A power conditioner is only necessary if there is noise on your mains. If you can't hear it, you may have it but it doesn't matter.
If you can hear noise, before running to the cost of a conditioner try the simpler solutions. Isolate the noisy equipment in the house - fridges, washing machines, anything with an electric motor (don't worry about your turntable). If this doesn't sort it out, re-run the supply to your system so that it branches before other circuits immediately after the main fuse and with its own fuse-box. Check the main earth and if it is poor, install a bigger one running deeper into the ground.
By now you probably won't be hearing the noise any more.