LABORATORY TEST REPORT
The Audio Analogue Maestro Anniversary revealed its ‘dual mono’ topology during the power output testing, where Newport Test Labs found that both channels delivered exactly the same output power, irrespective of whether one or both channels were driven. So for the sake of brevity, I’ll mention only the ‘both channels driven’ power output results, which you can also see in the accompanying power output table and also view in bar graph format.
At 1kHz, with both channels driven, the Audio Analogue Maestro Anniversary delivered 190-watts per channel into 8 , 361-watts into 4 and 544-watts into 2 . All are good results and all are above specification. But if you look at the results at 20Hz and 20kHz, you’ll find that the Maestro was also able to deliver exactly the same very high output levels at the frequency extremes. This is very rare—particularly at 20Hz—and so is a truly outstanding result for this amplifier.
Distortion at 1kHz at an output of one watt is shown in Graph 1 (for an 8 load) and in Graph 2 (for a 4 load). The distortion is obviously lower into the 8 load, with just a second harmonic at –94dB (0.0019%), a third harmonic at –87dB (0.0044%), a fifth at –95dB (0.0017%) and a seventh at –102dB (0.0007%). The noise floor is for the most part down at around –110dB, though the signals at the extreme left show some low-frequency noise components related to the amplifier’s power supply. Interestingly the noise floor drops to –120dB when the amplifier is driving the 4 load, but many more harmonic distortion components are evident, the most significant of which is the third harmonic at –60dB (0.1%). The other low-order components are all hovering around –90dB (0.0031%) while the sixth and higher-order harmonics are all below –100dB (0.001%).
At rated output power the distortion spectrum is roughly the same for both 8 and 4 loads, so I’ll look only at the 8 graph, which shows a second harmonic at –74dB (0.0199%), a third at –56dB (0.1584%) and a fourth at –81dB (0.0089%). The next 14 harmonic distortion components almost
alternate between –80dB/0.01% (odd order) and –90dB/0.0031% (even order). The noise floor has dropped to around –140dB at both impedances, except at low frequencies. The ‘grass’ on the noise floor reflects the stress on the power supply caused by the high output levels. Intermodulation distortion (Graph 5) shows a regenerated difference signal at 1kHz that’s 95dB down (0.0017%), and the sidebands either side of the test signals are 75dB down (0.0177%).
Looked at in total, the slightly higher-than-normal distortion results (at least for a solid-state amplifier) are presumably because whereas most amplifier manufacturers use negative feedback to reduce distortion, Air Tech says it isn’t using any feedback at all (the company claims the Maestro is a ‘zero feedback’ design).
Frequency response across the audio band was excellent, with Newport Test Labs measuring it as 20Hz to 20kHz ±0.13dB, no matter whether the amplifier was driving a standard non-inductive 8Ω laboratory test load (black trace on Graph 6) or a load that simulates one that would be presented by a typical loudspeaker (red trace). The frequency response was 1dB down at 5Hz and 51kHz, and 3dB down at 2.5Hz and 90kHz. This excellent performance is reflected in the results of the square wave testing, which also shows that the Maestro would be completely stable when driving highly reactive loads.
Channel separation was excellent, though the decrease at higher frequencies suggests some capacitive coupling, but it’s immaterial, because 71dB at 20kHz is an excellent result for an integrated amplifier.
The A-weighted signal-to-noise ratio of the Maestro was measured by Newport Test Labs at 80dB referred to one watt and 100dB referred to rated output. Again, excellent.
The Maestro’s output impedance was measured as 0.12Ω at 1kHz, leading to a measured damping factor of 50. This damping factor is still high enough that the Maestro will be able to control the behaviour of even the largest speaker cones. Again, the fact that the Maestro is a ‘zero feedback’ design is no doubt the reason the factor was not higher.
Audio Analogue’s Maestro Anniversary delivered excellent performance on Newport Test Labs’ test bench. The distortion levels, although higher than on amplifiers using high levels of negative feedback, are similar to that of valve amplifiers, and sufficiently low that they would not be audible, plus you need to factor in this amplifier’s impeccable power output results, its extended frequency response, and its low noise, plus the fact that its build quality is simply superb.
Steve Holding