Pre/Power Amplifiers

Unlike the original 33 preamp, the new model is set for unity gain at full volume (1V in/1V out, XLR in/out), yielding a stereo separation of >100dB (20Hz-20kHz) and a super-wide 93.7dB A-wtd S/N (re. 0dBV). Distortion is ~200x lower too at 0.00007-0.0003% from 20Hz-20kHz [black trace, Graph 2], while the response is now flat to within ±0.05dB from 3Hz-100kHz. This droops slightly to –3.5dB/100kHz with tone defeat ‘off’ and the Bass/Tilt controls set at a ‘neutral’ ±0.0dB. The ±3dB Bass control provides a 1dB, 2dB and 3dB cut and boost across 20-40Hz (re. 1kHz) while the Tilt facility offers the same 1dB, 2dB and 3dB maximum cut and boost at 20Hz and 10kHz, with the slope ‘pivoting’ at around 700Hz. As intended, these are gentle, low-Q tone adjustments operating over extended bandwidths.

The partnering 303 amp is a modern complementary Class AB amplifier again offering more power, far lower distortion and noise, and a flatter, more extended bandwidth than the original [see boxout]. The new 303 just nudges ahead of its 50W/8ohm specification, offering 2x56W/8ohm and 2x83W/ 4ohm with sufficient headroom to accommodate 72W, 125W and 145W into 8, 4 and 2ohm, respectively, under dynamic conditions. Output is current-limited to 85W (9.2A) into the lowest 1ohm loads [see Graph 1, below] so the 303 will just cope with Quad’s own Revela 2 [HFN Aug ’24]. Response reaches from 3Hz-20kHz within –0.15dB, and out to 100kHz/–1.7dB, while distortion increases with frequency from 0.0005-0.025% at 10W/8ohm [see Graph 2] and marginally with level from 0.001% (1-20W) to 0.0025% at the rated 50W (re. 1kHz/8ohm). The A-wtd S/N ratio is an impressively wide 92.1dB (re. 0dBW). PM