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December 2007
Superior Audio Equipment Review

Silicon Arts
ZL-120 Monoblock Power Amplifier &
Concert Fidelity
CF-080 Line Preamplifier

D.O. finds new reference a new reference!
Review By Dick Olsher
Click here to e-mail reviewer.


  Two products lines, one company, and one designer with over 30 years of experience in vacuum tube and solid-state amplification design. That's the bare bones background info on these two outstanding designs by Masataka Tsuda that have had me in aural rapture for the past several months. Tsuda-san tells me that he grew up in the midst of Japan's postwar economic recovery when a stereo system was a luxury and most homes could not afford one. And having heard a good system for the first time at the local department store, he became determined to build his own. He would get up early on recycling day (before the pickup truck came by) and rummage trough the neighborhood for discarded broken down TVs and radios. He enjoyed taking these sets apart to scavenge for usable parts. While other kids were reading comic books, he was engrossed with radio technology magazines, and in time became adept in reading circuit schematics. Since the 6BM8 tube was popular for TV set audio amplification, he managed to amass a total of ten of these tubes together with usable output transformers. At the age of 10, after six months of effort, and many tripped circuit breakers, he was finally able to get sound out of his first amplifier.

Concert Fidelity CF-080 Line Preamplifier Front and RearDuring his high school years he became absorbed with building vacuum tube amplifiers using a variety of output tubes, including the EL34, 6L6, 6B4G, 1619, 211, 845, 300B, 2A3, and 45. Interest in solid state developed after he successfully designed a high-voltage IC driver for his favorite 1619 tube. Shortly thereafter, MOSFETs became available, and when substituted for the 1619, the sonic results were sufficiently impressive to propel him into a long career of solid-state amplification design. In fact, the circuitry of his first solid-state amplifier would become the basis of the Indigo-90, his first commercial effort some years later in 1993. Us marketing was slow to evolve, starting with his first appearance at a US trade show, the 1996 CES.

His products have earned high compliments from yours truly over the years, but it seems that everything came together during the January 2007 CES/T.H.E Show in Las Vegas. My vote for "Best Sound" was earned by a system, which apparently represented Mike Slaminski's (Precision Audio and Video of Moorpark, CA) personal system, and which included the Venture Excellence speakers ($56,000/pr), Concert Fidelity CF-080 preamplifier ($18,000) and Silicon Arts Design ZL-120 power amplifiers ($23,000/pr). And so, some months later, Tsuda-san's latest solid-state amplifiers and tube-based line preamplifier arrived on my doorstep.


Technical Details

Tsuda-san's design philosophy is closely aligned with Albert Einstein's often quoted dictum to make things as simple as possible, but not simpler. More to the point is Einstein's corollary: "Any fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." In audio design terms, this means a minimalist approach and perfectionist emphasis on parts quality and circuit layout. A short signal path is an explicit design goal.

The main objective is ultimately to give the music full emotional scope of expression. Tsuda-san believes that during the transition from tubes to solid state many of the major strengths of tube circuits were forgotten and that is why so many audiophiles still feel that solid-state amps are musically inferior to well-designed tube amps. His major point is that vintage tube amps sounded as good as they did because of circuit layout, point-to-point wiring with a well-delineated ground, decoupled amplification stages, and power supplies that were the essence of simplicity. He believes that the problems of sluggish transient response and dynamic dullness that afflict so many high-power amplifiers can be directly traced to overly large power supplies, over regulation, and poor circuit topology with large current loops.
Concert Fidelity CF-080 Line PreamplifierThe gain topology of the CF-080 is hybrid since the input stage is solid state. Its tube pedigree is nicely concealed, but for a good reason. A pair of 12AU7 dual triodes are located on the back panel, mounted on a printed circuit board which is positioned just behind the panel, thereby reducing signal path length from input to output to an amazing four inches! Yet, the tubes are still easily accessible for tube rolling purposes. Each 12AU7 is connected as a cascode to provide 6dB of gain (there's also a 12dB gain option available). That's not much gain, but it's rather ideal for servicing digital front ends, even with insensitive power amplifiers. You'll need a phono stage upstream to accommodate an analog front end. There's another pleasant surprise hiding inside the chassis. Plate voltage for the output stage is supplied by a regulated power supply, using a 6CA4/EZ81 full-wave rectifier tube and a choke coil.

Input selectors on the CF-080 are high performance analog switches. The input signal is routed though a proprietary dual-channel electronic volume control using proprietary digital circuitry and software, which is said to be the result of many years of in-house development effort. The most noticeable external feature of the CF-080 is the blue LED volume level display. However, there's one control you will not find on the front panel. I recall, many years ago, J. Gordon Holt holding up a line preamplifier and quizzing me about what was wrong with it. Well, it turned out that it lacked a balance control, and to his way of thinking that was an unforgivable "sin." Should we condemn the CF-080 for this sin of omission? Admittedly, in an imperfect world it would have been useful to have independent control over the volume of each channel. Speakers and amplifiers don't always track perfectly, and it's not always easy to find NOS 12AU7s that are perfectly matched for transconductance. But in view of its sonic performance, there's no way I would let that interfere with my musical enjoyment.

