Pre/Power Amplifiers

With no phono stage or integrated DAC on board – BAT offers the VK‑P80 (50‑57dB gain) and VK‑P90 (45‑80dB gain) all‑tube MM/MC preamps, and REX 3 DAC [HFN May ’20], respectively, to fulfil these roles – the VK‑90 remains a fully analogue, balanced line preamplifier. BAT’s proprietary ‘electronic shunt volume attenuator’ claims 140 steps each of ±0.5dB resolution, though the top 10 steps – ‘130’ to ‘140’ – vary between ±0.9dB and ±0.4dB. However, (deep breath...) the average increments are ±0.58dB over the top 20 steps (an 11.6dB range between ‘120’ and ‘140’), ±0.53dB over the top 60 steps (a 31.6dB range), ±0.52dB over the top 100 steps (51.5dB range), and, finally, an average step accuracy of ±0.51dB over the full ‘001’ to ‘140’ volume setting (a 71.35dB useable range). Full gain, balanced input‑to‑output, is +19.6dB, requiring a 105mV input to raise a 1V/0dBV output at volume ‘140’.

BAT also rates the VK‑90’s maximum output as 40V, but the eight 6H30 ‘SuperTubes’ (four per side) actually deliver a massive 69V – sufficient to drive any power amp into destruction! No ‘overall feedback’ is claimed, but the –1.3dB/20Hz bass roll‑off [black/red traces, Graph 1] and increase in distortion at lower frequencies [see Graph 2] – the latter from a minimum of 0.0006%/5kHz to 0.0014%/1kHz, 0.035%/100Hz to 0.4%/20Hz and 2.8%/5Hz (all re. 0dBV) – are all linked to the transformer‑coupled output. There was a slight difference in treble response between channels in our sample at –0.3dB and –0.15dB/20kHz (left vs. right), but this will not be consequential in listening tests. Finally, the VK‑90’s A‑wtd S/N clocks in at a respectable 89.5dB (re. 0dBV) while the residual noise is, for an all‑tube preamplifier, very low indeed at –97.6dBV (13µV). PM