Well I have the amp hooked up on my C3 for a few days now; however sometimes it does not switch on; unless I connect it to a power source for a second.
After that it stays on fine; I will try charging it for a longer while to see if it is just the battery not not received a good charge yet or something else.
I'm trying to check if it sounds different with the SMSL sap 4s amp; but the differences are quite marginal at best. To be honest, I can't really tell if it sounds better with SAP4SL.
It sounds a tiny bit different though, but its so subtle I cannot really describe it. Also I don't hear any hiss at normal and loud volumes.
I am wondering though; people are reporting that the C3 player will go to the next level when paired with the C&C BH amp; well that does not seem the case with the SMSL.
Thats not a bad thing as the C3 sounds very good already and music can be played at much louder volume without degraded sound quality.
It looks quite nifty stacked with a C3 and the SMSL cable is nice too.
I am also planning to get the C&C BH and the Superlux 668B headphone, but that will atleast take another 4 weeks. I also have an IEM from Sony, which I got with my xperia Z smartphone (removed filter mod) and the Hisoundaudio Flamenco (not burned in yet) to test with the C3 without and with amp :).