Possibly you bumped it in pre mode lol? That’s real strange, if you have everything set accordingly I don’t see why xlr wouldn’t work outside of faulty cables
Yeah if rca works and you have it set right I really don’t know why you would get no output via xlr
I just tested on my THX 789…and it works… Ugh. I guess all that hype to get the topping and get a defective unit ? 
last thing to try would be messing with gain and the switch again on the a90? But otherwise that does seem pretty defective indeed
I’m pretty close to giving up. now the m500 has more noise than the SDAC on the THX 789 and the A90 refuses to output sound with XLR…and the RCA is not pretty lol
Thanks for your help. This may need me to crack a beer
That hiss or ground loop noise?
Oh boy
RMA time. Sounds like the PSU is only half-working or something.
A fine temporary solution 
So confirmed, it seems like the XLR input on the topping a90 is broken. When i switch back and forth from RCA to XLR, only RCA outputs, its like its not internally connected to what it needs to make the switch.
The THX 789 and M500 works as it should, but I definitely hear some hiss that wasnt there before.
However, I’ve just cracked open an Innis and Gun and i’m slightly less frustrated
Pretty sure I heard this issue on the ASR thread where the engineer who created the A90 responded. I would try there and do a search.
As amazing as the performance was in the little tests I got to do on the RCA - SDAC and SMSL m500, i’m not sure if these build design issues are worth it. I want to keep it honestly. I was so impressed with the music. ugh
Maybe a stupid question but just in case: there’s a toggle switch on front, for the rca and xlr inputs, yes? Did you toggle it to xlr?
Yeah, when it was RCA to the m500, i toggled it back and forth and it would always output no matter if XLR or RCA. If it’s XLR to the M500, then no sound whatsoever. if its thx 789 xlr to m500, works like a charm
Rats. that’s the sort of thing I miss and have 30 minutes of panic because of…
I just wanted end game gear not endgame issues lmaooo
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I actually don’t entirely understand your switching, comparing the the units, still. but I’m not altogether sober and the issue I’m talkig about is really simple. So I believe you. And yeah… that totally sux. On the other hand… I’ve seen they seem to respond to customer service issues like champs. Crossed fingers.
LOL i’ve had a few at this point. U mean u dont understand me buying the A90 when I had the thx 789? Yeah I contacted the amazon seller that i bought it from, hopefully they respond. Johnyang was kind enough to respond on audiosciencereviews as well
Actually I meant when switching the to m500… is that different amp? or DAC?
But the issue I’m talking about is the toggle switch on the front of the A90. I just want to make sure that if you’re using the XLR connectors on the back of the A90, you’re toggled to the XLR position on the FRONT of the A90, too.
So I trust I am being dumb.
Totally understand switching from the 789 to the A90, LOL. I would switch to the A90 if if was looking to spend (from the Monolith “887”, which is essentially the same thing as your 789). Not saying I would hear a difference, but I’d feel better about it!
ahha you’re not being dumb, i had to make sure I double checked it all.
and yes the SMSL “m500” is my DAC. !
I have the Topping working as RCA only now I may have to RMA or see what the amazon seller can provide because I truly want to use it as balanced.
