Act I: Where's the Soprano?
The U280-SC Blacks arrived the same day that John Quick and Brad O'Toole of dCS stopped by with review samples of the dCS Vivaldi 2.0 and Network Bridge. As I prepared lunch for our starving fish and…
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Also on the top deck are blue LEDs to indicate the power tubes' bias and operation. These light up only after several minutes, when autobiasing is completed and the U280-SC is ready to be used, and change intensity with the output level. If an LED's illumination remains constant, dims, or is rarely activated, there's likely a problem with the associated tube.
Sidebar 1: Specifications
Description: Tubed stereo power amplifier, strappable for mono, with selectable output transformer taps (8, 4, or 2 ohms) and modes (Ultralinear, Triode). Tube complement: four 12AU7, four KT88 (or 6550, KT99, KT100, KT120, KT150). All measurements at 8 ohms 1 khz input voltage 127V AC. Rated power output before clipping: stereo mode, 50Wpc Ultralinear (17dBW), 25Wpc Triode (14dBW); monoblock mode, 100W Ultralinear (20dBW), 55W Triode (17.4dBW); Inputs: 1 pair unbalanced (RCA). Outputs: 2 pairs binding posts. THD at 7V RMS output: 0.08%. Power consumption: 170W…
Sidebar 2: Associated Equipment
Digital Sources: dCS Paganini SACD/CD transport & Rossini DAC & Scarlatti Clock; Oppo Digital UDP-205 universal BD player; Apple MacBook Pro with Intel i7, SSD, 8GB RAM; external hard drives, USB sticks.
Power Amplifiers: Pass Labs XA200.8 monoblocks.
Loudspeakers: Wilson Audio Specialties Alexia, Harbeth M40.1.
Cables: Digital: AudioQuest Diamond (FireWire, Ethernet), Wireworld Platinum Starlight Cat8 (Ethernet), Nordost Odin 1 & Odin 2 & Valhalla 2 (USB). Interconnect, Speaker, AC: Nordost Odin 2.
Accessories: Grand Prix…
Sidebar 3: Measurements
I measured one of the the Margules U280-SC Blacks (S/N B-50003950517) using my top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It"). With two modes of output stage—Triode and Ultralinear—three choices of output-transformer tap, and the option of having its two channels strapped for mono operation, the Margules U280-SC is actually 14 different amplifiers in one enclosure. Although Jason Victor Serinus exclusively used the amplifiers as a pair of monoblocks, I performed a complete set of measurements for all 14 mono and stereo modes…
Manufacturers' Comment
Editor: Thank you for your time and effort put into the measurements of our amplifiers for this review. Your measurements are correct, but we must point out that the Margules U280-SC Black is definitely not a conventional tube amplifier. It has a different design approach, so it should be treated as such, and your comments are a good opportunity to explain the engineering behind the amplifier and to shed light on why Jason Victor Serinus's auditory evaluation and your technical measurements have differing outcomes.
Respectfully, and in the interest of…
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