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QUAD 405 British Stereo Power Amplifier

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QUAD 405 British Stereo Power Amplifier

Post by HiFiLab on Thu Jan 11, 2018 10:59 pm

Made In England

Technical Specification
Power output: 100 watts per channel into 8Ω (stereo)
Frequency response: -1db at 20Hz
                              -0.5db at 20kHz
                              -3dB at 50kHz
Total harmonic distortion: < 0.01%
Hum and Noise: ‘A’ weighted -96dB ref full power
Unweighted -93dB ref full power (15.7kHz measurement bandwidth)

Left/Right Channel Crosstalk: 80db @ 100Hz
                                          70dB @ 1kHz
                                          60dB @10kHz
Input sensitivity: 0.5V for 100 watts into 8 ohm load
Speaker load : 4 to 16 ohms (nominal)
Signal to noise ratio: 95dB
Speaker load impedance: 4Ω to 16Ω
Dimensions: 115 x 340.5 x 195mm
Weight: 9kg

After building a reputation for designing quality valve hi-fi amplifiers and electrostatic loudspeakers for the hi-end domestic market, Peter Walker applied a little known audio circuit technique called feed-forward error correction (first patented way back in 1929 by Harold Black) and designed the ‘current dumping’ Quad 405 power amplifier, an innovation still used in Quad power amplifiers to the present day.

From Peter’s December 1975 technical paper in the ‘Wireless World’ magazine,

‘An audio power amplifier is required to produce an output signal that differs from the input signal in magnitude only.  It must therefore have occurred to every circuit designer that it should be a simple matter to take a portion of the output, compare it with the input to derive an error signal. It is then only necessary to amplify the error signal and add it to the output in the correct amplitude and phase to cancel completely the distortion of the primary amplifier.’

Peter put this principle into practice using two amplifiers per channel instead of one.

The first stage ‘error’ amplifier is low powered but very high quality. The second amplifier is high powered, but of lesser audio high quality.  (It’s a lot more difficult to achieve very low distortion in high powered amplifier stages).  Peter designed a way to compare the high powered output with the original audio input and derive the required error correction signal which is then injected into the audio path, in such a way that the high power audio output achieves a very low distortion figure, even at very high power levels.

This innovative product earned Quad the Queen’s Award for Technological Achievement in 1978.

User Review for reference:

The Quad 405 has been around for 40 years and as other amplifiers have come and gone this machine is still regarded as one of the best British designs ever. The simplicity of design still looks good in todays modern age as it did in the 70s. The unique current dumping technology won its designer the Queens award for industry
Quad was a true British Icon the 405 being one of their masterpieces. My music tastes have changed over 50 years but the 405 has always managed to bring the music to life be it from vinyl, cd or other digital formats
A great retro look when partnered with Quads ESL 57's That combination still referred to as the "sound all other systems attain to be like. With a quality source and decent speakers the Quad 405 never disappoints ,great depth and sweet highs making the music very engaging end infinitely listenable, never once have I been fatigued with the sound of a quad 405.
If you get the chance, get one to listen to , My favourite test record for the 405 is James Last " This is James Last "
Experience the big band sound on a small amplifier with a big British heart.

Price : RM 2200
Contact Simon Ting 012-3612507

Last edited by HiFiLab on Thu Jan 11, 2018 11:31 pm; edited 1 time in total (Reason for editing : update info)

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Number of posts : 2392
Age : 39
Location : klang
Registration date : 2011-03-12

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