Quad 405-2 Current dumping amp

The Quad 405-2 Current Dumping Amplifiers are one of the most unique and much loved classic British made power amplifiers of the last twenty five years. The skill of the design, the engineering and thought that have gone into this amplifier make it stand out as an outstanding product and it is no coincidence that the Quad 405 first won a Design Council Award 1976 and then later in 1978, The Queen’s Award for Technological Achievement, the only Hi-Fi manufacturer to have won such awards.

The Quad 405-2 boasts a generous 100 watts per channel into 8 ohms, and has a very neutral open sound. The Amplifier has DMPS (Dual Mono) power supply which provides excellent channel separation.

The other beauty of these amps is because they operate in pure class A mode as opposed to class AB which requires bias adjusting after time, the amplifier will never sound different or degrade overtime so long as the capacitors are replaced every 10-12 years. This means that because of their build quality, the Quad 405-2 should keep on going and going without issue.

It is simply a classic British amplifier in perfect working order.

Current 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.

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

“Errr…..it’s a fine British amp:)”