Ayre Acoustics V-3 power amplifier Measurements
A full set of measurements of the Ayre V-3 was made using its balanced inputs, with selected measurements repeated in the unbalanced mode, as noted below.
Following its 1/3-power, one-hour preconditioning test, the V-3's heatsinks were very hot, though not beyond the normal range for this test. The Ayre's input impedance measured 20.8k ohms (10k ohms unbalanced). As expected from a design with no loop negative feedback, the output impedance was moderately high at a measured 0.33-0.38 ohms up to 1kHz, increasing to 1.14 ohms at 20kHz. Voltage gain into 8 ohms measured a high 32.5dB, balanced or unbalanced. Signal/Noise (ref. 1W into 8 ohms) measured 79dB over a 22Hz-22kHz bandwidth, unweighted, and virtually the same over a wider 10Hz-500kHz bandwidth,. The A-weighted S/N was 88dB. (The corresponding unbalanced figures were 74dB and 83dB.) The V-3 is noninverting when driven from its positive, unbalanced input; at the balanced, XLR input terminal, pin 2 is positive. DC offset measured a low 4.7mV in both channels.
Fig.1 shows the frequency response of the V-3 (the balanced result is shown, the unbalanced was a virtual overlay). Note the fairly pronounced high-frequency rolloff, plus the additional mid-treble dip into our simulated real load, caused no doubt by the Ayre's increasing output impedance at higher frequencies. This HF rolloff should be audible as a softening of the upper-frequency range; just how much will depend on the impedance characteristic of the loudspeaker, but it will never be less than the indicated response into a fixed load. A 1dB drop falling somewhere between 12kHz and 15kHz will be subtle, but not inconsequential.
Fig.1 Ayre V-3, balanced, frequency response (from top to bottom at 1kHz): at 1W into 8 ohms; 2W into 4 ohms; and into simulated speaker load (right channel dashed, 1dB/vertical div.).
The 10kHz squarewave response (fig.2) also clearly reflects this rolloff, with its noticeably rounded leading edge and reduced risetime. (The 1kHz squarewave response, not shown, is very good, with only a slight rounding of the leading edge.) Fig.3 shows the V-3's channel separation. The balanced result is a little better than the unbalanced, but both are pretty much beyond criticism.
Fig.2 Ayre V-3, balanced, small-signal 10kHz squarewave into 8 ohms.
Fig.3 Ayre V-3, crosstalk (from top to bottom at 10kHz): L-R, unbalanced; R-L, unbalanced; R-L, balanced; L-R, balanced (10dB/vertical div.).
The THD+noise percentage vs frequency curves are plotted in fig.4. The results show increasing levels of distortion into lower load impedances, this again due to the lack of overall negative feedback. The Alp-like distortion curve is that measured into our simulated load and is typical of an amplifier with a moderately high output impedance. The unbalanced input result, not shown, is virtually identical except for higher distortion from the right channel into an 8 ohm load (0.05% at 1kHz, increasing to 0.1% at 50kHz). The waveform of the distortion at 4W into 2 ohms is shown in fig.5. It is heavily third-harmonic, with noise. The waveforms into 4 and 8 ohms are identical, though with a higher proportion of noise (due to the lower magnitude of the distortion components).
Fig.4 Ayre V-3, balanced, THD+noise (%) vs frequency at (from top to bottom at 1kHz): 4W into 2 ohms, 2W into 4 ohms, 1W into 8 ohms, and 2.83V into simulated speaker load (right channel dashed).
Fig.5 Ayre V-3, balanced, 1kHz waveform at 4W into 2 ohms (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).