Pre/Power Amplifiers

Comparisons with the original Momentum Preamplifier [HFN Nov '13] reveal a series of subtle differences not reflected in the general description of the updates. For example, the application of the finest ±0.5dB volume control increments has been extended from the top 35dB to the top 42dB of its dynamic range while the overall gain has been boosted from +8.2dB to +12dB in the HD Preamp. Maximum output has increased too, from 20.5V to a massive 26.5V, so the HD Preamp will drive any likely power amp into clipping – including any of the Constellation power amps in their reduced-gain 'Direct' mode [HFN Oct '19]. The A-wtd S/N ratio is proportionally lower, however, from 96dB to 92dB here (all re. 0dBV) although the residual noise is still vanishingly low at –98dBV (13µV). That outboard PSU clearly confers benefits...

The preamplifier's output impedance is unchanged at 38-39ohm (20Hz-20kHz) but the response, previously extended to within ±0.02dB out to 100kHz, now features an ultrasonic roll-off amounting to –0.18dB/20kHz to –3.5dB/100kHz [not unlike the Relentless power amp – HFN Mar '20]. The broad subsonic boost of +0.4dB/20Hz and +0.78dB/5Hz is unchanged and also remains unaffected by the Tone in/out setting [see Graph 1 below]. The profiles of the 11 bass/treble tone settings are discussed in my sidebar. Distortion is now more consistent between L/R channels and still very low at <0.0005% from 5Hz-5kHz but, along with the mildly tailored response, THD also increases at HF up to 0.002%/20kHz and 0.01%/40kHz [see Graph 2]. We saw the same from the MLife preamp board, upon which the HD Preamplifier is based [HFN Apr '17]. PM