Sidebar 3: Measurements
Because JVS auditioned the Electrocompaniet AW 800 M as a pair of monoblocks, I performed a complete set of measurements of the amplifier in that mode with my Audio Precision SYS2722 system. I confirmed the results with the higher-performance APx500, then repeated some tests with the amplifier operating in two-channel mode.
I preconditioned the AW 800 M by following the CEA's recommendation, running it at one-eighth the specified power into 8 ohms for 30 minutes. At the end of that time, the top panel above the internal heatsinks was hot, at 117°F (47.3°C). The Electrocompaniet needs to be well ventilated.
The AW 800 M's input impedance was a very high 280k ohms at 20Hz and 1kHz, dropping to 44k ohms at 20kHz. The balanced input is wired with pin 2 hot and preserved absolute polarity. The voltage gain in mono mode at 1kHz was 35.3dB (footnote 1). In stereo mode, the gain was 29.3dB, the expected drop of 6dB.
With its very low levels of noise and distortion and its very high powers, the Electrocompaniet AW 800 M is a veritable paradigm of modern solid state amplifier design.—John Atkinson
Footnote 1: In the print version of this review, the voltage gain in bridged-mono mode was incorrectly stated as 32.3dB. This was a typo; the measured gain was the specified 35.3dB. Footnote 2: In his manufacturer's comment, Geir Svihus, Chief Product Developer Electrocompaniet. wrote "Regarding the blown fuse: We intentionally set the fuse ratings as low as possible to provide maximum protection against safety hazards. Dynamic output power is limited only by the output-current trip level. The AW 800 M has an output-current trip level of around 50A; the AW 800 M will happily supply output power up in excess of 1.5kW into 4 ohm and 2 ohm loads. However, prolonged operation at these levels even at output current below the trip limit, as can occur during heavy testing, may overload the main fuse. Such sustained power levels will never occur during music playback. The fuses will not blow."
Footnote 3: In mono mode the two channels' outputs are bridged, which, with perfect matching, will eliminate even-order distortion.
Fig.1 Electrocompaniet AW 800M, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), and 2 ohms (red) (1dB/vertical div.).
Fig.2 Electrocompaniet AW 800M, small-signal 10kHz squarewave into 8 ohms.
The output impedance in mono mode was 0.11 ohms at 20Hz and 1kHz, 0.18 ohms at 20kHz, all these values including the series impedance of 6' of spaced-pair cable. The stereo-mode impedances were not significantly lower, at 0.09 ohms at low and middle frequencies rising to 0.13 ohms at the top of the audioband. Even in mono mode, the variation in the small-signal frequency response with our standard simulated loudspeaker (fig.1, gray trace) was minimal. The response into 8 ohms (blue trace) and 4 ohms (magenta trace) is flat in the audioband, neither reaching –3dB until 100kHz, but the increase in output impedance at high frequencies reduces the 2 ohm bandwidth (red trace), the output at 20kHz lying at –0.5dB. The Electrocompaniet's reproduction of a 10kHz squarewave into 8 ohms (fig.2) was excellent, with very short risetimes and no overshoot or ringing.
Fig.3 Electrocompaniet AW 800M, spectrum of 1kHz sinewave, DC–1kHz, at 1Wpc into 8 ohms (linear frequency scale).
Fig.4 Electrocompaniet AW 800M, stereo mode, spectrum of 1kHz sinewave, DC–1kHz, at 1Wpc into 8 ohms (linear frequency scale).
The unweighted, wideband signal/noise ratio (ref. 1W into 8 ohms), taken with the input shorted to ground, was an excellent 79dB. This ratio improved by 10dB when the measurement bandwidth was restricted to 22Hz–22kHz and by another 3dB when A-weighted. This is a quiet amplifier. Spectral analysis of the low-frequency noisefloor while the Electrocompaniet drove a 1kHz tone at 1Wpc into 8 ohms (fig.3) revealed extremely low levels of both random noise and power supply–related spuriae at 60Hz and its odd-order harmonics. The random noise and the spuriae were even lower in two-channel mode (fig.4).
