Tube amp is loud at zero volume

I have a raysonic sp-120 integrated tube amp and as of today when I play anything (record, CD, ipod) it is very loud when the volume is set at zero. Any other volume setting doesn't seem to do anything.

Any ideas? Anything would help.

it's hard to tell without seeing a schematic . . . but my
first suspicion (knowing nothing about your amp)would be
that the volume pot is broken. I've had it happen before on
a guitar amp - the wiper separates from the shaft and stays
wherever it occurred. Of course it could be other causes -
need a tech to figure it out.
your volume control rotor may stock inside and in need of replacement.