The beautiful sound of ZEN
Written: Sep 6, 2002 (Updated Sep 6, 2002)
a Very Helpful Review
by the Epinions community
What is a Single-ended triode (SET) amplifier?
First, lets take a look at the term "SINGLE-ENDED". It simply means that the waveform is amplified by just one gain device - in this case a vacuum tube.
Next is the word "Triode". A TRIODE is a type of vacuum tube. This type of tube has only three elements consisting of a plate, a cathode, and a grid (whereas other types of power tubes have more than one grid, which is the controlling element of the tube). When more grids are added, there are more conflicting power fields to deal with. This then adds to distortion of the signal.
Thus, single-ended triode (SET) operation achieves some positive results. Among these results are minimal odd-order harmonic distortions, (which the listener can discern) as well as an unaltered waveform in the amp without phase inversion. Finally, a SET design makes for both linearity and gain stabilization.
Subsequently SET output stages operate in Class A by definition. The circuitry of a single-ended amp tends to be simpler than the more common push-pull design (hence the name ZEN for this amp). The downside is that it becomes more difficult to obtain higher levels of output power, as Class A is also an inefficient operating mode. Speaker matching thus becomes critical.
What then does all this mean? It means that for certain kinds of music a SET amp will present the listener with a very unique music experience. A properly matched SET amp will create a spacious 3-D image, an almost magical, non-fatiguing soundstage and very detailed music source presentation.
The Decware Zen Triode Model SE-84 Power Amplifier
The SE-84 is a small SET stereo tube amp, which measures only 10 x 6.25 x 6 inches. The amp weighs in at a moderate 10 lbs. The amp is hand-made in Illinois by Steve Deckert and his staff. No circuit boards are used in the assembly - only point-to-point wiring, with quality hand solder joints throughout. Gold and teflon input jacks are used in the construction of the unit. The amp also has a unique dual bias switch for different sonic signatures and comes with a removable IEC AC cord.
The exterior of the amp is finished in gray paint (semi-gloss) with exposed tubes and power transformer. An optional gray cage is available at additional cost.
The ZEN uses a 6N1P dual-triode tube in the driver circuit (one can substitute 6922) and a SV83 output tube for each channel. In addition a 5Y3 tube is used for rectification.
Tube maintenance is cost-effective in that the entire amp can be retubed for well under one hundred dollars. Another added feature is that retubing the ZEN does not require biasing or tube matching.
It produces about 2 Watts per channel @ 8 ohms impedance. The amp has a documented frequency range of 30 to 20,000 Hz at ±1.5dB or 25 to 25,000 Hz at ±3dB.
The System used
Steve Deckert recommends a 90 db or better efficiency with respect to speakers used in conjunction with the ZEN. Alas, I employed a pair of Reference 3As (92 db per watt/meter with minimal xover). As a source I used a Technics 1200 turntable with a Shure M94E MM cartridge and a Monolithic phono stage adjusted to a capacitance of 100pf (allowing 150 pf for the tone arm cable), gain set to 44db - appropriate for the low-powered 2 watt amp and loading resistance set to 47k ohms. Speaker cable and interconnect is MITerminator 2 and ZEN power cord is RWA. The system was hooked up via a Vans Evers Clean Line Jr line conditioner to minimize RF interference.
Finally, I replaced the 6N1P dual-triode tube with a NOS Brimar E88CC/CV5358 and the rectifier with a NOS Mazda ST type tube. The listening room is for this system is 15 x 10 x 8 feet.
The sound stage is wide and deep; extending well beyond the Reference 3As. There is definite separation of instruments as well as voices (depending on the quality of the recording). Clarity and detail are impressive. A comparison with a push-pull amp and a sold state amp indicated significant more overall tonality, depth and detail. The highs are crisp and smooth and bass extension is good for such a low-powered amp. The Zen's strong point, however is the impressive midrange - making the Zen incredibly musical.
Most music sounds very good at moderate sound levels. I was surprised that the little amp even handled the complex passages of Beethoven’s 9th, though it was starting to run out of breath a little. Admittingly, such passages which have a wide dynamic range are rather demanding on this little SET. However, selections from Stan Getz and John Coltrane sounded big and live - as if the artist was in fact present in the room. Acoustical instruments just sound rich and very natural on this amp. In like manner Pink Floyd's Wish You Were Here (British pressing) sounded full, detailed and non-fatiguing.
First, the ZEN cannot drive a lot of speakers. One will be limited to speakers which are (in my opinion) at least 92 db efficient. If speakers have complex crossovers one better consider 95 to 98 db efficiency.
I've tested several Klipsch speakers, which work out well. The Reference 3As are superior, but also less cost-effective.
Second, the bright sound and harsh quality of CDs stands out like a sore thumb on this amp (in contrast to the somewhat more natural and softer sound of LPs). The ZEN requires a quality DAC like the MSB and quality Telarc and MoFi recordings (which were tested) to make CDs more enjoyable. In my opinion the sound of vinyl seems to go hand-in-hand with tube amps, especiallly SET amps like the ZEN.
Beauty is in the eye of the beholder, but on a scale of one to ten the amp is... well - not on the scale - it is just plain ugly! If one has to consider the SAF (spouse approval factor) look elsewhere - unless you're a newlywed or have a very understanding and open-minded spouse. This amp looks better when the lights are out.
Finally, since the amp has a gain control it does not require a preamp (it actually sounds better without one). However, the gain control (and the on/off switch) is located on the rear of the amp, which makes it tough to adjust when the amp is sitting in a shelf unit, since you have to reach across hot tubes.
Looks and ergonomics aside this is a well-built, great-sounding amp suited for Jazz, New Age, chamber music and even more complex music syles(at moderate volumes). I liked the sound of this amp so much that it replaced a solid state unit which cost five times as much. Are there better sounding amps? Of course. However, if you are looking for a well-built, musical tube amp for a 2 channel system at a real-world price the ZEN ought to be a worth some serious thought.
I have owned four different tube amps, ten solid state amps not to mention numerous receivers and have not been able to find an amp that sounds as musical as the ZEN for under 3K.
Given the amps limitation and unusual design Sony will not have to worry about competition. However, for those few who enjoy the sonic signature of a SET amp and the soft glow of it's tubes at night this amp may well be a serious consideration.
I also wish to add that both Steve and Devon of Decware were courteous and helpful in answering questions I had. My amp was built to order, shipped and delivered in a timely fashion. The ZEN comes with a 30-day return policy and a lifetime warranty.
The little amp has become my priced possession and I have not felt the urge to upgrade this component (something very unusual for me). I highly recommend the unit.
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