Words by Rafe Arnott. Each column will examine an archetype of high fidelity and investigate its development, design, impact and legacy.
“A straight wire with gain,” is the preferred metaphor concerning a perfect amplification circuit according to audio engineer Peter J. Walker. While the idea continues to be strictly literary, Walker’s introduction of the QUAD solid-state 303 power amplifier in 1967 (and its accompanying 33 control preamplifier) did little to legitimize his prose: the more simple a circuit path is, the greater fidelity to signal. The 303 and its “triples” amplification output stage, while not overly complex, was nonetheless a somewhat radical approach at the time, and to this day the power amp remains as sought after by audiophiles as it was by transistor neophytes 54 years ago.
Walker, the founder of QUAD Electroacoustics – which came to being in London, England as S.P. Fidelity Sound Systems in 1936 – started out manufacturing public address equipment, but following WWII, the company began producing audio components for home use. With a foundation built on solid engineering approaches, S.P. Fidelity made a name for itself in the UK with room-filling sound in the ‘30s – a time when most P.A. systems were considered brash or lacking dynamics. Walker solved this problem by focusing on reducing distortion, and improving the output of available mono bloc valve amplification circuits. Known as a gifted electronics designer who emphasized measurements over listening tests, his pursuits were not at the expense of musicality, as he was also a saxophone player and flautist. According to longtime QUAD engineering fellow Peter Comeau, Walker was a product of his generation. One who saw subjective testing as less important. “He knew what you have to do to ensure something sounded good, but he didn’t actually tweak things too much, he just did what was necessary to get the job done,” said Comeau in a 2018 interview. “If he had just chased low distortion for its own sake, his products would have sounded less good. He was sophisticated in his approach and, for example, didn’t believe zero distortion was a necessity. He knew perfectly well that if you have second harmonic distortion below one per cent for example, you can’t actually hear it.”
In a 1978 interview, Walker, above with an award for his ESL-57 electrostatic speaker design, confessed that he “went into hi-fi as a sideline 'till the public learned to like it.” He outlined the process of entering into high-fidelity production as one of cottage-industry steps, saying “You made a set for yourself, you sold these to a few engineers, about five or six a week, that sort of thing.” Adding, “Then of course hi-fi came in, mainly with the LP record, and since we were already in the business one could get pushed up with it doing the right thing by luck at the right moment.”
While 1947 saw the birth of the transistor, Walker was still firmly entrenched in wresting the best possible performance from valve amplifiers. These efforts produced the QA12 and QA12/P in 1948; 12W mono blocs which the British Broadcasting Co. quickly incorporated into its hardware vernacular. Following these designs came the QUAD 1, an acronym based around the rather long-winded Quality Unit Amplifier Domestic, which in the end directly contributed to Walker changing the company’s title to QUAD Electroacoustics Ltd. Continuing to perfect his circuit, Walker persevered and the QUAD II came to market in 1953. This Class A, push-pull mono design produced 15 W of power, utilised a pair of KT66 output valves, a GZ32 rectifier valve and two EF86 pentodes, which when combined with a unique circuit configuration of cathode coupling through QUAD’s hand wound output transformers, saw near ruler-flat frequency response between 10Hz and 20kHz and 0.1 per cent of harmonic distortion. Outstanding numbers and a design which resonated with consumers, leading to some distress for Walker when the time came to replace it.
But, replace it he did in 1967 with the 303 and it’s accompanying 33 preamplifier – solid-state designs that saw the 303 touted as “the world’s first low-distortion transistor amplifier.” The 33 was equipped with its own power supply, and Walker included two switched sockets on the rear of the unit to feed mains to a tuner and the 303. The circuit design put QUAD and Walker at the forefront of high-fidelity amplification in the ‘60s. The heart of the 303’s success was Walker’s breakthrough “triples” transistor output configuration which forms a feedback amplifier-within-an-amplifier. It required far less negative feedback, possessed exemplary thermal stability (meaning the current in the output stage is practically immune to temperature fluctuations), and produced lower distortion. One publication of the era referred to the 303 as “the god of amplifiers” after it won a 1969 British Council of Industrial Design Award. The amplifier produced 45W/ch into an eight-ohm load and 28W/ch into 16ohms with a rated bandwidth of 20Hz~35kHz at -1dB.
Photos below: The 33/303, Left, and QUAD II mono blocs. Images courtesy QUAD.
We designed our valve (tube) amplifier, manufactured it, and put it on the market. and never actually listened to it. In fact, the same applies to the 303 and tile 405. People say, "Well that's disgusting, you ought to leave listened to it."
–Peter J. Walker, QUAD founder
A late adopter of the technology, Walker’s eventual embrace of solid state was as much engineering challenge as marketing genius. Transistor design and implementation within hi-fi circuitry was, according to Walker, hampered in the mid-‘60s by solid state’s audible subordination to valves. Regardless if it was considered the future or not, the QUAD name wouldn’t be seen riding the technology wave without merit – it went against Walker’s engineering principles. When prompted by the press to explain the company’s tardiness to embrace solid state compared to other UK manufacturers, as the Leak Stereo 30 was already enjoying some spotlight, Walker replied, “… early transistor amplifiers were inferior to good valve amplifiers and it has been necessary to develop a fundamentally new approach to circuit design to overcome this. The result is that the Quad 303 is superior to the best of valve designs in every respect.” Again, the BBC agreed, and adopted the 303 into its stable, adding to the considerable critical acclaim already conferred onto the amp by high-fidelity journalists at the time. While some today would argue the sound as too “lush,” it reflected a valve-inspired sonic sensibility, and while it may have certain limitations when viewed through the lens of modern high fidelity, it nonetheless was an exceedingly popular commercial design with 94,000 units produced and sold between 1967 and 1985.
