Determining the Source of Noise when TT is On

I can use a hand.  I have a scratchy noise coming out of my left front speaker whenever I have my TT on.  The sound is on without the TT turning.  The noise started about a month ago long after I had installed the component parts.  The TT is grounded.  I have a relatively new phono pre-amp MP 1100 with balanced cables going to a 5 yo MX 121 a/v control.  When I disconnect the left cable from the back of the phono pre-amp the noise stops.  Q: how can I determine if the defect is in the phono pre-amp or the a/v controler?  

Showing 1 response by petg60

Is the unit tubed?
If so there is your answer. Switch first the phono cables to eliminate that, then swap tubes left and right.