Margules U280sc 25th User Manual

Margules Audio
Amplifier U280SC
Congratulations!
The Margules U280-SC 25th Anniversary Stereo Tube Amplifier
combines the superior sound of vacuum tubes with new and
innovative technology. The results are clearly apparent in its quick
detailed dynamics and ultra-smooth transient response. Unusual
versatility and unprecedented reliability provide an exceptional
performance 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 an Active Servo
Bias (patent pending). The bias actively tracks the input signal,
permitting full class-A output, without overdriving the tubes.
Active Servo Bias also sets DC bias and AC drive levels, assuring
optimum electrical and sonic performance. Throughout the useful life
of the output tubes, no drive or bias adjustments are ever needed.
New tubes can be installed without test equipment or time-
consuming setup. Active Servo Bias also makes it possible to use a
variety of output tubes. The 6550, KT88, KT99, KT100, KT 120,
KT150 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 25th Anniversary Stereo Tube Amplifier includes
a new and improved differential output, as well, further reducing the
THD and transient distortion.
25 anivesary
Ultralinear / Triode & Strapped Operation
Audiophiles have argued the merits of Ultralinear v Triode operation
for 50 years. Triode operation provides lower distortion, at the price
of reduced power output.
The U280-SC resolves this predicament by providing switchable
Triode / Ultralinear operation. For those listening sessions where you
prefer a more soft sound, you simply switch to Triode Mode. And
when more power, dynamics, detail and punch is needed, you simply
switch to Ultralinear Mode. .
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—or to convert to triode
operation at the same power level.
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