I finally got around to measuring this amp. And building the contraptions needed to measure amplifiers.
3 sets of numbers here - for the amplifier at various volume knob positions as stated in the descriptions. (The -1.5dB refers to what the US-144 sees after the output has gone through the US-144's input's preamp, and is of no importance here.) From the noise level numbers you can see that most of the volume-control action happens in the first half of the knob. It is usually that way.
Again, bad crosstalk numbers because I did it in mono mode because I only had one contraption for one channel. See the graph for more accurate results.
Load is a 4.7ohm resistor. At 2 o'clock, output voltage is measured to be around 6V RMS, ±2dB because I don't know at exactly what level RMAA carries out its tests. (Arta didn't want to work with US-144 for some reason) At 6V RMS into 4.7ohm, that would be 7.7 watts.
THD pretty much stays the same or increasing slightly with output volume. The THD+N figures given by the datasheet is around 0.03%, so we are pretty much near the limit of the chip already (the measured THD+N is around 0.06%). And the complete product seldom hits component datasheet performance. For a cheap small class-D (or class-T) amp, this is pretty okay already, since bigger, more expensive amps are rating their powers at 0.1% THD+N, or even 1% and 10%.
IMD improves with output volume, but that is because IMD calculation is affected by noise, and SNR improves with output volume.
The next graphs to follow are the usually most pointless ones (unless something serious can be seen happening inside the graphs, which usually does not happen) - frequency response, noise level, and dynamic range. But for the sake of completeness I am including them.
The roll-off is steeper than expected and more funky. Possibly due to a 4.7ohm resistive load? Edit: On second thought, it could be due to the low-pass-filter of the recording device.
Nothing to see here. The noise drops swiftly from 20kHz onwards due to the output filter required for class-D amps. (Or due to the LPF of the recording device, or a combination of both.) With higher-impedance loads, like a real speaker or a tweeter where that frequency range is concerned, the roll-off would start at a higher frequency.
Also nothing to see here. Except for the 40+kHz noise from switching.
0.04% worth of THD. However, most the energy is concentrated at the higher odd-order harmonics so don't expect this 0.04% to sound as good as 0.04% from, say, a tube or transistor amp. A typical case of bad chip sound which I thought had been eradicated since recording studios started using equipment with chip amps in them.
IMD would've been okay if not for the strange peak at above 10kHz, possibly due to residual switching noise.
Stereo crosstalk. That is what happens in mono mode, ignore the white one and look at the green one. Otherwise, nothing special.
IMD vs frequency. Sharp rise due to the output filter, but I do not understand how the left channel got a different result. In fact I do not fully understand how mono mode in RMAA works. In fact I do not even trust the THD calculation, but nooooo, Arta refused to work.
I also measured another Tripath amp - Yulong T-Amp using the TA2024 and a linear regulated supply for comparison, and results are pretty much similar. The M20 EX3 has advantages at high output levels, where the TA2024 probably started struggling just that much earlier (1 watt) than the TA2021. At low output levels, tables turned with the Yulong delivering a nice 0.015% at Yulong's 9 o'clock, which is my normal listening position. BTW the Yulong's gain is around 2 "o'clocks" higher (or it needs 2 o'clocks less for the same volume) than the M20 EX3.
Noise numbers, Yulong has much worse numbers due to the hum from the linear power supply. Otherwise noise level is chip-limited and hence all perform similarly.
Well, note that the following observations have not been blind-tested, and after the pictures and measurements have been taken it reeks of placebo. (Even seeing the amp produces placebo effect; that is why wood is so expensive)
First impression when I plugged it in, nothing special. From personal experience, this is actually a good thing, because things that sound too different usually show up big problems when measured later.
After listening for a while, the differences between this and the Yulong are:
The highs sparkle less, and by sparkle I mean in a neutral way. It can be good or bad, depends.
Midrange - more air and lower-order harmonics observed.
Bass - Might be a tad bass shy, can't tell differences quality (a reduction can often be taken as more controlled, but this is not always the case), could be better or worse, I can't tell
Overall - sonic differences between these Tripath amps is smaller than between other amplifiers
It is a TA2021. It performs like a TA2021 should. Which AFAIK is just the SMD version of TA2020. (Some people even claim that TA2024 is also the same thing, but some differences in performance in the datasheets exist, particularly the THD, which the TA2024 is lower and more stable, which may explain why the MX20 EX3 got stuck at 0.03+% while the Yulong went down to half of that.) It does not measure significantly better, nor is it significantly worse. It even has that Tripath sound.
Is it the best (among TA2020/1/4 amps)? Most likely not. Is it the worst? I'm not sure, but I'm betting worse ones exist.
Is it worthy of being sold? At $60 SGD for a fully-cased T-amp and power supply shipped, it is rather cheap for something with -70dB distortion peaks. But there are cheaper amps that are based on TA2020/4 with a chance of doing the same or better. If the chip is the deciding factor, then it does not matter what other parts are used as long as they are decent enough. But looking at some TA2020 amps (tend to be the cheaper-looking ones), they visually seem to fall under the not decent enough category, so I'm gonna leave it at a 50-50. More comparisons are needed for this. (Anyone wants to donate an S.M.S.L or a Topping?)
But, among the TA2021 amps, this is one of the cheapest if not the cheapest. And the TA2021 has some advantages over TA2024. It may be a few bucks more expensive the most value-for-money-looking TA2024 amps, but consider paying a few bucks more for the TA2021 which seems to carry a price premium.
W A R N I N G !
W A R N I N G !
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