Another feature, which I would have appreciated but is admittedly difficult to engineer transparently, is a polarity inversion switch. With complex multi-track recordings it is difficult to pin down a correct absolute signal polarity and it is very helpful to be able to experiment with polarity on the fly, even from one musical selection to another. There's a power standby switch on the back panel, next to the power switch, which powers down the output stage tubes but keeps the solid-state circuitry (and rectifier tube) powered on. Clearly, leaving the unit in Standby between listening sessions makes it possible to warm up much more quickly to peak performance, but I'm not crazy about the idea of leaving the rectifier tube powered on continuously.

The ZL-120 is configured as a bridged amplifier whereby the voltage swing is obtained between in-phase and inverted-phase input signals. Following an input buffer stage based a high-performance OpAmp, a phase inverting gain stage provides an inverted high-fidelity copy of the input signal. A Class A driver Stage is used to drive a push-pull output stage consisting of two paralleled pairs of MOSFETs. Great care is taken to calibrate each stage during the assembly. Negative feedback is confined to local gain stages there is no global feedback. The amplifier's input impedance may be set via a switch on the back panel at either 20 or 100 kOhm to accommodate the needs of both low and high output impedance preamplifiers. I preferred the 100 kOhm position with the CF-080, but you should experiment with this setting to determine which works best within the context of your system. Note that it is permissible to toggle this switch while music is playing.


The Sound

What is most amazing about the sound of the CF-080 is that I found it impossible to characterize as either tube or solid state. Most vintage tube preamplifiers sound distinctly euphonic, slow and mellow, with a fat midrange and an overly liquid and fuzzy harmonic tapestry. Transistorized designs, on the other hand, deliver an abundance of detail, but tend towards a cool, sterile presentation, lacking emotional combustion, and generally failing to flesh out a believable spatial impression. For me, tube preamps have always represented the most musical choice, though I have been known to complain on certain occasions about less than sterling bass definition, transparency, and transient speed. Well, these are precisely areas in which the CF-080 excelled. I'm still shaking my head in disbelief: a tube gain stage and tube rectification, yet transient speed and low-level detail retrieval rivaled or exceeded the performance of all line stages I have auditioned over my entire audio lifetime.

This line stage quickly established itself as a master illusionist, virtually disappearing out of the signal path. It offered a highly transparent view of the soundstage with the sort of clarity and ability to zoom in on a particular spatial region that I have rarely experienced with reproduced music. There was no veiling to speak of. Intimate recordings remained just that, infused with the full dynamic spectrum of the original recording intact. Large ensemble music was reproduced with plenty of verve, kinetic energy, and fidelity of harmonic colors. Though I should stress that the latter performance parameter was dependent on the particular 12AU7 brand deployed in the signal path. Silicon Arts Design in fact encourages tube rolling and experimentation with NOS types. And that's part of the fun of owning tube gear. Mike Slaminski, Precision Audio and Video, was kind enough to provide me with genuine Philips Bugle Boys as well as a pair of Mullard Great Britain 12AU7s.

I also experimented with my own Gold Aero select East German RFT types as well as NOS 1960s Mullard Blackburn CV4003 with the box shaped plates. My Bugle Boy samples proved to be a bit reticent in the treble and too controlled dynamically, while the Gold Aero RFTs were peppy yet a bit bright sounding. The Mullard box anode types were the clear winners featuring an expansive soundstage with the sweetest and most pristine harmonic colors a music lover could dream of. Violin overtones and soprano upper registers shone with natural sheen, free of the sort of electronic glaze or film that seems to afflict most tube preamplifiers. Textures were not only squeaky clean, but imbued with the palette of vivid and fresh colors typical of live music. The tonal balance was as finely tuned as a Formula One race car suspension. There was no undue emphasis of any particular spectral region. The midrange sounded expansive but underpinned by a strong bass range and an effortless treble range. Of course, ultimate bass range definition and the associated amplifier and speaker impacted extension. After all, it's the power amplifier's job to dampen a speaker's bass resonance.

Silicon Arts ZL-120 Monoblock Power AmplifierThe ZL-120's sonic character perfectly complemented that of the line stage. Speak about clarity and transparency to die for! If I had to label its sonic character in a single word, "exhibitionist" would fit the bill perfectly. I think that's an apt label and a tribute to the manner in which it exposed the nuances of the midrange. Transients were uncoiled with speed and precision. Low-level detail appeared to bubble to the surface of a recording without attendant grain or brightness. Subjective distortion levels remained low even when driven hard, always an issue with solid-state power amplifiers. Tonally, its character hovered around neutrality. This was not a romantic sounding amplifier. If your system is in need of added warmth, you should look elsewhere. If your tastes run towards a soft presentation, then you'll be disappointed. While it's possible for an extended bandwidth design such as the ZL-120 to sound smooth and refined, excessive liquidity is in my experience symptomatic of limited bandwidth. Think single-ended triode amplification, with constricted output transformer bandwidth, that struggles to reach 20kHz. That's a recipe for transient softness. The ZL-120 avoids tube softness without ever sounding mechanical or forced in its delivery, and in this respect it transcended most of the solid state designs that have roamed the earth during the past 40 years.

