Aurorasound VIDA MkII Phono Preamplifier Lab Report

Lab Report

While passive RIAA networks are often employed for their perceived subjective advantage, conventional RC stages soak up a lot of gain (~20dB at 1kHz) and present a variable load for the input/buffer preamp. Bridged T-network LCR filters can be designed for a constant input impedance without sacrificing as much gain, but optimising the inductor value (against its series resistance) is a trade-off, especially in the low-pass arm of the network. Aurorasound's latest circuit offers about 2dB extra MM gain vs. the VIDA MkI (+40.5dB vs. +38.4dB) with a +1dB 'boost' for MCs (+65.1dB vs. +64.2dB) at the expense of slightly reduced input overload margins – 128mV vs. 163mV (MM) and 7.0mV vs. 8.6mV (MC). The MM margin is still more than sufficient, offering +28dB headroom for a 5mV/1kHz (5cm/sec) rated pick-up, this coupled with a worthy 82dB A-wtd S/N ratio. The MC input has a good 76dB S/N but is arguably less well suited to very low output types where a 70dB+ gain is required, or very high output MCs where the +22.9dB input margin (re. 500µV) may be insufficient.

Distortion is reduced to 0.0015% through the midrange in the MkII although low frequency THD is slightly higher at 0.017% [see Graph 2, below] – all these figures being two or three orders of magnitude lower than that from a 'real world' pick-up. The equalised response shows a mild +0.2dB lift through the bass (~60Hz) and treble (~10kHz) and boasts slightly greater extension over the MkI, reaching +0.11dB/20kHz and –5.3dB/100kHz. The low bass extension of its DC-coupled output stage is extreme, just –0.6dB/1Hz, while the AC-coupled subsonic filter shows an improved –10dB/5Hz attenuation [see Graph 1, below]. Finally, the MkI's high 1.1kohm output impedance has been slightly reduced to 850ohm in the MkII. PM


RIAA-corrected MM frequency response from 5Hz-100kHz re. 0dBV (subsonic filter dashed)


Distortion versus frequency re. 0dBV from 20Hz-20kHz (MM, black; MC, red)

Input loading (MM/MC) 47kohm/100pF / 30-470ohm/1kohm
Input sensitivity (re. 0dBV) 9.42mV / 554µV (MM/MC)
Input overload (re. 1% THD) 128mV / 7.0mV (MM/MC)
Max. output (re. 1% THD) / Imp. 13.5V / 850ohm
A-wtd S/N ratio (re. 0dBV) 81.9dB / 76.0dB (MM/MC)
Freq. resp. (20Hz-20kHz/100kHz) –0.0dB to +0.20dB / –5.25dB
Distortion (20Hz-20kHz, re. 0dBV) 0.0015–0.017% (MM)
Power consumption 8W
Dimensions (WHD) / Weight 260x100x250mm / 2.8kg (1.4kg, PSU)
Price £3659 (+£369 for variable MC loading)

Aurorasound Inc
Supplied by: Pure Sound, UK
01822 612449