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QUAD hifi gear: how it stacks up 30 years on Quad introduced the world’s first full-range electrostatic speakers in 1957. Our photo shows two ESL63 second generation units from the early 1980s, together with a Quad CD player, FM tuner, stereo preamplifier and 100W/channel stereo power amplifier. Thirty years ago, any hifi enthusiast worthy of the name would have hocked his soul for a Quad hifi system with electrostatic loudspeakers. But how does the Quad gear of that era stack up against modern hifi gear? Q UAD WAS A NAME revered by those who were into hifi sound during the 1950s, ’60s, ’70s and ’80s. Founded in the UK in 1936, they made a name for themselves building highquality power amplifiers, speakers and other audio gear. They introduced the world’s first full-range electrostatic speakers in 1957. So when our very own Serviceman told us he had inherited a Quad elec20  Silicon Chip trostatic system from a relative in the UK and asked if would we like to listen to it, we jumped at the opportunity. At the forefront of our minds was the question: how would the legendary Quad system compare to the best audio equipment available today? Did it deserve its reputation? Line-up and appearance The system consists of seven com- ponents: two Quad ESL63 electrostatic loudspeakers, one Quad “L-ite” subwoofer, the amplifier/preamplifier/FM tuner group and a Quad 66 CD player (a relatively recent addition). The ESL63s are second-generation electrostatic speakers introduced in 1981. Their appearance is consistent with that era – whether that is a good or bad thing depends heavily on taste. The subwoofer has a more modern, polished metal appearance with a LED display at the front. The amplifier/preamplifier/FM tuner group is made of three distinct units stacked in a small wooden cabinet, which is painted dark grey to match them. Individually they are the Quad FM4 tuner, Quad 44 preamplifier and Quad 405-2 100W Stereo Current siliconchip.com.au 05/13/10 07:40:55 Quad Pre+Amp Frequency Response (4 ) +10 +8 +6 By NICHOLAS VINEN Output Level (dBr) +4 +2 -0 -2 -4 -6 -8 -10 10 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k Frequency (Hz) Fig.1: the frequency response of the Quad 405-2 amplifier. The -3dB points are 15Hz and 35kHz, which is within its specifications but not as flat as many modern amplifiers. 5 Quad 405-2 THD+N vs Power (8Ω) 05/12/10 14:34:01 2 1 THD+N (%) 0.5 0.2 0.1 0.05 0.02 0.01 50m 100m 200m 500m 1 2 5 10 20 50 100 Power (Watts) Dumping Amplifier. Interestingly, the amplifier pre-dates the ESL63 speakers – it was released in 1975 and was regarded as a landmark unit at the time. Their front panels feature nicely machined metal switches, pushbuttons and knobs. Because all mains power passes through it, turning on the preamplifier also turns on the other components. It has five stereo inputs, a volume knob with 22 detents, a bass lift filter, a “tilt” filter (which cuts treble while it boosts bass and vice versa) and an adjustable low-pass filter. There is also a balance control and a stereo/mono switch. The FM tuner is rather simple, with seven station preset buttons and a manual “tune” button. Tuning is accomplished with a knob and the nearest frequency (to within 50kHz) is shown on a digital display. The power amplifier has no front panel as such, instead sporting a substantial black, finned heatsink across the full width. The Quad CD player is similarly spartan, with just a power switch, eject button and display. The other controls siliconchip.com.au Fig.2: THD+N vs Power for the Quad 405-2 amplifier at 1kHz/8Ω, measured with a 20Hz-22kHz bandwidth. Its distortion at low powers is relatively high due to noise. are on the remote. Similarly, the subwoofer controls are handled entirely by the infrared remote. Electrostatic speakers Before we begin discussing the performance, it is worth explaining how these speakers work. Modern “dynamic” loudspeakers use a voice coil/cone assembly and a rear-mounted permanent magnet. If an audio signal is fed to the voice coil, it interacts with the magnetic field produced by the magnet and the cone moves back and forth as a result to generate the sound waves. By contrast, electrostatic loudspeakers use an electric field rather than a magnetic field. Each driver consists of a metallised plastic panel suspended between perforated sheet metal grids at the front and rear. This conductive sheet is charged up to a high voltage (in this case, 5.25kV). August 2010  21 Quad 405-2 THD+N vs Power (4Ω) 05/12/10 14:32:27 5 2 2 1 1 0.5 0.5 THD+N (%) THD+N (%) 5 0.2 0.1 0.05 0.05 0.02 0.02 200m 500m 1 2 5 10 20 50 0.01 50m 100m 100 200m 500m 1 2 5 10 20 50 100 Power (Watts) Power (Watts) Fig.3: THD+N vs Power for the Quad 405-2 amplifier at 1kHz but with a 4Ω load. More power is available but noise and harmonic distortion levels are higher. It is generated from the mains voltage so each electrostatic speaker needs a mains power connection (via an IEC socket on the base stand). The audio signal from the amplifier is stepped up by a transformer which drives both grids. As a result, the very thin metallised sheet is moved by the electric field in a push-pull