LABORATORY TEST REPORT
Newport Test Labs’ tests of the SAP201V showed that it did not meet the power output claims made for it, according to the Australian standard, which requires that an amplifier must be able to deliver its claimed power output at all frequencies from 20Hz to 20kHz when both channels are driven. Our review sample of Mitchell & Johnson’s SAP-201V only delivered its claimed rated output with both channels driven at the 1kHz test frequency. When both channels were driven into 8Ω it delivered only 35-watts per channel at 20Hz and 36-watts per channel at 20kHz. With both channels driven into 4Ω loads, it delivered only 42-watts at 20Hz and 47-watts at 20kHz. Newport Test Labs’ testing also showed that although the SAP201V was able to drive 2Ω loads, it was not able to deliver any more power into the lower impedance than it could at 4Ω, which I presumed to be the result of some internal current-limiting circuitry. As you can see from the tabulated results and the bar graphs accompanying this review, the SAP201V was able to deliver its rated output at all frequencies when only a single channel was driven, producing between 44-watts and 48-watts into 8Ω loads, and between 66-watts and 68-watts into 4Ω loads, depending on the frequency of the test signal.
Frequency response was a little restricted at low frequencies, with Newport Test Labs measuring the SAP201V’s frequency response as being 1dB down at 12Hz and 3dB down at 5Hz. There were no such limitations on the high-frequency response, with the –1dB down-point being measured at 57Hz and the –3dB point at 117kHz. The audio band frequency response, which is shown in Graph 6, was 20Hz to 20kHz ±0.15dB into a standard resistive load (black trace). Into a reactive load that simulates that of a two-way loudspeaker (red trace), the response was almost equally good, measuring 20Hz to 20kHz ±0.2dB.
Channel separation was adequate, and more than sufficient to ensure good stereo imaging and channel separation, but a little less than I am used to seeing, particularly at 20kHz, where Newport Test Labs measured only 46dB. At 20Hz the lab measured 57dB, with the best result of 63dB being measured at 1kHz. The interchannel phase results were excellent, with the lab measuring 0.32 degrees at 20Hz, 0.01 degrees at 1kHz and 0.34 degrees at 20kHz, this last being a particularly good result at this frequency. Channel balance at 1kHz was also excellent at 0.08dB— and far better than will ever be required.
The signal-to-noise ratios measured by Newport Test Labs revealed the presence of some unwanted noise, with the 1-watt result being only 74dB without weighting, increasing to 79dB with standard A-weighting. Referred to rated output, these S/N ratios climbed to 89dB unweighted, and improved to a very creditable 95dB with A-weighting.
Distortion at an output of 1-watt into 8Ω was relatively low, as you can see from
Interchannel phase results were excellent, with the lab measuring 0.32 degrees at 20Hz, 0.01 degrees at 1kHz and 0.34 degrees at 20kHz
Graph 1, which shows a second harmonic component at –71dB (0.02818%), a third at –87dB (0.00446%), a fourth at –82dB (0.00794%), a fifth at –108dB (0.00039%), a sixth at –92dB (0.00251%), a seventh at –107dB (0.00044%) and an eighth at –100dB (0.001%). When the load impedance was halved to 4 and the output power kept constant, distortion increased slightly, as you can see from Graph 2, with slight increases in the levels of the even-order harmonics, greater lifts in the levels of the odd harmonics, and the appearance of additional high-order harmonic distortion components, albeit at very low levels (all more than 100dB down).
Total harmonic distortion increased quite substantially at rated output, with the performance into 8 loads again being superior to that into 4 loads. Into 8 , the second and third harmonics were both at around –71dB (0.02818%), the fourth at –78dB (0.01258%), a fifth at –95dB (0.00177%), a sixth at –88dB (0.00398%). After this, odd harmonics hovered around –110dB out to 20kHz, while even harmonics hovered at around –100dB (0.00031%) out to the same frequency. Graph 4 shows distortion at rated output into 4 and you can see the harmonic distortion components gradually diminishing in level from –63dB (0.07079%) for the second harmonic down to –93dB (0.00223%) for the ninth, after which odd-order harmonic components came in at a bit below –100dB (0.001%) and even-order harmonics a bit above.
Intermodulation distortion was interesting. Although the high-frequency IMD sidebands were quite low in level, at around –70dB (0.03162%) for
High-frequency IMD sidebands were quite low in level at around –70dB
the 18kHz/21kHz sidebands, then around –95dB (0.00177%) for the 17kHz/22kHz sidebands, the unwanted regenerated signal down at 1kHz was at –50dB (0.31622%)—a level I am more used to seeing with valve amplifiers.
The Mitchell & Johnson’s tone control action showed room for considerable improvement. Firstly, using the controls affects midrange volume level by about ±4dB. Second, the high-frequency boost is not shelved, so using excessive treble boost could stress your tweeters or super-tweeters. The bass tone control provides maximum boost and cut at around 120Hz and only around ±4dB at 20Hz, so it should be useful in helping with room modes and bass adjustment without overly-taxing the amplifier’s output stages, or unduly stressing your speakers with unwanted low frequencies, such as turntable rumble.
The SAV201V’s square wave performance was excellent, as you can see for yourself from the four oscillograms, although the 100Hz wave of course necessarily showed the amplifier’s limited low-frequency response by displaying considerable tilt. However the ‘flat’ of the tilted waveform was not curved, so there’s no group delay. The 1kHz square was not ideal, showing some slight rounding, but is very good nonetheless.
The 10kHz square wave showed a very good rise-time and good high-frequency performance. Performance into a highly capacitative load was excellent, with minimum initial overshoot and quickly damped ringing. Steve Holding Readers should note that the results mentioned in the report, tabulated in performance charts and/ or displayed using graphs and/or photographs should be construed as applying only to the specific sample tested.