Product: SE84B Zen Triode, power amplifier
Manufacturer: Decware, High Performance Audio - USA
Retail price: $749.00 USD (suggested) - $549.00 USD (factory direct)
(kit, $449.00 USD factory direct)
Reviewer: Richard George

The SE84B Zen Triode is one of the lowest priced, new manufacture, single-ended triode (SET) amplifiers on the market. While the SE84B is an inexpensive amplifier, it is anything but cheap. The quality of components and construction are exemplary. This amplifier appears to have two primary design goals: 1) to provide the best possible sound, and 2) to keep the price reasonable.
These seem to be contradictory ambitions, but the emphasis here has been solely on high quality audio output. As a result, little effort has been made toward visual aesthetics, which are so important to the Mass Market. While that same market may be very impressed by the appearance of audio equipment, the most important aspect to most audio enthusiasts is how it sounds.

Single-ended triode (SET) amplifiers are generally very expensive. While high-end SET amplifiers remain obscenely expensive and well beyond the financial capabilities of most people, there has been a minor revolution at the low end of the price spectrum.
At least one SET amplifier has a retail price under $500 USD, and there are others with prices a few dollars to a few hundred dollars more.

What Is the SE84B Zen Triode?

The Zen is a small, simple, stereo, vacuum tube power amplifier. It is a single-ended design with output tubes wired in triode mode. RMS measurements of the Zen indicate an output of 2.4 W/channel at 8 ohms impedance.
The owner's manual states that the Zen will reliably drive speakers rated at only 2 ohms. Additionally, the two channels of this amp may be wired in series with both channel inputs linked (instructions are included with the owner's manual) that will allow it to be used as a monobloc amplifier with 8W to 9W output. The frequency range of the amp is given as 30 to 20,000 Hz at ±1.5dB or 25 to 25,000 Hz at ±3dB. The Zen Triode measures 15 x 25 x 16 cm, and weighs about 4.5 kg (10 x 6.25 x 6 inches, 10 lbs).

The Zen uses four tubes: a single Svetlana, 6N1P, dual-triode tube in the driver circuit, one Philips 5Y3GT rectifier tube, and one, Svetlana SV83 output tube for each channel. Unlike some single-ended designs at the lower end of the price spectrum, the Zen uses no negative feedback.
Retubing this amplifier will cost as little as $30.00 USD. It should be noted that the driver and rectifier tubes will last for years in normal use; only the power tubes will require regular replacement. Both power tubes in the Zen can be replaced for about $10 USD, no biasing or matching required. Cheap tubes are a good thing with this amplifier as Steve Deckert, designer and builder of the Zen and other products, has biased the output tubes on the high side to improve sound at the expense of tube life.
He recommends replacing the output tubes once per year under normal usage, or every three months, if used continuously.

The output transformers are located inside the chassis near the front of the amp. The oversized, Hammond power transformer is centered near the back edge of the chassis (note: the recently available "C" model, pictured below, uses a new, custom wound, power transformer. The "B" model is still available). The RCA input connectors, on/off power switch, and the gain control knob are located on the back panel next to the A/C power cord.
This amplifier may be used with 100/117/230VAC @ 50/60Hz. The three-way, banana-plug speaker connectors are located on top of the chassis on either side of the power transformer. The four tubes form a diamond shape centered near the front of the chassis.
A bias switch is located on top of the chassis near the front. This switch changes the biasing of the input tube to two different settings. The character of the sound changes enough with the bias switch that it is almost like having two amplifiers to play with.

According to Steve Deckert, a key to high fidelity is to have as few parts as possible in the signal path. The website also says that the Zen amp has only one capacitor, two resistors, and 11 solder points between input and output jacks. This amplifier is easily one of the simplest tube stereo designs - perhaps the simplest - that I have ever seen.
Hence, the name "Zen". The Zen Triode uses point-to-point wiring, high quality components, and clean, professional, hand solder joints throughout.
This amp is well finished in basic, semi-gloss, gray paint with exposed tubes and power transformer. A screened cage is optional for additional cost.

Simple, Low-Powered, Single-Ended, and Triode Connected

Decware recommends speakers with a sensitivity of 90dB/1w@1m. Steve Deckert states that speakers often do not match their rated sensitivity. He recommends listening to your existing speakers to determine if they are up to the task. In addition, he maintains a list of speakers that Zen amp owners have used satisfactorily. The speaker list is available on his website. The speakers I used for the evaluation were B&WDM 602s, with a rated sensitivity of 90dB. I was concerned that these speakers would not be sensitive enough for the very modest power output of this amp and would require different speakers for proper evaluation.
This concern proved largely unwarranted for most music types. However, complex musical passages with wide dynamic range became problematic with the B&Ws. A single, brief followup test with a borrowed pair of Klipsch KSB 3.1 speakers indicated that an additional 4dB of sensitivity was very useful when using an amplifier that has less than 3 watts per channel.

