The first thing to do is verify that the preamp is indeed the culprit. To this end:
run the amp with no input- no interconnect cables attached. Is the buzz still there? If yes- its the amp, if no:
Reconnect the preamp. Do not have any other component attached. This is important- if a ground loop is causing this it can be coming from another component. Is the buzz present? If no, swap the interconnect cables left for right at the preamp end and see if the problem moves. If it does, the preamp is indicated. If it does not, its a cable.
If yes, in both channels: Try floating the ground pin of the AC power cord as suggested on this thread. This is for testing only. If this fixes it, you need to talk to the manufacturer about fixing the preamp's ground problem. If it does not, you need to talk to them about fixing the preamp- any number of internal faults can cause this.
Good Luck and please report your findings.
run the amp with no input- no interconnect cables attached. Is the buzz still there? If yes- its the amp, if no:
Reconnect the preamp. Do not have any other component attached. This is important- if a ground loop is causing this it can be coming from another component. Is the buzz present? If no, swap the interconnect cables left for right at the preamp end and see if the problem moves. If it does, the preamp is indicated. If it does not, its a cable.
If yes, in both channels: Try floating the ground pin of the AC power cord as suggested on this thread. This is for testing only. If this fixes it, you need to talk to the manufacturer about fixing the preamp's ground problem. If it does not, you need to talk to them about fixing the preamp- any number of internal faults can cause this.
Good Luck and please report your findings.