Quad 405-2, The Current Dumping Amplifier (Page 1)
dumping is a Quad invention, and describes the first successful
application of feed-forward error correction to audiopower
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.
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.
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.