Integrated Amplifiers

While the maximum preamp output is 5.8V (re. 1kHz/0dBFs) it is not safe to run the Pendulum at this output because the power amp remains in-circuit and will be driven into clipping even without a (speaker) load attached. Muting the power amp also mutes the preamp, so this is not a solution! All subsequent tests were run via the network/optical inputs and balanced analogue outs at 2.23V – this is the maximum preamp output that can be tolerated without the amp dropping into protection at high frequencies. THD reaches 0.0014%/1kHz and 0.010%/20kHz with a peak (0dBFs) digital input and falls to a minimum of 0.0005% (with 3rd, 5th and 7th harmonics in the ascendant) over the top 30dB of its dynamic range [black trace, Graph 1]. The ES9039Q2M DAC can achieve lower distortion but these levels are low enough and also more likely to arise from the Momentum C2 preamp-inspired line stage. The 105dB A-wtd S/N ratio is also ample and sufficient to provide for a low-level resolution of ±0.1dB at –100dBFs and ±0.8dB at –110dBFs.

Response and stopband rejection are largely dictated by the (fixed) selection of ESS’s slow roll-off minimum phase digital filter. In this instance it offers a worse-case image rejection of just 8.4dB traded against much reduced time-domain distortion and a treble roll-off amounting to –3.4dB/20kHz with 44.1kHz (CD) digital inputs and –1.6dB/20kHz with 48kHz files, up to –4.5dB/45kHz and –9.5dB/90kHz with 96kHz and 192kHz media, respectively. Output impedance is uniform across 20Hz-20kHz but still a little high at 316ohm (balanced). Correlated jitter, meanwhile, is almost fully rejected but at the expense of an obvious, uncorrelated phase noise [x10 zoom, grey spectrum, Graph 2] with a maximum ±100Hz bandwidth. PM