Very few Hi-Fi components are as instantly recognisable as the QUAD 33 and 303, and for that we make no apologies!
Still one of the most popular models in the history of one of the world’s most poignant Hi-Fi brands, the QUAD 33 and 303 are benchmarks in almost every angle of desirable audio equipment – performance, reliability, industrial design, value and musical romance.
By revisiting the QUAD 33 and 303 components, QUAD demonstrates its authenticity, pedigree and excellence as a juggernaut of the British hi-fi world – past and present.
In listing the names involved in the development of this stunning iteration of an icon, you’ll find a calculation of close to 200 years of engineering experience and 100+ years of QUAD-exclusive design and service.
A dream team of Rob Flain & Paul McConville (the world’s most experienced QUAD service engineers), Jan Ertner (30 years of experience in QUAD design), Peter Comeau (the acoustic director behind some of QUAD’s most successful loudspeakers) and David McNeill (the industrial designer responsible for two decades of QUAD innovations) were all a part of this labour of love, making no compromise in the demand for a product that could bear the name of 33 and 303.
QUAD 303 power amplifier
The QUAD 303 power amplifier was intended for normal domestic use with loudspeakers of moderate efficiency, but was also used by broadcasting and recording studios, worldwide, who appreciate its excellent performance and dependability. The ethos hasn’t deviated.
The outstanding performance of the QUAD 303 is still celebrated to this day, and is largely due to the unique output circuit developed by QUAD.
In reissuing the QUAD 303 power amplifier concept, exactly like the matching 33 preamplifer, QUAD’s incomparably experienced service team was matched with the equally adept engineering team to reinvoke the design, romance and performance in a thoroughly modern iteration of a hi-fi legend.
As with the new QUAD 33, every aspect of design and performance has been analysed and re-engineered way beyond simply modernising components and refreshing of specifications.
The QUAD 303 power amplifier was intended for normal domestic use with moderately efficient loudspeakers, but it was also used by broadcasting and recording studios worldwide, who appreciated its excellent performance and dependability.
The ethos hasn’t deviated. The original 33 and its partnering 303 were awarded with a ‘Council ofIndustrial Design Award in 1969’. Even today, the original design is celebrated and confirmed by its presence at the Museum of Modern Art in New York. The new 33 and 303 have been industrially engineered to surpass those original standards, with a truly modern appearance and functionality.
However, much like the original, the new QUAD 303 maintains its faithfulness to the original by employing the famous QUAD ‘symmetrical triples’. Employed to provide a completely symmetrical output stage, greatly reducing distortion and rendering the resting current independent of output transistor temperature.
This development enables the designers to reduce distortion to emphatically low levels without sacrificing stability and to maintain this excellence under all dynamic conditions.
To put this in perspective, the lowest theoretical distortion present on the very source material will still be some hundred times greater than that the QUAD 303!
Such a level is, of course, completely inaudible no matter how refined the test.
The use of ‘triples’ permits simple and effective control of the output current and since the voltage is also controlled, the output transistors are completely protected and must always operate within their ratings with the obvious advantages of greatly improved reliability under all conditions, without the use of elaborate and expensive circuitry.
Due to the lack of complementary transistors (NPN and PNP power transistors) in earlier times, the older QUAD 303 used a quasi-complementary output stage. The new version of the QUAD 303 now uses a fully complementary output stage, providing better linearity, more stable static bias, and improved stability under high voltage and large current conditions. Using premium power transistors, the 303 offers excellent gain linearity for accurate reproduction of the input signal with greater dynamic range.
The amplifier cannot be upset even when overdriven by an asymmetrical signal or by shorting or disconnecting the loudspeakers.
A brand new 200VA, custom-specified, low-noise toroidal transformer has been developed for the new 303.
The output stage of the discrete power amplifier circuit employs an advanced feedback topology to ensure superior linearity and exceptional thermal stability. Through its Class AB design, the ideal current is maintained independently of the temperature of the output transistors.
The result is a compact, cool-running power amplifier that possesses the capacity to deliver dynamic power and maintain a firm hold on the music while providing rich sonic detail.
Always respected for its conservative but consistent power-output, the classic QUAD 303 was officially rated at 45W @ 8 ohms. A modest but honest output, the 303’s venerability is in the finesse of the performance, not just the raw power. The new model is thoroughly the same.
However, with some tweaking and enhancements, the 303 is loaded with a little extra power – offering 50W @ ohms (70W @ 4 ohms) with a maximum current delivery of 10A into difficult loads. The original 303 was known to have issues with lower impedance loads, the new 303 has no such trouble. Perfectly suited to the more demanding requirements of the modern audiophile, it ensures any speakers – even including QUAD’s electrostatic designs – can be driven with ease. Connectivity options comprise single-ended RCA and balanced XLR inputs, a 12V trigger input and high-quality speaker binding posts. Simple, solid and thoroughly authentic, inside and out. The power output for ‘bridged mode’ (for use as a mono-block power amplifier) reaches 140W @ 8 ohms or 170W @ 4 ohms (bridged mono).
QUAD 33 Preamplifier
The external design is specifically intended to continue the QUAD tradition of practical simplicity. Yet, it would be foolish to ignore the implementation of modern-day capabilities, such as an informative backlit display, delicate LED illumination and remote control functionality. And just like the original, the overall appearance is unmistakably QUAD, albeit now with a premium machined and anodised front panel and all-metal chassis.
