Seventh Circle Audio

I just finished building 4 a12's and 2 C844s. The A12's seem ok and are nice and quiet. However, the C84s both have a nasty buzz with the gain turned up to 6 or 7 or so. I fixed the problem by moving the C84's to the end of the chassis furthest from the power supply and this cured the problem. I noticed an earlier post about the same problem occuring with different mics but I had the problem with an AT 4050, an Oktava MC012, and a Lawson tube mic. I also noticed that with no cable connected, the buzz was less pronounced. and the quality of cable seemed to make a small difference. The output of my C84's were going right into my Lynx Aurora converters but were multed, unbalanced, to a Mackie mixer for monitoring. I didn't change anything but the physical location of the C84s to correct the problem. I can live with the situation just fine for now, but in the future I'd like to fill the two empty slots with a couple of J99's. Will I have a problem putting them close to the supply or will I need another chassis? BTW I recorded acoustic bass with the C84 and I think I like it better than the BA 1272's that I had previously used for this application:?:

Did you try the mod suggested in the last post of this thread? If jumpering out L3 makes a difference, you may want to substitute DigiKey part number PLK1248-ND instead of the choke that came with the kit. You should be able to put any module anywhere in the chassis.