This is a review and detailed measurements of the SMSL PA-X GaN based Class D stereo amplifier. It was sent to me by
Shenzhen Audio and costs US $699.
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The PA-X is gorgeously designed. It would look even better with the display on, had I not damaged the unit in testing (see below). A volume control IC is used allowing use of remote control:
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I wish SMSL would include trigger functionality. The unit weighs a "ton" for its size, oozing feeling of quality.
If you are not familiar with my
amplifier measurements, please watch this tutorial:
SMSL PA-X Amplifier Measurements
With balanced amplifiers, I start with that input:
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Usually that produces better performance but not in this case as RCA does better:
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Likely some kind of conversion is performed from balanced to unbalanced (due to volume control IC?), degrading performance. Either way, the PA-X scores well when it comes to noise and distortion:
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At the bottom is one of the first GaN based designed I tested. So not bad at all.
We can see the better noise figure for RCA input with our SNR tests:
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Frequency response shows some load dependency. It is manageable but at the cost of 4 ohm roll off:
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Crosstalk performance is a bit disappointing in the way it gets worse with lower frequencies. Usually it is the other way around as we see from our references:
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Multitone performance is good:
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Due to increasing distortion at higher frequencies, 19+20 kHz intermodulation distortion test shows worse performance (typical):
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PA-X more or less meets is power specs:
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There is a curious menu option to set the load to 4 or 8 ohm. It has no impact on the testing above, but does boost the power for 8 ohm:
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At this point, I ran my FTC like power sweep where the amplifier is repeatedly pushed into clipping in order to generate the max power possible at 1%THD. The sweep starts from right and goes to the left:
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Measurements stopped around 40 Hz. I looked at the amp and it had shut down. This is typical as many amps will complain and turn off. Alas, the PA-X would no longer power on.

I waited a while until it cooled off and it still doesn't power on. I will test it again tomorrow but I suspect it is permanently damaged.
As I have said countless times, such stress times can damage amplifiers for no good reason. No one is going to push an amplifier into clipping for such extended amount of time as I did above. And at any rate, there is little industry awareness that such tests need to be passed. So to some extend, I feel responsible for damaging the unit.
Amplifier is stable on power up:
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Conclusions
Other than the frequency response droop, the PA-X performs well and looks gorgeous while doing it. With the data we have, if it had not been damaged, I would have likely recommended it. As is, I am sitting here with a sense of regret.
My appreciation to Shenzhenaudio.com for sending the amplifier in for testing.
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