ONE OWNER kept this set of Quad electronics working for 30 years, including the FM4 tuner, the 34 preamp and the real gem of this set, the 405-2 Current Dumping power amplifier, all being sold as a complete set, with all boxes and packaging.
The preamplifier has a moving magnet phono stage installed and a Quad moving coil phono stage ready to install if desired. It works but does not turn off and the balance control is missing. The amplifier and the tuner are perfect and have been thoroughly checked out by a technician.
Current dumping is a Quad invention, and describes the first successful application of feed-forward error correction to audio power amplifiers. A current dumping amplifier consists of a high power heavy duty amplifier, and a low power very high quality amplifier. The low power amplifier is arranged so that it constantly monitors input and output. It detects any difference and feeds forward the necessary correction to the output of the main amplifier. Quality is solely dependent upon the performance of the low powered high quality amplifier together with four passive components. When correctly designed all distortion in the output stage is reduced to zero.
With this technique it is possible to produce an amplifier of very high performance without using carefully matched relatively fragile output devices. There are no crossover biasing problems, no alignment or adjustment is required to obtain optimum performance and nothing can go out of alignment during life. In the event of component failure, replacement can be effected and performance restored without realignment.
"Current Dumping" was originally presented as a paper to the AES 50th Convention. Since then a number of technical articles and papers have appeared which confirm the inherent advantages of current dumping over conventional class B techniques. Reliability of the Quad 405-2 is assured by an elegant Quad designed protection circuit which overcomes the problems associated with conventional 'load line' protection circuits. The load sensitive time dependent circuit effectively places no limitation on the amplifier when playing music programme through loudspeakers but provides full protection for the amplifier should anything go wrong. The Quad 405-2 also incorporates speaker protection circuitry which prevents damage to the loudspeaker in the unlikely event of component failure in the amplifier. The Quad 405 has won both a Design Council Award 1976 and The Queen's Award for Technological Achievement 1978.
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