I bought a DTA-100a and it is a great little amp. But it is what it is, cheap! (when I removed one of the RCA cables from the back, it pulled the conncetor out from the back of the unit but it easily pushed back in and is working fine. I am going to solder them in place) I have it in my bedroom system running a pair of Monitor Audio S1 speakers rated at 89dB. It plays fairly loud in my 17x17x12H room. But if you want to use it for outdoor use at loud volumes, look else where unless you are using some efficient speakers and heavy gauge speaker wire. It defintely sounds like a much more expensive amp. Bass is deep and tight and it has plenty of air. It leans on the sunny side of neutral. It sounds even better when I hooked it up to my sons Maverick Audio TubeMagic DAC/Pre. The sound actually blew me away. It warmed up the sound, the midrange became silky smooth with more warmth and depth without losing any air or transparency. And treble had greater detail and resolution. it just took the sound up a couple of notches.
I think that the DTA is a great little budget amp that needs a good source component and efficient speakers if you want to play it loud.
By the way, most of the drift problems were with the original DTA-100, not the 100A which I have.
I looked up that SA-50 amp, it looks well made inside. It looks like a clone of the DTA but I cant find any spec on it. The RCA connectors on the back look to be of better quality. I doubt that it can play 50wpc without distortion just like the DTA which is rated at 50wpc but is more like 20-30wpc in real world use. Keep in mind that Parts Express is a reliable dealer and will stand by the DTA if you have problems with it!
I hope this helps some.
Larry
