Ayre Acoustics V-3 power amplifier Measurements part 2
Fig.6 Ayre V-3, balanced, spectrum of 50Hz sinewave, DC-1kHz, at 134W into 4 ohms (linear frequency scale). Note that the third harmonic at 150Hz is the highest in level, at -50dB (about 0.3%).
Fig.7 Ayre V-3, balanced, spectrum of 50Hz sinewave, DC-1kHz, at 91.5W into simulated loudspeaker load (linear frequency scale).
Fig.8 shows the output spectrum with a combined 19+20kHz signal—the intermodulation products resulting from an input signal consisting of an equal combination of these two frequencies—at 88W into 4 ohms. (Visible clipping is present above this output with this input signal.) The difference-frequency artifact at 1kHz is low—below -80dB, or 0.01%—though there are some higher-frequency artifacts evident, peaking at about -38dB (or about 1.4% at 18kHz). At 44W into an 8 ohm load (not shown, and again just below visible clipping) the result was similar, though the artifacts were slightly lower between 15kHz and 17kHz.
Fig.8 Ayre V-3, balanced, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 88W into 4 ohms (linear frequency scale).
The manner in which the V-3's THD+noise changes with output power with a 1kHz input signal is shown in fig.9. The curves here are very unusual for a solid-state amplifier, which most typically will display a very low level up to the breakpoint or "knee," with a rapid increase beyond that point. The V-3's curves more closely resemble the gradual increases seen in tube amplifiers. Note that while taking the 2 ohm measurement, I blew a power-supply rail fuse; Ayre provided replacement 10A fuses (higher than the standard rating) and recommended that these be used in checking the higher impedance performance. After I substituted these fuses, the remainder of the measurements proceeded without incident. (The very unusual rail fuses used by Ayre resemble small resistors right down to their pigtail leads, which are inserted into small screw-clamp terminals. Combine this with the marginal accessibility of two of them, and the result is rail fuses that are a royal pain to change.)
Fig.9 Ayre V-3, balanced, distortion (%) vs output power into (from bottom to top): 8 ohms, 4 ohms, and 2 ohms.
The discrete clipping levels for the V-3 are shown in Table 1. Note that the clipping levels shown are less than the manufacturer's specified 100W into 8 ohms and 200W into 4 ohms. But the specification does not indicate a distortion level, nor does it indicate whether one or both channels are driven. From fig.9 it can be seen that the amplifier will reach these higher power levels with one channel driven, though with 2-3% THD+noise.
Table 1 Ayre V-3 Clipping (1% THD+noise at 1kHz)
|Both Channels Driven||One ChannelDriven|
|Load||W (dBW||W (dBW)|
|8||79.9 (19)||79.8 (19)||85.4 (19.3)|
|4||130.5 (18.2)||133.5 (18.3)||148.4 (18.7)|
The Ayre produced a reasonable set of measurements, though inferior to those of many solid-state amplifiers (including much less expensive ones). The areas of sacrifice are those which might have been expected, given its no-feedback design: signal/noise, frequency response, distortion, and output impedance (with the inevitable resulting load sensitivity). Ayre has sacrificed a little in static bench-test measurements for the presumed sonic benefits of zero-feedback design—benefits that do not show up in such measurements. I can't ignore the fact that I have, in the past, come down hard on other amplifiers—usually single-ended tube designs—that tested poorly on the bench. But the difference here is one of degree. The Ayre's measurements are not poor, just rather unremarkable for a modern solid-state amplifier. But some of the anomalies measured, particularly the frequency response, will be marginally audible in many systems.—Thomas J. Norton