leema-acoustics Pulse III, Руководство пользователя, Страница: 14 / 20

Technical Discussion
Topology
Starting with the pre-amp and control stage, input selection is performed by gold over silver contact relays under control of
the microprocessor. The audio is then buffered by audiophile quality OP275 amplifiers in order to present the Burr Brown
precision attenuators with a low impedance drive signal. Next, the controlled signal passes to the class B power amplifiers,
the class A headphone amplifiers and to the pre-amp outputs.
The power amplifiers use a well established topology comprising differential input stage, class A voltage amplifier stage and
class B output stage. Each stage is highly optimised following the general teachings of design guru Doug Self, with notable
additions drawn from our own design research.
Each output stage uses a class A driver stage and a pair of very high performance output transistors incorporating integrated
thermal feedback.
The amplifier sections use multi-slope over-current protection in addition to thermal shutdown and fault monitoring.
After distortion measurement, the square wave performance of an amplifier is the ultimate timing test. A look at the square
wave performance of Pulse is testament to the time domain performance of the design. Apart from the gentle rounding of
the corners caused by amplifier input bandwidth filtering, the square wave response is virtually perfect and has no overshoot
or ringing. On the subject of ringing, if the amplifier is tested in to a load including a capacitive element, inaccurately trying to
simulate an electrostatic loudspeaker, ringing will be observed at the output in response to transient signals. In fact, this
ringing is not caused by the amplifier. It is simply the resonant combination of the amplifier output inductor and load
capacitance. No notice should be taken of any test reports including the level and makeup of this ringing, as the results are
totally dependant upon load type and applied stimuli.
Topology
PULSE III
12