Pre/Power Amplifiers

When Ayre claims ‘100% zero-feedback’ this presumably refers to global rather than the local compensation necessary to manage interstage impedances, bandwidth and distortion. The response is indeed very wide, flat to within ±0.03dB over the 20Hz-20kHz audio range and falling to just –0.8dB/100kHz. Into 1ohm the response is wider still at just –0.2dB/100kHz although the VX-8’s high, but equally ‘flat’, 0.24ohm output impedance means that larger response variations will occur when driving speakers with big swings in impedance. Ayre also suggests the VX-8 has been engineered to deliver a ‘tube-like warmth’, at least partially explained by the slightly reduced deep bass damping, but more likely attributable to the moderate levels of, mainly, 2nd/3rd harmonic distortion. Distortion increases with level from 0.006%/1W to 0.02%/10W before flattening off and then rising again to 0.09% at the rated 100W (all re. 1kHz/8ohm). Importantly, from a subjective standpoint, distortion holds steady with frequency and only increases at HF at higher power [see Graph 2].

Distortion does increase under dynamic conditions and into lower impedances, however, almost doubling between 8ohm to 4ohm, then 2 and 1ohm for a given power output [see Graph 1, below]. Talking of which, Ayre rates the VX-8 at 100W/8ohm and 170W/4ohm, figures just met in practice at 2x112W and 2x195W, respectively, though the stiff supply regulation and limited headroom leaves it with 115W, 220W, 320W and a reduced 210W into 8, 4, 2 and 1ohm loads under dynamic conditions [again, see Graph 1 below]. Otherwise, overall gain is a very sensible +26.3dB, requiring 1.4V for its rated output, while the 88.5dB A-wtd S/N ratio is par for the course. PM