August 1999Margules Audio U280sc Amplifier
by Mike Masztal
Margules Audio - Tel Rad S.A. is a family-owned company that researches, designs, and manufactures preamplifiers, power amplifiers, and loudspeakers. The origins date back to 1926 when Jacobo Margules founded Emporio Electrico, which later became Casa Margules specializing in electrical components for radio broadcasters, radio amateurs and service technicians. That company then became Radio Surtidora S.A., the oldest company in Mexico. Margules currently specializes in electronic measurement equipment and industrial electronic components. Tel Rad was founded in 1954 as the manufacturing branch for audio components, and for the past 14 years has developed its own technology.
Julian Margules designs all of the products. He started as an electronics hobbyist at a young age and built his first amplifier when he was 12 years old; he is about to obtain his Ph.D. in Engineering Sciences. Margules is the president of Mexicos Consumer Electronic Association and also technical advisor for the Mexican audio magazine ALTAVOZ.
While all of the Margules products at the CES looked and sounded great, it was the amplifier that really caught my interest. The $3250 U280sc has got to be the most versatile and user-friendly amp Ive seen in a long time. It offers a wide variety of functions that would appeal to a large number of audiophiles. All controls for the various functions are located on the top of the amp, making access a breeze. These controls include: an ultralinear/triode switch for each channel, individual volume controls, a stereo/mono strap switch, and impedance selectors offering 2-, 4-, and 8-ohm output. The tube complement is four 12AX7s in the driver/gain stage and four 6550 power tubes. The U280sc also accepts KT88, KT90 and KT99 tubes without any internal modification. While the separate volume controls can allow for plugging a CD player or DAC directly into the amp, they also allow precise output balance (useful with many of todays preamps that dont have balance controls) and balance in bi-amplified systems.
Operation is class A using "Active Servo Bias" (patent pending), which actively tracks the input signal and permits full class-A operation without saturating the output transformer and overdriving the tubes. The Active Servo Bias also sets DC bias and AC drive levels so that no drive or bias adjustments are needed and new tubes may be installed without any complicated setup. Additionally, the U280sc uses zero feedback. While this usually results in a low damping factor and marshmallow bass, Margules has developed BEFS (Back Electromotive Force Sensor), which reportedly changes the amplifiers output impedance as the load requires.
Looking under the chassis shows excellent wiring, metal film resistors, polypropylene capacitors and a silver-coated PC board. The U280scs appearance belies its weight. Measuring 17.5"W x 14"D x 7.5"H, it weighs in at a hefty 64 lbs. Output power is 60Wpc in ultralinear and 30Wpc in triode. In monoblock configuration, the output is 120 watts in ultralinear and 60 watts in triode.
Source: CAL Delta transport, CAL Alpha DAC retubed with Mullard 12AX7 tubes, Audiomat Tempo2 DAC. Preamp: Aronov LS-9000. Amps: Aronov LS-9100 monoblocks sitting on Golden Sound DH cones and squares and Osiris Giza bases. Speakers: Silverline Panatella, SR17 or Equation 7. Interconnects: JPS Superconductor, Silverline Sterling. Speaker cables: Silverline Sterling Signature. Power Cords: JPS Labs Digital AC, Analog AC and Power AC cords. Accessories: TDS Passive Audiophile. All components were plugged into a homemade, non-filtered outlet strip that in turn was powered by a dedicated outlet. My listening room is 12'W x 18'L x 8.5'H and complemented by Corner Tunes and homemade "room tunes."
Given the variety of tubes the U280sc will accept, I experimented with the Svetlana 6550Cs (supplied), EI KT90s and Sovtek KT88s. All tubes had distinct sonic characteristics that might appeal to different users. The Svetlanas had their usual warm, friendly midrange and reasonably controlled bass and highs, while the Sovteks had an exaggerated bass and some lack of clarity in the mids and highs. The EI KT90 was the best output tube in the amp. It had the most linear sound and was slightly better-sounding than the Svetlanas. I recommend that all owners of 6550-based tube amps check out the KT90.
