[greyscale]

  Feel kinda dumb asking this, but here goes. I have a recently repaired 7BST  amp pair and a BP -25 preamp. I had to relocate the Sts and need longer cables between the 7BSTs and the BP-25. I received some cables when I bought the setup and they work fine. My question is what type of cable are they. The cables have RCA banana plugs on the ends. I tried a subwoofer cable but that did not work, only a buzz from the speakers. Are these just RCA cables the same as the rca cables I run between my CD player and the BP-25? 
Thanks
greyscale

[skunark]

Yup,  RCA cables.  You can use about any RCA cable too.    Most likely the subwoofer cable is bad if you are hearing buzzing sounds, but how long of a cable is it?   

Folks will have lots of opinions about cables, but you can’t go wrong with what Bryston or Benchmark sells online.   If the distance is more than six feet / 2meters, you might opt for XLRs.   

[skunark]

I assume the amps are on the same circuit?   

[Elizabeth]

Good point about AC. I would check the amps AC by getting/borrowing some long enough (temporary) extension cords and use the original outlets for the amplifiers! to see if the buzzing stops.

[greyscale]

I assume the amps are on the same circuit?

Yes, both amps are on the same circuit(condo). When I use the RCAs i received with the amps, the buzzing is there until i use the ground lift switch, then all is quiet.
Thank you all for your help. Now of to get some WHITE 20ft rca cables. Got a feelin this will not be a simple task. ;>)
Edir: found White rca cables at Wireworld.

[skunark]

With 20ft long runs, i would use XLR cables. 

A condo can have more than one circuit. Can you try to see if it all works from a single outlet, if you dont want to use the ground lift?