Integrated Amplifiers

To an extent, the ‘Amp’ is a WiiM Pro Plus network-attached streamer/preamp [HFN Aug ’24] with a TI TPA3255 Class D power module attached. However, while both employ a TI PCM1861 ADC for the line input, the Pro Plus uses an AKM AK4493SEQ DAC and the WiiM Amp an ES9018K2M DAC by way of alternative. There’s also a PCM5121 DAC onboard but this looks to be driving the user-configurable subwoofer output. Moreover, while WiiM has chosen a linear phase digital filter offering 83dB stopband rejection (44.1/48kHz data), it has less impact on the overall frequency response than the uncompensated (reactive) LPF at the output of the amplifier [see boxout, p73]. And power? TI rates the TPA3255 at ‘2x150W/8ohm in BTL configuration’ while WiiM specifies 60W/8ohm, doubling to 120W/4ohm. In practice, it meets this at 64W and 125W into 8/4ohm while, in common with some other Class D amps, headroom is slightly negative with outputs of 59W, 110W, 194W and 135W under dynamic conditions into 8, 4, 2 and 1ohm, respectively [see Graph 1].

The direct optical, HDMI and Ethernet inputs yield superior results over the analogue line input, bypassing the ADC. For example, at 1W/8ohm distortion is 0.005-0.10% but falls still further to 0.00045-0.013% via the digital ins. Noise is lower too via the direct digital ins, achieving an A-wtd S/N ratio of 98dB vs. a still above-average 88dB from the line input (all re. 0dBW). As all inputs are digitally processed and then converted back to analogue prior to the TPA3255 amp, there’s ample opportunity for low-rate jitter/phase noise to creep in [see Graph 2]. However, correlated jitter at 480psec is really very well controlled indeed bearing in mind the cost/compactness of this busy little box. PM