Laboratory test report
Since the Redgum Magnificata System uses two monobloc amplifiers, Newport Test Labs measured only one, as the results for the other would be identical. In terms of power outut, the Redgum Magnificata delivered 378-watts continuously into 8Ω loads at 60Hz and 1kHz, with output dropping just 0.2dB for a maximum power output at 20kHz of 353-watts. Since Redgum specifies power output of the Magnificata as being 350-watts into 8Ω, all these results are better than specification. Into a 4Ω load, Newport Test Labs measured power output at 625-watts at 1kHz, 622-watts at 60Hz and 621-watts at 20kHz— once again all very comfortably higher than Redgum’s specification of 550-watts.
Redgum is one of the very few manufacturers these days that not only builds amplifiers capable of driving 2Ω loads, but are also capable of delivering their full rated output into 2Ω loads. As you can see from the chart, the Magnificata was able to deliver nearly one kilowatt of power into 2Ω loads: 933-watts at 60Hz, 968-watts at 1kHz and 960-watts at 20kHz.
Technically-minded readers paying attention to detail might have noticed that the low-frequency power measurements were made at 60Hz, rather than 20Hz, which is the usual frequency for low-frequency power output testing. This was because the Magnificata has inbuilt protection circuitry that starts limiting continuous power output below 60Hz, with the level of protection gradually increasing with decreasing frequency, so that at 20Hz, maximum continuous power output into 8Ω is limited to 171-watts. However, the circuit only triggers with continuous signals, such as the sine waves used for testing. With music signals, the protection only starts cutting in at 350-watts (8Ω), 550-watts (4Ω) and 900-watts (2Ω).
Protection circuitry is also used to limit the Magnificata’s low-frequency response to 6Hz, as you can see from the tabulated figures which show the –1dB response as extending from 6Hz to 82kHz and the –3dB response as extending from 6Hz to 116kHz. Although these are the points at which the high-frequency responses are 1dB and 3dB down respectively, the low-frequency response of the Magnificata is boosted at low frequencies, as you can see on Graph 6, where it’s +0.09dB at 160Hz, +0.7dB at 50Hz, +3.0dB at 20Hz and +7dB at 8Hz. So a ‘normalised frequency response, which would include both ‘plus’ and ‘minus’ dB variations, would be 20Hz to 116kHz ±3dB.
Graph 6 shows the Magnificata’s frequency response into both an 8Ω non-inductive laboratory test load (black trace) and when the amplifier is driving a simulated loudspeaker load (red trace). You can see that both traces are virtually identical, which means the Magnificata’s ‘sound’ will remain the same no matter what the impedance (and irrespective of variations in that impedance) in the loudspeakers you use in conjunction with it. The low-frequency response of those speakers will, however, be gradually and very slightly boosted below 160Hz, as shown. Note that although the low-frequency rise looks a little alarming on the graph, this is merely a consequence of the graph scaling. The rise is so minor that if music were playing at, say, one watt, the result would be an output of only two watts at 20Hz. ( Editor’s Note: See Breakout Box ‘LF Rise in Redgum Anps’ on page 42 for Redgum’s reason for this rise.)
The output impedance of the Magnificata was measured at 0.02Ω at 1kHz, putting the amplifier’s damping factor at an outstanding 400—far in excess of what would be required to keep even the largest bass drivers under control.
Distortion is shown in Graphs 1 through 4, the first two showing distortion at one watt into 8Ω and 4Ω loads, and the second two showing distortion at rated output into both loads. Overall distortion was slightly lower into 8Ω than into 4Ω, but the differences were minor. As you can see, when driving an 8Ω load, with the exception of the third harmonic at –78dB (0.0125%) all other harmonics were below 80dB (0.01%) with the odd-order harmonics predominating.
Distortion at rated output was similar in magnitude to that at one watt (Graphs 3 and 4) and again with the 8Ω result displaying marginally lower distortion than the 4Ω result. This time, however, rather than the odd-order harmonics predominating, the odd-order and even-order harmonics are more balanced. The most obvious difference is the much-lower noise floor, as you’d expect, though some low-frequency, mains-related noise is still visible at the far left of each graph.
Newport Test Labs measured the signalto-noise ratio of the Magnificata at 77dB unweighted and 91dB A-weighted, referred to an output of one-watt, and 103dB unweighted and 115dB A-weighted referenced to rated output. Input sensitivity was 68mV for a onewatt output and 1.27-volts to achieve rated output, and the amplifier will pull 547-watts from your 240-volt mains power supply when operating at maximum output.
Newport Test Labs usually measures and reports on power amplifier heat sink temperatures, and for the Magnificata, after one hour of continuously operating with a sine wave at an output of one-watt, that temperature was just 40°C. Although this power output is far higher than would be used domestically, the lab then measured the temperatures after the amplifier had been operating at 100-watts for
one hour (around one-third rated power, which is the point at which the amplifier’s thermal efficiency is lowest and therefore a ‘worst-case’ scenario for heat). After one hour at 100-watts continuous output with a 1kHz sine wave, the hottest point on the heat sink was measured at 78°C and the coolest point at 55°C. The technicians also removed the casing from the amplifier immediately after the test and measured the temperature of each of the ten capacitors (which are rated at 105°C) in the power supply and found those temperatures differed very slightly on each, but the average was 49°C. Redgum’s Magnificata has very obviously been designed with sonic preferences prevailing over ‘numbers’ and also with a view to ‘bullet-proofing’ the circuitry to ensure the amplifier will be completely protected in all ‘misadventure’ situations.
The result is that it will certainly sound different to amplifiers whose designers are following the ‘straight wire with gain’ approach to amplifier design, but if one allows for this design philosophy, its actual electronic performance is excellent.