manner, generating the sound waves. To get good performance across the audio spectrum, it is necessary to break the panel up into multiple zones of different shapes and sizes which 5 05/12/10 15:08:08 0.2 0.1 0.01 50m 100m Quad Pre+Amp THD+N vs Power (4Ω) Fig.4: the same measurement as Fig.3 but with the Quad 44 preamplifier in circuit. It adds a lot of noise, increases the distortion level and reduces channel tracking, since there is no way to disable the balance control. are electrically independent (aside from the common high-voltage bias). Smaller sections reproduce treble and larger sections bass. A crossover filter network distributes the audio signal appropriately. Each ESL63 has eight of these zones. One typical problem with electrostatic speakers is that, due to the transformer-coupled input, the DC resistance across the input terminals can be quite low which means that a special amplifier is required. However, the ESL63’s input has just under 4Ω DC Quad Pre+Amp THD+N vs Frequency (4Ω) 05/12/10 15:10:30 resistance so a standard 100W amplifier can be used (provided it is stable with transformer loads). Subjective impressions Before we hooked the gear up to our test equipment we thought we would have a listen. Since all the gear had been sent to the Quad factory in the UK for a check-up before being despatched to Australia we expected that it would all be performing up to scratch. So how did it sound? Hmm, to be Quad FM4 Tuner Quieting Performance +10 0 2 -10 Signal-to-Noise Ratio (dB) 1 THD+N (%) 0.5 0.2 0.1 -20 -30 -40 -50 -60 0.05 -70 0.02 -80 0.01 20 50 100 200 500 1k 2k 5k 10k Frequency (Hz) Fig.5: this graph shows THD+N vs frequency for the amplifier and pre­amplifier combination at 5W output into 4Ω. The distortion is above 0.04% across much of the frequency range. 22  Silicon Chip 2 10 20k Mono Noise Mono Signal 100 Signal Level (µV) Stereo Noise Stereo Signal 1k 10k 20k Signal Strength Indicator Fig.6: this graph shows how the tuner’s signal-to-noise ratio is affected by RF signal strength. The ultimate signalto-noise ratio is -75dB for mono and -72dB for stereo. siliconchip.com.au honest we were not overly excited. It was OK. In more detail, our impression was that the treble was distinctly muted and certainly lacked the “sheen” of a system with a top-end ribbon or dome tweeter with ferrofluid cooling. Nor was the bass particularly notable, with the lowest octave from a piano, pipe organ, double-bass or harp just not there. The midrange was good; very smooth and without any tendency to emphasise voice or brass instruments. On the other hand, sibilants were muted, as were cymbals, snare drums and so on. The sound lacked zing. To paraphrase that old Duke Ellington classic, “It don’t mean a thing, if it ain’t got that zing”. Furthermore, stereo imaging is diffuse due to the large radiating surfaces. You cannot pinpoint voices or instruments across a “stereo stage” as you can with a stereo system with conventional tweeters which are effectively point sources. Initially, we listened to the system without the subwoofer but noting that low bass was missing, we connected it up and listened again. It gave a big improvement to the bass response, although the subwoofer needs careful adjustment to avoid giving exaggerated bass. In fact, we have always felt this way about subwoofers, unless they are very carefully set up so that the upper bass and low bass levels are correct. Measurements Overall, we were disappointed with our first listening session. So what was letting the side down? Was it the muchvaunted ESL-63 electrostatics, the famous Quad 405 “current dumping” amplifier, the Quad 44 preamplifier or the Quad CD player? Or all of the above? It is difficult to measure the performance of the speakers themselves since we don’t have a set-up with calibrated microphone and software but we made extensive measurements of the amplifier, preamplifier, tuner and CD player with our Audio Precision distortion analyser. This revealed that, compared with the best hifi equipment available today, the Quad gear is fairly average. Sorry Mr Quad but this is the truth. Let’s look at the Quad 405 first. It has a reasonably flat frequency response which is -1dB at 20Hz and 20kHz (see Fig.1). Furthermore, its THD+N siliconchip.com.au Unlike the Japanese gear of the era, Quad hifi equipment was disarmingly simple in appearance. This photo shows Quad’s 66 CD player (top), FM4 tuner, 44 stereo preamplifier and 405-2 stereo power amplifier (bottom). (total harmonic distortion + noise) is around 0.01% for 8Ω loads and 0.02% for 4Ω loads (see Figs.2 & 3). Again, this is good but hardly world-beating. The relative flatness of the distortion curve indicates that the distortion is mostly harmonic, rather than the result of noise. It also has a below average damping factor of 45 at 4Ω and 88 at 8Ω, although that isn’t low enough to cause any serious degradation of the frequency response. So why are we so cool on the Quad 405? Take a look at Table 1. It compares THD+N measurements of the Quad 405-2 to a progression of SILICON CHIP designs. As you can see, our Ultra-LD designs from the last 10 years or so are at least an order of magnitude better (ie, more than 10 