Very volume control is a resistive device. the good ones are a resistive ladder. the poor ones are a sliding resistor. It is best to get the sliding resistor out of the circuit.
I have a great preamp so I use it for volume control and turn the amp to full up (which is how an amp is made that doesn't have volume control).
Also, most sliding contact controls have a good metal to metal contact at the full up position so at full up you should get the best contact.
If you are planning to keep the amp and the preamp is excellent, then I would have a technician take the amp volume control out of the circuit.
OTOH, there are people that swear they have a position on the amp that they like best.
Jerry