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November / December 2004
The CODA Power Amplifier S12
Exterior Tour The rear panel has the corresponding input jacks, one set of five-way loudspeaker terminals, the IEC AC input, and a main power rocker switch. (CODA recommends that the amplifier be left powered up at all times, with operation enabled by the Bias switch.) I tip my hat to CODA's designers for placing the signal inputs and outputs along the top of the rear panel, facilitating the use of bulky audiophile cables. Impressively heavy-duty heat sinks extend front to back on the left and right sides of the chassis. Supplied with the review amplifier was an optional universal learning remote control, chock-full o' buttons. Most of its functionality appears to be intended for controlling a CODA preamplifier. For the S12 it enables remote on/off of the Bias standby and RCA/XLR input switching. I confess I never took the remote wand out of its bubble wrap, since I had no need to access either of those functions from my seat during listening sessions.
Technical Highlights Like many solid-state amplifiers, the S12 delivers more power as the speaker load impedance drops: the nominal both-channels-driven continuous power rating of 125 wpc into 8 ohms doubles to 250 into 4 Ohms and quadruples to 500 into 2 Ohms. In bridged mono mode the S12 puts out 500 watts into 8 ohms and 1,000 watts into 4 ohms. CODA's "Precision Bias" is configured in the S12 to produce up to 20 wpc of pure "Class A" power; the amplifier transitions into "Class AB" operation at higher levels. CODA offers a sibling amplifier, the S5, which is essentially identical in hardware and price to the S12 but biased to produce a maximum 55 wpc in "Class A." In addition, the company's web site now shows monoblock models whose appearance and power ratings are very similar to the bridged stereo amplifiers. Despite those similarities, the monoblocks differ from the bridged stereo amplifiers. The monoblocks have a high-impedance balanced configuration that provides better distortion specifications than the bridged amplifiers, and unlike the bridged amps they may be connected via an unbalanced RCA input as well as a balanced XLR input. CODA has made very good choices in the circuit design and parts for the S12. The input stage has a MOSFET-based voltage gain configuration, whereas many solid-state amplifiers use current gain stages for both input and output. A voltage gain input stage typically sounds smoother and less aggressive than current gain, and is often described as having a more "tube-like" sound. The output stage employs 60 high-speed (50Mhz) bipolar transistors in a current gain configuration; each is rated at 8 Amperes and 150 Volts. Given the amplifier's 125-wpc maximum power rating, this must be regarded as luxurious -- approaching extravagant -- overbuilding. No doubt the generous headroom built into the output stage is a major factor in the ability of the S12 to swing over 100 Amperes of current on transients-a number that exceeds many amplifiers nominally rated for higher power output. It goes a long way toward explaining the sense of relaxation and effortless dynamics that has characterized my experience of listening to the S12. This direct-coupled high-speed audio circuit is well isolated from the amplifier's support circuitry. There are no capacitors in the audio path, and no global feedback is used. This "minimalist," very pure circuit achieves the very low output impedance of 0.04 ohms and a damping factor of 200, numbers that predict very effective control of loudspeakers. An especially valuable safeguard for this fast DC-coupled amplifier is the proprietary input filter, which blocks incoming DC and other line noises from entering the signal path. Pressing the Bias (standby) button deactivates the bias current that drives the output stage, leaving the rest of the amplifier fully powered up. That means that when the bias current is reactivated, the S12 reaches thermal stability and its characteristic sonic profile within a few minutes rather than the hour+ typically required from a cold start. An examination of the interior of the S12 reveals many examples of quality construction. The S12 is quasi-dual mono with independent transformer windings, rectification and power supply capacitors for each channel. Double-sided gold-plated circuit boards suggest long-term trouble-free use, and the many high-quality parts In evidence include 60 custom wirewound Mills copper/nickel alloy emitter resistors, IXYS fast-recovery rectifiers, and the use of lead-free silver/copper solder throughout the amplifier.
