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Nested Differentiating Feedback Loops in Simple Audio Amplifiers

Many audio power amplifiers consist in essence of a long-tailed-pair first stage, a lag-compensated common-emitter stage with its emitter on a supply rail, a complementary-emitter-follower output stage, and overall negative feedback. Two nested differentiating feedback loops can be added to this basic topology, to achieve between one and two orders of magnitude reduction in distortion, at little increase in component cost. Six extra components are essential; two small-signal transistors, one resistor, and two capacitors. Further small components such as zener diodes and bypass capacitors may be required, depending on the details of the supply rails the amplifier.

JAES Volume 30 Issue 5 pp. 295-305; May 1982
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AES - Audio Engineering Society