T+A Elektroakustik S10 User Manual - page 26
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Circuit design
The S10 features an overall circuit design which is
unique in the world: the voltage amplification is carried
out with the help of valves (tubes), and all the valves
operate in Class A mode, resulting in a superbly
harmonious sound image. The input stage takes the
form of a symmetrical differential amplifier based on an
all-valve cascode circuit. The result is that the whole
amplifier offers excellent bandwidth and speed.
The current amplifier stages at the input end feature
MOS-FET driver transistors. At the output end the
current amplifiers are equipped with no fewer than
twenty extremely high-performance ring emitter bi-polar
transistors. These transistors satisfy the most
demanding requirements in terms of current delivery
capability and bandwidth.
All the amplifier stages of the S10 are designed in such
a way that they are totally linear and undistorted in
operation. Achieving this performance required the use
of nothing but the best possible components; these
parts are carefully matched to each other and calibrated
in-house for each machine using sophisticated
selection processes.
The level of linearity and bandwidth achieved with the
S10 is so high that it has been possible to avoid the use
of overall negative feedback completely.
Mains section
The S10 features a total of three independent mains
power supply units with three high-quality torroidal
transformers with low leakage fields. A high-voltage
mains section with extremely sophisticated stabilisation
measures powers the valve circuits of the voltage
amplifier section. The constancy of the valve operating
voltages is better than 10 ppm!
The two power amplifiers are fed by two high-perfor-
mance transformers, each rated at 750 Watts, and with
a total reservoir capacity of more than 180,000 µF. This
guarantees more than adequate power reserves at any
time, capable of coping with any imaginable load
situation. Another truly unique feature is the facility to
switch the operating voltage of the S10 output stages
between the values +/- 40 V (High Current mode) and
+/- 80 V (High Power mode). Selecting the lower
operating voltage more than doubles the idle current in
the output stages, with the result that the current
amplifiers of the S10 generate up to about 35 Watts in
Class A mode. We particularly recommend this
High Current mode of operation if your system features
high-efficiency loudspeakers, and for general listening
at normal volume levels.
The High Power mode enables the amplifier to
generate a maximum output of 700 Watts (into 4 Ω).
This mode of operation is especially recommended for
use with high-impedance loudspeakers (impedance
higher than 6 Ohm), and for general use when high
power is required.
Protective circuit
The S10 features a micro-processor controlled
protective circuit which shields the amplifier itself, and -
wherever possible - the connected loudspeakers, from
damage.
The protective circuit monitors the mains voltage, the
internal operating voltages and the operating temperature
of the S10. The loudspeaker outputs are also monitored
for D.C. voltage errors, short-circuit and overload
situations.
If overloading or a malfunction occurs, the protective
circuit instantly switches the loudspeaker outputs off. At
the same time the operating voltages and idle currents
are reduced in order to promote rapid cooling. As soon
as all the operating parameters have returned to the
permissible range, the S10 switches itself on again, and
operating voltages and idle currents are re-adjusted to
optimum values for high-quality sound.