We have a mystery problem with a client trying to interface a new Vision SET 400 power amplifier with his MacIntosh C47 preamplifier.
When the SET 400 is plugged into the unbalanced RCA output 1 set on the Mac preamp, the system produces audible white noise.
His other power amp, a Prima Luma is quiet with the same connection.
However, when the SET 400 is plugged into the unbalanced RCA output 2 set on the Mac, it is quiet.
The amp also is quiet on my test bench and in my reference system with any preamp we use here.
It is also quiet with open inputs.
Although it appears that the issue is some incompatibily with the Mac audio output unbalanced set 1, I have no clue what that could be.
The customer is returning the amp.
Any thoughts there as to what the issue could be? Anyone know of anything unusual about the C47 RCA output set 1?
This is a one off issue that we cannot identify so far. The SET 400 has a 65K ohm pure resistive input impedance so should not be loading down the preamp or producing an unusual load for it.
Thanks for your help.