John Darko
The 2024 editions of Quad’s iconic 33 pre-amplifier and 303 stereo power amplifier have landed in Berlin for review. Here are 20 more thoughts on their designs:
1. Released in the late 1960s, the original 33 and 303 were Quad’s first all-transistor amplifiers.
2. Most transistor-based amplifiers of the time were integrated designs whose pre-amplifier and power amplifier stages were combined in a single box. The 33 and 303 put the power and pre stages in separate boxes to audibly benefit from separate power supplies, transformers and wall socket connections.
3. The 303 power amplifier’s vertical orientation was intended to help with tucking it away out of sight to leave only the 33 pre-amplifier in view. I have mine on the floor because the taller design looks disproportionately large when sat next to the 33 pre-amplifier on top of a USM Haller sideboard.
4. The original 33 and 303’s unconventional aesthetics netted them a Council of Industrial Design Award in 1969.
5. Quad’s decision to rework the 33 and 303 was largely due to the ongoing demand for the original amplifiers. They still fetch good money on the second-hand market four decades after they were discontinued.
6. A new team was assembled to design the 2024 editions. This team included: Quad’s most experienced service engineers Rob Flain and Paul McConville; Quad’s industrial design chief for the last two decades, David McNeill; Quad and Audiolab’s lead electronics designer, Jan Ertner. Along with Wharfedale, Castle and Leak, Quad and Audiolab are now owned by China’s IAG.
The 2024 Quad 33 pre-amplifier
7. The new 33 pre-amplifier dispenses with the original’s DIN sockets in favour of three single-ended RCA inputs, a balanced XLR input, and a phono input that’s switchable between MM and MC (both with fixed loading).
9. The filters for vinyl are no more; and the bass, treble and slope dials have been replaced by bass, tilt and balance.
10. Tilt? It adjusts both ends of the frequency spectrum together on a 700Hz axis. It either
attenuates the bass and lifts the treble for a cooler sound or it lifts the bass and attenuates the treble for a warmer sound.
11. There is no DAC inside the 33. That rear-panel USB-A socket is for firmware updates.
12. The 33’s user interface is microprocessor-controlled,
13. Volume control comes from a (remote-controllable) motorised Alps potentiometer.
14. The 2024 take on the 33 is built around a new circuit that features a low-noise custom toroidal transformer, numerous reservoir/smoothing capacitors and five regulated power supply rails.
15. The dedicated headphone amplifier is a current feedback design with (according to Quad) a high slew rate.
The 2024 Quad 303 power amplifier
16. Quad refers to the original 303 as βthe worldβs first low-distortion transistor amplifierβ, so claimed because of the 303’s βtriplesβ output stage that effectively formed a feedback amplifier-within-an-amplifier. This reportedly required less negative feedback to net lower distortion and better thermal stability.
17. The new 303βs βsymmetrical triplesβ output stage is faithful to the original but is now completely symmetrical for even lower distortion. This Class A/B output is powered by a low-noise 200VA toroidal transformer designed explicitly for the new 303.
18. The original 303 promised 45wpc into 8 Ohms, dropping off significantly into 4 Ohms; and with current output limitations. The new 303 is rated at 50wpc into 8 ohms, rising to 70W into 4 Ohms.
19. I am currently using a pair of 303 amplifiers as monoblocks for 140wpc into 8 Ohms or 170wpc into 4 Ohms. They are fed by the 33 pre-amplifier over balanced XLR wire but I am not using the 303’s 12V trigger inputs. Instead, I must play cat and mouse with the EU-mandated power saving circuit that kicks in to put the 303 into standby after 15 minutes of silence.
20. Our video review about the 2024 Quad 33 and 303 will land on YouTube sometime before the end of the year but kindly note that I do not have the original 33 and 303 to hand.
Further information: Quad Hifi
