Integrated Amplifiers

Mola-Mola's NCore-inspired Class D power amp section did meet its 150W/8ohm specification but fell short of delivering 300W/4ohm unless under dynamic conditions where 155W, 300W, 175W and 104W was delivered at <1% THD into 8, 4, 2 and 1ohm loads, respectively. Maximum current is limited to ~10A [see Graph 1]. Gain is a sensibly low +28dB (instead of the +40dB offered by many integrateds), the 88dB A-wtd S/N (re. 0dBW) is rather wider than achieved by most analogue Class D amps, and bass/midrange distortion remains very low at 0.0004% up to 10W, increasing to merely 0.002% at 100W [see Graph 2].

Distortion increases more rapidly above 10kHz, however, to 0.015%/20kHz/10W, in line with the tailored response of –0.5dB/20kHz to –3.75dB/60kHz. Incidentally, THD is also higher, watt-for-watt, under dynamic conditions as Graph 1 vs. Graph 2 illustrates. Remarkably, the output impedance remains <0.005ohm (<5mohm) from 20Hz-20kHz, so the Kula's system response is almost entirely immune to swings in loudspeaker impedance. Chalk-up another advantage to designer Bruno Putzy's NCore/Purifi range of Class D amplifiers.

The Kula DAC module is clearly derived from the Makua/ Tambaqui [HFN Aug '17 & Nov '19] but could only be tested here via the main outputs (thus including the Class D pathway). At 2V output, low-level linearity is true to within ±0.4dB over a 110dB range even though the S/N is reduced to 84dB. Distortion, too, is remarkably low at 0.00005-0.0005%/1kHz over the top 30dB of its range, increasing to 0.0009-0.003%/20kHz as a function of the Class D amp. Jitter is incredibly low: less than 25psec, all sample rates/all inputs, through the DAC/amp signal path. PM