I recently picked up a Loomis Sig used as my first 7 but unfortunately the original owner liked his action touching the roof. I have set up every guitar i own with comfortable action and no buzz through a clean channel however this one is proving tricky.
The top 6 strings (EADGBe) are relatively easy to set up but the low A string is buzzing on every fret. I currently have it tuned to drop A with a 9-46 set and a low 66 (all d'addario). When fretted at the first and 24th fret there is approximately .015" space between the low A string and the 7th fret. The action is set to approximately 2.5mm at the 12th fret on the low A string. The other 6 strings aren't a problem and are a joy to play. I use a black jazz III but even soft picking creates a buzz.
I have also rocked a credit card over all the frets excluding the very top few (which it was too long for) and it wouldn't move on any of the frets.
If it helps i can record a D.I clip of the buzz and upload pictures.
I would have taken it to my local luthier by now but he is on holiday for 2 weeks and the only local shop I trust charge a lot and don't stock sevenstrings.
Any advice is greatly appreciated!
I'm sure someone else will come in here with more knowledge, but have you adjusted the truss rod? Does the buzzing continue if you tune the the low A string up to B? Did the original strings buzz at all?