Unusually for a solid-state amplifier, soundstage spatial impression was nearly 3D while image outlines were nicely fleshed out. Massed voices were readily resolvable. This was no "water color" rendition. Individual voices did not run or blend together into a homogeneous spatial blob and instead were given distinct features. And most important of all, there was plenty of dynamic propulsion. With the right speaker load, all rocket thrusters were engaged. This was no dull, polite, smooth, simply going through the motions performer. It kindled microdynamics with verve. And neither were macrodynamics a problem: it shifted gears from soft to loud with conviction, leaving no doubt about its dynamic reserve.

In my opinion, reviewing a power amplifier is one of the most difficult tasks facing a reviewer, as the final impression is critically dependent on the amplifier-speaker interface that can make or break the review findings. Frequently, reviewers simply drop an amplifier into their reference system and the amp either sinks or swims in that narrow context. Instead, I have made an effort to audition the ZL-120 with several speaker loads in order to obtain a fair and balanced view of its performance. It became clear over time that this was no universal amplifier that mated perfectly with a wide range of loads. By virtue of its avoidance of global feedback, output impedance is high by solid-state standards, probably approaching 1 Ohm. That opens the door for interactions with the speaker's impedance magnitude, especially in the case of a capacitive load that dips to around 1 Ohm in the extreme treble.

For example, it rolled off the extreme treble of the Final Sound 1000i ESL, noticeably altering the perceived tonal balance. Relative to amplifiers such as the LAMM Audio ML1.2 Reference monoblocks and Son of Ampzilla 2000 the treble loss amounted to several dB above 10 kHz. Another side effect of a high output impedance is reduced bass damping factor. A common complaint of mine had to do with loss of bass definition. Bass lines were generally not tightly controlled, and certainly not to the exemplary standard set by the LAMM Audio amplifiers. But there was one glorious exception. With the TEAC Esoteric MG-20s, it was master and commander, besting all other amplifiers in the house. Bass definition was no problem and layers of veiling were lifted away from the soundstage, making for a stronger connection to the original performance. The coherence and harmonic integrity of the MG-20s were totally in evidence. The experience was so musically compelling that it reminded me of listening to a live microphone feed in a recording studio. Now that's a marriage made in heaven and highlights the need to seriously investigate synergy, the cooperative action of several components, when building one's audio system.



There is no doubt in my mind that Masataka Tsuda's designs push the state-of-the-art forward, in both solid-state and vacuum tube design arenas. Now that's a remarkable feat! His "secrets" have nothing to do with complicated and overly designed circuitry, but reside in the potent combination of a minimalist (but not too simple), Zen-like design philosophy and perfectionist execution focused on parts quality and circuit layout. The end result is fantastic transparency and clarity a closer approach to the live experience in the home. In particular, I cannot imagine life without the Concert Fidelity CF-080 line preamplifier. It is the best of the best; king of the hill, and it gives me great pleasure to declare the CF-080 as my new reference.



ZL-120 Power Amplifier
Type: Monoblock power amplifier
Power Output: 120 wpc @ 8 Ohms
Power Bandwidth: 0.5Hz to 100 kHz (-0.8dB)
Frequency Response: 0.5Hz to 30kHz (0dB), 0.5Hz to 100KHz (-0.8dB)
THD+N: 5W=0.102%
IMD: 0.1% at rated power, SMPTE 4:1 method
Input Sensitivity: 2V for Rated Power 
Input Impedance: 20kOhm (Low), 100kOhm (High)
Voltage Gain: 20dB
Dimensions: 450 x 150 x 360 (WxHxD in mm)
Net Weight: 48 lbs
Price: $23,000 per pair 


Concert Fidelity CF-080 Line Preamplifier
Type: Stereo vacuum tube preamplifier
Inputs : Four line level 
Input Impedance: 100kOhms 
Gain: 6dB 
Tube Complement: two 12AU7 for gain (tube-swapping possible, NOS tubes preferable); and one 6CA4 for rectification 
Dimensions: 450 x 100 x 310 (WxHxD in mm) 
Net Weight: 19 lbs.
Price: $18,000


Company Information

Silicon Arts Design & Concert Fidelity, Inc. 
598-13 Nagakura
Karuizawa-machi, Nagano-ken

Fax: +81-267-44-6184
E-mail: info@siliconarts.jp
Website: www.siliconarts.jp














































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