Ayre V-1 power amplifier Measurements

Sidebar 3: Measurements

A complete set of measurements was performed on the Ayre V-1 in the balanced mode, with selected readings repeated in the unbalanced (single-ended) configuration. Except where noted otherwise, the following results refer to balanced operation.

Following its one-hour preconditioning test, the Ayre's heatsinks were quite hot, but could be touched for several seconds with no discomfort. The DC offset was 8.2mV in the left channel, 9.0mV in the right. The V-1 is noninverting at its unbalanced input; pin 2 of the balanced input is wired as positive. The S/N ratio (at 1W into 8 ohms) measured 89.6dB over a 22Hz-22kHz bandwidth and 88.4dB from 10Hz to 500kHz, both unweighted, and 93.3dB A-weighted. The unbalanced S/N measurements were, in each case, less than 1dB higher than the balanced figures. The voltage gain into 8 ohms measured 25.8dB, balanced or unbalanced.

The Ayre's input impedance measured 20.9k ohms balanced and 10k ohms unbalanced. Its measured output impedance varied from 0.32 to 0.47 ohms, the higher figure at 20kHz into a 4 ohm load. These are higher figures than we normally see in solid-state amplifiers (though far lower than in most tube amps), and will have a small effect on the V-1's frequency response into real-world loudspeaker loads. This can be seen in fig.1, which shows the modification of the response with our simulated speaker load, along with the amplifier's response into fixed resistances of 8 and 4 ohms.

Fig.1 Ayre V-1, frequency response at (from top to bottom): 1W into 8 ohms, and 2.828V into simulated loudspeaker load (0.5dB/vertical div., right channel dashed).

Fig.2 shows the V-1's 10kHz squarewave response: There is a slight rounding of the leading edge (very common) and a short risetime. The 1kHz squarewave (not shown) is nearly textbook-perfect. The V-1's crosstalk (not shown), was very low, at better than -100dB over most of the band. The channel separation decreased above 3kHz, reaching a still-excellent 72dB at 50kHz, due to capacitive coupling between the channels.

Fig.2 Ayre V-1, small-signal 10kHz squarewave into 8 ohms.

Fig.3 plots the small-signal THD+noise percentage against frequency, a respectable but not unusual result for a good solid-state amplifier. With unbalanced drive, the THD+noise figure was slightly higher. Balanced inputs do not invariably have lower distortion than unbalanced ones. In fact, the opposite is often the case, though the differences in linearity are usually small. The 1kHz THD+noise waveform at 2W into 4 ohms is shown in fig.4. The distortion is heavily third-harmonic, plus noise. The third harmonic also predominates into 8 and 2 ohms (results not shown).

Fig.3 Ayre V-1, THD+noise (%) vs frequency at (from top to bottom at 2kHz): 4W into 2 ohms, 2W into 4 ohms, 1W into 8 ohms, and 2.83V into simulated loudspeaker load (right channel dashed).

Fig.4 Ayre V-1, 1kHz waveform at 2W into 4 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

The distortion spectrum resulting from a 50Hz input at 268W into 4 ohms is shown in fig.5. Note the dominance of odd-order distortion products. At 150Hz (third harmonic) the distortion is 50.9dB, or about 0.3%; at 250Hz (fifth harmonic) it is -73.3dB, or just under 0.025%. The 19+20kHz intermodulation spectrum at 243.5W into 4 ohms is shown in fig.6. (Visible signs of clipping begin to appear with this signal at higher power readings.) The highest-level IM artifact is -39.9dB (just above 1%) at 18kHz. At 125.5W into 4 ohms (not shown) the IM distortion is lower: a maximum of -42.7% (about 0.75%) at 18kHz.

Fig.5 Ayre V-1, spectrum of 50Hz sinewave, DC-1kHz, at 268W into 4 ohms (linear frequency scale).

Fig.6 Ayre V-1, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 243.5W into 8 ohms (linear frequency scale).

The V-1's THD+noise percentage vs continuous output power curves are shown in fig.7, with the discrete clipping levels shown in Table 1. While the amplifier easily meets its specified power into 8 ohms, it doesn't do so into 4 ohms, though the line voltage during the test was slightly lower than normal. (Such doubling capability is rare among power amplifiers.) In order to test the amplifier using continuous test signals into 2 ohm loads, we had to replace—at Ayre's recommendation—the V-1's internal 10-amp resistor-fuses with 15A versions.

Fig.7 Ayre V-1, distortion (%) vs continuous output power into (from bottom to top): 8 ohms, 4 ohms, 2 ohms.

Table 1 Ayre V-1 Clipping
(1% THD+noise at 1kHz)
Both Channels DrivenOne Channel Driven
LoadW (dBW)W (dBW)
8233.6 (23.68)234.2 (23.7)250.4 (23.99)
4350.9 (22.45)351.8 (22.46)404.8 (23.07)
2555.5 (21.45)

The 10A fuses would blow at high power into 2 ohms with sinewaves, though I would not expect this to be a problem with normal program material, which can be seen in fig.8, the amplifier's clipping performance with just one channel driven but now driven with a low-duty-cycle 1kHz toneburst (10 cycles on, 40 cycles off). Strangely, less power was available with this signal than a continuous sinewave?W vs 233.6W at 1% THD+N—though now it did double every time the load impedance was halved, with 1020W (equivalent to a maximum current of 31.9A) available into 1 ohm. Other than with the punishing 1 ohm load (green curve), the clipping was gentle, reminiscent of tube amplifier overload. (The magenta line in fig.8 shows the usual 1% THD+N (-40dB) limit we define as the clipping point.)

Fig.8 Ayre V-1, distortion (%) vs burst output power into 8 ohms (black trace), 4 ohms (red), 2 ohms (blue), and 1 ohm (green).

The slightly high distortion levels and high output impedance of the V-1 relative to many comparable solid-state amps are typical of low-feedback designs. It's something of an audiophile mantra, if a controversial one, that very low negative feedback grants sonic benefits—but it rarely makes for wowie-zowie measurements. Despite this, the Ayre's test-bench results are good.—Thomas J. Norton

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