The U280sc offers both ultralinear and triode modes. After careful listening to both modes, I found I preferred triode for most types of music. The air and dimensionality the amps produced made long-term listening totally effortless and non-fatiguing, and the bass was better than you might think. The ultralinear mode was, of course, a bit punchier and better suited to heavy jazz and rock, but the soundstage didnt have the dimensionality of triode mode. Actually, I consider the switching capability a strong attribute of the U280sc as it offers the listener a real choice in customizing the sound he wants from his amp. I also tried using the volume controls provided on the U280sc and got very good results with proper harmonic texture and decent soundstaging, but using a preamp does produce a tad more refined sound.
Running through some of my favorite CDs, I first put on "You Wont Forget Me," the title cut from the Shirley Horn collection that features Miles Davis [Verve 847 482-2-4]. Horns skillful piano work meshes wonderfully with Miles Davis characteristic muted trumpet, creating a romantic mood heightened by the U280scs bloom and texture. A neighbor was visiting during this listening session and seemed aroused listening to this CD. He asked to borrow it for what I believe ended up being an amorous evening. This album, along with the rest of Horns albums, is an extremely well-recorded offering with excellent ambience and soundstaging.
Even the over-played Diana Krall discs sounded fresh through the U280sc. While Love Scenes [Impulse IMPD-233] may be the more popular of her recent two releases, All For You [Impulse IMPD-182] is probably the better recorded of the two discs. Cuts like "Frim Fram Sauce" and "Boulevard of Broken Dreams" possess a decent amount of low-level detail that is deftly handled by the Margules amp without the hyper-detailed harshness that first impresses, then fatigues.
Its easy to see why many classical music lovers gravitate toward triode amplifiers. The Bach and Scarlatti guitar transcriptions heard on Baroque Inventions [Dorian 90209] and featuring Julian Gray and Ronald Pearl have some very quick passages that are reproduced without any smearing or loss of the guitars tonality. Barbara Bonneys lovely soprano flows from the U280sc. Her excellent Teldec recording Schubert Lieder [Teldec 4509-90873-2] has her voice and piano wonderfully reproduced. Which cut? All of them.
Orchestral passages are handled well too. Despite triodes having a reputation for being, well, sort of soft, the U280sc can handle loud, room-filling transients without sounding exhausted. Mussorgskys "Great Gates of Kiev" on Reference Recordings Tutti! [Reference Recordings-906-CD] should portray a soundstage larger than the room, and the U280sc accomplishes just that. The drive, anticipation and excitement of this recording clearly come through and lead up to the climactic finale.
The drum solo on "Nardis" from Patricia Barbers Café Blue [Premonition 737-2] is a good cut to discern the difference in the U280scs operating modes. The ultralinear mode has impressive dynamics and a clearly delineated trap set, but in triode the sound gains more texture and three-dimensional body. This isnt to say that the ultralinear mode lacks performance. It sounds better than a lot of other amps out there, but the triode is just sooooo good -- way better than other triode amps Ive heard.
In comparing the Margules U280sc to my Aronov monoblocks, I found the differences between the amps quite striking. The Aronov monos have much of the bass control of solid-state amps and the musicality of tubes, including an impressive midrange, sweet highs and good soundstage dimensionality. Listening to the Margules in the ultralinear mode, I found its sound quite similar to that of the Aronovs, albeit a tad more two-dimensional. The U280 was also a bit less punchy, but then there is a sizeable difference in the power ratings: 60Wpc for U280sc versus 110Wpc for the Aronov amps.
I heard the biggest differences with the U280 operated in triode mode. The Aronov monoblocks simply do not have the refinement and spatial resolution of the triode Margules U280sc. Had I the opportunity to do the review with two U280scs in triode-mono configuration, I believe the punch and bass output would easily have rivaled that of the Aronovs. Rockers would probably prefer the Aronovs, but anyone listening to vocals, jazz, small ensemble or orchestral music should hear what the triode U280sc can do.
Julian Margules has done a commendable job designing and building an excellent amplifier that offers the consumer real options for customizing its sound. Build quality is first rate, and I think other manufacturers can learn a lot about functionality from Margules. The sound of the U280sc that initially drew my attention at the CES didnt disappoint me after having spent several weeks with the amp, proving that the U280sc is worth considering for the long haul.
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