Margules U280SC User Manual

Amplifier U280SC

Margules Audio

Amplifier U280SC

Congratulations!

The Margules U280-SC amplifier combines the superior
sound of vacuum tubes with innovative technology. The
result is exceptionally good sound and unusual
versatility.
You acquire a piece that is state of the art, we are
positive that will bring you long hours of listening
enjoyment.

Introduction:

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 gotten around this problem by
incorporating Active Servo bias (patent pending).
The bias actively tracks in input signal, permitting full
class-A output, but without overdriving the tubes.
Active Servo Bias also sets DC bias and AC drive levels
automatically, 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 a
time-consuming setup.

Active Servo Bias also makes it possible to use a variety of
output tubes. The 6550, KT88, KT99, or KT100 can be
interchanged, without modification.
Active Servo Bias is implemented with semiconductors
designed for the aerospace industry, assuring long, trouble­free operation.

Regulated Power Supply

The input and driver stages incorporate classic, time-proven
circuitry used by many other manufacturers. The U280-SC’s
design differs because it includes tightly regulated high
voltage for these critical circuits. Good regulation reduces the
loss of signal integrity that occurs when the signal itself shifts
the amplifier’s operating point.
Each channel has separate regulators for improved imaging.

Zero Feedback

The U280-SC does not use overall negative feedback. This
would normally result in a low damping factor, which is not
desirable for most speakers. Margules has developed the
BEFS (Back Electromotive Force Sensor), which changes
the amplifier’s output impedance as the load requires.
BEFS permits the amplifier to drive difficult speaker loads
with exceptional dynamics and extended, controlled bass.
The U280-SC’s innovative design is complemented with
precision metal-film resistors and polypropylene capacitors.