Aragon 8008 power amplifier Measurements
Following its 1/3-power, one-hour preconditioning test, the heatsinks of the 8008 were too hot to touch comfortably for more than a few seconds. The Aragon is noninverting. The input impedance of the 8008 measured 23k ohms at 1kHz. The output impedance was 0.037 ohms up to 1kHz, remaining below 0.048 ohms at 20kHz. Voltage gain into 8 ohms measured 24.2dB. DC offset was 0.3mV in the left channel and 0.2mV in the right. Unweighted signal/noise (ref. 1W into 8 ohms) measured 87.7dB over a 22Hz-22kHz bandwidth (88.9dB, A-weighted).
Fig.1 shows the frequency response of the 8008. It is near-ideal—even with a simulated loudspeaker load, the deviation from flat is insignificant. (The response at 2W into 4 ohms is identical to the 8 ohm measurement and is not shown.) The 10kHz squarewave (fig.2) is also excellent, with a short risetime, sharp corners, and no overshoot or ringing. (The 1kHz squarewave response is nearly perfect and is not shown.)
Fig.1 Aragon 8008, frequency response at 1W into 8 ohms (top at 8kHz) and into simulated speaker load (right channel dashed, 0.5dB/vertical div.).
Fig.2 Aragon 8008, small-signal 10kHz squarewave into 8 ohms.
The channel separation shown in fig.3 is hard to fault, with only the normal increase at high frequencies apparent, due to capacitive coupling between channels. Though the two channels are not identical, even at its poorest the crosstalk is audibly insignificant.
Fig.3 Aragon 8008, crosstalk (from bottom to top at 1kHz): L-R, R-L (10dB/vertical div.).
The THD+noise vs frequency result (fig.4) is extremely good. Note the very high power output required to get a reasonable reading; at lower levels, the distortion disappeared into the noise floor. The result was a little more typical into our simulated real load; the curve shown in the graph is for the power level we usually use for this measurement: 2.83V. The Aragon's distortion waveform (fig.5) indicates a predominant second-harmonic component at medium power levels (at higher power, it transitioned to third-harmonic), plus some higher harmonics at a much lower level. The results for 2, 4, and 8 ohm loads were very similar; only the 4-ohm result is shown.
Fig.4 Aragon 8008, THD+noise vs frequency at (from top to bottom at 1kHz): 100W into 2 ohms, 50W into 4 ohms, 2.83V into simulated speaker load, and 25W into 8 ohms (right channel dashed).
Fig.5 Aragon 8008, 1kHz waveform at 20W into 4 ohms (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).
The spectrum of the 8008's output reproducing a 50Hz input at 268W into 4 ohms is shown in fig.6. This is a superb result; all of the artifacts are well below -80dB (0.01%). Since our simulated loudspeaker load will not accept anything like 268W, I ran the 8008 at 50W into this load (22.9V across 10.5 ohms which is the approximate impedance of the simulated load at 50Hz). The result (fig.7) indicates an increase in the third (150Hz) and fifth (250Hz) harmonics over the pure-resistance, high-power result, though only the former is greater than -80dB (-69.5dB or about 0.035%)
Fig.6 Aragon 8008, spectrum of 50Hz sinewave, DC-1kHz, at 268W into 4 ohms (linear frequency scale).
Fig.7 Aragon 8008, spectrum of 50Hz sinewave, DC-1kHz, at 50W into simulated loudspeaker load (linear frequency scale). Note that the third harmonic is the highest in level at -69.5dB (about 0.035%).
Fig.8 shows the 8008's output spectrum reproducing a combined 19+20kHz signal at 231W into 4 ohms. The largest intermodulation artifacts are at 18kHz and 21kHz (-74dB or 0.02%). The artifacts from the same test signal at 131W into 8 ohms (not shown) were lower still.
Fig.8 Aragon 8008, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 231W into 4 ohms (linear frequency scale).
The 1kHz, THD+noise vs output power curves for the 8008 are shown in fig.9, with the discrete clipping levels (at 1% THD+noise) listed in Table 1. Note that while the 8008 would put out significant power into 2 ohms, like the Sumo Andromeda I reviewed last month, it blew one of its power-rail fuses before I could get a stable reading. This suggests that the amp will overheat if asked to produce 2 ohms for more than a brief period, and that the manufacturer has specified a slightly undersized fuse to prevent this from happening.
|Table 1: Aragon 8008 Clipping (1% THD+noise at 1kHz)|
|LOAD||Both Channels Driven||One Channel Driven|
|ohms||W (dBW)||W (dBW)|
|8||245.9 (23.9)||245 (23.9)||260.8 (24.2)|
|4||408.1 (23.1)||408.2 (23.1)||445 (23.5)|
Fig.9 Aragon 8008, distortion (%) vs output power into (from bottom to top at 100W): 8 ohms, 4 ohms, and 2 ohms.
The Aragon's test-bench measurements were excellent, the only possible exception being its fuse-popping when driving very high power into 2 ohms for more than a second or two. The latter should not have repercussions in normal use except with the most difficult loads at high levels. (It is very unlikely that you will ever put over 700W into a loudspeaker for more than an instant. Longer than that and the loudspeaker is likely to pop before the fuse does.)—Thomas J. Norton