It could be dirty 6922 tube pin/tube socket contacts in the Line One preamp.
Usually just pulling the tube/s out of the socket and reinstalling it repeatedly a few times will clean the tube pins and tube socket. You can also use rubbing alcohol sparingly on a q tip to clean the tube pins. Even then I would still install the tube, pull it out, and and install it repeatedly a few times to clean the tube socket contacts.
Jim
Usually just pulling the tube/s out of the socket and reinstalling it repeatedly a few times will clean the tube pins and tube socket. You can also use rubbing alcohol sparingly on a q tip to clean the tube pins. Even then I would still install the tube, pull it out, and and install it repeatedly a few times to clean the tube socket contacts.
Please note that all the components involved are always in stand-by. The components involved are a Sonic Frontiers Line 1 preamp, and Parasound JC1 mono amps.Why do you leave the Line One preamp in standby 24/7? Even in standby you are shortening the life of the tubes. The tube filaments are still energized.
Jim