Hanging off different ports of a TDM400 I have a mechanical bell and a fax machine. The bell wouldn’t ring so I set boostringer=1 and all was well until I realized with the setting causes my fax machine to fail to answer calls. Boostringer brings the voltage up on all the ports and the fax machine doesn’t like it. Is there anyway to raise the line voltage per port individually? A second option, can I put something inline to restrict the voltage (i.e. resister)?
I would contact digium for info on this. You have support for your product so use it 
. I am sure that your local electronic store can get you something that will lower the voltage on a line.