The Quad 405 Current Dumping Amplifier from 1975

The famous Quad 405 ‘Current Dumping’ amplifier was launched in the mid 1970’s, and featured feed forward error correction that effectively removed the class B cross over distortion that plagues this type of output circuit structure. The design featured no adjustments in production, but the circuit components around the output (L2, R36, R38) had to be accurately matched to achieve the specified performance. The design caused quite a stir in the audio industry at the time, and was the subject of a patent and a paper at an AES convention a year earlier. Although the 0.005% midband distortion placed it firmly in the upper eschelons of measured performance in the industry at the time, some reviewers failed to warm to the sound. Nevertheless, this was a landmark design that creatively solved the cross over distortion problem. Quad_405_Power_Amplifier_Wireless World Article.pdf