The new QUAD 33 is supported by digital microprocessor control but is otherwise faithful to a classic analogue design.
The 33 feeds the loudspeakers via the power amplifier using dedicated stereo pre-outputs, with an RCA line-level and balanced XLR pre-out option. For additional versatility and functionality, there’s also an AUX output.
Now equipped with fully balanced XLR inputs and outputs, the 33 is set apart from other preamplifiers and even its forefather model.
The brand new phono stage is Moving Magnet and Moving Coil compatible with the ability to simply switch between the two options – no mods or board upgrades necessary. With a gain of 46dB for the MM and 63.5dB for the MC, the input stage uses ultra-low noise audio op-amps. This ultra-low noise performance is combined with high slew rates and very low distortion specifications. The RIAA processing circuit has its own dual Bipolar/JFET Audio Operational Amplifier. The JFET portion of the input stage enables high slew rates to keep distortion low, even when large output swings are required.
The controls are comprehensive but simple. Again, this echoes the original design concept. Logically grouped to facilitate selection and control of the programme, a backlit LCD screen relays settings, adjustments and values. The same backlighting principle is applied to each of the push buttons, further enhancing the intuitive design with a visual indication of input selection and mode. Illumination settings for buttons and the LCD screen allow for brightness adjustment, contrast adjustment, and a simple on/off setting to suit the user’s preference.
The master volume control is a fully analogue, precision motorised ALPS potentiometer offering long-life and low-noise performance. The volume control is not only tactile and precise; its motorised operation will automatically rotate when adjustments are made via the remote control. A further row of three endless rotary encoders offer intuitive and immediate control over the QUAD-specific fine-tuning settings.
The original QUAD 33, as with many previous and subsequent QUAD preamplifier components, offered filters considered essential for ‘modern good quality speakers’ (as was stated at that time). Such controls are no longer required; therefore, in applying modern-day logic and suitability to today’s technology, the new QUAD 33 presents bass adjustment, tilt control and balance control to allow tuning to a fine degree without intruding unnecessarily into the harmonic range essential for realistic reproduction.
The bass control allows adjustment from-3dB to +3dB. Perfect for subtle adjustments in the low-end, as a solution to adding body to thinner source material. Or conversely, reducing bass tones in the event of room-affected ‘boominess’. In comparison to the time of launch of the original QUAD 33, loudspeakers and source materials have evolved mainly for the better. This evolution saw the adoption of ‘Tilt’ control in the QUAD 33’ssuccessor, the QUAD 34 (1982).
Developed by QUAD founder, the legendary Peter Walker, the Tilt control is an audiophile-quality solution for adjusting tone. Its design stems from the belief that traditional tone and EQ controls are inadequate and clumsy when adjusting tonal balance.
The Tilt control differs in that it adjusts both ends of the frequency spectrum together, either attenuating the bass and lifting the treble, or lifting the bass and attenuating the treble in 1dB steps.
Essentially, it rotates – or tilts – the audible frequency range on a 700Hz axis, thereby adjusting the overall sound balance with ‘warm’ or ‘cool’ hints without altering volume or adding colour to the sound. This feature is unique to QUAD and offers a subtle, precise, and consistent way to adjust your system’s performance and compensate for recordings or environments.
The Tilt control, Bass control, and Balance controls are all composed of low-noise op-amps, electronic switches, and MELF low-temperature coefficient metal film resistors, forming a negative feedback adjustment circuit.
No one knows more about the QUAD 33 than the immensely experienced QUAD service department – still based at QUAD HQ in Huntingdon, Cambridgeshire, England.
Upon initiating this project of passion, it was determined that the new 33 and 303 combination will only see the light of day if the performance stands true and improves on the original.
In over 50 years since the release of the original 33 and 303, innovations and developments have been exponential, but only some have been employed and each with good reason. Each stage of the development and every innovation was subject to thorough testing and complete agreement with the QUAD technical design AND service team.
It is bold but fair to claim that the low-noise, custom-specified toroidal transformer, numerous reservoir/smoothing capacitors, and an impressive number of regulators put the new QUAD 33 technically ahead of the original. The power supply incorporates five regulated supply rails, including multiple ultra-low-noise regulators with extensive measures employed to prevent contamination and cross-coupling. Following traditional QUAD practices, the core signal path is short and direct to preserve signal purity, and volume is adjusted purely in the analogue domain under microprocessor control. No one will champion the virtues of the original QUAD 33 more than QUAD, ourselves. However, side-by-side, technical innovations and improvements in signal processing cannot be denied.
The QUAD 33 has a crisp and clean aesthetic that evokes QUAD’s past yet sits in the modern-day with a futuristic accent. The housing is rigid and oozes quality. The end-finish is precise, just like the audio signal path. The anodised and custom-tooled fascia demonstrate the quality and level at which the new QUAD 33 will be recognised. No longer subject to cracks, fading or other issues associated with classic front panels, the QUAD 33 is ready for a lifetime of performance.
Ultimately, the new QUAD 33 considers every angle and aspect to underline the faithful evolution of the ‘33’ concept. With each step in transitioning from concept to reality, the commitment to ‘the closest approach to the original sound’ is evident.