The primary source used for this evaluation was a Rotel RCD-955AX CD-player with digital output through a silver coaxial cable to a California Audio, Sigma DAC with a tube output stage. The DAC was input directly to the amp.
No preamplifier was used during testing with the CD player. I had not planned to use LPs for this evaluation because I am dissatisfied with my present turntable; it fits my "budget" but not the rest of my system. However, after I listened to the Zen for a while, I found that I could not resist the temptation to try it with an analog input.
Despite my initial misgivings, I used an ancient Philips 312 Electronic turntable with a Shure V15 Type III cartridge. The turntable output was directed to a Conrad Johnson PV2a preamp, then into the Zen. Alas, my Dynaco PAS 3X is sitting on my bench awaiting repair.

As usual, several music types were used to evaluate this amplifier. These included rock, blues, vocal/acoustic, country, classical, and soundtracks.

Positive Impressions

The strong presence of music played with this amplifier is clear, even at very low volume. At higher listening volume, the clarity and detail are impressive. The highs are crisp, smooth, and very well detailed; the mids are smooth, clean, and wonderfully musical, and the bass is surprisingly deep and tight but not very strong with the B&W speakers. While this amplifier provides acceptable bass with the B&W speakers, the bass was noticeably improved when played through the more efficient Klipsch speakers.

Stereo imaging is one of the strong points of this little amplifier. The sound stage is wide and deep; with good recordings, it extends beyond the speakers to the sides, begins behind the speakers, and seems to extend forward to an area immediately in front of the listener. There is clear separation of instruments and voices with lots of 'air' between them, provided the recording is up to the task. The Zen transmits more musical detail through the speakers than almost any amplifier I have listened to, regardless of price.

The Zen amp works very well with most types of music, provided the speakers are efficient enough. Rock, blues, and country sound superb. With appropriate speakers, the bass is deep, strong, tight, and very clean. On the other end, cymbals and bells shimmer and ring, while electric guitars are free to sing or scream as intended by the musician.
Certain stereo effects that were mixed into recordings, as in Pink Floyd's Dark Side of the Moon, or almost anything by Emerson, Lake, and Palmer, are more effective than I have experienced with any other amplifier to which I have listened.
B.B. King's new CD, Riding with the King, is simply wonderful - the subtle, and not-so-subtle, nuances of his performance with Eric Clapton are captivating. While not as fine as a live performance, this felt like the next best thing.

Classical music, with its frequently complex passages and wide dynamic range, is very demanding on an amplifier. As such, I had to use the Klipsch KSB 3.1 speakers to finish the evaluation: the amp clipped noticeably while using the B&W speakers at a listening volume that allowed the full dynamic range of the music to be appreciated.
Again, the clarity and detail drew my attention, despite the use of the KSB 3.1 speakers. Aspects of recordings I thought I knew well became audible to me for the first time. This is a very fast amplifier, as evidenced by its clean playing of complex passages. Classical and other orchestrated music really comes alive with the Zen.

However, as with several SET amplifiers I have listened to, the Zen really excels at reproduction of acoustical instruments and vocals. In particular, female vocals sound stunning; the emotional impacts of their performances are not hindered by the Zen.
This amplifier reproduces vocals with rich and complete tonal quality, as good as anything I have listened to in the past, and definitely better than anything else that I have been privileged to audition in its class. Acoustical instruments sound so rich and natural, they sound as though they are in the same room.

Negative Impressions

Three arguably negative aspects of this amplifier actually result from the high quality output and faithful reproduction of the input signal.
First, weakness or poor quality of other components in the system now stand out, begging for replacement or revision. For instance, my Conrad Johnson preamp added substantial coloration to the sound, coloration that was previously less evident, and more acceptable. Adding the Zen Triode to a system could cost more money as weak components demand replacement.

The quality of the Zen Triode is also very revealing when it comes to recorded media: the quality of recordings being played is very much an issue. Lower quality recordings may not sound as good as they do on lesser amps because flaws are no longer masked by the amplifier. Truly inferior recordings are often glaringly apparent.
As a result, I now find myself eliminating from my frequent play list substandard recordings that used to be among my favorites; the flaws simply have become too irritating.

The third interesting aspect of the high quality output of the Zen became clear after listening to both CDs and LPs. After playing the CDs and LPs on three different amplifiers I found that the Zen doesn't "smooth out" the sound of CDs as some other tube amps do. The bright, somewhat harsh quality of CDs stands out in contrast to the somewhat softer, but smoother and more natural sound of vinyl LPs.
This, of course, is precisely why vinyl has seen a resurgence of popularity in recent years. The difference between media types can be heard on my 7868 and Dynaco ST70 amplifiers, but on the Zen the contrast is much more apparent.

