Positive Feedback ISSUE 42
march/april 2009

silicon arts design

ZL-120 amplifiers

as reviewed by Mike Wechsberg

One of the great things about reviewing for PFO is the opportunity to listen to some terrific equipment in my home rather than in a store or show environment, including gear that is only affordable to the very fortunate. The Silicon Arts Design ZL-120 is an example. Silicon Arts Design is a Japanese company somehow affiliated with another company named Concert Fidelity Inc. Actually these two appear to be the same company but with separate identities. I recently reviewed the Concert Fidelity CF-080 line stage, which I found to be an outstanding instrument (see PFO issue 41). The same brilliant person, Masataka Tsuda, who is slowly creating a legend with his exemplary electronic designs, designs the ZL-120.  Where the CF-080 is a hybrid design using a combination of tube and solid-state devices, the ZL-120 is a pure solid-state design. The amplifier has a switchable input impedance to enhance compatibility with either tube or solid-state preamps. This is noted in these basic specifications from the Silicon Arts web site:

• Input: RCA only

• Input Sensitivity: 2V for Rated Power

• Power Output: 120W / 8Ω; 200W / 4Ω

• Frequency Response: 0.5Hz to 30KHz (±0dB); 0.5Hz to 100KHz (-0.8dB) @0.125W

• Input Impedance: Selectable between 20KΩ (for use with solid-state line stages) and 100KΩ (for use with tube line stages)

• Voltage Gain: 20dB

• Power Requirements: 110-120VAC / 60Hz

• Power Consumption: 140W (Operation)

• Dimensions: 450mm (W) X 150mm (H) X 360mm (D)

• Net Weight: approx. 20KG per monoblock

A major design driver for the ZL-120, that the company follows "fanatically" according to their web site, is keeping the circuitry simple and signal paths as short as possible. The theory is to keep anything that might harm the music as it passes through the amplifier to a minimum. This philosophy requires an especially deep understanding of electronic circuits and devices. The ZL-120 uses just two pairs of MOSFETs per channel to realize its 120W of output, and the circuit layout is very cleverly arranged. Instead of parts scattered throughout the chassis as in most similar designs, all the components are concentrated in the center of the chassis. Heat sinks are mounted internally and surround the other electronic components. The chassis is a simple rectangular aluminum box with ventilation holes on the top and bottom. The understated and elegant front panel has just a lighted power switch and a second indicator light (labeled "operation") that illuminates when the amplifier leaves the mute mode. The back panel has the RCA input connector, two pairs of good quality output terminals for bi-wiring, and a connector for the power cord. There is also a toggle switch that changes the input impedance as mentioned above and a second toggle for grounding that can be used to minimize hum in the system. The amplifier is internally bridged so the ground is ordinarily floating.

The manual that comes with the ZL-120s implies that only a couple of days of playing are required for break-in, and right out of the box the amplifiers sounded a bit flat. I let the amps play for 24 hours straight and then gave them another week of casual playing one or two hours a day before I began any serious listening. Silicon Arts Design requires the user to install four mounting feet on each amp. The ones supplied are pretty perfunctory plastic feet but the manufacturer anticipates the user will substitute alternative feet of his choice. Well I didn't have any spare feet handy so I used those that came with the amps. I placed each amp on a Target stand, which seemed to work fine as you'll read below, but I'm sure you can squeeze a bit more out of these amps with better vibration isolation. The same can be said for the power cord. The ZL-120s come with decent quality AC cords, but the user is encouraged to try others. I used the ZL-120s with their companion Concert Fidelity CF-080 Line Stage that I reviewed recently in Positive Feedback Online. Together the two make a wonderful pair. The sound was slightly better with the input impedance switch set to 100Kohms with this pairing. For most of my listening I hooked up the ZL-120s to my Wilson Cub speakers using MIT cables. I tried MIT and Audioquest cables for the input but settled on the Audioquest as the better match. I'm sure this equipment can sound even more spectacular with more upscale cables as the amplifiers are designed to be very revealing. I tried the amplifiers plugged directly into the wall socket and also operating from the PS Audio Power Plant Premier. On my Krell amplifier this change made a dramatic difference, but on the ZL-120s the difference was subtler. This may mean the ZL-120 has a more effective power supply design compared to the Krell, or it may just mean that the power coming into my house was well behaved that day. In either event, the soundstaging and depth perception were both improved with the monoblocks plugged into the Power Plant so that is the way I left things for the majority of my listening.

