked in and there was more music in the mid-treble. The downside of this combination was an increase in grain, more vagueness in the soundstage and less tonal coloration. Because of the different volume controls of the two preamplifiers it was impossible for me to match levels but the differences were obvious enough to make the point that what goes in will have a significant impact on the output of the power amp. The 2A3-S deserves a very high quality preamplifier and source; it was not out-classed by the Coincident Statement Line Stage.


Time For A Nightcap
As I heard in my review of the EL84TT integrated amp and the 2A3 Classic Mk2, Carl acknowledges the Mundorf ZN Tin Foil capacitors impart a more brilliant treble something we both prefer. That's an important point. At this high level of performance it becomes a matter of personal preference and the choice becomes more wisely made when you have broader experience. I've learned a lot from listening to these three amps from Triode Lab. When it comes time to drop the ice cubes into the glass, you get to choose what to pour over them and savor as you listen to the music. Carl even offered to "drive by" and swap out the Mundorf oil caps for the ZN caps, but I didn't want to put him to the task. From my experience with the three amplifiers it was easy to envision the very fine qualities of the 2A3-S enhanced with a bit more treble extension and dynamics offered by the ZN caps. My opportunities for listening do not regularly allow extended sessions of more than a few hours and I cherish the transparency and dynamics that encourage the fantasy of "being there". I also have those "aging ears" that can benefit from a stronger treble of high quality that would come with the ZN caps. I should also mention that Triode Labs offers the option of using Jensen capacitors, another popular brand with which I have some familiarity in my reference monoblocks but I'll get into that in another review.

Carl had some pertinent comments on the Mundorf EVO caps. He wrote:

The Mundorf EVO Silver Gold Oil Caps to my surprise didn't add any greasiness or slowness to the sound at all like some oil caps do (or in short, the cap's personality override everything else). [With] some oil caps I also hear a bigger treble rolled off, which could be a problem to classical music listener, because the pitch of force striking the piano key will be gone and now the violin high note passage [will] sound more like a viola high note. Some micro details in the high frequency can also be gone. Anyway, it did not happen with the [Mundorf] EVO S/G/O cap and it actually added a grand kind of sweet coating on it... some of the micro details actually come out more clearly.


The Last Dance
At four watts per channel the Triode Lab 2A3-S is not an amplifier for everyone. It is a thoroughbred designed for very high efficiency speakers. It will require some research to find a match that is easy to drive. If your budget restrains you, take a look at their EL84TT or the 2A3 Classic Mk2. But if visual design is important and you can afford a speaker that will not wilt in the presence of this gorgeous amp, I highly recommend you seek it out. When I closed my eyes it was hard to believe I was not listening to a much more powerful amplifier driving a much larger loudspeaker.  Take heed of the nuances of capacitor choices I've spoken of above. Triode Lab, being a small scale manufacturer is personable enough to work with you to custom design an amplifier to suit your preference and your loudspeakers. Not only is the 2A3-S the "little engine that could", Triode Lab is the little company that can. From what I've seen and heard of their products both in my home for review and on display at the Canadian Exhibit at the Montreal show, they are destined for much greater acceptance and success. This is easily the most beautiful amplifier I've had the pleasure of dating and it will be hard when it comes time to kiss her goodbye.



Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution

Soundscape Width Front

Soundscape Width Rear  
Soundscape Depth Behind Speakers

Soundscape Extension Into Room


Fit And Finish

Self Noise

Value For The Money


Type: Vacuum tube stereo power amplifier
Tubes: Tung Sol 6SN7 GTB, CV 593 rectifier tube and 2A3C power tubes
Output: 4 watts per channel @ 8 Ohms
Output: Class A, autobias
Inputs: Line level via RCA jacks
Speaker Outputs: Gold-plated binding posts
Output Impedance: 4 and 8 Ohm, with 16 Ohm available
Total Harmonic Distortion: Less than 1% at THD+N
Hum & Noise (A-Weight): 80dB or better at rated power
Price: from $3888 CAD ($3650 USD)


Company Information
Triode Labs
Toronto, Ontario, Canada
E-mail: Email@TriodeLab.com
Website: www.TriodeLab.com














































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