Pre/Power Amplifiers

The exceedingly powerful and yet 'gentle' sound of the S5 power amp is fully explained by the measurements. The 2x500W/8ohm and 2x800W/4ohm spec. is very conservative as the S5 actually delivers 2x670W/8ohm and 2x1.17kW/4ohm with 691W, 1.39kW and 1.78kW achieved under dynamic conditions into 8, 4 and 2ohm. A 30A current limit gives a dynamic output of 902W/1ohm [see Graph 1]. THD climbs slightly with output, from 0.0015%/1W to 0.002%/10W, 0.0027%/100W and 0.0037% at the rated 500W/8ohm (all at 1kHz). Distortion also climbs at HF, from 0.0003%/20Hz to 0.002%/1kHz and 0.016%/20kHz (all 10W/8ohm) and noise is quite low, yielding a healthy 93dB A-wtd S/N ratio (re. 0dBW). But the response is not flat, shelving down above 5kHz to reach –0.4dB/10kHz, –0.65dB/20kHz and –1.0dB/100kHz. This trend is magnified into lower loads, reaching –0.5dB/10kHz, –0.9dB/20kHz and –2.3dB/100kHz into 2ohm.

The P5 preamp offers a maximum 22.6V balanced output, clipping at vol '90' with a peak level digital input. Tested at a 6V (vol '72') the P5 offers a modest 106dB A-wtd S/N ratio, minimal ±0.1dB error in linearity over a 100dB range and very low THD – between 0.0002-0.0006% through the midrange over the top 30dB of its dynamic range, increasing to 0.001-0.006% at 20kHz [see Graph 2]. Alias rejection is merely 'average' at 69dB because Rotel has elected for the minimum phase/steep roll-off digital filter option of the AK4490EQ DAC – the impulse test showing no pre-ringing but extended post-ringing. Responses extend out to –0.2dB/20kHz, –1.3dB/45kHz and –3.9dB/90kHz with 48kHz, 96kHz and 192kHz media while its source impedance increases from 120ohm and high/mid freq. to 375ohm/20Hz (bass). PM