Pre/Power Amplifiers

Lab Report
There are numerous ‘shifts’ in the P5 S2’s performance over the original P5. Maximum gain is still +10.8dB and the maximum balanced output is still 22.8V, but while the inaugural P5 clipped at vol ‘90’ with a peak level (0dBFs) digital input, the P5 S2 makes it all the way to ‘Max’ (or vol ‘96’) with a phase-inverted output of 12.9V at 0.00045% THD. As we saw in the X3 S2, the S/PDIF and USB ins are now handled by an ES9028PRO DAC in place of the AK4490EQ used in the P5. Tested at a nominal 6V balanced output (vol ‘78’ in contrast to ‘72’ on the P5) the P5 S2 offers an improved 107.2dB A-wtd S/N ratio (by 1dB), minimal ±0.3dB error in linearity over a 110dB range but a slight increase in distortion from 0.0002-0.0006% (P5) to 0.00035-0.0016% (P5 S2) through the midrange over the top 30dB of its dynamic range. At 20kHz there’s an increase from 0.001-0.006% (P5) to 0.0095-0.0038%.

Jitter is a little lower at 180psec (from the P5’s 375psec) with 48kHz/24-bit data but the pattern is still untidy for an ESS DAC. Otherwise, a ‘fast’ minimum phase digital filter is used that offers a 76dB stopband rejection and response that reaches out to –0.17dB/20kHz, –1.0dB/45kHz and –4.7dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. The P5 S2’s ‘analogue’ response is flat to ±0.05dB from 20Hz-100kHz with an output impedance that increases from 121ohm/1kHz to 314ohm/20Hz, coinciding with a roll-off in deep bass response to –3dB/3Hz. Analogue distortion is very low too, from 0.00012-0.0015% (re. 20Hz-20kHz at 0dBV), and the A-wtd S/N suitably wide at 92.8dB (re. 0dBV). All told, the balanced preamp is a solid platform for Rotel’s ESS-based digital solution.

THD vs. 48kHz/24-bit digital signal level over a 120dB dynamic range (1kHz, black; 20kHz, cyan) versus P5 (1kHz, grey dashed; 20kHz, blue dashed)

High-resolution 48kHz/24-bit jitter spectrum with markers identifying 52 discrete sidebands