Review Setup The S12 arrived for review at a busy time, when the Donnelly Audio Evaluation Lab -- AKA my living room -- was hosting a number of interesting products for review. I had ample opportunity to see how well it works with not only my reference VTL 7.5 preamplifier and Eggleston Andra II+ loudspeakers, but also the Atma-Sphere MP 3 preamplifier and Oskar Heil Kithara, Von Schweikert VR-4jr and Meadowlark Blue Heron2 loudspeakers. In the interest of economy, I note that the S12 performs flawlessly with both preamplifiers. Since both have fully balanced differential circuit designs, I ran them primarily in balanced mode. However, the performance of the system while driving the S12 from the two preamplifiers' single-ended outputs was nearly indistinguishable from operating in balanced mode. The most notable differences were a slightly quieter, darker background and slightly freer high-level dynamics in the balanced configuration. The S12 also drove the Kitharas, VR-4jrs and Blue Heron2s with no perceptible limitations on headroom; clipping was never audible at any volume at which I was willing to stay in the room. And driven by the S12, all three loudspeakers sounded tonally accurate and harmonically balanced, with impressively broad and deep soundstage presentations. Although I have for about the last decade favored tubes for my reference amplifiers, I never had any sense that these loudspeakers' recreations of the many recordings played through them were in any serious way compromised by this 125 wpc solid-state amplifier. As I would have expected, it was my Egglestons that posed the toughest speaker compatibility challenge for the S12. These loudspeakers are moderately inefficient, and even harder to drive and control than their nominal 86.5dB sensitivity spec might suggest -- especially in the bass, where two isobarically mounted [i.e., one behind the other, with the space between them sealed] 12-inch Dynaudio woofers in a smaller-than-ideal sealed enclosure are specified to produce accurate output into the mid-30Hz range. Of the numerous amplifiers I have placed in front of the Egglestons over the years, none has made them perform better than my VTL MB-750 Reference monoblocks. Those massively powerful 750-watt tube amplifiers are in effect just loafing even when pushing the hard-to-drive Egglestons at neighbor-traumatizing levels. The only solid-state amps that have performed at the same level in this setup are the John Curl & CTC Builders-designed Parasound Halo JC-1 impressive 400-watt monoblocks, which I have previously praised extravagantly in Superior Audio. The comments that follow are primarily based on listening to the S12 in the reference system in place of the MB 750s.
Listening to the S12 To complete the discussion of speaker-driving capability, let me say that the S12 took the Eggleston challenge in stride. Yes, I was able to induce clipping a few times, mostly in traditional system-buster demos such as the Telarc SACD of the 1812 Overture and the huge climax of the "Appian Way" finale of Respighi's Pines of Rome on the Reference Recordings CD. But those instances occurred at "stupid" playback levels - the volumes that an immature audiophile such as yours truly may recklessly go for when showing off his system. At very robust but realistic - as opposed to demonstration -- levels, the S12 always sounded relaxed and fully in control. Once I asked a regular visitor to guess the power of the amplifier that was making the system boogie so energetically, and he was sure it must be at least a 250-wpc amp with lots of headroom. 'nuff said on that subject. Even more impressive -- and important -- is the ability of the S12 to bring to convincing life a broad range of music. I am especially struck by how beautifully the S12 reproduces vocals, from the classical perfection of soprano Renee Fleming to the quirky folk-rock of Patty Griffin to the throaty, torturous stylings of Tom Waits. The S12 also has a pellucid see/hear-through quality, illuminating inner voices and microdynamics so clearly yet unobtrusively that with every listening session I find myself drawn inexorably into the texture of the music, just as happens when I listen to my big VTLs. When these virtues meet the right music-for instance, Rene Jacobs' stunning new authentically "Neoclassical" SACD recording of The Marriage of Figaro (Harmonia Mundi), the result is sheer musical bliss. There really isn't much to complain about with the S12. As one might expect from a carefully executed wideband design, the frequency extremes are superbly reproduced. Bass is lightning fast and extremely well defined, powerful without the exaggerated "slam" so beloved of some amplifier designers. High frequencies are so open and natural sounding, harmonically rich and with abundant air, that I am reminded of my reference VTLs. Thinking back for other comparisons, it seems to me that the S12 sounds very much like a somewhat less-powerful cousin to the aforementioned JC-1 monoblocks. In other words, it delivers about as good a solid-state musical presentation as I have heard, and it is not eclipsed by comparison to my beloved tube amplifiers.
Final Thoughts The Amplifier S12 is the first CODA product I have reviewed, and it has proven to be an auspicious debut. My first thought upon unpacking it was "$3,750 for this little thing?" But having lived with this gutsy, refined and unfailingly musical amplifier for a good three months, I get it. The money is in the sound. Highly recommended, and worthy of placement in Superior Audio!
Specifications Type: Stereo solid-state amplifier
Stereo Mode Bridged Mono Mode Operating Mode: "Class A" to 20 wpc into 8 Ohms, sliding to "Class AB" at higher levels Frequency Response: DC to -3dB at 100kHz Distortion: Less than 0.03% from 10 Hz to 20kHz at 125 Watts, both channels driven, into 2 Ohms through 8 Ohms Gain: 26dB Maximum Current: Greater than 100 Amperes peak per channel S/N Ratio: Greater the 120dB Input Impedance: 50 kOhms unbalanced; 1 kOhms balanced Output Impedance: 0.04 Ohms from 20Hz to 20kHz Damping Factor: Greater than 200 Dimensions: 5.75 x 17.5 x 12.5 (HxWxD in inches) Weight: 45 lbs. Warranty: 10 years, transferable 5 years Price: $3,750
Company Information CODA Technologies Inc. Voice: (916) 383-3653 |
The Amplifier S12 represents the latest generation of CODA's "S Class," amplifiers: DC-coupled designs based on the high-speed circuit topology of the company's flagship System
S100. The S12 is modest in size and unprepossessing in appearance, but sonically quite ambitious. Rated at 125 watts per channel into 8 Ohms, the
S12 delivers a gratifyingly "big" and dynamic sound, driving loudspeakers that typically need higher-powered amplification, delivering a smooth, luxurious, virtually grain-free and spacious presentation.
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