times better). That’s a big difference. Oh, and that’s without considering our 20W Class-A design which is in a class of its own. When the Quad 44 preamplifier performance is coupled to the amplifier it adds significant distortion, as can be seen in Fig.4. In fact, there is so much noise from the preamp that the THD+N measurement at 50mW is doubled. It also adds a moderate amount of additional harmonic distortion, bringing the minimum level up to 0.015% for 8Ω loads. So even though the Quad 405 “current dumping” amplifier was a very significant design when it was first introduced in the late 1970s, it has been well and truly left behind. FM tuner By contrast, the Quad FM tuner performs well by modern standards. Its frequency response is ±1dB from 20Hz to 15kHz in both mono and stereo. THD+N is 0.09% for mono signals and 0.15% for stereo at 1kHz. Fig.6 shows the quieting curves along with the signal strength indicator bar reading (which is a 10 dot dual bargraph). Ultimate signal-to-noise ratio is above 70dB for mono and stereo Table 1: Power Amplifier Performance Comparison Amplifier THD+N <at> 1kHz 8Ω THD+N <at> 20kHz 8Ω Quad 405-2 0.01% 0.02% Studio 200 (February 1988) <0.01% Not stated Plastic Power (April 1996) 0.0025% 0.01% Ultra-LD (May 2000) 0.0015% 0.004% SC-480 (January 2003) 0.003% 0.02% Ultra-LD Mk.2 (August 2008) 0.0008% 0.0045% August 2010  23 Frequency response is flat at -0.01dB and +0.05dB over 20Hz-20kHz; also pretty good. Test reactions Quad’s ESL63 electrostatic loudspeakers. Each driver consists of a metallised plastic panel suspended between perforated sheet metal grids at the front and rear. The plastic panel is charged to 5.25kV and the audio signal is stepped up by a transformer and applied to the grids. signals which is quite good. Interestingly, while the FM tuner does have a digital frequency readout, it is not a synthesised design and it is tuned in the old-fashioned way by a tuning gang and knob, rather than in precise 50kHz steps denominated by a microprocessor. It is also quite difficult to tune precisely on station, necessary to get the best performance. That is one reason why frequency-synthesised designs took over. CD player The Quad 66 CD player is a reasonable performer by modern standards, although it has a surprisingly sharp rise in distortion above 12kHz. Compared to a 15-year old run-of-the-mill Sony CDP-XE300, the Quad 66 has lower distortion between 5kHz and 12kHz but somewhat higher distortion outside this range (see Table 3). It has a digital output so it could be connected to an external DAC (such as the SILICON CHIP DAC, September-November 2009) for lower distortion. Its signal-to-noise ratio is good at -107dB and channel separation is excellent at -106dB at 10kHz. Overall linearity is also very good, with its output at -91.9dB for a -90dB signal. Table 2: Quad FM4 Tuner Performance Mono Stereo THD+N 0.09% 0.15% Signal-To-Noise Ratio 75dB 72dB Minimum Signal Level for 3% THD+N 7µV (28dBf) 15µV (35dBf) 50dB Quieting 22µV (38dBf) 25µV (39dBf) Measurement Table 3: Quad 66 CD Player vs Sony CDP-XE300 Measurement Quad 66 CD Player Sony CDP-XE300 THD+N, 1kHz (20Hz-22kHz) 0.00487% 0.00281% THD+N, 10kHz (20Hz-80kHz) 0.00564% 0.01838% THD+N, 15kHz (20Hz-80kHz) 0.02720% 0.02222% THD+N, 20kHz (20Hz-80kHz) 0.18525% 0.01767% 24  Silicon Chip Our overall reaction to the above tests was that clearly, while the individual Quad components were decent performers at the time they were released, they have been well and truly left behind as technology has progressed. The electrostatic speakers have a certain charm with a smooth midrange but they struggle at the extremes of the audible range. Neither the Quad 4052 amplifier nor Quad 44 preamplifier have particularly low distortion or noise. A modern, good quality amplifier/preamplifier combination will outperform them. The FM tuner is fine but superior units are available from companies like Yamaha and Denon. The Quad CD player is merely average compared to most brand-name players released in the last 15 years and also the better quality DVD or BluRay players. Finally, we decided to listen to the Quad ESL-63s when driven by an Ultra-LD Stereo Amplifier (SILICON CHIP, November 2001-January 2002) and the abovementioned Sony CD player, together with the Quad subwoofer. Talk about chalk and cheese! This combination gave extended treble and much more extended bass and was much more satisfying overall, on a wide variety of music. In fact, while you might want to keep the ESL-63s, you would not now bother with the rest of the original system. No, that’s not right – you would not bother with the electrostatics either. You would opt for a decent pair of dynamic loudspeakers – even Quad make those now! Conclusion All this is not to say that the (previously) revered Quad system sounds bad. It’s still quite pleasant to listen to. We somehow needed to convey this reaction to our Serviceman. Remember that he paid a motsa to have the whole system checked over by Quad in the UK and then had it shipped out to Australia. Should we sugar-coat our reactions? In the end, we gave it to him straight, “Mate, it’s pretty ordinary”. He took it reasonably well, considSC ering. siliconchip.com.au