Had the SA300 for some time, and just thought I'll do some quick measurements between it and the Yamaha A-S500. Found an interesting difference.
Before that difference, these are the measured frequency responses for both amps.
I've kept the Xonar U7 dac / Windows volume constant and varied the volume so that both amps register 96 dB on 1 kHz tone on REW. However, SA300's increments are more coarse, so I settled for ~0.5 dB higher volume than the A-S500. Mic is about an inch from the cone center.
Blue (Yamaha) / Orange (SMSL) charts - JBL A130 tweeter and mid
Green (Yamaha) / Orange (SMSL) charts - JVC UX2000 (as a representative for 4 ohm speakers)
In the context of these 2 speakers, the SMSL is performing as well as the Yamaha, both FR tracking each other end to end.
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The difference that I spotted was in the distortion graphs. When measuring the A130 tweeter, SA300's distortion went up about 5 dB beyond 15kHz.
Distortion for Yamaha. No rise beyond 15 kHz.
Distortion for SMSL. ~5dB rise beyond 15 kHz.
Final FR didn't seem to get affected though. Not sure the significance for this, just thought I'll put this observation up. Or should I be concerned?