The Complementary Sziklai Output

Named after a prolific inventor by the name of George C. Sziklai, this version sports a Sziklai output section, or what is sometimes called the "Complementary Feedback Pair".

What is a Sziklai?
In essence, a high gain super transistor, somewhat similar to a Darlington. But there are major differences. Unlike Darlingtons, there is some voltage gain with Sziklais. Another unique feature is local feedback.

Why is it not as popular as EF?
Basically, more difficult to design then EF. When local feedback is nested in a global feedback, an amplifier is more prone to instability. In other words, it is easier to break out into high frequency oscillations. But a well designed Sziklai Output can often be outstanding.

Performance Factor
This is where it probably makes a real difference. With listening tests, the Sziklai Outputs are the most enjoyable of the three designs. It sounds faster and the highs are smoother. This is probably due to a wider bandwidth and faster rise time. All these are achieved without compromising bass slam and definition. 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.

Mr George Clifford Sziklai is credited for inventing the full complementary symmetrical output that we take so much for granted today. More information on his illustrious career can be found at this Los Altos Town Crier article by writer Linda Taaffe.

THD of c200.2 complementary Sziklai output

Biasing 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