the bias servo transistor or diodes be thermally matched to the lower power driver transistors; they need not (and should not) be placed on the main heatsink. This potentially simplifies the design and implementation of a stable class AB amplifier, reducing the need for emitter resistors. This significantly reduces the number of components which must be in thermal contact with the heatsink and reduces the likelihood of thermal runaway. Optimal quiescent current in an amplifier using complementary feedback pairs also tends to be much lower than in Darlington-based output stages, on the order of 10 mA vs 100 mA or more for some emitter follower output stages. This means that idle power consumption is on the order of a few watts versus tens of watts for the same performance in many cases. This is a very compelling reason to use the Sziklai pair in cases where output power is moderate (25 W to 100 W), fidelity is critical, and relatively low idle power consumption is desired. Quasi-complementary output stages Historically, designers frequently used the "quasi-complementary" configuration, which uses a Darlington push pair (ie, 2 NPN transistors) and a complementary feedback pull pair (ie, 1 PNP and 1 NPN transistor). This configuration, which uses 3 NPN transistors and 1 PNP transistor, was advantageous because for decades the most common small signal transistors were germanium PNPs (silicon PNP power transistors were slower to develop and were for years more expensive than their NPN counterparts). Alternately, if a germanium PNP device was used, it would have significantly different characteristics than the silicon NPN transistor. In the quasi-complementary topology, the performance of the lower pull pair, which uses a single NPN transistor, more closely matches the performance of the upper push pair, which consists of two NPN transistors and an identical power device. While for decades the quasi-complementary output stage made sense, because PNP and NPN power transistors are now equally available and have more closely matched performance characteristics, modern audio power amplifiers often use equivalent topologies for both pairs: either 2 Darlingtons or 2 Sziklai pairs. References External links Multistage semi-conductor signal translating circuits. G.C.Sziklai, December 27, 1960 Push-pull complementary type transistor amplifier. G.C.Sziklai, September 11, 1956 Push-pull amplifier with complementary type transistors. G.C.Sziklai, May 7, 1957 ECE 327: Procedures for Output Filtering Lab — Section 4 ("Power Amplifier") discusses design of a BJT-Sziklai-pair-based class-AB current driver in detail. Multi-stage transistor amplifiers