Leema-acoustics TUCANA II Handbook - Technical Discussion
Technical Discussion
Topology
Starting with the pre-amp and control stage, input selection is performed by gold-over-silver contact relays under control of a
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 dual-mono class B power amplifiers and
also to the buffered pre-amp outputs.
The left and right power amplifiers are totally separate and have their own power transformers, rectifiers and reservoir capacitors. A
third transformer powers the control electronics, thus completely separating the microprocessor from the audio electronics.
The power amplifiers use a well established topology comprising differential input stage, class A voltage amplifier stage with
constant current load 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. This is particularly evident in the ultra low-distortion printed circuit
layout.
Each output stage uses a class A driver stage and has three pairs of very high performance, hand-matched Thermal Trak™ output
transistors, resulting in total removal of thermal distortion. Recently, some reviewers have been critical of the use of multiple output
devices. This is completely unfounded, as multiple devices offer many benefits over single pairs of devices:
Distortion is greatly reduced at lower load impedances due to reduced gain loss with increasing current.
Output impedance is reduced due to multiple parallel-connected emitter resistors.
Device electrical and thermal stresses are reduced offering increased reliability.
Output current capability is increased.
Safe operating area of the output stage is increased.
Topology
TUCANA II
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