The greatest drawback of the Zen Triode is that it simply doesn't have the power to drive most common speakers.
My B&W speakers are reasonably efficient by modern standards, yet when complex musical passages with wide dynamic range were played at reasonable listening volume, clipping resulted. It is very distracting and disappointing; it is not what high fidelity is all about. There are two solutions to this problem.
The first is to match this amplifier with very efficient speakers, 94 dB or better. The second is to use it as a monobloc with a second Zen Triode to power the second channel. If this is done, moderately efficient speakers would still be required, probably 90dB or greater, as there still would be only about 8 watts per channel available. Of course, adding a second Zen then doubles the power amplier price and removes it from the budget category.

Ergonomically, the Zen Triode could use a little refinement. The on/off switch is on the back panel. You have to reach over very hot tubes and the power transformer, then past the speaker and input cables to turn the power off.
A switch on the front of the top panel, which is readily accessible, looks like an on/off switch, but instead controls input tube bias; it can be confusing to the uninformed. Throwing the bias switch with the power on results in a loud "pop" through the speakers. This is not supposed to be damaging to the amp, but it could put speakers at risk. If the bias control and on/off switch locations could be exchanged or the on/off switch simply moved up front, it would be a significant improvement in the ergonomics of the Zen Triode.

The gain control knob is also on the back panel. Again, you must reach over or around the hot tubes, power transformer, and right side speaker cable to adjust the volume.
I suspect these switches and knobs were placed in their respective locations to keep the signal path as short as possible. If this results in superior fidelity, then it is worth the inconvenience on this amplifier. But, these minor ergonomic problems must be kept in mind if non-enthusiasts are to use the Zen Triode.

Finally, the visual aesthetics of this amplifier are not impressive. It has the appearance of a well constructed kit, rather than a modern, well-engineered piece of audio equipment. To me, the Zen amp's visual aesthetics are completely irrelevant because of its price and the quality of its audio output, but some people may be annoyed by the "kit" appearance of the factory assembled product. This is not to say that it is poorly finished.
Indeed, it is very well finished, but the design and choice of finish were not chosen to appeal to the mass market.

Conclusions

Overall, I was very impressed with the SE84B Zen Triode. This is a well-made, reasonably-priced, SET power amplifier. The expectation for an amp in this price range is that its sound quality would be well above the norm for mass market stereo equipment, but somewhat below audiophile standards.
The Zen Triode exceeded my expectations; occasionally, you get more than you pay for. There are several minor complaints with this amp, but nothing that hinders its audio performance. Ergonomically, it is somewhat challenging, as the controls one often would use are all on the back side after a long reach over hot parts.
Aesthetically, it leaves something to be desired - there are no chrome chassis, reflective panels, wood cases, or any other accouterments intended to add visual appeal. But none of these aesthetic shortcomings affect the audio quality, which is, after all, the reason for buying this amp.
While the Zen Triode is not perfect, its audio quality is nearly unassailable. The Zen's high quality output has a negative side: it is so revealing that other components in a system may not be up to the task. In addition, efficient speakers are absolutely required. Fortunately, there are some fine, reasonably-priced and reasonably-efficient speakers available in today's market.
Are there better sounding amps? Certainly. If you are an audiophile who must have the best, this amp is probably not for you, although if you audition it, you still may be pleasantly surprised. Nearly all power amplifiers that sound better than the Zen Triode are priced several times higher.

As with a similar product, the ASUSA K2003, one is reminded by the equipment performance that high-fidelity sound reproduction entails much more than just impressive specifications and high technology. It is about emotional involvement in music.
In our desire to have the best, we often forget the reason we strive to improve the quality of sound reproduction, namely, the music. Many amplifiers are difficult or fatiguing to listen to because of harsh overtones, distortion, grittiness, detail veiling, or other sonic debris that clutters the output and deadens the impact of music on the listener. Becoming truly involved in music becomes impossible with some audio equipment, especially most equipment in the "affordable" range.
With an amplifier as expressive and as purely musical as the SE84B Zen Triode, involvement becomes not only possible but very nearly unavoidable.

Would I own this amplifier? As I look across the room at the quartet of tubes glowing in the dark, the answer is obviously, "Yes". After a period of evaluation and comparison, I chose the Zen Triode to perform duty as my primary audio amplifier, subjugating my now second favorite amp, the Woodside Engineering 7868, to audio semi-retirement in the dubious service of "home theater".

© Copyright 2000 Richard George - http://www.tnt-audio.com