The Dynamic Duo
Sydney Morning Herald
Monday July 7, 2003
Few hi-fi components have won the Queen's Award for Technological Achievement. The first was the revolutionary Quad Model 405 power amplifier. It was also the first model to successfully implement feed-forward error correction to reduce harmonic distortion, a trick Quad calls "current dumping".
In a current-dumper design, a heavy duty high-power amplifier connects to a much lower-powered but very high-quality amplifier stage. The current-dumping circuit compares the music waveform at the input of the low-powered amplifier with the waveform at the output of the high-powered amp. If any difference is detected, a special signal is fed forward to correct it before it reaches the speaker terminals.
This enables high power output and low distortion without the need for carefully matched output devices. It also simplifies production because there are no transistor-biasing problems.
From a user's viewpoint, the circuit means there's nothing to go out of alignment and if a transistor ever fails it can be replaced quickly, easily and cheaply. Quad 405 amplifiers are no longer in production but second-hand ones are in such high demand, particularly from owners of Quad electrostatic speakers, that those in good condition cost more now than they did when they were new.
The 99 Series power amplifier is essentially an updated version of the 405 in a much smaller, more attractive but equally solid diecast aluminium case. Although it is a stereo amplifier, it can be connected to a multichannel audio system using Quad's proprietary AmpBus sockets. We suggest hi-fi purists connect it directly to Quad's matching CD-P CD player, using the variable outputs on the rear panel. The CD-P is no ordinary CD player. It upsamples the 16-bit, 44.1kHz data on a CD to a 24-bit, 192kHz bitstream. A proprietary filter then extracts the audio signal. Six external digital inputs are provided, so you can use the CD-P to improve the sound of an older CD player as well as connect and switch between an MD player, CD recorder and DVD player.
Quad has gone to some trouble to make these two components work as one, both operating with the same remote control. The volume defaults to your usual listening level or, if someone has been interfering with the controls, one that's not too loud. The digital volume indicator works sensibly, with higher numbers indicating higher volume levels. For those who don't like lights flashing on their components, the green front-panel display can be turned off. The CD-P player is programmable, with random and repeat play modes, and can handle CD-R and CD-RW discs.
Don't be fooled by the system's modest size - it packs a real punch. Power output was tested at 92 watts continuous per channel, both channels driven, at which point the signal-to-noise ratio was 108dB and THD less than 0.004 per cent. Connected to a pair of speakers, the duo provided a sweet, sparkling sound that remained captivatingly live and fresh across the full range of volume settings.
Info file
Quad 99 CD-P CD Player and Stereo Power Amplifier
RRP: Amplifier $2699 / CD player $2999
International Audio Group Pty Ltd
Unit 30, 398 The Boulevarde
Kirrawee, NSW 2232
9521 4844
iagaus@bigpond.com
www.wharfedale.co.uk/australia
© 2003 Sydney Morning Herald