ZL-120 Monoblock Power Amplifier &
CF-080 Line Preamplifier
D.O. finds new reference a new reference!
Review By Dick Olsher
here to e-mail reviewer.
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.
During 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.
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.
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.
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
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.
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
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)
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
Type: Stereo vacuum tube preamplifier
Inputs : Four line level
Input Impedance: 100kOhms
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.
Silicon Arts Design & Concert Fidelity, Inc.