In my case, it is not a SRM-T1S but rather a SRM-323S. The seller advertised it as a 120V USDM amplifier but I see quite clearly now on the back that it is labeled 220-240V 50/60Hz. The internals were not tampered with so I highly doubt it was wired to 120V input.
I hadn't noticed any hiccups in performance or operation using it up until I had noticed this (several months). I'll have a bone to pick with the seller for sure.
In the case of a solid state amp, it becomes considerably more likely that it'll seem to be working since there are no filaments. The only way it can actually work properly with either voltage is if it had a switching supply, which I'm guessing Stax amps never do.
That leaves two possibilities, either it was modified, or you're using it at half voltage. In most amplifiers, this would take stages out of proper bias, reduce voltage swing by a factor of two, and greatly hurt amplifier linearity and sound quality, but it'd likely still act as an amplifier. In most but not all cases, there'd also be severe 60hz humm since you wouldn't be over the linear regulator dropout. It seems unlikely you wouldn't know if this is the situation, but I could certainly see it as conceivable. (Inconceivable if you have a lot of experience with Stax products and would notice half volume, poor linearity, etc.)
Kind of puts you in a sticky situation, since if it was modified to operate on 110v and you connect 220v it'll blow up! I would definitely contact the seller and ask for details on the input voltage.
Edited by dude_500 - 1/23/14 at 11:23am