NAD M32 digital amplifier Sidebar

Direct Digital DAC/Amp

The M32 amplifier does not defer to the Hypex UcD Class D technology that we've seen rolled out in NAD's M22 power amp [HFN Apr '15] and D 3020 integrated [HFN Aug '14]. Instead, this new amp returns to the 'Direct Digital' technology we saw in the original M2 Master series [HFN Jun '10]. Historically, the Direct Digital Feedback Amplifier (DDFA), a proprietary and highly scalable digital Class D audio amplifier technology, was originally developed by Zetex Semiconductors back in 2006. Also called 'Class Z' at the time the technology was latterly acquired by Cambridge Silicon Radio Ltd May 2013, which was mopped up by mobile tech giant Qualcomm in August 2015.

The DDFA's (PWM) modulator is synchronised directly to the incoming sample rate and supplies a discrete range of pulse 'widths' – rather than continuously variable 'widths' – to the high-speed MOSFETs at the output. As a result it ranks as one of the few genuinely digital Class D amplifiers available, executed here in Qualcomm's CSRA6601 DSP chip. Like other Class D amps of this ilk, however, the final frequency response is influenced by the impedance trend of the attached loudspeaker. Hence the 'speaker compensation' facility buried in the M32's menu. This has nothing to do with power delivery into low impedances but everything to do with 'best guessing' the flattest response. For example, set to '8ohm' the response (into 8ohm) is +0.1dB/20kHz to +2.9dB/45kHz with 96kHz media but falls to –0.1dB/20kHz to –1.5dB/45kHz into a 4ohm load unless the 'speaker compensation' is also reduced to 4ohm. PM

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