I think the guy who sold me his sap9 via eBay was someone in this discussion board. Well, generally this is an interesting toy to play with and it’s the cheapest balanced headphone amp you can find (at least it looks like a balanced amp LOL).
Cokeman is right, this amp’s single-ended output is not really powerful but the balanced output has the strength to drive hd6xx/650/600/580. I honestly don’t know whether it’s “true balanced” or not (though SMSL clamis it’s true balanced) but I can tell when using its xlr inputs (if you have a DAC with balanced xlr out) the amp’s balanced output indeed sounds different than the single-ended out. For hd650, sap9’s balanced headphone jack could make the headphones‘ low end sound more “solid” than using the single-ended. And what about a better channel separation that a balanced amp is meant to have? I have to say not so much you can hear.
So what is its overall sound signature? Bright as someone here suggested? Yup, sort of bright. However IMO sap9’s problem is “thin and flat” rather than just “bright“. The thin sound sig actually makes you feel it’s bright.
So is it worth buying? Go for it if you happen to already have a balanced DAC and a pair of hd6xx/650/600 with balanced cable and you don’t want to spend at least $300 to buy a single-ended amp that is capable of powering the infamously hard-to-drive Senn’s 6 series. Sap9 won’t bring you those fancy terms such as “vast soundstage”, “deep bass”, “airy”-you name it; but it can at least give your balanced hd650 an acceptable solid sound that most sub-100 singl-ended amps wouldn’t be able to have. Plus, don’t forget it has a balanced 2.5mm jack for IEMs or some balanced portable headphones from Pioneer.
Ok, so far it sounds like sap9 is kinda not bad but why did I call it “toy” in the beginning? That’s because I am using it for my PC video game system LOL (check out my picture). Sap9 might not be good enough to match the word “audiophile“ but it can truly enhance your experience with the finest video games. A balanced system plus a pair of hifi headphones are better than those blinking 5.1/7.1 gaming headsets, IMHO.