amplifier module
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amplifier module
The 250MR power amplifier includes a self-
contained power module, as shown above.
The module is a complete amplifier, with its
own power transformer, bridge rectifier,
energy storage capacitors and amplification
stage, requiring only mains supply and
control signals to function.
Control signals are used to switch the
amplifier module on/off and to protect it in
case an error condition, such as a short
circuit in the loudspeaker, is detected.
the traditional TO3, enhancing the amp-
lifier’s reliability for many years to come.
exceptionally accurate quiescent stability
It is universally accepted that accurate
setting and stability of quiescent conditions
is crucial to optimal Class-B amplifier
operation. The bias range over which the
best linearity is obtained is narrow, and
on either side of it crossover distortion
increases markedly. The 250MR has one
of the most accurate quiescent controls
ever implemented, stabilising against
output level, load impedance and mains
voltage changes.
sophisticated muting
The 250MR has a sophisticated muting
system, which stops you hearing loud,
annoying switching noises and protects
both the amplifier and the loudspeakers.
Particular care has been taken to make
sure that the muting circuitry, when
switched off, doesn’t affect the sound
quality. For this purpose carefully selected
relays with minimal crosstalk between coil
and contacts have been used.
an optimised mix of global and local
negative feed back
The 250MR gives excellent linearity and
low distortion without relying on high global
negative feedback, which can present
difficulties when handling rapidly changing
signals. The amplifier implements at each
amplifying stage a controlled amount of
local feedback, which not only linearises
but also defines the gain and other vital
parameters closely.
cascode compensation
The 250MR uses an advanced stabilisation
concept called Cascode Compensation.
This might be the first time that this
sophisticated and elegant system has been
used in an audio amplifier. Its advantages
are excellent stability, inherently good
supply-rail rejection and a reduction in DC
drift. This gives outstanding stability with
performance drifts being virtually eliminated.
output transistors
The output devices are bipolar junction
transistors chosen for maximum linearity. The
advanced MT-200 package is used which
gives a greater area for heat transfer than
The module has a high-efficiency aluminium
heatsink for excellent heat dissipation,
allowing it to drive even the most critical
loudspeakers safely and dependably. This
results in uncompromised sound quality
with perfect channel separation.
Each 250MR delivers typically 255 Watts
into 8 ohms, 400 Watts into 4 ohms and
will drive 1000 Watts into 2 ohms for short
durations.
As a result of the 250MR‘s monobloc
construction, this performance is wholly
independent of the number of system
channels being driven and thus even
during the loudest passages of your
favourite movie the soundstage remains
stable, controlled and detailed.
There are many design features which have
been derived from our excellent 100x5R
and our F1-600MR amplifiers to make this
amplifier very special. We have listed a
few on the following pages.
deep under the skin
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