The Quasi-complementary output
c200.1 is similar to the c200 except for the output stage. Notice
that all the output transistors are NPN types. This output configuration
is known as "Quasi-Complementary".
Quasi-complementary outputs came about in the early years
of solid state designs where pnp transistors were few, costly
and don't quite complement their npn counterparts. Nowadays, with
modern complementary transistors sharing similar properties, this
output topology is not often favored. One reason is probably due
to the lack of performance of the early designs that left a bad
impression. Nonetheless, quasi-complementary outputs do have their
advantages, the most obvious being that all output transistors
are identical, unlike npn and pnp, which in reality is never truly
The key is in Q8. Sometimes called a "complementary
phase splitter", it is actually more of a level shifter.
Together with the output transistors, they form a Sziklai pair.
Is the Quasi-complementary inferior to the more common Emitter-follower
configuration? I don't think so, at least not in THD terms. In
amplifier stability, it is just as stable as any well designed
amplifier with EF outputs, unlike the Compound Feedback Pairs,
which can be tricky to make stable at times. Clip characteristics
are similar to c200 (EF version), with no signs of distortion
and instability when driving 8 and 4 ohms test loads up to rated
power. Sonically, I am unable to tell the difference between the
two. In short, it is just as good and reliable as an EF design.
Actually, the thought of having all outputs identical is a very
of c200.1 quasi-complementary output
of output transistors
All THD readings were done with outputs biased to 12mV across
0.22 ohms emitter resistor. This works out to approximately 55mA
per output transistor in idling state.
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