Photo above: QUAD advertisements from the '60s and '70s. Images courtesy of QUAD.
Time passed with little change made to the basic 303. It maintained its DIN-type umbilical with the 33, and its fully-regulated power supplied via a 3-pin connector – much of the run (S/N 80,500 and below) were configured with a three-pin Bulgin socket, the later versions were equipped with a three-pin IEC connector, and much to the chagrin of the chrome and twinkle hi-fi set, the olive-green/grey colour scheme endured. Nonetheless, it continued to sell, and unlike many of its contemporaries in the late ‘60s, it was ahead of the curve for smoothness, presence, tone and timbral accuracy – avoiding the sonic harshness plaguing many early transistor amplifiers. So much so, that neither its aesthetic or sound were anachronistic 18 years into its production run, when it was replaced by the 405, a current-dumping solid-state design that some thought muscled-up the 303 sound. While 18 years might not be considered a long run, it has been 54 years since its introduction, and five decades on the 303 is still actively trading on the secondhand market. It’s no stretch to say it is sought after and indeed embraced by many in the vintage hi-fi scene for its performance and robust construction (or acquired by those adroit enough to perform online research and purchase one based on the many glowing reviews or personal blogs detailing QUAD appreciation).
Photo above: Original QUAD 303 Driver and Regulator boards. Image courtesy DocPlayer.net.
Indeed, part of QUAD’s longstanding appeal has been product durability, a lesson learned by Walker in the ’30s and early ‘40s when he was designing components meant for public address venues. Gear which often had to stand-up to the rigours of transport that portability inferred, but this also translated into a domestic-market focus on durability. He chose to design circuit architecture around easily available components which were used as much for their sonic capabilities as their durability. A case in point being how little of the circuit path requires servicing or replacement by QUAD itself (who still repairs them) and the numerous Quad restoration companies which have sprung-up catering to 33/303 owners. Most charge approximately $400 USD for an overhaul of the preamp and power amp. Both of which have been out of production for almost 40 years. Most 303s require only replacement of passive components such as capacitors, carbon resistors, small electrolytics, or engagement adjusters like potentiometers. Some could benefit from updated wiring or minor soldering, but that’s it – a testament to the quality control of the company, especially from a time when everything was done by hand and strict tolerances had to be accounted for by humans – no robotics or computers involved.
Photos above: Donna Leake in her London home with her Tannoy/QUAD systems. Photos by Silvia Gin.
When she’s wasn’t curating playlists for her monthly radio show on NTS, or dropping the needle on sets at London’s slow-music haven, Brilliant Corners, UK selector, and rare-groove collector Donna Leake was quietly building out her vintage Tannoy and QUAD home system. Her time at the East London restaurant exposed her to the ability of a well thought-out sound system to move people on the dance floor – to energize a room. “I realized exactly how the speaker alone is not the whole sound, I learnt how the amps/preamp, mixer, needles, the room, etc., all played a part in what one was hearing.” Practical in her appreciation of the QUAD 303, of which she currently owns three, Leake sought out advice from friends with hi-fi experience before deciding to solely use QUAD amplification in her set-up. Two 303s and a 405 drive a pair of Tannoy Ardens, Tannoy Berkeleys and 15-inch Tannoy 3809 studio monitors via a bespoke E&S DJR 400 mixer, the third 303 is driven by a QUAD 44 preamplifier and runs Rogers Studio 1 monitors. Describing her dive further into hi-fi, Leake said, "...it certainly made me appreciate the beauty of an album and by extension the quality of the recording, production and mastering of an album. You really hear an LP in a different light when you’ve set it up in a certain way on a specific system. Sometimes I’ll hear an instrument I’ve never heard in an album I thought I was totally familiar with ... I have become interested more in the subtlety of slightly more experimental or ambient sounds since starting to listen on sensitive systems.”
Many 33/303 combinations are easily found with an online search through local secondhand classifieds ranging from $400 USD~$900 USD depending on their condition. Add-in a CD, or turntable as source and a pair of reasonably-driven vintage loudspeakers and suddenly, for a nominal investment, one has access to sonic fidelity which is off-putting to many audiophiles having spent far more, only to not better it. Therein lies the key to the QUAD 33/303’s longevity and continued influence: they were designed and built for a tomorrow that came and went, and then came back again. They’ve been around so long that not only did they impact amplifier aesthetics and signal paths, they helped determine a metric for sound of an era. An era that is gaining notoriety today for durable, simplistic construction, out-of-the-box circuit design, along with dynamic, present and satisfying playback. Qualities that resonate with music lovers and record or CD collectors who appreciate great sound from hi-fi kit without the cost many espouse as essential for modern fidelity. With modest service requirements needing to be addressed only after decades of use, the 54-year-old QUAD 303 power amplifier and its matching 33 control preamplifier are two of the most elegant hi-fi bargains to ever play music.