yeah, a common problem with chinese amps, the pots are garbage as a whole. you could also add in a cheap chinese pre-amp. It will give you more volume on the same device, and more control over the volume. the solid state ones are 30-40$, the tube ones are about 10$ more.
edit: What does a pre amplifier do?
A preamplifier ( preamp or " pre ") is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted.
from wiki on preamps.