Fig.5 Electrocompaniet AW 800M, distortion (%) vs 1kHz continuous output power into 8 ohms.
Fig.6 Electrocompaniet AW 800M, distortion (%) vs 1kHz continuous output power into 4 ohms.
Fig.7 Electrocompaniet AW 800M, stereo mode, distortion (%) vs 1kHz continuous output power into 8 ohms.
Electrocompaniet specifies the AW 800 M's maximum power in mono mode as 800W into 8 ohms (29dBW), 1500W into 4 ohms (28.75dBW), and 2200W into 2 ohms (27.4dBW). With our usual definition of clipping—when the THD+noise reaches 1%—the AW 800 M exceeded its specified maximum power, clipping at 1000W (30dBW, fig.5). However, when I repeated this test into 4 ohms, the 10A fuse on the rear panel blew at 1300W (28.2dBW), which is why the trace in fig.6 stops when the THD+N was 0.01% (footnote 2). In stereo mode with both channels driven, the AW 800 M didn't quite meet its specified power of 300Wpc into 8 ohms and 600Wpc into 4 ohms (both powers equivalent to 24.77dBW), clipping at 290Wpc into 8 ohms (24.6dBW, fig.7) and 460Wpc into 4 ohms (23.6dBW). At these high powers, the shortfall will be inconsequential.
Fig.8 Electrocompaniet AW 800M, THD+N (%) vs frequency at 28.3V into: 8 ohms (blue), 4 ohms (magenta), and 2 ohms (gray).
The downward slope of the traces below 100W in figs.5 and 6 indicates that below this power, actual distortion lies below the noisefloor. I examined how the percentage of THD+N in both channels varied with frequency at 28.3V, equivalent to 100W into 8 ohms, 200W into 4 ohms, or 400W into 2 ohms (fig.8). While the distortion rose as the impedance decreased, the THD+N percentage was still very low. More importantly, it didn't rise significantly in the top audio octaves.
Fig.9 Electrocompaniet AW 800M, 1kHz waveform at 100W into 8 ohms, 0.00085% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).
Fig.10 Electrocompaniet AW 800M, spectrum of 50Hz sinewave, DC–1kHz, at 100W into 8 ohms (linear frequency scale).
Fig.11 Electrocompaniet AW 800M, spectrum of 50Hz sinewave, DC–1kHz, at 200W into 4 ohms (linear frequency scale).
Fig.12 Electrocompaniet AW 800M, stereo mode, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red; linear frequency scale).
The distortion waveform in mono mode was predominantly the third harmonic (fig.9), lying close to –110dB (0.0003%) with the amplifier driving 28.3V into 8 ohms (fig.10). While the third harmonic rose to –90dB (0.003%) at the same voltage into 4 ohms (fig.11), this is still extremely low. As expected (footnote 3), the second harmonic was higher than the third with the amplifier in two-channel mode (fig.12), but both harmonics were still extremely low in level.
Fig.13 Electrocompaniet AW 800M, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 200W peak into 4 ohms (linear frequency scale).
With the AW 800 M in mono mode driving an equal mix of 19 and 20kHz tones at 200W peak into 4 ohms (fig.13), the level of the 1kHz difference product was negligible, and the higher-order intermodulation products all lay below –86dB (0.004%).
Footnote 1: In the print version of this review, the voltage gain in bridged-mono mode was incorrectly stated as 32.3dB. This was a typo; the measured gain was the specified 35.3dB. Footnote 2: In his manufacturer's comment, Geir Svihus, Chief Product Developer Electrocompaniet. wrote "Regarding the blown fuse: We intentionally set the fuse ratings as low as possible to provide maximum protection against safety hazards. Dynamic output power is limited only by the output-current trip level. The AW 800 M has an output-current trip level of around 50A; the AW 800 M will happily supply output power up in excess of 1.5kW into 4 ohm and 2 ohm loads. However, prolonged operation at these levels even at output current below the trip limit, as can occur during heavy testing, may overload the main fuse. Such sustained power levels will never occur during music playback. The fuses will not blow."
