Pre/Power Amplifiers

While we have teamed-up the new C41 with this C21 power amp – MBL’s own suggested pairing – the latter is, in fact, a ten-year veteran of the Cadenza range and host to the brand’s ‘mk1’ LASA (Linear Analogue Switching Amplifier) Class D output stage. As a result, its performance pre-dates the Ncore-based LASA 2.0 technology employed in the N15 power amplifier [HFN Feb ’22] from the Noble range. Certain LASA traits are retained, including a very useable dynamic headroom – something rarely encountered with Class D stages where power output under continuous and dynamic conditions is typically the same. So, while the C21 meets its rated 180W/8ohm and 300W/4ohm specification at 2x200W and 2x350W, respectively, it goes on to deliver a full 265W/8ohm and 510W/4ohm under dynamic conditions (1kHz/10msec at <1% THD) before falling back to 352W/2ohm and 205W/1ohm [see Graph 1, below]. Graph 1 also suggests that the C21 is arguably better suited to 4ohm rather than 8ohm loads, the former enjoying a lower 0.003-0.01% THD rather than 0.001-0.025% over a 1-50W range (all re. 1kHz).

That said, MBL’s LASA output stage avoids the load-dependent response issues seen with other, older, Class D solutions. In practice, the C21 offers a fairly uniform 0.011-0.035ohm source impedance (20Hz-20kHz) alongside a response that holds to –0.75dB/20kHz, within –0.2dB, into all loads from 8ohm down to 1ohm. The A-wtd S/N ratio is slightly below average at 80dB (re. 0dBW), not because of an increase in white noise often seen with Class D amps, but courtesy of a spurious peak at 7.4kHz. Without this, likely inaudible tone, the C21’s A-wtd S/N would be closer to a very fine 88dB (re. 0dBW). PM