No sound on Mac via USB

[DennisO]

I am trying to hook up a record player to my Mac so that I can digitise my old albums but am unable to get any sound on my Mac. I don't even know if what I am trying to do will work so could do with some help.
I have a record players with RCA outputs that I have connected to a preamp. The preamp is connected to the Mac via an RCA to USB-C cable. When I plug the usb-c into the Mac it is recognised OK but I get no sound. I have checked and selected the usb as sound input etc but nothing.

When I connect the preamp to speakers they work fine so I know I am getting sound from the record player to the preamp.
Should this set up work? Any ideas why the Mac isn't outputting any sound?

 

[Lufbrarunner]

Have you checked the Output on the Mac?
Is the volume turned down or muted?

 

[DennisO]

MC outputs is fine. When I use internal mic I can see the sound waves on Audacity and it records OK. When I switch to usb I get no soundwaves and nothing records