How do the ZL-120s sound? Absolutely wonderful! Some of the adjectives I would use to describe them are fast, dynamic, refined, and revealing. They don't give you the big, fat, warm sound of some tube amps, but neither do they sound thin or harsh like some solid-state gear. First, the low end is very fast, tight and accurate. My Wilsons aren't capable of exploring the very lowest depths, but the ZL-120s made them sound as "ballsy" as I've ever heard them and at least as good as the Krell KAV-250 that they replaced in my system. In fact, the ZL-120s had better bass transients than the Krell (this is also a virtue of the Concert Fidelity line stage) and more detail in the low end as well.

For me midrange is all about how voices sound and here the ZL-120s put on their best face. Combined with the Concert Fidelity line stage rendering of both female and male voices was about as realistic as I've heard out of my system and room. Whether it was opera from Renee Fleming, classic pop from Julie London, or modern jazz from Patricia Barber the ZL-120s made female vocalists seem like they were singing in the room. Oddly the quality of the accompanying voices and instruments was, as a whole, a little less realistic and highly recording dependent. Male vocalists like classic Johnny Cash or Roy Orbison sounded equally impressive, especially the chest tones. I found it especially easy to follow the lyrics with these monoblocks compared to other amplifiers I've listened to lately.

In classical music I enjoyed smaller pieces like solo piano or string quartets more than I normally do. I think these amps revealed more of the microdynamics and small-scale dynamic contrasts than I was used to thus enabling a more emotional connection with small-scale music. The big bombastic symphonies were appealing for the same reasons. I listened to three versions of the Dvorak 9^th Symphony through these amps just to gain more of an appreciation of the how each conductor handled small shadings in interpretation. The ZL-120s were great at revealing such subtle differences, which are so important to the emotional impact of the music.

The best way to describe the high frequencies of the Sonic Arts Design amplifiers is "sweet". I tried an experiment. I wasn't feeling that I was hearing all that was there in the highs through the Wilson speakers so I rolled out my old pair of Apogee Centaur Minors. For those who don't remember this is a ribbon speaker, crossed over to a sealed-box dynamic driver for the lows. I just plopped the Apogees down next to the Wilsons so they didn't integrate that well into the room, but I focused just on the high frequency end produced by the ribbon. It was wonderful—extended, transparent, and very sweet. Those subtle high-end sounds such as cymbals, triangles, violin upper harmonics, etc. that can make or break a recording were all reproduced with astonishing clarity.

Silicon Arts Design has also provided soundstaging champs in the ZL-120s. The soundstage I heard through these amps was amazingly broad with distinct depth layers. Instruments were placed rock solid on the stage with plenty of air around them. Nothing to complain about in this area.

I haven't yet given you any comparisons between the ZL-120s and other amplifiers. Clearly these monoblocks are the best amplifiers I've had in my home over the past few years. They are better amplifiers in many ways compared to my stock Krell amplifier (they had better be as they cost nearly 10 times as much). Probably the closest competitor I've heard recently is the Clayton M300 monoblocks that I reviewed back in Issue 40. The Claytons did an astonishing job of making my speakers disappear, and they were equal to the Silicon Arts Design amplifiers in low-end clout and dynamics. In my system anyway I would give the Clayton's a slight edge in soundstaging and imaging, but the Silicon Arts Design amplifiers are better in most other ways; far as memory serves since I no longer have the Claytons here to compare to. The Claytons are about half the price of the Silicon Arts Design amps and they provide more than twice as much power, quite a bargain as these things go (If both amplifiers were made in the USA like the Claytons they might end up retailing for about the same price. The current high value of the Japanese yen hurts the Silicon Arts Design amps in the marketplace). But Silicon Arts Design has accomplished a spectacular amplifier design. I've not had experience with some of the best amps out there but surely the ZL-120s must rank way up there.

In conclusion, I encourage you to seek out the Silicon Arts Design ZL-120 amplifiers even if just to listen to how a superior amplifier can elevate your musical enjoyment for a few minutes. They are hard to afford, especially in these troubled economic times, but I hope there are some out there who will take the plunge because we need to encourage this level of audio engineering art to continue. Mike Wechsberg

Silicon Arts Design ZL-120 amplifiers
Retail: $24,000 per pair (soon to be raised to $28,000)

Silicon Arts
web address: www.siliconarts.jp/index.html