Vintage

While Sansui was not making any particular assertions about the

AU-D33's speaker-driving ability, its 'Super Feedforward' topology did make a claim for very low distortion. The latter was realised in practice with a midband THD of 0.0005-0.001% over the full 50W range specified for this integrated amplifier. There is some suggestion of crossover distortion at very low power – the minimum THD being achieved at ~10W/8ohm – but even at high frequencies the AU-D33 holds true to just ~0.004%/20kHz [see Graph 2, below]. CCIR intermodulation distortion is also a very low 0.0002% although stereo separation begins to 'close up' to around 40dB at 20kHz, possibly through capacitive coupling between tracks/wiring on the PCB. Overall gain is a sensibly modest +39.8dB – lower than the excessive 45dB+ of many integrateds from this era – requiring 205mV to raise the rated 50W/8ohm from the output. The A-wtd S/N ratio is bang-on 100.0dB at this output (and 83.0dB re. 0dBW).

The frequency response is very extended, so while the –0.25dB bass shelf (2Hz-200Hz) was unexpected, the treble rolls away to an imperceptible –0.2dB/20kHz and then to –4.7dB/100kHz. The moderate 0.15-0.20ohm output impedance will give rise to further shifts in balance when paired with low/variable-impedance loudspeakers – the latter are not especially recommended if only because the AU-D33 is current-limited to just 4.5A, achieving an underwhelming 32W/2ohm and 18W/1ohm. Into 'easier' loudspeaker loads the AU-D33 fares well enough, besting its rated 50W with 2x70W/8ohm and 2x55W/4ohm, and with sufficient headroom into these higher impedances to support 103W/8ohm [see Graph 1, below]. PM