boatman Posted August 4, 2015 Share Posted August 4, 2015 I have a Shure FP11 on the bench which creates severe hum when switched on. I have downloaded the user manual which includes a schematic and I see that the connector shells are connected to the cable screen. Opening the case has confirmed this. I'm wondering if removing these links may cure the problem. Has anyone else had a similar problem with the FP11? Link to comment Share on other sites More sharing options...
Simon Lewis Posted August 5, 2015 Share Posted August 5, 2015 I think that's a fairly old design? Does it have the pin one problem? Link to comment Share on other sites More sharing options...
boatman Posted August 6, 2015 Author Share Posted August 6, 2015 Indeed a very old design and it works well most of the time and pin 1 is connected to the cable screen correctly, but its also connected to the chassis (a diecast custom box), so there's the possibility of a short to mains earth. The box is usually lying in the middle of a field in wet grass so I'll try cutting the links between the chassis and cable screen and see if that fixes the problem. Link to comment Share on other sites More sharing options...
Simon Lewis Posted August 6, 2015 Share Posted August 6, 2015 I'm not an audio electronics expert, but I understood that it was the audio earth being connected to the PSU 0V that introduced noise in the pin 1 problem, and that the correct solution was to connect shield to the case (rather than 0V)... How the psu 0V was referenced to mains earth was a designer decision... Hope your approach works though! Lifting the cable shield at one end or using a 1:1 transformer may also be a possible solution... Link to comment Share on other sites More sharing options...
boatman Posted August 6, 2015 Author Share Posted August 6, 2015 It's unusual these days, but the online user manual also contains the full parts list and schematic. It can be found here: http://www.shure.com/user-guides/us_pro_fp11_ug.pdf I'll let you know if cutting the link on both input and output connectors fixes the problem. Link to comment Share on other sites More sharing options...
Sound Man Posted August 8, 2015 Share Posted August 8, 2015 I've just looked at the schematic and I think that pin 1 of the XLR should be connected to the PCB ground. As it's battery powered there shouldn't be any issues with ground loops or noise problems. David Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.