Aleph 30 hums

I just finished one channel of the Aleph 30 amp. And it works ok.. However when I connect it to my preamp it starts to hum really much (It's a BoZ). The volume pot is located directly after the preamp, and when the volume is set low the hum is low. The more I turn up the volume the louder it hums.

But if i remove the CD-player coupled to the preamp input the hum goes away.

What should I do?