Strange issue with cables on McIntosh C47
 

When using most cables I am getting loud hiss , high frequency noise with volume set at 0 on C47 to Bryston 4B cubed ( main out to power amp ) Does not matter whether you choose main 1 or main 2 out.

This happens on all RCA interconnects including Cardas Crosslink.

Also same issue with Cardas Quadlink XLR balanced 1.5m and Kimber Cable XLR balanced 2m cables

When using Cardas Crosslink balanced (XLR ) 1m or 2.5m cables no issue or Bryston 1m XLR cable

Same issue with 1st McIntosh C47 preamp :no: and dealer replaced it.
How is it possible to have same problems on 2 preamps in a roll?

Never seen this type of problem when I had C2300 + MC302, all cables worked fine.

I have owned many different power amps and preamps since the early 80's and never seen this before.

I own a C47 + MC152 and have not experienced this type of issue. I use the RCA interconnects as well. There are a short run of Transparent Super's.

Could you take the C47 to your dealer and using your cables hook it up to a Mac amp of some sort (or any other amp) as a test to remove the Bryston out of the loop? Not throwing your amp under the bus. Just a test to see if the problem follows the C47 from amp to amp.

BTW, I hada Dual 508 in high school and a set of MG1.6 a few years back.

I was using different preamp with Bryston 4B without any issues

Try loosening then tightening silver screw in back of the C47. Chuck Hinton of McIntosh advised me to do this when I had a similar problem. This restores the ground connection which can come loose.

Have you tried adjusting the gain control on the rear panel?

I could not find an input sensitivity spec for the Bryston unit but it sounds to me there may be a mismatch between C47's output and the amplifier's input sensitivity thus elevating the noise floor. The symptoms as described do not sound cable-related to me.