UK-based hi-fi specialist Quad has brought back its 1960s-style 33/303 two-box pre/power amp with upgrades to design, engineering and manufacturing.
The reimagined Quad 33 preamplifier and 303 stereo power amplifier, originally launched in the 1960s, were teased in prototype form at the High End audio show in Munich in May. The 33 and 303 had become the most sought-after ‘vintage’ amplifiers on the second-hand market after their discontinuation in the 1980s.
The new editions, engineered by Quad’s technical service team led by Rob Flain and Paul McConville, include tilt control and independent bass adjustment.
The new Quad 33
The new 33 remains an ‘analogue’ preamplifier with no built-in DAC for digital sources, but its facilities have been adapted to better suit contemporary requirements. The filters for vinyl have gone and the bass, treble and slope dials have been replaced by bass, tilt and balance.
Quad’s founder Peter Walker created the ‘tilt’ control as a more sophisticated form of tone control, introduced in 1982 on the 34 preamp which succeeded the 33 as a classic brand feature.
The tilt control 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. The control works in conjunction with independent bass adjustment, accurately applied from -3dB to +3dB to tailor tonal performance to a range of music sources like streaming.
The original 33 used DIN sockets for its inputs and outputs, since swapped out for a mix of single-ended RCA and balanced XLR sockets to offer a wider range of cable options. The original’s four source inputs – labelled ‘disc’ (for vinyl), ‘radio 1’, ‘radio 2’ and ‘tape’ – have been replaced by four line-level inputs (three RCA and one XLR) and a phono input alongside a choice of RCA and XLR outputs to connect the 303.
A motorised Alps potentiometer adjusts volume, while the three rotary encoders for bass, tilt and balance provide digital control in the analogue domain.
The new circuit design includes a low noise, custom-specified toroidal transformer, reservoir/smoothing capacitors and five regulated supply rails, improving on the original’s sonic performance. There is also a low-noise phono stage to advance vinyl audio, with adjustable gain for MM and MC cartridges, RIAA equalisation, precision input filtering and an upgraded power supply. The dedicated headphone amp is a new addition.
The new Quad 303
Reliability, flexibility and high-performance sound shape the new 303, which develops the core circuit of Quad’s original using a new generation ‘triples’ design and 200VA low-noise toroidal transformer.
Peter Walker’s circuit innovation for the 303 – the ‘triples’ output stage – remains at the new amplifier’s heart. The transistor amp design effectively forms a feedback amplifier within-an-amplifier, offering less negative feedback, thermal stability and lower distortion.
The new 303’s ‘symmetrical triples’ design is faithful to the original, providing a symmetrical output stage and rendering the resting current independent of output transistor temperature. Distortion is reduced to low levels without sacrificing stability, maintaining this performance under all dynamic conditions.
The new amp is rated at 50W per channel into 8 ohms, rising to 70W into 4 ohms with a higher current delivery of 10A driving demanding loads. An upgrade path is also offered, with the ability to connect two 303s in bridged mode and combine each amp’s two stereo channels into a single mono channel.
