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Margules Audio U280SC Black Power Amplifier
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The U280SC Black high end tube amplifier, with over 20 years of evolution, is positioned as a sonic reference thanks to its ability to produce a sweet, lively natural sound, full of detail, richness and precision. Its full Class A, adjustments free design, has turned it into a favorite in the demanding audiophile community for its abilities to drive a wide variety of loudspeakers.


U280-SC Black
Stereo Tube Amplifier
“Just when you thought everything was written, a new idea comes and
restates everything to approach perfection”
The U280 Project began 30 years ago, where it was issued the first active
servo control that allows for the first time the use of the tubes in full class A
without any adjustments and an unprecedented thermal efficiency. Today
we began a complete new and fresh design of the original idea with all the
accumulated knowledge and experience of all these years.
The U280SC Black Stereo Tube Amplifier combines the superior sound of vacuum tubes
with new and innovative technologies.
The results are clearly apparent in its quick detailed dynamics and ultra-smooth transient
response. Unusual versatility and unprecedented reliability provide an exceptional perfor-
mance upgrade to an already remarkable amplifier.
Class-A Output Stage & Active-Servo Bias
Vacuum tube power amps with class-A outputs are rare. Class-A operation causes the
tubes to run quite hot, and increases the chance of saturating the output transformer.
Margules has resolved this problem by incorporating a redesigned Active Servo Bias 12
generation, with a faster and precise bias setting.
The active servo bias actively tracks the input and output signal, allowing a full class-A
output at any level or mode, without overdriving the tubes and transformers.
Active Servo Bias also sets DC bias and AC drive levels, assuring optimum electrical and
sonic performance throughout the lifespan of the output tubes, no drive or bias adjust-
ments are ever needed. New tubes can be installed without test equipment or time-con-
suming setup.
Active Servo Bias also makes possible to use a variety of output tubes. The
6550, KT88, KT99, KT100, KT 120 can be interchanged without modification.
Active Servo Bias is implemented with semiconductors, which are designed for the
aerospace industry, assuring long, trouble-free operation.
The New U280-SC Black Stereo Tube Amplifier includes a new and improved differential
output circuit, for further reduction of the THD and transient distortion.
Ultralinear / Triode & Strapped Operation
Audiophiles have argued the merits of Ultralinear v Triode operation for 50 years. Triode
operation provides lower distortion in the odd harmonics, at the price of reduced power
The U280-SC resolves this predicament by providing switchable Triode / Ultralinear opera-
tion. For those listening sessions where you prefer a softer sound, you simply switch to
Triode Mode. And when more power and punch is needed, you simply switch to Ultralinear
Unlike most vacuum tube amplifiers, the U280-SC's outputs can be strapped, for twice the
output. Start with a single amp, then add a second U280-SC for increased power.
Separate gain controls for each channel make precise balancing easy. This simplifies the
setup of bi-amped systems, as well.
Regulated Shunt Power Supply
The input stages of the new U280-SC 25th anniversary include a special SHUNT power
supply for these critical circuits. Shunt technology provides a dramatic improvement in Q
damping, the key factor in regulating voltage for those stages.
Good regulation reduces the loss of signal integrity that occurs when the signal itself shifts the amplifier’s operating point. Each channel uses separate
regulators that further improve the U280-SC’s already excellent imaging.
Damping is critical to overall performance including smoother transient response and overall staging. Further improvements in quickness, dynamics
and the overall life-like listening experience result..
Our new Power Supply is virtually indestructible due to specially designed regulation technology that protects the amp from major tube failures.
Zero Feedback
The U280-SC does not use negative feedback as do most tube amplifiers. Negative feedback results in a loss of detail and sound richness. Margules
has developed the BEFS (Back Electromotive Force Sensor), which changes the amplifier’s output impedance per load requirement. BEFS along with
the active servo allows the amplifier to drive difficult speaker loads with exceptional efficiency, dynamics and extended controlled bass.
The U280-SC's Black improved technology and aesthetic design is complemented with a new
epoxy pc boards lay out, military grade potentiometers, precision metal-lm resistors and audio grade interstage capacitors.

Ultralinear: 75w
Triode: 40w